Measuring Stress Velocity Index Using Mean Blood Pressure

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O R I G I N A L A R T I C L E

Measuring Stress Velocity Index Using Mean Blood Pressure:Simple yet Accurate?

Sanjeev Aggarwal Michael D. PettersenJoellyn Gurckzynski Thomas LEcuyer

Received: 10 April 2007/ Accepted: 28 June 2007/ Published online: 3 October 2007

Springer Science+Business Media, LLC 2007

Abstract The stress velocity index, or the relationship of

the rate-corrected mean velocity of circumferential short-ening (VCFc) to the end systolic wall stress (ESWS), is a

sensitive, load-independent measure of left ventricular

contractility. ESWS is technically difficult to obtain and

requires simultaneous blood pressure measurement, carotid

artery tracing, and phonocardiogram. We report our com-

parison of two simpler methods of measuring ESWS and,

therefore, stress velocity index. Patients with normal car-

diac anatomy who had completed anthracycline

chemotherapy were evaluated. ESWS as measured by the

standard method using a carotid artery tracing (ESWScar)

was compared to ESWS obtained using mean arterial

pressure (ESWSmap) or systolic blood pressure (ES-

WSsbp). The cohort included 63 patients, with 37 (59%)

males and a median age of 13.1 years. The mean (SD)

ESWScar was 53.315.3 g/cm2 (range, 26.394 g/cm2);

ESWSmap, 53 13.4 g/cm2 (range, 27.186.1 g/cm2); and

ESWSsbp, 72.9 18.2 g/cm2 (range, 40.8117.2 g/cm2).

ESWSmap and ESWSsbp closely correlated with ESWScar

(coefficient correlationr= 0.88 andr= 0.87, respectively).

Using ESWSmap, all patients were correctly classified as

having normal or abnormal contractility as defined by

stress velocity index, whereas ESWSsbp detected only two

of the six patients with impaired contractility. We conclude

that ESWSmap is a simple, highly sensitive and specific

method for assessing left ventricular contractility. ESWS-

map correlates closely with ESWScar and can be

incorporated into the monitoring of cardiac dysfunction in

the anthracycline-treated population. Further studies areneeded to determine if this simplified measure accurately

assesses the ESWS in other cardiac disease states.

Keywords Left ventricle Systolic function

Echocardiogram Load independent

Left ventricular (LV) function may be impaired in various

congenital heart defects, in myocarditis, after ischemic

injury, and secondary to drug toxicity. LV function is

routinely evaluated using echocardiographic parameters

such as ejection fraction and shortening fraction. The dis-

advantages of these parameters are that they are dependent

on the heart rate, preload, afterload, and ventricular con-

tractility [3, 8]. Therefore, they do not provide a specific

direct assessment of left ventricular contractility.

Thestress velocity index, or the relationship of the rate-

corrected mean velocity of circumferential fiber shortening

(VCFc) and end-systolic wall stress (ESWS), has previ-

ously been established as a sensitive, noninvasive measure

of LV contractility [4]. The index is independent of preload

and incorporates afterload, heart rate, and LV dimensions.

However, its measurement requires simultaneous acquisi-

tion of an M-mode echocardiogram, carotid pulse tracing,

phonocardiogram, and blood pressure measurement. The

phonocardiogram is required to determine the timing of

end systole by the first component of the second heart

sound. The carotid pulse tracing is used to obtain intra-

ventricular end-systolic pressure by assignment of systolic

blood pressure (SBP) to the peak and diastolic blood

pressure to the nadir and then by linear interpolation to the

level of dicrotic notch (Fig.1). The dicrotic notch on a

carotid pulse tracing corresponds to end-systolic pressure

S. Aggarwal (&) M. D. Pettersen J. Gurckzynski

T. LEcuyer

Division of Cardiology, Department of Pediatrics, Childrens

Hospital of Michigan, Wayne State University, 3901 Beaubien

Boulevard, Detroit, MI 48201, USA

e-mail: [email protected]

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Pediatr Cardiol (2008) 29:108112

DOI 10.1007/s00246-007-9101-3


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in the left ventricle. Obtaining a carotid artery tracing is

especially difficult in the pediatric population due toshortness of the neck, discomfort, and fast heart rate, which

preclude the routine use of this measure.

Two previous studies have evaluated an alternative

simpler method of obtaining this index using mean blood

pressure (MAP) [6, 9]. One study used a direct invasive

measure of blood pressure during cardiac catheterization

and the other involved patients with a variety of congenital

heart defects, which might affect the correlation of MAP

and end-systolic pressures. Peak systolic stress using the

SBP has also been described as a simpler approach to

measuring stress velocity index [11]. The slope of the

regression line of the peak systolic wall stress-VCFc wasfound to be nearly identical to, and the y intercept slightly

higher than, the regression line relating ESWS-VCFc [11].

The present report compares the stress velocity indexes

obtained by conventional carotid artery tracing with those

obtained by MAP and SBP in a homogeneous pediatric

cohort with structurally normal hearts.

Materials and Methods

The study included 63 patients who underwent detailed

echocardiograms as part of a research protocol for assess-

ment of ventricular function in anthracycline (AC)-treated

children. Each patient underwent an echocardiogram

including M-mode, two-dimensional, and color Doppler

using a Phillips Sono5500 ultrasound machine. Standard

technique was used to obtain M-mode measurements [10].

Simultaneous carotid artery tracing, electrocardiogram,

phonocardiogram, and blood pressure were recorded. Each

measurement was obtained for three to five cardiac cycles.

Blood pressure was recorded using a Dinamap automatic

machine. All studies were performed in the quiet, awake,

and nonsedated state. All measurements were performed

off-line by a single cardiologist (M.P.). End-systolic wall

stress (ESWScar) was measured by the method described

by Colan et al. [4]. Wall Stress [g/cm2] = (1.35)

(P)(LVEDd)/(4)(LVPWs)(1+LVPWs/LVEDs), where P is

the intraventricular end-systolic pressure obtained from

carotid artery tracing (Fig. 1). LVEDd is the left ventric-ular internal dimension at end diastole (defined as the onset

of QRS complex); LVEDs and LVPWS are the left ven-

tricle internal dimensions and left ventricle posterior wall

thickness, respectively, at end systole defined by the aortic

component of the second heart sound. Similarly, ESWS-

map was obtained by replacing P with MAP as obtained

by Dinamap. ESWSsbp was obtained by using SBP in

place ofP.

Mean velocity of circumferential shortening was cal-

culated using LVEDd LVEDs/LVEDs ETc, where ETc

is the heart rate-corrected ejection time as measured by

Doppler interrogation of left ventricular outflow.

Statistics

Data were analyzed using SPSS software version 12 for

PC. Data are expressed as mean SD, median, or numbers

as appropriate. The two methods for calculating ESWS

were compared to the standard measurement of ESWS by

plotting the difference between the methods against their

means [2]. ESWS was defined as abnormal at values[60

gm/cm2 [7]. Sensitivity, specificity, positive and negative

predictive values, and 95% confidence intervals of the

simpler methods of calculating ESWS were computed

using ESWScar as gold standard.

Results

The study group consisted of 63 patients who had com-

pleted AC chemotherapy and underwent echocardiographic

assessment of LV function. There were 37 (59%) males

and 26 (41%) females. The median age at enrollment was

13.1 years (range, 6.5 to 26.5 years) and the median

interval since completion of AC treatment was 3.8 years

(range, 1.1 to 17.5 years). The clinical diagnoses included

acute lymphocytic leukemia in 29 (46%), Wilms tumor in

12 (19%), osteosarcoma in 12 (19%), and lymphoma in 10

(16%) patients. The mean (SD) cumulative dose of AC

received was 215.5 116.7 mg/m2 (range, 45520 mg/m2;

median 160 mg/m2).

The average ( SD) MAP as measured by Dinamap was

77.4 10.65 mm Hg (range, 51107 mm Hg), while the

mean intraventricular pressure as calculated by carotid

SBP

DBP

A B

P = DBP+ {(SBP-DBP)XB/A}

P=left ventricular end systolic pressureSBP=Systolic blood pressure

DBP= Diastolic blood pressure

Fig. 1 Carotid artery tracing depicting the method of calculating

intraventricular end-systolic pressure

Pediatr Cardiol (2008) 29:108112 109

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positive predictive values compared to the SBP method. In

addition, the mean (SD) difference between ESWScar and

ESWSsbp was significantly greater than that between

ESWScar and ESWSmap.

The relationship between velocity of circumferential

fiber shortening and ESWS is a sensitive, load-independent

index for assessment of LV systolic function. It has been

shown to reliably detect patient deterioration and response

to medications in critically ill pediatric patients [5]. The

index is reproducible over time and is considered ideal for

longitudinal studies, especially when the preload status is

abnormal such as with anemia, with fever, or in the post-

operative period [4]. In the AC-treated population, 40% of

patients have late cardiotoxicity even at low cumulative

AC doses, previously thought to be safe [1]. Therefore,

longitudinal surveillance for prolonged periods is indicated

for life in patients after receiving AC. In this vulnerable

group, ESWS is well known to be a superior early marker

of cardiac dysfunction [7]. Unfortunately, this measure-

ment is difficult to obtain, at least partly due to difficulty inobtaining a carotid pulse tracing. Therefore, simpler

methods of measuring contractility are of clinical value.

Two previous studies have reported an excellent corre-

lation between ESWS and ESWSmap [6, 9]. One of these

compared direct arterial pressures from femoral arterial/

aortic pressure transducer obtained during cardiac catheter-

ization and LV end-systolic pressure. The mean difference

reported was 0.3 mm Hg (SD, 2.9 mm Hg) [9]. In another

study, the MAP obtained by a Dinamap machine was used to

calculate ESWS [6]. The correlation coefficient between

MAP and pressure obtained with carotid artery tracing was

0.84. The correlation coefficient between ESWScar and

ESWSmap was 0.98, similar to our results. However, the

patient group was diverse and included patients receiving

chemotherapy, with congenital heart defects, dilated car-

diomyopathy, hypertension, and transplanted heart.

A single study evaluated LV contractility using the

relationship of VCFc to stress at peak systole in 25 normal

children [11]. The reported correlation coefficient between

ESWScar and ESWSsbp was 0.91. In our group, the cor-

relation coefficient was comparable, at 0.87. This method,

however, had poor specificity and positive predictive value

for ESWS and identified only two of the six patients with

impaired contractility. To the best of our knowledge, ours

is the first study comparing ESWS obtained by the standard

method to ESWS obtained using MAP and SBP.

Conclusion

We conclude that ESWS and, therefore, stress velocity

index can be measured easily and with excellent sensitivity

and specificity by using MAP obtained by a Dinamap

ESWScar (g/cm2)

1009080706050403020

ESWScar-ESW

Smap(g/cm2)

50

40

30

20

10

0

-10

-20

-30

-40

-50

ESWScar: End systolic wall stress using carotid tracingESWSmap: End systolic wall stress using mean blood pressure

Fig. 5 Difference in the individual measurements of ESWSmap and

ESWScar versus their means

ESWSmap (g/cm2)

1201101009080706050403020

VCFc(c/s)

1.6

1.5

1.4

1.3

1.2

1.1

1.0

.9

.8

.7

.6

.5

.4

ESWSmap: End systolic wall stress using mean blood pressure

VCFc: rate corrected mean velocity of circumferential fiber shortening

Fig. 6 Relationship of VCFS and ESWSmap for estimating the stress

velocity index for assessing left ventricular contractility

Table 1 The sensitivity, specificity, and positive and negative pre-

dictive values (95% confidence intervals) of EWSWmap and

ESWSsbp using ESWScar as the gold standard

ESWSmap (CI) ESWSsbp (CI)

Sensitivity 95% (82%99%) 100% (86%100%)

Specificity 96% (90%97%) 37% (30%37%)

Positive predictive value 90% (77%94%) 40% (35%40%)Negative predictive value 98% (92%99%) 100% (84%100%)

Note. ESWSmap, end-systolic wall stress using mean blood pressure;

ESWSsbp, end-systolic wall stress using systolic blood pressure; CI,

95% confidence interval

Pediatr Cardiol (2008) 29:108112 111

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machine in place of obtaining a carotid pulse tracing. This

method can be incorporated into the long-term monitoring

of LV contractility in AC-treated children. Further studies

are needed to validate this simplified measure in other

cardiac conditions.

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Measuring Stress Velocity Index Using Mean Blood Pressure