Official Journal of the American Osteopathic College of ... · Advanced cardiac imaging, including both cardiac computed tomography ( T) and cardiac magnetic resonance ( MR), is a

ISSN: 2165-3259

JJAAOOCCRR

Official Journal of the American Osteopathic College of Radiology

CARDIAC IMAGING

Guest Editor: Kevin Steel, D.O., FACC

Editor-in-Chief: William T. O’Brien, Sr., D.O.

April 2013, Vol. 2, Issue 2

J Am Osteopath Coll Radiol 2013; Vol. 2, Issue 2 Page i

JAOCR About the Journal

Aims and Scope The Journal of the American Osteopathic College of Radiology (JAOCR) is designed to provide practical up-to-date reviews of critical topics in radiology for practicing radiologists and radiology trainees. Each quarterly issue covers a particular radiology subspecialty and is composed of high quality review articles and case reports that highlight differential diagnoses and important teaching points. Access to Articles All articles published in the JAOCR are open access online. Subscriptions to the journal are not required to view or download articles. Reprints are not available. Copyrights Materials published in the JAOCR are protected by copyright. No part of this publication may be reproduced without written permission from the AOCR. Guide for Authors Submissions for the JAOCR are by invitation only. If you were invited to submit an article and have questions regarding the content or format, please contact the appropriate Guest Editor for that particular issue. Although contributions are invited, they are subject to peer review and final acceptance. Editor-in-Chief William T. O’Brien, Sr., D.O. San Antonio, TX Design Editor Jessica Roberts Communications Director, AOCR Managing Editor Tammam Beydoun, D.O. Farmington Hills, MI Editorial Board Susann Schetter, D.O. Daniel J. Abbis, D.O. Les R. Folio, D.O. Michael W. Keleher, D.O. Rocky Saenz, D.O. Kipp A. Van Camp, D.O. John Wherthey, D.O.

Page ii J Am Osteopath Coll Radiol 2013; Vol. 2, Issue 2

Table of Contents

Cardiac Imaging

Editor: Kevin Steel, D.O., FACC

Title/Author(s) Page No.

From the Guest Editor 1

Review Articles

Review of Cardiac MR Perfusion Imaging 2

Sheldon Jenson, DO, Steven Craig, MD, Gerald York, MD, Kevin Steel, DO FACC

Perioperative Cardiovascular Evaluation: Is There a Role for Coronary Computed Tomography Angiography? 8

James L. Furgerson, MD

Radiation Exposure and Associated Cancer Risk With Cardiac Diagnostic Imaging 14

Anjeli K. Nayar, MD; Bryan M. White, MD, FACC; Kenneth E. Stone, MD; Ahmad M. Slim, MD

Case Reports

Delayed Myocardial Enhancement 21

Aaron Betts, MD, Daniel A. Dolewski, MD, Gerald York, MD

Pulmonary Artery Sling Initially Presenting with Symptoms During Exercise 24

Kurian Maliel, MD, Javed M. Nasir, MD, Kevin Steel, DO

JAOCR at the Viewbox

Arteriovenous Fistula Between the Left Circumflex and Left Atrium 27

Kimberly Lochner, MD, and Ahmad Slim, MD

Metastatic Carcinoid Tumor 28

John Magulick, MD, Kevin Steel, DO

Coronary-Pulmonary Artery Fistula 29

Michael Rose, DO, Wesley Clarkson, DO

J Am Osteopath Coll Radiol 2013; Vol. 2, Issue 2 Page 1

From the Guest Editor

In This Issue

Kevin Steel, D.O., FACC

Cardiovascular Diseases Fellowship Program Director, San Antonio Military Medical Center, TX

Advanced cardiac imaging, including both cardiac computed tomography (CCT) and cardiac magnetic resonance (CMR), is a rapidly growing field both in cardiology and in radiology. Over the past 10 years there has been a growth of over 300% in peer reviewed articles covering the areas of advanced cardiac imaging and we are now seeing the development of cardiac imaging subspecialty training programs.

This issue of the Journal of the American Osteopathic College of Radiology focuses on the areas of both CCT and CMR. Through the collaboration of our local Departments of Radiology and Cardiology we have been able to build a very successful cardiac imaging program for which our patients and referring physicians have benefitted greatly. Our cardiac imaging program is now an integral part of our radiology residency and cardiology fellowship curriculum. This would not be possible without the alliance of both departments working side-by-side and is reflected in the quality of articles submitted into this edition of the journal.

The review articles cover differing aspects of cardiac imaging. These include an overview of differing published radiation doses as they pertain to cardiac imaging, the clinical application of CCT in the perioperative evaluation of cardiac risk in patients undergoing non-cardiac surgery, and an evaluation of myocardial perfusion imaging by CMR. These described novel

applications of both CCT and CMR cover upcoming areas of rapid utilization within the United States and provide the reader with a better understanding of where cardiac imaging is headed over the next few years.

The case specific articles describe some of the unusual findings that can present with even the most benign patient history. Metastatic carcinoid tumor, coronary fistulas, vascular rings and patterns of myocardial delayed enhancement on CMR are presented in differing formats in this edition. Each of these cases provide an interesting discussion which brings to light some of the complexities of imaging the heart and vascular system.

I would like to thank William O'Brien, D.O., Gerald York, M.D. and the AOCR for the chance to be a guest editor for this cardiac imaging issue. It is an honor as a cardiologist to be able to present our work to the AOCR community. All of our authors drew on experience gained while practicing at the San Antonio Military Medical Center. The challenge of balancing academic projects with the demands of military medicine cannot be understated but it is something that each and every one of the authors has risen to meet. With their efforts we have compiled a collection of articles that will leave the reader asking for more and hopefully be a starting point for other imaging programs to focus their efforts into the growing realm of cardiac imaging.

"In the long history

of humankind (and

animal kind, too)

those who learned

to collaborate and

improvise most

effectively have

prevailed."

-Charles Darwin

The views expressed in this material are those of the author, and do not reflect the official policy or position of the U.S. Government, the Department of Defense, or the Department of the Army or Air Force.

Page 2 J Am Osteopath Coll Radiol 2013; Vol. 2, Issue 2

Cardiac Perfusion, Jenson et al

Introduction

The lack of blood flow and oxygen delivery to myocardial tissue results in a progression of events. These events begin with subendocardial ischemia and, if oxygen delivery to the tissue does not improve, transmural ischemia will ensue. This is followed by diastolic dysfunction, systolic dysfunction, electrocardiographic changes, and finally angina. The early occurrence of abnormal perfusion in this cascade of events emphasizes the importance of perfusion imaging.

Multiple modalities have been employed to evaluate myocardial perfusion. These include fluoroscopic angiography, single photon emission computed tomography (SPECT), positron emission tomography (PET), contrast echocardiography, and cardiac magnetic resonance imaging (CMR). This article focuses on the myocardial perfusion techniques of CMR including contrast agents, pharmacologic stressors, sequences, imaging planes, image post processing, and future applications.

With the exception of contrast echocardiography, CMR is the only listed modality that does not require ionizing radiation, making it a useful tool for serial exams. CMR offers high spatial resolution which is ideal for evaluating the subendocardial layer. Rapid tracking of contrast agents utilizing CMR’s high temporal resolution provides detection of myocardial blood flow both under pharmacologic stress and rest. The perfusion characteristics can be combined with anatomic structure, function, and tissue characterization in the same exam. Additional imaging including blood flow characteristics of both right and left sided valves can also be completed. A myocardial perfusion study including cardiac structure, biventricular function, valvular assessment, stress and rest myocardial perfusion, and infarct imaging can be completed in 30 minutes. This makes stress CMR a well fitting modality in today’s complex multimodality imaging world.

Contrast Agents

Cardiac MR techniques are being explored for the possible perfusion assessment without IV contrast agents. However, until methods of blood oxygen level dependent (BOLD) imaging or arterial spin labeling (ASL) of the heart are perfected, IV contrast agents are required for perfusion assessment. MRI contrast agents function by affecting the relaxation rates of surrounding water protons. This quality is related to unpaired electrons as found in paramagnetic substances. While there are other paramagnetic metal ions, gadolinium is accepted as the standard MRI contrast agent. The majority of the different brands of gadolinium contrast agents all have similar properties when it comes to myocardial perfusion, differing predominantly in their chelation preparation around the gadolinium.1 Gadolinium chelates are water-soluble and are able to diffuse rapidly into the extracellular space across the capillary membrane. They are not, however, able to enter through intact cardiac cell membranes.

Coronary perfusion is the primary factor affecting the concentration of the gadolinium compound in the myocardial tissue. Myocardial ischemia is detected by reduced or delayed early-enhanced signal intensity. The heterogeneity of the ischemic tissue does not last long as recirculation leads to equilibration between the vascular and extracellular compartments, usually within seconds. This emphasizes the importance of first-pass imaging of the contrast agent.

The gadolinium contrast agent is delivered as a bolus intravenous injection. Intact right ventricular and left ventricular function is necessary to keep delivery of the agent to the coronary arteries in its concentrated state. Patients with impaired cardiac function, such as right or left ventricular dysfunction or valvular incompetence, can compromise the contrast delivery and should be recognized by the clinician prior to contrast injection.

Review of Cardiac MR Perfusion Imaging

Sheldon Jenson, D.O.a, Steven Craig, M.D.a, Gerald York, M.D.a, Kevin Steel, D.O. FACCb

aDepartment of Radiology, San Antonio Military Medical Center, San Antonio, TX

bCardiology Service, San Antonio Military Medical Center, San Antonio, TX



Gadolinium-based chelates are among the safest injectable contrast agents in current medical use and have a reputation for being safer than their X-ray contrast counterparts.1 Mild adverse reactions such as nausea and hives are among the most common adverse reactions and are self-limited. Despite its safety record, there are reports of serious adverse reactions, including life-threatening anaphylactic reactions with a rate between 1 in 200,000 and 1 in 400,000.2 Nephrogenic systemic fibrosis (NSF) is a very rare irreversible disease linked with gadolinium administration in the setting of advanced renal function impairment. Strict screening protocols of renal function prior to gadolinium administration have been put in place in to eliminate occurrence of this disease.

Pharmacologic stressors

Perfusion defects are more readily detected during stress conditions. First-pass imaging is commonly performed during chemical stimulation, which is used to increase blood flow to the myocardium. Physical stress is not a practical method of cardiac stress for CMR imaging due to limited space within the magnet bore and risk of creating motion artifacts.

Stenotic coronary vessels are unable to respond to the vasodilatory stimulation to the same degree as normal vessels, exaggerating regional differences in myocardial blood flow. The differences in regional signal intensity can be caused by loss of distal myocardial perfusion and redirection of flow to the epicardial layer. Generalized vasodilation may also impair high resistance collateral flow.

Historically, adenosine and dipyridamole have been the most commonly used pharmacologic stressors for vasodilatation. A newer agent approved by the FDA in 2008, Lexiscan® (regadenoson), has gained popularity. Adenosine acts on the vascular smooth muscle surface to cause vasodilation. Dipyridamole inhibits the cellular uptake and metabolism of adenosine thereby causing an increase in the interstitial adenosine concentration. Lexiscan® is an adenosine receptor agonist. These agents give rise to a super-physiologic increase in vascular flow as opposed to the approximate two-fold increase of vascular flow seen with dobutamine or exercise.

Contraindications to administering adenosine and adenosine agonists include asthma, high-grade AV block, sinus arrhythmia, stenotic valvular disease, and carotid artery stenosis. Several substances are competitive inhibitors of adenosine including aminophylline, theophylline, and other xanthine containing foods, such as coffee, tea, cocoa products, and soft drinks. These should be restricted for approximately 24 hours prior to the study. Due to the medications’ actions, patients can be become symptomatic reporting nausea, dizziness, flushing, and chest discomfort. Indications for stopping the infusion and terminating the scan include bronchospasm, ventricular arrhythmia, new onset AV block, and bradycardia. An antidote to both adenosine and dipyridamole of IV aminophylline should be on hand for immediate administration.

Dobutamine has also been used in CMR stress and perfusion imaging. Dobutamine increases heart rate, blood pressure and contractility similar to exercise. Using progressively increasing doses of dobutamine, the heart can be imaged to look for systolic dysfunction at high heart rates. Considering the progressive cardiac changes to ischemia, systolic dysfunction will precede both electrocardiographic changes and angina. Dobutamine has also been used in conjunction with adenosine for more complex stress CMR protocols. Dobutamine can also be used for evaluation of wall motion abnormalities. Studies have demonstrated dobutamine CMR to be a reliable tool in the decision making process to proceed to invasive procedures versus continuing with medical management.3

Adenosine has an extremely short half-life of 10-30 seconds. This characteristic makes it a more favorable agent in the setting of adverse reactions. Since becoming generic, adenosine has become less expensive. The protocol calls for giving adenosine over a 4-minute infusion. Dipyridamole has a half-life of 30 minutes. Adverse reactions have the potential to continue even after the administration of aminophylline. Lexiscan® has an intermediate biologic half-life and is injected over a 10-second duration. Dobutamine has a half-life of approximately 2 minutes. Side effects usually subside rapidly. Beta blockers and theophylline should be on hand to potentially treat a prolonged adverse event.



Imaging Protocol

Patients undergo first-pass contrast-enhanced CMR perfusion using a body coil or specialized cardiac coil. Scout imaging and cine short axis/long axis slices are performed initially to determine the cardiac position and geometry. The scouts are then used to plan the subsequent scans.

Imaging is performed at stress and rest during intravenous injection of the gadolinium-based contrast agent via a power injector at a rate of 5 mL per second. A single-shot gradient echo sequence with saturation-recovery magnetization preparation for T1 weighting and linear k-spacing is used for the first pass. Simulated stress imaging is performed with the infusion of a stress agent, as described previously. The scan is repeated at rest after adequate time for the effects of the stress agent to subside. (Movie 1, Figure 1).

Perfusion is determined in at least 3 short-axis slices of the left ventricle located at the base, middle, and apex. Additional long axis slices can be obtained if heart rate allows. The patient is asked to perform shallow breathing during the exam to minimize respiratory motion.

Delayed enhancement imaging is completed 10-15 minutes after the injection of gadolinium. The infarct information gained from this sequence has an additive diagnostic effect when used with both stress and rest perfusion imaging (Figure 2).

Image Post Processing

Contrast-enhanced magnetic resonance imaging can be used to evaluate myocardial perfusion patterns. Ideally, first-pass imaging with gadolinium-based contrast agents should result in images with signal intensity directly proportional to gadolinium concentration, allowing for accurate perfusion measurements. Perfusion can be qualitatively assessed or quantified using computer analysis of changes in signal intensity (SI) over time. Both relative and absolute flood blows can be quantified by the first-pass method. Quantification requires a rapid bolus of contrast by a power injector, producing a single sharp spike determined at time zero.

The heart is divided into 3 major segments – base, middle, and apex. The base and middle are divided into six sectors while the apex is divided into four (Figure 3). The apical cap is sometimes included if long axis perfusion is performed. Coronary distribution is assigned to their respective sectors using the 17-segment model for tomographic imaging of the heart (Figure 4).4,5 A comparison of the SI curve for each sector should be made with the left ventricular blood pool. This semi-quantitative image can be placed in a polar plot for quick review (Figure 5).

The initial amplitude of the SI curve corresponds with the absolute myocardial blood flow. The myocardial perfusion reserve can be calculated as the ratio of myocardial blood flow at stress over the myocardial blood flow at rest.

Applications

Conventional coronary angiography is the gold standard in evaluating the severity of obstructive coronary disease. However, the invasive nature, expense, and ionizing radiation involved with conventional coronary angiography make it an ineffective tool for screening purposes in patients with

Figure 1. Mid chamber short axis gadolinium first pass perfusion still select image demonstrating anteroseptal perfusion defect (black arrows).



Figure 2. Selected short axis images from an abnormal MRI perfusion scan showing associated mid anteroseptal and anterior wall motion abnormality, rest and stress perfusion abnormality (black arrows), and myocardial delayed enhancement (white arrows) consistent with infarct. (A) Short axis cine end diastole, (B) Short axis cine end systole, (C) Rest perfusion, (D) Adenosine stress perfusion, (E) Delayed enhancement.

Figure 3. Mid chamber short axis perfusion image divided into cardiac segments based on a 17-segment model. (1) Mid anterior, (2) Mid anterolateral, (3) Mid interolateral, (4) Mid inferior, (5) Mid inferoseptum, (6) Mid anteroseptum.

Figure 4. Mid chamber short axis perfusion image divided into coronary perfusion territories. Individual patients may demonstrate variability of these locales. (LAD) Left anterior descending coronary artery, (CFX) Circumflex coronary artery, (RCA) Right coronary artery.



suspected CAD. Other imaging modalities are available for risk stratification among these patients. A meta-analysis performed in 2007 showed CMR to have a sensitivity and specificity of approximately 85% for the detection of myocardial ischemic reactions in the setting of obstructive coronary lesions evaluated by conventional angiography.6 Another study looked at CMR as the sole clinical decision maker whether to proceed with invasive procedures versus continuing with medical management with results similar to baseline.3 A study performed by M. Costa et al suggests that quantitative CMR can be safely used to determine the hemodynamic significance of coronary stenosis and to exclude the presence of significant CAD with a high degree of accuracy.4 CMR has shown the ability to provide robust risk stratification for patients who present with symptoms of ischemia.7

Coronary artery disease is a major cause of morbidity and mortality in patients with diabetes

mellitus. A study by Coelho-Fiho et al in 2011 evaluated diabetic patients referred for suspicion of myocardial ischemia.8 They showed a correlation of a three-fold increase of a major adverse cardiac event in those that demonstrated evidence of ischemia on CMR perfusion. In a separate study, the authors also showed robust prognostic information for risk of major adverse cardiac events beyond the presence of scar, left ventricular ejection fraction, and clinical and ECG markers of cardiac prognosis.9

SPECT imaging has been a noninvasive workhorse in evaluating patients for suspected significant coronary artery disease. A single-center study out of Europe published in 2008, and a multi center follow on study in 2012, found CMR to be as effective as SPECT in detection of significant CAD and proposed CMR as a viable alternative to SPECT imaging for the workup of patients with known or suspected disease.10

Multiple studies have shown utilization of CMR to

Figure 5. Semi-quantitative myocardial perfusion analysis per cardiac segment with associated polar plots (courtesy of MedVoxel Systems, British Columbia, Canada).



5. Coelho-Filho et al.: Combined stress myocardial perfusion and

late gadolinium enhancement imaging by cardiac magnetic

resonance provides robust prognostic information to cardiac

events. Journal of Cardiovascular Magnetic Resonance 2011

13(Suppl 1):O2.

6. Manning WJ, Atkinson DJ, Grossman W, et al. First-pass

nuclear magnetic resonance imaging studies using gadolinium

-DTPA in patients with coronary artery disease. J Am Coll

Cardiol 1991;18:959-965.

7. Lauerma K, Virtanen KS, Sipila LM et al. Multislice CMR in

assessment of myocardial perfusion in patients with single-

vessel proximal left anterior descending coronary artery

disease before and after revascularization. Circulation

1997;96:2859-2867.

8. Nandalur KR, Dwamena BA, Choudhri AF, Nandalur MR, Carlos

RC: Diagnostic performance of stress cardiac magnetic

resonance imaging in the detection of coronary artery

disease: a meta-analysis. J Am Coll Cardiol 2007, 50:1343-

1353.

9. Gebker et al.: The role of dobutamine stress cardiovascular

magnetic resonance in the clinical management of patients

with suspected and known coronary artery disease. Journal of

Cardiovascular Magnetic Resonance 2011 13:46.

10. Schwitter J et al.: MR-IMPACT: Comparison of perfusion-

cardiac magnetic resonance with single-photon emission

computed tomography for the detection of coronary artery

disease ina a multicenter, multivendor, randomized trial. Eur

Heart J. 2008 Feb;29(4):480-9. Epub 2008 Jan 21.

11. Costa M et al.: Quantitative Magnetic Resonance Perfusion

Imaging Detects Anatomic and Physiologic Coronary Artery

Disease as Measured by Coronary Angiography and Fractional

Flow Reserve. J Am Coll Cardiol 2007, 50:514-522.

12. Cerqueria MD, Weissman NJ, Dilsizian V, et al. Standardized

myocardial segmentation and nomenclature for tomographic

imaging of the heart: a statement for healthcare professionals

from the Cardiac Imaging Committee of the Council on Clinical

Cardiology of the American Heart Association. Circulation

2002;105:539–542.

evaluate for reperfusion in patients status post revascularization.11,12 The increased perfusion correlated with regions of perfusion defects seen in preprocedural scintigraphy12 and coronary stenosis seen in prior angiography.11

Summary

CMR has the potential of being a one-stop shop when it comes to imaging evaluation of the heart. In contrast to other perfusion imaging modalities, CMR can offer noninvasive examination of the anatomy, function, and perfusion of the heart, all without the use of ionizing radiation. Contraindications for CMR include similar factors as those for other MR imaging. Newer MR safe cardiac pacers make it possible for pacer-dependent patients to receive a magnetic resonance imaging exam.

Studies continue to show the utility of CMR as a valuable imaging tool in the assessment of myocardial ischemia. Although more work needs to be done, CMR has a promising future in the comprehensive examination of myocardial perfusion.


References

1. Higgins CB, Roos AD. Cardiovascular CMR & MRA. Sensky PR,

Cherryman GR. Philadelphia: Lippincott Williams & Wilkins,

2003.

2. Edelman RR, Hesselink JR, Zlatkin MB, Crues JV. Clinical

Magnetic Resonance Imaging. Larson AC, Li D, Simonetti OP,

Oesingmann N. Philadelphia: Elsevier, 2006.

3. Carr JJ: Magnetic resonance contrast agest for neuroimaging:

Safety issues. Neuroimaging Clin N Am 4:43-54, 1994.

4. Coelho-Filho et al.: Stress myocardial perfusion imaging by

cardiac magnetic resonance provides strong prognostic value

to cardiac events in patients with diabetes. Journal of

Cardiovascular Magnetic Resonance 2011 13(Suppl 1):O87.


CCTA, Furgerson

Introduction

Perioperative cardiovascular complications resulting from non-cardiac surgery are an important cause of morbidity and mortality. Using a step-wise approach and selective cardiac testing, those at highest risk of cardiovascular complications can be identified and offered medical therapy and revascularization – when indicated – in order to reduce the risk of perioperative myocardial infarction and other cardiovascular complications and improve their overall prognosis. Currently used non-invasive techniques have some limitations, especially in those who cannot exercise adequately prior to surgery. Coronary computed tomography angiography (CCTA) is now a well-established non-invasive technique which is very effective at identifying those with advanced multivessel and left main coronary artery disease and may have a future role in the cardiac evaluation of patients prior to non-cardiac surgery. In this review, current guidelines on perioperative cardiovascular evaluation are reviewed with a focus on non-invasive imaging techniques, including CCTA.

Background

Perioperative cardiovascular complications of moderate to high risk surgery are an important source of morbidity and mortality. Of the approximately 230 million noncardiac surgeries performed each year worldwide, approximately 2,300,000 major cardiovascular events and 690,000 cardiovascular deaths result.1 The short term mortality associated with perioperative MI (PMI) is estimated at 3.5-25%, and the occurrence of PMI results in substantial increases in hospital stay and cost.2,3 Identification of patients who are harboring advanced coronary artery disease prior to surgery may allow for optimal risk reduction for cardiovascular events in the perioperative period using medical therapy and selective revascularization.

Noninvasive Preoperative Cardiovascular

Assessment

Current guidelines for preoperative cardiovascular assessment call for careful clinical assessment to identify active cardiovascular conditions, such as unstable angina, decompensated congestive heart failure, and severe valvular heart disease.4 In patients without active conditions, the use of additional testing to further define cardiovascular risk is controversial and is generally reserved only for cases when the outcome of such investigation will affect subsequent management.

Consideration of noninvasive testing for coronary artery disease is appropriate when the patient will be undergoing intermediate or high risk surgery, has poor functional capacity, and carries three or more clinical risk factors. While exercise testing is preferred, preoperative patients are frequently not capable of exercising adequately, and a history of poor functional capacity exacerbates the problem of effectively exercising patients as a form of risk stratification prior to the planned procedure. For those patients who cannot exercise adequately, the following noninvasive options are available: vasodilator nuclear perfusion imaging, dobutamine stress echocardiography, dobutamine magnetic resonance imaging, vasodilator magnetic resonance perfusion imaging, and coronary CT angiography (CCTA). The diagnostic accuracy of these techniques is given in Table 1.

Vasodilator nuclear perfusion imaging, using adenosine, dipyridamole, or a newer adenosine agonist is supported by robust clinical investigation data showing its value in predicting perioperative events and outcomes.5,6 However, nuclear perfusion imaging in general is hampered by the occurrence of soft tissue attenuation and other imaging artifacts which can adversely affect the specificity of the test and its corresponding positive predictive value. Additionally, in patients with advanced multivessel disease, the presence of "balanced ischemia" may give

Perioperative Cardiovascular Evaluation: Is There a Role for Coronary Computed Tomography Angiography?

James L. Furgerson, M.D.

Cardiology Service, Brooke Army Medical Center, Fort Sam Houston, TX


CCTA, Furgerson

a falsely negative test result, particularly when the added value of exercise ECG testing is not available.7

Dobutamine stress echocardiography also has extensive prior investigational data associated with its use in the periprocedural period,4 and is a useful test in patients who can tolerate dobutamine infusion and have adequate acoustic windows for detailed myocardial imaging, which is required for this test. While the risk of dobutamine infusion is relatively low and acceptable in most situations, care must be used to avoid precipitating ischemia and or complex ventricular arrhythmia with the administration of this agent. Additionally, considerable expertise is required on the part of the echocardiographic technician in obtaining adequate images and similar expertise is required by the interpreting physician, which may not be available in many centers.

Magnetic resonance imaging to detect inducible wall motion abnormalities with the infusion of dobutamine or by detection of perfusion defects with first pass imaging to vasodilator is well-developed in a few centers where operating characteristics are favorable compared with other noninvasive tests.8,9 However, this is not well proven in the perioperative setting.

CCTA is known to be a highly sensitive modality for detecting coronary atherosclerosis and has received increasing acceptance after multiple clinical trials have

shown very good accuracy when compared with invasive coronary angiography.10-12 Radiation exposure, use of radiocontrast media, and limited specificity when imaging patients with extensive coronary calcium, large body habitus, and irregular rhythm, have traditionally been detractors of this technology. However, with the latest technology, radiation exposure has become acceptable in most clinical scenarios, and arrhythmia and body habitus are less problematic than in the past.

Invasive Preoperative coronary Angiography

For preoperative patients who have undergone noninvasive testing, indications for preoperative invasive coronary angiography are similar to those identified in the nonoperative setting.13 Specifically, in the asymptomatic patient, the occurrence of high risk findings should lead to consideration for referral for invasive coronary angiography. Such high risk findings include greater than 10% ischemic myocardium or transient ischemic dilation by nuclear perfusion imaging, stress-induced wall motion abnormality in greater than or equal to two myocardial segments, or stress induced left ventricular dysfunction by stress echocardiography. In the patient with symptoms of ischemic heart disease, abnormal findings on noninvasive testing, baseline resting left ventricular

Table 1. Accuracy of Noninvasive Techniques for Detection of Coronary Artery Disease .

Modality Sensitivity Specificity

Exercise ECG (27) 0.68 0.77

Exercise Echo (28) 0.86 0.81

Dobutamine Echo (28) 0.85 0.85

Exercise Nuclear Perfusion (29) 0.87 0.73

Pharmacologic Nuclear (29) 0.86 0.75

Dobutamine MRI (9) 0.86 0.86

MRI Perfusion (8) 0.86 0.76

CT Coronary Angiography (11) 0.95 0.83


CCTA, Furgerson

dysfunction with a positive viability study, and high clinical suspicion of disease without further noninvasive testing would be indications for invasive coronary angiography. In a patient with established atherosclerotic heart disease, uncontrolled ischemic symptoms, which are worsening or limiting on medical therapy, and high risk findings by noninvasive testing might prompt referral for invasive coronary angiography.

Prophylactic revascularization prior to noncardiac surgery is a highly controversial practice. The rationale behind such revascularization seems to be that bypassing or dilating areas of high-grade stenosis within the coronary tree will prevent the occurrence of ischemia and ultimately infarction related to periods of high myocardial oxygen demand in the perioperative setting. However, this rationale is not well supported, and greater than half of all PMI is associated with in situ coronary thrombosis, which frequently occurs in areas without high-grade fixed disease preoperatively.14 Thus, the increase in inflammatory activity, procoagulant activity, and shear stress within the coronary tree and the affect of these factors on nonobstructive atheroma with subsequent plaque rupture and thrombosis is an important mechanism of PMI;3 this cannot be predicted by invasive coronary angiography or attenuated by coronary revascularization in many cases. However, some PMI is likely related to high-grade fixed disease and periods of supply-demand mismatch.15 Within the last decade, at least two important randomized clinical trials have been conducted to examine the role of prophylactic revascularization prior to high risk surgery.16,17 Both studies showed no improvement in short-term or long-term prognosis with successful preoperative coronary revascularization. Conversely, while also somewhat controversial, medical therapy using heart rate control has in general been shown to favorably affect outcomes in patients with ischemic heart disease when carefully provided.18-21

Current guidelines for prophylactic revascularization are based on traditional indications for coronary bypass surgery in improving survival in patients with advanced coronary artery disease.22 Such patients include those with greater than 50% left main stenosis, greater than 70% stenosis in 3 epicardial vessels, greater than 70% stenosis in the proximal LAD with one additional vessel stenosis, those with two-vessel

disease with extensive ischemia, and those with proximal LAD or two-vessel disease with left ventricular dysfunction and demonstrable viability. These indications for prophylactic revascularization are largely based on the individual’s coronary anatomy as determined by invasive coronary angiography. Additionally, a recent prospective randomized study of a systematic strategy of prophylactic coronary angiography versus a "selective strategy" using coronary angiography on the basis of abnormal noninvasive testing showed improvement in long-term outcome in patients who underwent routine invasive coronary angiography prior to vascular surgery.23

Cardiac CTA

CCTA is a highly sensitive test for coronary atherosclerosis with excellent sensitivity and specificity for coronary artery disease when compared with invasive coronary angiography (Figure 1).10-12 The negative predictive value for left main and left anterior descending artery obstruction by coronary CT angiography is especially high,24 which is of particular importance when identifying patients thought to benefit from prophylactic coronary revascularization prior to non-cardiac surgery. However, there are no randomized controlled data from clinical trials to examine outcomes when CCTA is used in the preoperative setting. It is currently considered an "uncertain" indication for preoperative assessment in patients waiting intermediate to high risk surgery with a low functional capacity and who carry three or more clinical risk factors.25

An ongoing clinical trial at Brooke Army Medical Center will examine the role of CCTA versus vasodilator nuclear perfusion imaging in the preoperative assessment of patients awaiting intermediate to high risk surgery with three or more clinical risk factors who cannot adequately exercise. Since many of the patients enrolling in the study will have peripheral vascular disease and by proxy underlying advanced coronary atherosclerosis, the presence of coronary calcium may become problematic in identifying patients with left main and proximal three-vessel disease by CT angiography. Conversely, with a relatively high pretest likelihood of advanced coronary atherosclerosis, the potential for a false negative vasodilator perfusion scan related to


CCTA, Furgerson

balanced ischemia will be a potential risk of the vasodilator perfusion imaging in this setting. If adequate coronary imaging can reliably be performed in this group of patients which will likely have rather advanced atherosclerosis, it is felt that CT coronary angiography will be an ideal method to identify patients at risk of ischemic complications in the perioperative period, as well as identifying patients who will benefit from prophylactic coronary revascularization and additional medical therapy.

It is likely that continued advances in CCTA, which will lessen imaging artifacts associated with coronary calcium, will lead to additional acceptance of the use of this modality in preoperative cardiovascular risk assessment. A similar anatomy-based approach has been suggested and is being tested in patients with non-acute symptoms of ischemic heart disease;30 it has been well established as a safe, effective, and cost-conscious means of evaluating those with acute symptoms of possible acute coronary syndrome and low or intermediate pretest probability of coronary artery disease.26

Summary

Perioperative cardiovascular complications resulting from non-cardiac surgery are an important cause of morbidity and mortality. Using a step-wise approach and selective cardiac testing, those at highest risk of cardiovascular complications can be identified and offered medical therapy and revascularization when indicated in order to reduce the risk of perioperative myocardial infarction and other cardiovascular complications and improve their overall prognosis. Currently used non-invasive techniques have some limitations, especially in those who cannot exercise adequately prior to surgery. Coronary computed tomography angiography (CCTA) is now a well-established non-invasive technique which is very effective at identifying those with advanced multi-vessel and left main coronary artery disease. Since much of the data supporting current guidelines on medical management and coronary revascularization of those at risk for perioperative adverse cardiovascular events are based on the presence and

Figure 1. Correlation of CT Angiography with Invasive Coronary Angiography. Reformatted cardiac CTA images (A thru C) demonstrate obstruction of the mid right coronary artery. Corresponding image by invasive coronary angiography (D) demonstrates similar/identical findings.


CCTA, Furgerson

severity of anatomic coronary stenoses, there is a strong rationale for use of CCTA in the preoperative assessment of these patients. Additional research data are needed to establish CCTA as an effective means of cardiovascular risk assessment prior to intermediate or high risk surgery. With further improvements in CCTA imaging technology, which will lessen the impact of coronary calcium on image quality, and additional research efforts, it is likely that CCTA will be accepted as an effective means of preoperative risk assessment. strategies.

8. Jaarsma C, Leiner T, Bekkers SC, et al. Diagnostic performance of noninvasive myocardial perfusion imaging using single-photon emission computed tomography, cardiac magnetic resonance, and positron emission tomography imaging for the detection of obstructive coronary artery disease: a meta-analysis. J Am Coll Cardiol. 2012;59(19):1719-28.

9. Nagel E, Lehmkuhl HB, Bocksch W, Klein C, Vogel U, Frantz E, et al. Noninvasive diagnosis of ischemia-induced wall motion abnormalities with the use of high-dose dobutamine stress MRI: comparison with dobutamine stress echocardiography. Circulation. 1999;99(6):763-70.

10. Meijboom WB, Meijs MF, Schuijf JD, et al. Diagnostic accuracy of 64-slice computed tomography coronary angiography: a prospective, multicenter, multivendor study. J Am Coll Cardiol. 2008;52(25):2135-44.

11. Budoff MJ, Dowe D, Jollis JG, et al. Diagnostic performance of 64-multidetector row coronary computed tomographic angiography for evaluation of coronary artery stenosis in individuals without known coronary artery disease: results from the prospective multicenter ACCURACY (Assessment by Coronary Computed Tomographic Angiography of Individuals Undergoing Invasive Coronary Angiography) trial. J Am Coll Cardiol. 2008;52(21):1724-32.

12. Miller JM, Rochitte CE, Dewey M, Arbab-Zadeh A, Niinuma H, Gottlieb I, et al. Diagnostic performance of coronary angiography by 64-row CT. N Engl J Med. 2008;359(22):2324-36.

13. Patel MR, Bailey SR, Bonow RO, et al. ACCF/SCAI/AATS/AHA/ASE/ASNC/HFSA/HRS/SCCM/SCCT/SCMR/STS 2012 Appropriate Use Criteria for Diagnostic Catheterization: A Report of the American College of Cardiology Foundation Appropriate Use Criteria Task Force, Society for Cardiovascular Angiography and Interventions, American Association for Thoracic Surgery, American Heart Association, American Society of Echocardiography, American Society of Nuclear Cardiology, Heart Failure Society of America, Heart Rhythm Society, Society of Critical Care Medicine, Society of Cardiovascular Computed Tomography, Society for Cardiovascular Magnetic Resonance, and Society of Thoracic Surgeons. J Am Coll Cardiol. 2012;59(22):1995-2027.

14. Dawood MM, Gutpa DK, Southern J, et al. Pathology of fatal perioperative myocardial infarction: implications regarding pathophysiology and prevention. Int J Cardiol. 1996;57(1):37-44.

15. Landesberg G. Monitoring for myocardial ischemia. Best Pract Res Clin Anaesthesiol. 2005;19(1):77-95.

16. McFalls EO, Ward HB, Moritz TE, et al. Coronary-artery revascularization before elective major vascular surgery. N Engl J Med. 2004;351(27):2795-804.

17. Schouten O, van Kuijk JP, Flu WJ, et al. Long-term outcome of prophylactic coronary revascularization in cardiac high-risk patients undergoing major vascular surgery (from the randomized DECREASE-V Pilot Study). Am J Cardiol. 2009;103(7):897-901.

18. Dunkelgrun M, Boersma E, Schouten O, et al. Bisoprolol and fluvastatin for the reduction of perioperative cardiac mortality and myocardial infarction in intermediate-risk patients undergoing noncardiovascular surgery: a randomized controlled trial (DECREASE-IV). Ann Surg. 2009;249(6):921-6.


References

1. Weiser TG, Regenbogen SE, Thompson KD, et al. An estimation of the global volume of surgery: a modelling strategy based on available data. Lancet. 2008;372(9633):139-44.

2. Mackey WC, Fleisher LA, Haider S, et al. Perioperative myocardial ischemic injury in high-risk vascular surgery patients: incidence and clinical significance in a prospective clinical trial. J Vasc Surg. 2006;43(3):533-8.

3. Landesberg G, Beattie WS, Mosseri M, et al. Perioperative myocardial infarction. Circulation. 2009;119(22):2936-44.

4. Fleisher LA, Beckman JA, Brown KA, et al. ACC/AHA 2007 guidelines on perioperative cardiovascular evaluation and care for noncardiac surgery: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Revise the 2002 Guidelines on Perioperative Cardiovascular Evaluation for Noncardiac Surgery) developed in collaboration with the American Society of Echocardiography, American Society of Nuclear Cardiology, Heart Rhythm Society, Society of Cardiovascular Anesthesiologists, Society for Cardiovascular Angiography and Interventions, Society for Vascular Medicine and Biology, and Society for Vascular Surgery. J Am Coll Cardiol. 2007;50(17):e159-241.

5. Shaw LJ, Eagle KA, Gersh BJ, et al. Meta-analysis of intravenous dipyridamole-thallium-201 imaging (1985 to 1994) and dobutamine echocardiography (1991 to 1994) for risk stratification before vascular surgery. J Am Coll Cardiol. 1996;27(4):787-98.

6. Hendel RC, Whitfield SS, Villegas BJ, et al. Prediction of late cardiac events by dipyridamole thallium imaging in patients undergoing elective vascular surgery. Am J Cardiol. 1992;70(15):1243-9.

7. Berman DS, Kang X, Slomka PJ, et al. Underestimation of extent of ischemia by gated SPECT myocardial perfusion imaging in patients with left main coronary artery disease. J Nucl Cardiol. 2007;14(4):521-8.


CCTA, Furgerson

26. Hoffmann U, Bamberg F, Chae CU, et al. Coronary computed tomography angiography for early triage of patients with acute chest pain: the ROMICAT (Rule Out Myocardial Infarction using Computer Assisted Tomography) trial. J Am Coll Cardiol. 2009;53(18):1642-50. PMCID: 2747766.

27. Gibbons RJ, Balady GJ, Bricker JT, et al. ACC/AHA 2002 guideline update for exercise testing: summary article. A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee to Update the 1997 Exercise Testing Guidelines). J Am Coll Cardiol. 2002;40(8):1531-40.

28. Cheitlin MD, Armstrong WF, Aurigemma GP, et al. ACC/AHA/ASE 2003 guideline update for the clinical application of echocardiography--summary article: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (ACC/AHA/ASE Committee to Update the 1997 Guidelines for the Clinical Application of Echocardiography). J Am Coll Cardiol. 2003;42(5):954-70.

29. Klocke FJ, Baird MG, Lorell BH, et al. ACC/AHA/ASNC guidelines for the clinical use of cardiac radionuclide imaging--executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (ACC/AHA/ASNC Committee to Revise the 1995 Guidelines for the Clinical Use of Cardiac Radionuclide Imaging). J Am Coll Cardiol. 2003;42(7):1318-33.

30. Prospective Multicenter Imaging Study for Evaluation of Chest Pain (PROMISE). http://clinicaltrials.gov/ct2/show/NCT01174550, accessed July 14, 2012.

19. Mangano DT, Layug EL, Wallace A, et al. Effect of atenolol on mortality and cardiovascular morbidity after noncardiac surgery. Multicenter Study of Perioperative Ischemia Research Group. N Engl J Med. 1996;335(23):1713-20.

20. Poldermans D, Boersma E, Bax JJ, et al. The effect of bisoprolol on perioperative mortality and myocardial infarction in high-risk patients undergoing vascular surgery. Dutch Echocardiographic Cardiac Risk Evaluation Applying Stress Echocardiography Study Group. N Engl J Med. 1999;341(24):1789-94.

21. Devereaux PJ, Yang H, Yusuf S, et al. Effects of extended-release metoprolol succinate in patients undergoing non-cardiac surgery (POISE trial): a randomised controlled trial. Lancet. 2008;371(9627):1839-47.

22. Patel MR, Dehmer GJ, Hirshfeld JW, et al. ACCF/SCAI/STS/AATS/AHA/ASNC/HFSA/SCCT 2012 appropriate use criteria for coronary revascularization focused update: a report of the American College of Cardiology Foundation Appropriate Use Criteria Task Force, Society for Cardiovascular Angiography and Interventions, Society of Thoracic Surgeons, American Association for Thoracic Surgery, American Heart Association, American Society of Nuclear Cardiology, and the Society of Cardiovascular Computed Tomography. J Thorac Cardiovasc Surg. 2012;143(4):780-803.

23. Monaco M, Stassano P, Di Tommaso L, et al. Systematic strategy of prophylactic coronary angiography improves long-term outcome after major vascular surgery in medium- to high-risk patients: a prospective, randomized study. J Am Coll Cardiol. 2009;54(11):989-96.

24. Meijboom WB, Van Mieghem CA, van Pelt N, Weustink A, et al. Comprehensive assessment of coronary artery stenoses: computed tomography coronary angiography versus conventional coronary angiography and correlation with fractional flow reserve in patients with stable angina. J Am Coll Cardiol. 2008;52(8):636-43.

25. Taylor AJ, Cerqueira M, Hodgson JM, et al. ACCF/SCCT/ACR/AHA/ASE/ASNC/NASCI/SCAI/SCMR 2010 Appropriate Use Criteria for Cardiac Computed Tomography. A Report of the American College of Cardiology Foundation Appropriate Use Criteria Task Force, the Society of Cardiovascular Computed Tomography, the American College of Radiology, the American Heart Association, the American Society of Echocardiography, the American Society of Nuclear Cardiology, the North American Society for Cardiovascular Imaging, the Society for Cardiovascular Angiography and Interventions, and the Society for Cardiovascular Magnetic Resonance. Circulation. 2010;122(21):e525-55.


Radiation Exposure, Nayar et al

Synopsis

Diagnostic modalities for CAD involving ionizing radiation have rapidly increased over recent years despite direct epidemiological evidence from atomic bomb survivors of the stochastic risks of radiation exposure. Although the individual patient risk of cancer is small with a favorable risk-benefit ratio even for high-dose radiological procedures, concerns arise when imaging is used without proven clinical rationale, when alternative modalities can be employed with equal efficacy, or when imaging is repeated unnecessarily secondary to inadequate communication within the medical care community1. Research demonstrates that physicians and patients who undergo diagnostic imaging involving significant radiation exposure have insufficient awareness of the environmental impact, biorisk, and the dose exposure from radiation.2-4 The most widely used studies include nuclear medicine myocardial perfusion imaging, computed tomography coronary, aortic and pulmonary angiography, and cardiac catheterization. The methodology used to quantify radiation exposure, the doses associated with typical protocols, and the techniques employed to reduce exposure are addressed. Greater radiation awareness among providers may prompt use of alternative imaging, more careful selection of current imaging and patients, and changes in imaging technique or equipment to decrease cancer risk from future diagnostic imaging.

Introduction

Coronary artery disease (CAD) is the leading cause of mortality in the United States, accountable for 1 in 5 deaths, and is associated with $142 billion in annual health care expenditures.5 Diagnostic imaging modalities have rapidly advanced such that medical exposures now represent the majority of effective radiation dose individuals receive; this has increased seven-fold over the past 25 years.1,6 It is estimated

that >10% of overall radiation exposure to a U.S. inhabitant is attributable to nuclear and radiologic tests.2

As the diagnostic gold standard for CAD, coronary angiography procedures have increased from 2.45 to 3.85 million annually over the course of almost a decade from 1993 to 2002.7 Noninvasive modalities with ionizing radiation have also significantly expanded. In 1990, fewer than 3 million nuclear medicine studies were performed in the United States; however, by 2002, this number more than tripled to 9.9 million.8 Specifically, high-dose, dual isotope myocardial perfusion imaging (MPI) is among the highest of all medical diagnostic tests; nonetheless, its use nearly doubled from 19 to 30% between 1997 to 2002, and it currently comprises 36% of all outpatient MPI tests9. Given that 72% of approximately 6 million patients who present for chest pain annually in U.S. emergency rooms will be hospitalized,5 computerized tomography coronary angiography (CTCA) provides a rapid diagnostic tool for triage. However, up to one-third of CT scans in the U.S. are ordered without proven clinical rationale, when alternative modalities are equally efficacious. or are repeated unnecessarily.1 Despite radiation exposure and clinical indication concerns, the volume of computed tomography (CT) scans has increased over 20-fold over the past 25 years and is now equivalent to more that 62 million scans annually.1,10

Dosimetry

Although imaging procedures are ideally performed in accordance with the As Low As Reasonably Achievable (ALARA) principle,9 there is direct epidemiologic evidence of the stochastic implications of even low-dose radiation, such as that from a few CT scans or from other high-dose radiologic procedures.1,10-12 The updated stochastic effects of low-dose ionizing radiation are addressed in the BEIR VII report.13 The risk depends on the absorbed dose, type

Radiation Exposure and Associated Cancer Risk With Cardiac Diagnostic Imaging

Anjeli K. Nayar, M.D.a; Bryan M. White, M.D., FACCb; Kenneth E. Stone, M.D.a; Ahmad M. Slim, M.D.a

aCardiology Service, San Antonio Military Medical Center, San Antonio, TX

bCardiology Service, Wright-Patterson Medical Center, Dayton, OH



of radiation, and the specific organ or tissue irradiated. Many radiation organizations support the linear no-threshold model (LNT) such that cancer risk proceeds in linear fashion without a lower threshold. In general, stochastic risks have been shown to decrease with age, are higher in women, and are dependent on underlying predisposing factors unique to the patient.

The effective dose (E) is a common index value to compare patient radiation exposure from different diagnostic procedures, regardless of the medical facility or type of imaging performed. It is the weighted average of the mean absorbed radiation dose to various body organs that is multiplied by a tissue weighting factor published by the International Commission on Radiological Protection (ICRP). Equivalent dose is a radiation protection quantity related to the stochastic risk from absorbed doses in a population exposed to radiation.14 Cristner et al demonstrated that effective dose approximations may vary substantially depending on which tissue weighting coefficients published in various ICRP publications are used.15 Specifically, the most significant variance is demonstrated in deriving coronary artery E from CT chest examinations depending on which breast tissue weighting factor is used.15 There are various ways for determining E for nuclear medicine, computed tomography, and fluoroscopy. Current dosimetry models allow only estimates of doses that vary with the patient’s weight and organ size, assuming standardized biokinetic data and uniform radiopharmaceutical activity within organs.9 Dose reference levels (DRL) have been proposed by the ICRP as protection quantities used to establish limits of exposure to both workers and the general public.

Nuclear Medicine Myocardial Perfusion (MPI)

The ICRP has compiled a series of models and dosimetry tables for a variety of radiopharmaceuticals, the most recent in 2007, Publication 103.16 MPI at the San Antonio Military Medical Center is largely performed with technetium (99mTc) sestamibi, or Cardiolite. Patients receive two doses of technetium-99m sestamibi total: 8 mCi for rest and 24 mCi for stress testing in single-day imaging process. Although manufacturers provide package inserts (PI), the total body dose that is reported is lower than the effective dose and fails to consider nonuniform dose

distribution.9 The effective dose to a typical patient during a standard cardiac study may be estimated by using dose coefficients, tissue weighting factors, radionuclide activities, and mathematical equations. Although studies have shown the effective dose for MPI may range from 2.2 – 31.5 mSv, the mean for a 99mTc-sestamibi rest-stress 1-day protocol have been cited as 9.4 and 11.1,6, 9 which is approximately 512 times more radiation than a posterior-anterior chest radiography (0.02 mSv)2 and 3 times more than the annual background radiation in the United States (3 mSv).17 This corresponds to an estimated lifetime attributable risk (LAR) of 1 cancer in 1,000 exposed subjects, per the BIER VII Committee 2005,25 with an LAR of fatal cancer of >1 in 10,000 cases.2

Computed Tomography

With CT, radiation exposure is expressed as volume CT dose index (CTDI vol), which is the average radiation dose over a volume scanned expressed in units of mGy * cm.9,10 The integrated sum comprises the dose length product (DLP) for the complete CT exam. In practice, the actual dose may be measured using any of the following three approaches: 1) calculations based physical phantoms measurements; 2) CTDI vol or DLP values modified by a conversion coefficient (k); or 3) Monte Carlo simulations that model photon transport through a simulated, mathematical patient phantom taking into account tissue-weighting factors.9,15 Huda et al has introduced E/DLP conversion factors specific for cardiac CT examinations that depend on the proximity of the radiographic (X-ray) beam to the heart, increase as X-ray tube voltage increases, and are modified by patients’ weight.18

Until recently, conventional chest CT scans had been used to approximate E from cardiac CT exams; however, the cardiac region has shown to be more radiosensitive than previously assumed. Organ dose for CT coronary angiography (CTCA) may range from 40-100 mGy, compared to 0.01-0.15 mGy for a chest radiograph.1 Prior studies have shown that the mean effective dose for CTCA ranges from 5-32 mSv;6 female breasts, lungs, liver, and esophagus correlate with the highest equivalent doses. 9 Average mean effective doses have been cited as 12 and 16 mSv,5, 6 though estimations are scanner dependent. Philips 16-slice



scanners average 4.9 and 8.1 mSv with and without electrocardiography-controlled tube current modulation (ECTCM), respectively. Per Einstein et al, the LAR of cancer from CTCA without ECTCM using Monte Carlo simulations and the BEIR VII approach to determine cancer risk for women aged 20, 40, 60 and 80 years was 1 in 143, 1 in 284, 1 in 466, and 1 in 1338, respectively.5 The risk decreased as a function of age with the greatest proportion of cancers derived from breast and lung tissues.5 Comparatively, for men of the same age groups, the LAR of cancer was 1 in 686, 1 in 1007, 1 in 1241, and 1 in 3261.5 Although reducing the tube current by 35% resulted in an estimated 35% cancer risk reduction, the greater stochastic risk to females across all age groups was suspected secondary to their increased intrinsic radiosensitivity and degree of breast tissue exposure.5

In a retrospective review of 1119 consecutive adult patients by Smith-Bindman et al, the range of effective doses for computed tomography pulmonary angiography (CTPA) was 2-30 (median 8) mSv,19 similar to that cited by Mettler (13-40 mSv with a mean of 15 mSv).6 The effective dose range for an abdominal CT to evaluate for dissection ranged from 4-69 (median 24) mSv.19 The LAR of cancer for a CTPA and an abdominopelvic aortic dissection CT scan in a 20-year-old woman was approximately 1 in 330 exposed female patients.19 This was approximately 1.3 times the risk in males of the same age, though it decreased for both genders by an approximate factor of 1.5 with every 20-year increase in age. The gender disparity in risk with increasing age was comparatively less with aortic dissection CT scans.19

In general, radiation doses for computed tomography scans may vary significantly between and within study types, as well as within and across medical institutions. Effective dose also depends on the number of scans obtained, patient size, the product of tube current and scan time (mAs), and various scanner parameters, including design, pitch, axial range, and maximum tube voltage (kVp).1,10

Coronary Angiography

Radiation from coronary angiography is reported as the dose-area product (DAP) or air kerma (KAP), which is energy released per unit mass of irradiated air multiplied by radiographic beam cross-sectional area;

it is measured in units of Gy*cm squared. 9 Similar to CT imaging, dose measurements can be performed via one of three ways which result in similar E estimates: 1) use of physical anthropomorphic phantoms; 2) DAP values modified by a conversion factor; or 3) Monte Carlo simulations.9 Conversion factors may range from 0.12 to 0.26 mSv [Gy * cm2] -1, although the most widely used are proposed by the National Radiological Protection Board (NRPB) and may vary depending on the radiographic view. Skin dose may be measured with thermoluminescence dosimeters; however, DAP provides a more accurate estimation of E since it considers body surface area and secondary extent of body organ irradiation.

Mean effective doses from conventional coronary angiography may vary widely, from 2.3 - 22.7 mSv, secondary to procedural complexity, protocol, equipment, and operator skill.6,9,20,21 Coronary percutaneous transluminal angioplasty procedures may impart from 6.9 - 57 mSv, with a mean of 15 mSv,6 translating to approximately 5-fold greater radiation exposure than annual background radiation (3 mSv) and a 700-fold increase in radiation compared to a posteroanterior chest radiograph (0.02 mSv).6,22 Typically, fluorography contributes to the majority and fluoroscopy to less than half of the radiation dosage for diagnostic cardiac catheterizations.9 Leung and Martin’s study of six cardiologists showed an average E of 1.1 mSv from fluoroscopy during left heart catheterizations and an average total E of 3.1 mSv.21 In comparison, Mettler et al estimates 7 mSv as the average effective dose for diagnostic coronary angiography.6 For right heart catheterizations and coronary bypass grafts performed, ≥ 50% DAP originated from fluoroscopy.21 The third quartile of actual measurements has been accepted in most publications as the diagnostic reference level (DRL), specifically 105 Gy*cm2 per the ICRP Publication 60.8 This level provides a radiation dose reference at which acceptable image quality and diagnostic information should be achieved commensurate with the medical imaging task.

Increased effective doses have been associated with radial approach catheterizations.23 Similarly, specific projections, such as the right anterior oblique caudal and left anterior oblique cranial, account for a disproportionately high percentage of KAP.21, 22 A prior study determined the total risk of developing fatal



cancer over forty years following percutaneous coronary intervention was 84 and 68 per 100,000 patients for men and women, respectively22. Overall, the effective dose received depends on multiple factors including operator experience, technique, and lab equipment.9, 22

Estimating Cancer Risk From Radiation

As Hall et al proposes, epidemiological data from atomic bomb survivors have provided the “gold standard” in the quantitative assessment of carcinogenic risk from low-dose radiation, such as from cardiac diagnostic imaging, for several reasons: 1) the study involves a large, randomized population of approximately 100,000 persons of both genders and spanning all ages; 2) approximately 30,000 survivors were exposed to low-dose radiation between 5-100mSv (mean dose 40 mSv), equivalent to exposure from single and multiple CT scans; 3) cancer incidence and mortality data has surfaced since the study’s inception over sixty years ago; and 4) mortality follow-up is nearly completed for those exposed as adults and >50% for those exposed as children.1, 22 The current, unanimous consensus among national and international organizations for exposures less than 100 mSv is the “linear no-threshold” (LNT) model that proposes risk of stochastic effects decreases linearly without threshold with decreasing radiation dose.5, 24-

26 Though unproven, this hypothesis may still be applied to many cardiac imaging procedures, since they impart doses in ranges where credible, direct evidence has shown increased cancer risk.

Several analyses of atomic bomb survivors have concluded that the lowest mean dose associated with a statistically significant estimate of excess relative risk (ERR) is about 35 mSv, equivalent to maximum organ doses imparted by two or three CT scans.11,12 Furthermore, a large study piloted by the International Agency for Research on Cancer (IARC) of 400,000 nuclear industry workers exposed to a mean dose of 20 mSv showed a statistically significant ERR estimate of 0.97 per Sv, resulting in 1-2% of cancer deaths attributable to radiation; this is statistically consistent with atomic bomb survivor data.27, 28 These findings have been further supported by preliminary results of the Techa River in Russia, a large-scale, low-dose cohort study.29 The Biological Effects of Ionizing

Radiation (BEIR VII, Phase 2) committee has since developed LAR of cancer risk models based on atomic bomb survivor data in response to the US Environmental Protection Agency’s request to evaluate the health effects of low level ionizing radiation.5

Prior studies have shown lung and breast malignancy are primary contributors to lifetime attributable risk (LAR) of cancer, a finding reflected by the increased breast tissue weighting factor in the most recent ICRP Publication 103.5 Incidence is highest in women and in children and young adults since the radiosensitivity of many organs decreases with age. A long lag time is typical from acute radiation exposure to the development of malignancy, which may not ultimately manifest in the elderly or those with decreased life expectancy.

Despite extensive epidemiologic based research, extrapolated data only provides estimates of stochastic risk from radiation exposure. Limitations in the BEIR VII risk models include the methods used to transpose Japanese atomic bomb survivor data to U.S. populations given their disparate baseline cancer rates, sampling variability, dose and dose-rate effectiveness factor (DDREF), biological aspects of different sources of ionizing radiation,n and assumptions derived from the theoretical LNT model.8 In Report 126, the US National Council on Radiological Protection and Measurements (NCRP) quantified various estimations of uncertainty in total fatal cancer risk derived from epidemiological (±25%) and dosimetric (0-30%) data, the transfer of risk between populations (-30 to +65%), and projections to lifetime risk (-50 to +10%).30 The overall uncertainty was a factor of approximately 3 above and below the estimated value with the greatest contributor from extrapolation of risk for doses lower than those considered in the atomic bomb study.30

Methods to decrease radiation exposure

Studies show that patients undergoing diagnostic imaging involving significant radiation exposure have little, if any, awareness of the nuclear medicine dose and the associated risk of cancer.2-4 Furthermore, there is a general lack of awareness among physicians, regardless of specialty, gender or age, regarding the dose exposure, environmental impact, and biorisk of radiation. As awareness of stochastic implications



grows within the context of unrestricted access to technology, it is incumbent on the medical community to identify and execute radiation-sparing techniques.

Myocardial perfusion imaging dose exposure can be reduced by using a stress first/stress only protocol with 99mTc sestamibi for patients with a low CAD pre-test probability.9 However, diagnostic performance and prognostic value have not been extensively evaluated for this strategy compared to combined stress and rest imaging. Although a second visit may be warranted for some patients, appropriate communication between physicians and nuclear medicine personnel to ensure accurate pretest risk stratification may decrease this probability.9 Adequate hydration and early micturition are also encouraged during post-exposure care.

For computed tomography, effective dose may be decreased via minimizing the number of scans received, limiting the exposed scan region, and optimizing tube current and voltage with respect to the scanner type and patient habitus.9 Using multiple x-ray sources and longer detection rays can also increase the pitch of the scan and reduce overlap between gantry rotations.9 Additionally, prospective gating combined with “step-and-shoot” non-spiral scanning can result in significant exposure reductions.31 For CTCA specifically, electrocardiogram-controlled tube current modulation (ECTCM) can optimally decrease the dose nearly 50% by employing reduced tube current during the cardiac cycle intervals in which coronary motion precludes reliable data collection. Similarly, adjuvant use of beta-blockers can decrease coronary artery velocity to improve image quality and decrease exposure times.5,9 Although CTCA bypasses the complication risks of invasive coronary angiography, such imaging should be avoided in young women, despite radiation-reducing methods, given their particular radiosensitivity.

Strategies to minimize ERR from fluoroscopy and fluorography of cardiac catheterization include employing the slowest times frames, the least image magnification, and the fewest number of views without simultaneously compromising image quality or diagnostic accuracy. Other methods include minimizing the distance between the image detector and x-ray tube to the patient, optimizing beam collimation, and shielding all radiosensitive organs. Additionally, left ventriculography may be omitted if

the information can be ascertained via other tests. Fluorography (cineography) time should also be limited as much as possible during coronary procedures.22

Conclusion

In this expanding field of ionizing radiation, technological advancements must be cautiously weighed in light of various unknowns. For example, further research is needed regarding the effects of age, gender, and body habitus on dosimetry as the degree of estimation uncertainty increases with patient anatomical variation from phantom models used to derive tissue weighting factors. Clarification of radiation levels leading to stochastic verse deterministic effects is also important; in other words, determining the maximum exposure thresholds that may induce cancer compared to organ toxicity and tumor cell kill.14 Furthermore, despite various radiation reduction strategies, the resulting sensitivity, specificity, and dosimetry of each requires further exploration. At this point, there are no large-scale epidemiologic studies of the cancer risk specifically associated with medical imaging.

In summary, diagnostic modalities for CAD involving ionizing radiation have rapidly increased over recent years despite direct epidemiological evidence of the stochastic risks of exposure. This poses significant ethical concerns, demanding greater radiation awareness within the medical community and potential broadening of informed consent to include the stochastic risks of radiation.3,17,32 For the majority of radiologic procedures, the clinical indication exceeds the potential risk; however, alternative imaging modalities of equal efficacy should be considered as appropriate. Particular caution should be employed in cases of inadequate clinical rationale, when inadequate communication may result in unnecessary repetition of studies, or for defensive medicine purposes.1,10 Careful selection of patients and optimization of scanning protocols may help to limit cancer risk from radiation.




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Cardis E, Cox R, Davis S, Dewey WC, Gilbert ES, Kellereer AM,

Krewski D, Lindahl TR, Rowan KE, Sankaranarayanan K, Schafer

DW, Stefanski LA, Ullrich RL, Jostes R. National Research

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Organ Doses: Consequences of Adopting International

Commission on Radiological Protection Publication 103 or

Dual-Energy Scanning. American Journal of Roentgenol.

2010;194(4):881-9.

16. 2007 Recommendations of the International Commission on

Radiological Protection: ICRP Publication 103. Ann ICRP.

Excerpt available at: http://www.icrp.org/docs/

ICRP_Publication_103_Annals_of_the_ICRP_37(2-4)-

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19. Smith-Bindman R, Lipson J, Marcus R, Kim KP, Mahesh M,

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Jankowski J, Torbica P, Kepler K, Dowling A, Milu C, Tsapaki V,

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Case Report, Betts et al

Delayed Myocardial Enhancement

Aaron Betts, M.D., Daniel A. Dolewski, M.D., Gerald York, M.D.

Department of Radiology, San Antonio Military Medical Center, San Antonio, Texas

Figure. Delayed enhancement cardiac MRI demonstrates full-thickness enhancement of the anterolateral wall (yellow arrow).

Case Presentation

A 50-year-old woman with a 40 pack-year smoking history suffered a large myocardial infarction and underwent 2-vessel percutaneous coronary intervention with placement of bare metal stents. Follow-up transthoracic echocardiogram showed depressed left-ventricular ejection fraction (estimated 25-30%) with anterior wall motion abnormalities. However, the patient denied symptoms of congestive heart failure. Physical examination showed no jugular venous distension or peripheral edema. Heart rate and rhythm were normal without murmurs. Lungs were clear to auscultation. Patient was referred for cardiac MRI to measure ejection fraction, assess myocardial viability and scar, and further characterize wall motion abnormalities. Cardiac MRI showed a large area of full-thickness delayed enhancement in the lateral wall of the left ventricle with some involvement of the anterolateral and inferolateral walls. (Fig.) Left ventricular ejection fraction measured 46%.



Key clinical finding

Wall motion abnormalities and diminished LVEF on echocardiogram.

Key imaging finding

Delayed myocardial enhancement

Differential diagnoses

Myocardial infarction

Myocarditis

Non-ischemic cardiomyopathies

Discussion

Delayed gadolinium-enhanced magnetic resonance imaging can be used to evaluate pathologic processes that affect the myocardium. Gadolinium enhancement follows a predictable course through the cardiac blood pool, coronary circulation, and myocardial interstitium. Many pathologic processes of the myocardium will cause delayed washout of the gadolinium from the myocardium. Using a pulse sequence with an initial saturation pulse that nulls the signal of normal myocardium will yield sensitive evaluation for delayed myocardial enhancement. Dynamic fast gradient echo sequences can also be used for evaluation of left ventricular function and ejection fraction.1

Myocardial infarction.

Myocardial infarction is caused by compromised coronary blood flow due to in situ thrombus, vasospasm, or hypoperfusion.2 In acute myocardial infarction, there may be hypoenhancement due to persistence of compromised blood flow within the infarct core on first-pass gadolinium enhanced images. However, if there has been reperfusion, the infarct core may not always be visualized. On delayed imaging, there will be hyperenhancement corresponding to edema and myocyte necrosis. In the later stages of healing, the myocardial tissue within the infarction will be replaced by fibrosis, which will show delayed enhancement. The pattern of the delayed enhancement will reflect the vascular

distribution of the affected vessel. The location of delayed enhancement within the myocardium will show either subendocardial or transmural enhancement.1,3

The role of MR in myocardial infarction is to assess the size and vascular territory of the infarction scar. Dynamic fast gradient echo imaging can also be used to assess wall motion abnormalities. This modality also provides information about the viability of the myocardium for planning revascularization therapy. Viable myocardium (stunned or hibernating) will show wall motion abnormalities or decreased ventricular function with normal enhancement kinetics, and carries a favorable prognosis for revascularization therapy. Infarction scar that involves greater than 50% of the myocardial thickness is unlikely to show return of function with revascularization.1,3-5

Myocarditis.

Infection is the most common etiology of myocarditis. In the US, viral infection accounts for most cases of infectious myocarditis, particularly infection with Coxsackie B virus. Other infectious etiologies include bacterial, HIV, Lyme disease, and Chagas disease. Non-infectious etiologies include drug hypersensitivity and radiation. Clinical presentation may range from mild non-specific chest pain to severe chest pain simulating acute myocardial infarction.2 On cardiac MR imaging, the myocardium will show delayed enhancement in a predominantly subepicardial location. Delayed enhancement may also progress to transmural involvement. The regions of enhancement will typically not be confined within a singular vascular territory. Additionally, the areas of involvement will show edema manifesting as intense T2 bright signal.6

Non-ischemic Cardiomyopathies.

Infiltrative/Inflammatory Cardiomyopathies

Many systemic conditions have been associated with cardiomyopathy secondary to deposition or infiltration of the myocardium. The two most common systemic conditions in this category are amyloidosis and sarcoidosis. Amyloidosis may be either primary or secondary to multiple myeloma or chronic inflammatory states. Both primary and secondary



amyloidosis may lead to deposition in the myocardial interstitium, thereby expanding the extracellular space of the myocardium. The pattern of delayed enhancement will be patchy early in the disease process and will usually progress to a pattern of subendocardial delayed enhancement. Because it is a systemic process, there may be involvement of all four chambers of the heart. Clinically, this manifests as a restrictive cardiomyopathy. Sarcoidosis is a systemic granulomatous disease that may affect any organ system. When sarcoid infiltrates the myocardium, it will typically manifest early as increased edema in the subepicardial and mesocardial locations with later appearance of patchy or nodular delayed enhancement. Clinical manifestations of sarcoid cardiomyopathy include ventricular arrhythmias and restrictive cardiomyopathy.3,6,7

Other non-ischemic cardiomyopathies

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant congenital cardiomyopathy that causes myocardial thickening without left ventricular dilatation. The myocardial thickening may be diffuse or predominantly within the interventricular septum. Mid-myocardial enhancement may be seen within areas of fibrosis, and this finding has been associated with an increased risk of arrhythmia and sudden cardiac death.3,6,8

Dilated cardiomyopathy is an acquired cardiomyopathy that is often idiopathic. Other etiologies include drug toxicity, chronic alcohol abuse, or myocarditis. The predominant findings include left ventricular chamber enlargement and decreased ejection fraction. Similar to HCM, foci of mid-myocardial delayed enhancement correspond to foci of fibrosis and may be associated with increased risk of arrhythmia and sudden cardiac death.7

Peripartum cardiomyopathy is a condition in which congestive heart failure develops in the peripartum period, with approximately half of patients recovering full left ventricular function. On imaging, there is often delayed mid-myocardial enhancement in the anterior and anterolateral left ventricular walls. The loss of delayed enhancement often corresponds to recovery of left ventricular function.7


Diagnosis

Myocardial infarction

Summary

Cardiac MRI can be a useful modality in the workup of many ischemic and non-ischemic cardiac diseases. Delayed gadolinium enhancement of the myocardium may be seen with many conditions affecting the myocardium. Using clinical context as well as the pattern and location of myocardial enhancement, a specific diagnosis or focused differential diagnosis can be made.

References

1. Miller SWA, S.; Boxt, L.B. Cardiac Imaging: The Requesites. Third Edition ed. Philadelphia: Mosby Elsevier; 2009.

2. Harrison's Principles of Internal Medicine. 15th ed. New York: McGraw-Hill; 2001.

3. Vogel-Claussen J, Rochitte CE, Wu KC, et al. Delayed enhancement MR imaging: utility in myocardial assessment. Radiographics. May-Jun 2006;26(3):795-810.

4. Dulce MC, Duerinckx AJ, Hartiala J, et al. MR imaging of the myocardium using nonionic contrast medium: signal-intensity changes in patients with subacute myocardial infarction. AJR Am J Roentgenol. May 1993;160(5):963-970.

5. Reeder SB, Du YP, Lima JA, Bluemke DA. Advanced cardiac MR imaging of ischemic heart disease. Radiographics. Jul-Aug 2001;21(4):1047-1074.

6. Cummings KW, Bhalla S, Javidan-Nejad C, Bierhals AJ, Gutierrez FR, Woodard PK. A pattern-based approach to assessment of delayed enhancement in nonischemic cardiomyopathy at MR imaging. Radiographics. Jan-Feb 2009;29(1):89-103.

7. O'Donnell DH, Abbara S, Chaithiraphan V, et al. Cardiac MR imaging of nonischemic cardiomyopathies: imaging protocols and spectra of appearances. Radiology. Feb 2012;262(2):403-422.

8. Chun EJ, Choi SI, Jin KN, et al. Hypertrophic cardiomyopathy: assessment with MR imaging and multidetector CT. Radiographics. Sep 2010;30(5):1309-1328.


Case Report, Maliel et al

Pulmonary Artery Sling Initially Presenting with Symptoms During Exercise

Kurian Maliel, M.D.,a Javed M. Nasir, M.D.,b Kevin Steel, D.O.b

a Department of Medicine, San Antonio Military Medical Center, San Antonio, TX b Department of Cardiology, San Antonio Military Medical Center, San Antonio, TX

Figure. Axial contrast-enhanced CT image through the chest demonstrates an anomalous course of the left pulmonary artery between the

esophagus posteriorly and the tracheobronchial tree anteriorly. There is associated narrowing of the main stem bronchi and compression

of the esophagus.

Case Presentation

The case presented is a 22 year-old United States Air Force Basic Military trainee who presented to the Emergency Department with atrial fibrillation with rapid ventricular rate. His rate was controlled with intravenous diltiazem and he spontaneously converted to normal sinus rhythm shortly after admission. He denies having similar palpitations in the past, but reports that he had developed chest discomfort and dyspnea during his military physical training activities. Prior to joining the military he indicates he was very sedentary. Review of systems were notable for only mild dysphagia with solid foods, although this was intermittent and he had never sought medical advice for this symptom before. His physical exam, electrocardiography (after spontaneous cardioversion), chest roentography, and transthoracic echocardiography were normal. Given exertional chest discomfort and dypsnea, he underwent a gated cardiac CT. This demonstrated normal coronary origins, but his left pulmonary artery took an anomalous course between the trachea and esophagus. This anomaly has been described in the literature as a pulmonary artery sling (PAS, Fig.) and was thought to be the etiology of his dysphagia and exertional dyspnea.



Key imaging finding

Vascular Ring

Differential diagnoses

Pulmonary Artery Sling (PAS)

Double Aortic Arch

Right Sided Aortic Arch with Aberrant Left Subclavian Artery

Discussion

Vascular rings are congenital anomalies that can present with a variety of pulmonary and gastroesophaeal symptoms. Patients will usually present with symptoms of airway obstruction due to tracheal compression manifesting as stridor, recurrent infections, wheezing, and cough. Esophageal complaints are also common and include dysphasia and vomiting. CT or magnetic resonance angiography is the preferred method of diagnosing vascular rings.

Pulmonary Artery Sling.

PAS is a rare vascular anomaly first described by Glaevecke and Doehle in 1897.1 It has been proposed that a PAS forms by the connection of the left post-brachial plexus with the right pulmonary artery, resulting in the left pulmonary artery coursing posterior to tracheobronchial tree.2 While a PAS can occur in isolation, many patients have associated congenital heart disease (e.g. atrial septal defects, ventricular septal defects, or patent ductus arteriosus) or noncardiac anomalies (e.g. tracheal stenosis, tracheomalacia, or lung hypoplasia). 3,4 Patients with PAS are typically symptomatic and present within the first year of life with signs and symptoms of respiratory obstruction,3 with two-thirds of the patients presenting in their first month of life.2 However, in some case series, up to 12% of patients with PAS are asymptomatic.2 Although extensive review of the literature shows no clear guidelines regarding specific indications for surgery, corrective surgery is the mainstay of treatment if life-limiting symptoms such as severe dyspnea, stridor, or dysphasia are present.2,3 Asymptomatic patients do not require surgery and have an excellent prognosis.5

Double Aortic Arch.

With a double aortic arch, the ascending aorta arises normally but divides into two aortic arches as it leaves the pericardium. The arches join back together to form the descending aorta. This anomaly is due to the failure of remodeling during embryogenesis. Patients usually present with symptoms similar to a pulmonary artery sling.6 Esophagram will show bilateral impressions on the thoracic esophagus. CT angiography or MRI is preferred over esophagography or angiography prior to surgical management.7

Right Sided Aortic Arch Arch with Aberrant Left Subclavian Artery.

This anomaly is due to the interruption of left aortic arch between the left common carotid artery and the left subclavian artery. The aorta descends to the right of midline and a posterior left subclavian artery arises from the diverticulum of Kommerell, which is a remnant of the left sided arch.7 This anomaly is associated with cardiac defects in about 5% - 10% of cases. Complications such as aneurysmal dilatation or dissection of the anomalous vessel may result in symptoms of dysphagia. Esophagram will show posterior vascular indentation and a right-sided arch impression. Cross-sectional imaging is required to confirm the anatomy and to visualize the diverticulum of Kommerell.7



Diagnosis

Pulmonary Artery Sling

Summary

Pulmonary artery sling is a rare vascular anomaly that is usually symptomatic within the first year of life. Symptoms are usually respiratory and/or gastro-esophageal and require surgical intervention. In patients with symptoms of dysphasia, barium esophagram can be used to exclude vascular ring. Asymptomatic presentation is less common and is usually found incidentally on CT or MRI. Asymptomatic patients typically have a good prognosis. Our patient had resolution of all his symptoms when he abstained from rigorous physical training exercises; he opted to separate from the military.


References

1. Gaevecke H, Doehle H. Uber cineeltene angeborene anomalie der pulmonalarterie. Munch Med Wochenschr 1897; 44: 950.1.

2. Sade RM, Rosenthal A, Fellows K, Castaneda AR. Pulmonary artery sling. J. Thorac. Cardiovasc. Surg. 1975; 69: 333–46.

3. Goldstein BH, Bergersen L, Powell AJ, Graham DA, Bacha EA, Lang P. Long-term outcomes of surgically repaired unilateral anomalous pulmonary artery origin. Pediatr. Cardiol. 2010; 31: 944–51.

4. Fiore AC, Brown J, Weber T, Turrentine M. Surgical treatment of pulmonary artery sling and tracheal stenosis. Ann Thoracic Surgery, 2005; 79: 38–46

5. Dupuis C, Vaksmann G, Pernot C, Gerard R, Martinez J, Van Egmond H. Asymptomatic form of Left Pulmonary Artery Sling. Am J Cardiol 1988; 61: 177-81

6. Backer CL, Ilbawi MN, Idriss FS and DeLeon SY. Vascular anomalies causing tracheoesophageal compression. Review of experience in children. J Thorac Cardiovasc Surg 1989; 97: 725–731

7. Hernanz-Schulman M. Vascular rings: a practical approach to imaging diagnosis. Pediatr Radiol. 2005 Oct; 35(10):961-79.


JAOCR At the Viewbox


Kimberly Lochner, M.D., and Ahmad Slim, M.D.

Department of Cardiology, San Antonio Military Medical Center, San Antonio, TX

Arteriovenous fistula between the left circumflex and left atrium.

A 47-year-old man presented to the emergency room with recurrent episodes of left-sided chest pain that occurred at rest and were associated with shortness of breath, nausea, dizziness, and palpitations. Physical examination, EKG, and cardiac biomarkers were all normal. Cardiac CT angiography was performed, demonstrating a vascular connection or fistula (arrows) between the left circumflex coronary artery and the left atrium.

The incidence of coronary arteriovenous fistulas (CAVFs) is approximately 0.1-0.2%. They typically drain into the right atrium, right ventricle, or right atrial-superior vena cava junction. Around 10% of CAVFs drain into left-sided cardiac structures; of these, approximately 80% drain into the left atrium.

CAVFs can cause angina from coronary “steal”, as well as congestive heart failure, pulmonary hypertension, endocarditis, spontaneous rupture, or arrhythmia depending on the size of the CAVF, its origin, and the chamber in which it empties. Small asymptomatic CAVFs require no further treatment, but monitoring echocardiography can be considered. Large CAVFs, the presence of a continuous murmur, or symptomatic CAVFs should be closed by either a surgical or transcatheter approach.





John Magulick, M.D.1, Kevin Steel, D.O.2

1Department of Medicine, San Antonio Military Medical Center, San Antonio, TX 2Department of Cardiology, San Antonio Military Medical Center, San Antonio, TX

Metastatic Carcinoid Tumor.

This is a case of a 62-year-old woman status post wedge resection of the liver, right hemicolectomy, and resection of the terminal ileum for metastatic carcinoid tumor arising in the terminal ileum. She also had regional mesenteric lymph node involvement. After resection, she continued to have elevated chromogranin A levels, as well as occasional flushing and diarrhea which progressed to gastroparesis and episodes of fainting. A detailed cardiac workup revealed no significant findings on echocardiogram, nuclear medicine stress test, or holter monitoring. Further evaluation with octreoscan revealed a small focus of abnormal uptake adjacent to the left atrial appendage. The patient subsequently underwent a gated cardiac CT, which revealed a 1.5 cm soft tissue mass splaying the left anterior descending artery and first diagonal branch of the coronary arteries (arrows). After resection of the cardiac lesion, the patient continued to report occasional flushing with resolution of diarrhea, gastrointestinal, and systemic symptoms.

Carcinoid is a neuroendocrine tumor which most often occurs in the gastrointestinal tract or bronchopulmonary tree. Metastatic disease is common; in the abdomen, there may be regional spread to lymph nodes or hematogenous spread with distant metastases. Regional mesenteric spread often leads to desmoplastic or fibrotic changes in the abdomen. The liver is the most common site of hematogenous spread. Hepatic metastases are typically hypervascular on contrast-enhanced studies. 111In-octreoscan is a useful adjunct, since carcinoid deposits may be readily identified as regions of increased uptake.





Michael Rose, D.O., Wesley Clarkson, D.O.

Department of Cardiology, San Antonio Military Medical Center, San Antonio, TX

Coronary-Pulmonary Artery Fistula.

Cardiac CT and coronary angiography of a 61-year-old woman demonstrates two coronary-pulmonary artery fistulae (arrows). Further evaluation revealed that her fistulae were not hemodynamically significant, as evidenced by no increase in oxygen saturation on her right heart catheterization, normal left ventricular function by echocardiography, normal fractional flow reserve measurement of the left anterior descending coronary artery, and no clinical or electrical evidence of ischemia on surface EKG during exercise.

Coronary artery fistulae involve a communication between a coronary artery and a chamber of the heart (coronary-cameral fistula) or a segment of the pulmonary or systemic circulation (coronary arteriovenous fistula). Most are small, asymptomatic, and found incidentally. Large fistulae, however, can cause symptoms, hemodynamic compromise, coronary steal, and high-output congestive heart failure. Transcatheter closure involves either coiling the fistula or deploying an umbrella device. A small to moderate-sized fistula in the presence of documented myocardial ischemia, arrhythmia, otherwise unexplained ventricular systolic or diastolic dysfunction or enlargement, or endarteritis should be closed via either a transcatheter or surgical approach after delineation of its course and the potential for obliteration of the fistula. Clinical follow-up with echocardiography every 3 to 5 years may be useful for patients with small, asymptomatic fistulae to exclude development of symptoms or arrhythmias, progression of fistula size, or cardiac chamber enlargement.


Documents

Official Journal of the American Osteopathic College of ... · Advanced cardiac imaging, including both cardiac computed tomography ( T) and cardiac magnetic resonance ( MR), is a