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2.2 The Heart- ECG

Room 23-H-24 (entrance H25)

Table of Contents 1. INTRODUCTION .............................................................................. 3

1.1. COURSE AIMS: .............................................................................. 4

2. ECHOCARDIOGRAM (DEMONSTRATION) .................................... 5

2.1. INTRODUCTION .............................................................................. 5

2.2. AIMS ............................................................................................ 5 The Cardiac Cycle (Timing Diagram) .................................................................. 6

3. AUSCULTATION OF HEART SOUNDS AND PHONOCARDIOGRAM .......................................................................... 7

3.1. INTRODUCTION .............................................................................. 7

3.2. AIMS ............................................................................................ 8

3.3. METHOD ....................................................................................... 8 Auscultation ......................................................................................................... 8

Results and Interpretation ................................................................................... 8

4. ELECTROCARDIOGRAM (ECG) ..................................................... 9

4.1. INTRODUCTION .............................................................................. 9 Schematic account of the depolarization and repolarization of the heart with the

correlating ECG ................................................................................................... 9

ECG................................................................................................................... 10

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ECG electrode positions and ECG measurements ........................................... 10

What are the deflections (peaks and curves) seen on an ECG readout? .......... 11

Determining the mean electric axis of the heart ................................................ 12

Conclusions ....................................................................................................... 13

4.2. AIMS .......................................................................................... 13

4.3. METHOD ..................................................................................... 13 Standard ECG ................................................................................................... 14

Respiratory sinus arrhythmia ............................................................................. 14

Results and Interpretations/ calculations ........................................................... 15

5. GLOSSARY .................................................................................... 17

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1. Introduction The heart is a dual pump made up of two functionally sequential and anatomically

parallel pumps. An interruption of about 10 seconds in the circulation of blood to

the brain can lead to loss of consciousness. A break of more than a few minutes

can lead to irreversible brain damage. Hence it is of vital importance that the heart

functions stably and continuously.

In this course you will have the opportunity to examine and carry out important

noninvasive methods used to examine heart function and to assess their rele-

vance.

How well a particular heart is functioning is first examined by careful study of the

patients’ case history, physical inspection of the patient, palpation, and ausculta-

tion. If abnormal heart sounds, heart murmurs, or arrhythmias are detected during

auscultation, this may indicate a congenital or acquired functional and/or morpho-

logical defect (i.e. defective valve or other heart problems).

The ECG registers differences in electrical currents on the body’s surface. These

differences generated by the depolarization and repolarization of the heart spread

to surrounding tissues and to the body’s surface. The ECG provides details about

heart rhythm and allows investigation of the spread of cardiac excitation. ECGs

are also used to judge myocardial ischemias and heart attacks.

Echocardiography (ultrasound for the heart) is used to examine the mechanics of

the heart (valve movement, chamber volumes) with a high resolution in space

and time. At the same time a Doppler can be employed to measure the direction

and speed with which the blood is traveling through the heart.

The more invasive ways in which the heart can be examined (i.e. catheters) will

not be discussed in this course. However, catheters are used to determining in-

tracardial pressure and blood flow, visualizing the coronary arteries, and for in-

tracardial ECGs.

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1.1. Course Aims: 1. General: Get to know noninvasive techniques for examining heart function

2. General: Understanding and interpreting the heart cycle (electrically as well

as mechanically) as a function of time

3. Echocardiogram (ultrasound of the heart) demonstration: introduction to

method and understanding of heart mechanics

4. Auscultation: Become familiar with the first and 2 heart sounds and their

origins. Understanding heart murmurs (pathology). In addition you should

be able to correlate the heart sounds with the pulse.

5. ECG: carry out ECG (positioning of electrodes) and practice recording and

interpreting a normal ECG.

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2. Echocardiogram (Demonstration)

2.1. Introduction The echocardiogram is an important noninvasive method to investigate and diag-

nose the condition of the heart. It is an ultrasound of the heart. The echocardio-

gram is based on the fact that ultrasound waves are partially reflected by tissue

boundaries. The echo transducer, which sends and receives ultrasound waves,

is covered with a special gel and held against the patient’s chest. Now the ultra-

sound waves can be registered by the machine and projects an image of the

heart on the monitor.

The dynamic sections visualized using this method allows for investigations into

the heart’s anatomy and movement (pumping action). For example, ventricle area

can be measured before and after ventricular contraction allowing the ejection

fraction to be calculated. At the same time Doppler measurements can be taken

in order to analyze the direction and speed of blood flowing within the heart. Con-

sequently heart valves can be examined not only from a physical and motional

perspective, but their hemodynamic function can also be evaluated. Finally, pres-

sure gradients can be calculated based on the flow characteristics.

2.2. Aims

• An echocardiogram demonstration by a qualified USZ Cardiologist

• To understand the basics of what an echocardiogram is and how it is useful

as a diagnostic tool

• Understanding the mechanics of the heart by visualizing the heart cycle

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The Cardiac Cycle (Timing Diagram)

Central Venous Pressure

Taken from:

http://www.genderandhealth.ca/en/modules/cardiovascular/imageContent/cardiac-cycle.gif

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3. Auscultation of heart sounds and phonocardiogram

3.1. Introduction Heart sounds (physical sounds) are strictly defined vibrations (≤ 50 Hz) in the

heart. These vibrations can be transmitted to the thorax, and can then be heard

or registered using a stethoscope or phonocardiogram. The first heart sound (S1)

results from the closure of the atrioventricular valves, mitral and tricuspid, at the

beginning of ventricular contraction, or systole. The second heart sound (S2) is

caused by the closure of the aortic valve and pulmonary valve at the end of ven-

tricular systole. As the left ventricle empties, its pressure falls below the pressure

in the aorta, and the aortic valve closes. Similarly, as the pressure in the right

ventricle falls below the pressure in the pulmonary artery, the pulmonary valve

closes.

During inspiration, negative intrathoracic pressure causes increased blood return

into the right side of the heart. The increased blood volume in the right ventricle

causes the pulmonic valve to stay open longer during ventricular systole. This

causes an increased delay in the P2 component of S2. During expiration, the pos-

itive intrathoracic pressure causes decreased blood return to the right side of the

heart. The reduced volume in the right ventricle allows the pulmonic valve to close

earlier at the end of ventricular systole, causing P2 to occur earlier, and "closer"

to A2. It is physiological to hear the splitting of the second heart sound by younger

people and during inspiration. During expiration normally the interval between the

two components shortens and the sound becomes merged. A third (rapid filling

of the ventricle) and/or fourth heart sound (atrium contraction) are usually only

audible in pathological cases.

Pathological heart murmurs (between sounds, at higher frequency) are the result

of turbulences in blood flow. Systolic noise is usually only heard in aortic or pul-

monary valve stenosis (restriction) or insufficiencies of the atrioventricular valves.

Diastolic noise is audible in patients with stenosis of the atrioventricular valves

and insufficiencies of the aortic or pulmonary valves. In the case of anemia, the

decrease in blood viscosity (due to low hematocrit) and increase in the cardiac

output leads to the development of turbulences.

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3.2. Aims Understanding the way in which normal and pathological heart sounds develop

Being able to discern the difference between the first and second heart sound

with auscultation (note position of subject and where auscultation is being per-

formed)

Chronological coordination of EKG (phonocardiogram) and pulse

3.3. Method Auscultation

Subjects should listen to each others’ auscultations using the stethoscope in two

different positions. First the subject should be lying down, and then he should be

sitting up (bent slightly forward towards the listener). Having the subject bend

towards the listener should make the sounds more audible as the heart is against

the inside of the thorax. In this position heart tones should be very clear when the

stethoscope is placed in the 3rd intercostal space on the left parasternal side.

In order to evaluate the longer and duller first heart tone, it may be best to listen

for the mitral auscultation and the tricuspid auscultation. For mitral auscultation

place the stethoscope at the 5th intercostal space medioclavicular to a subject

lying on his left side to optimize audibility. For optimal tricuspid auscultation place

the stethoscope in the 5th intercostal space on the right parastenal side of the

subject. When the carotid artery is palpated simultaneously, the chronological

correlation of the first heart sound and the pulse can be determined.

The second heart sound is evaluated using the same criteria. The components

of the aortic valve are easiest to hear in the 2nd intercostal space parasternal right

while the pulmonary valve is easiest to hear in the 2nd intercostal space left. Note

the split in the two components when the subject breathes deeply.

Results and Interpretation

Each student should be able to hear the heart sounds using the stethoscope. In

addition you should be able to correlate the heart sounds with the pulse.

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4. Electrocardiogram (ECG)

4.1. Introduction The ECG registers differences in potential on the body’s surface which are gen-

erated by the heart’s activity.

General Information on the generation of the measured potentials:

The progressive stimulation (depolarization) of individual myocardial cells leads

to a progression of electronegativity on their surfaces. This causes an electric

dipole to develop between those cells or regions which are stimulated (electro-

negative) and those which are not yet stimulated (electropositive). These differ-

ences can be described or interpreted as vectors which move from the stimulated

(negative) areas to the not yet stimulated (positive) areas. The sum of all these

single vectors gives rise to a sum or integral vector throughout heart stimulation.

A large portion of these vectors cancel each other out. During repolarization the

surface electronegativity has to be reverted so that the next dipole vector can

again move from the stimulated (negative) to the unstimulated (positive) areas of

the heart. When this integral vector meets with a positive or unipolar electrode it

leads to a positive deflection.

Schematic account of the depolarization and repolarization of the heart with the correlating ECG

Electrode (-)

Electrode (+)

Depolarization vec-tor (from – to +)

Progression of

the dipolarization

R peak T-wave

T

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ECG

ECG electrode positions and ECG measurements

V1 4 l.C.R. parasternal ri V2 4 l.C.R. parasternal le V3 Between V2 and V4 V4 5 l.C.R. medioclavicular V5 Height of V4, anterior axillary line V6 Height of V4, left midaxillary line

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What are the deflections (peaks and curves) seen on an ECG readout?

P-wave: represents the wave of depolarization that spreads from the SA node

throughout the atria, and is usually 0.08 to 0.1 seconds (80-100 ms) in duration.

The brief isoelectric (zero voltage) period after the P wave represents the time in

which the impulse is traveling within the AV node (where the conduction velocity

is greatly retarded) and the bundle of His. Note that the repolarization of the

atrium is not visible because it correlates chronologically with the QRS complex.

P-Q (P-R interval): This interval represents the time between the onset of atrial

depolarization and the onset of ventricular depolarization. Since the mass of cells

which are depolarizing at this time point is small (AV node and His bundles) the

P-R segment is isoelectric. If the P-R interval is >0.2 sec, there is an AV conduc-

tion block, which is also termed a first-degree atrioventricular block if every im-

pulse is still able to be conducted into the ventricles.

QRS Complex: This complex represents ventricular depolarization. By definition

a negative peak is called Q when it precedes a positive peak (R). A positive peak

following a positive peak is referred to as R’ and a negative peak following a

positive peak is S. First the upper septum muscles are stimulated from the left

side. This can lead to a small Q peak if we interpret it ‘from the left perspective’

(I, II, AVL, V4-V6). The stimulation then proceeds down to the cardiac apex and

beyond by moving along the chamber walls until it reaches the level of the valves.

In order to understand the direction of the integral vector that makes up the QRS

complex one must remember that chamber myocardial tissue is always stimu-

lated from the inside out. Since, under normal circumstances the integral vector

is mostly defined by the left ventricle (bigger muscle), the vector usually points

downwards and/or slightly to the left (between -30º and 120º). The angle at which

the mean electric axis of the heart is positioned in the chest can be determined

based on ECG peaks (see figure below). Several parameters can effect the po-

sition of the heart including age, physical build, thorax shape, and physical fit-

ness. Pathological changes can result from things like cardiac hypertrophy, re-

duction in physical performance, or a heart attack.

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Determining the mean electric axis of the heart

Orientation of the electrical axis of the heart using the Einthoven triangle. According to the “text-book” method (dashed red line) specific configurations will not result in a common intersection point. The underlying problem is that the R-wave from all three electrodes is not at its maximum at the same time point. In this example although the R-wave has reached a maximum for elec-trode II, it has already returned to the baseline in the case of electrode I and for electrode III it is at some intermediate value. To overcome this problem, the difference between the R-wave and the S-wave (green arrow) is used instead of the difference between the baseline and the R-wave (dashed red arrow). This example results in an electrical heart axis of 90o (blue). (N.B. Axis nomenclature in the US is as follows: normal –30o to +90o; left axis deviation: -30o to –90o ; right axis deviation: +90o to +180o ; indeterminate axis: the remainder (from –90o to +/-180o).

ST Segment: This segment represents the time during which the ventricles are

contracting and emptying. Normally it is isoelectric (except in right measure-

ments) since the entire chamber is depolarized. A vertical shift in the ST segment

is often observed in ischemia patients (insufficient blood supply due to coronary

artery narrowing) or after a heart attack (myocardial cell death due to interrupted

perfusion of a certain area).

T-Wave: This represents repolarization of the ventricular myocardium which

starts where the stimulation was active last. This accounts for the fact that the

Einthoven-Dreieck Cabrera-Kreis

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peak is generally concordant (deflecting in the same direction) with the QRS com-

plex. Possible exceptions to this are measurements taken at V1 and V2.

QT interval: The stimulation of the entire chamber lasts from the beginning of the

QRS complex to the end of the T wave. The time this takes depends on the heart

rate (~0.25 – 0.45 sec) and, to a lesser extent, on the mass of the electric diastole

in the chamber.

Conclusions

The ECG can provide important clues about heart rhythm and the dipole stimula-

tion and conduction from the sino-atrial node via the AV node to the myocardium

in the ventricle. Additionally, diagnosis of coronary insufficiencies leading to my-

ocardial ischemia) and heart attacks are possible with information provided by

the ECG. The role of the ECG has become secondary, however, to an echocar-

diogram when diagnosing hypertrophy and other morphological pathologies of

the heart.

4.2. Aims Each experimenter should perform an ECG on a test subject and be able to an-

alyze the results.

4.3. Method The electrodes are fixed to the subject according to the scheme provided and

attached to the recording apparatus. Please remember to decrease the re-

sistance between the electrodes and the skin by applying a small amount of sa-

line solution at the contact areas.

Recording: The following measurements can all be made at once and will come

as a printed ECG at the end of each measurement.

1. Einthoven (standard bipolar) 2. Goldberg (peripheral unipolar) 3. Wilson (unipolar chest)

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Standard ECG

1. turn on with green key 2. enter data of patient with patient data/ECG-shift key 3. go back with same key 4. place electrodes 5. check ECG-curves on monitor. When ok start recording with green START-key

Respiratory sinus arrhythmia

1. with key choose Einthoven (I, II, III)

2. press manual start (2nd key from right, below the screen)

3. reduce paper speed to 10 mm/sec (key 7, first row) 4. breathe slowly and deeply in and out 5. Press red STOP-key shortly before the end of the page 6. press red STOP-key again => perforates the paper

1

v

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Results and Interpretations/ calculations

Findings:

P-wave:

Frequency

Rhythm (regular, respiratory sinus arrhythmias)

Shape: Positive in measurement II:

P-Q interval:

Length and regularity

(Normal: 0.12 – 0.20 Sek. 1 degree AV block: >0.20 sec:)

QRS complex:

Frequency, regularity (difference from P) Length (normal: ≤ 0.10 sec) Geometrical position I the thorax Transition region (R=S in Wilson) Height of the QRS complex: Sokolow-Lyon Index (S in V1 + R in V5)

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ST-segment

Is it isoelectric?

T-waves:

Are they concordant (except V1 and V2)?

Are there extrasystoles?

Comments:

Observe the relationship of the Q-T segment and the distance between T and the

next Q in a few patients with varying heart frequencies.

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5. Glossary Anemia

decreased hemoglobin concentration in the blood

Auscultation

listening to sound from the body with a stethoscope

Doppler Measurement

exploiting the change in frequency measured by the ultrasound to determine the

movement (flow) of the erythrocytes

Echocardiography

using ultrasound to visualize the heart

ECG

an electrocardiogram, used to measure the difference in potential (differences in

electrical voltage) which are caused by the heart’s activity

Ejection fraction

the portion (in %) of the enddiastolic ventricular volume which is ejected during

the systole

Heart murmurs

bruits caused by turbulence in the heart which are at higher frequency than nor-

mal heart sounds

Heart rhythm generation

Pace maker activity in the sino-atrial node

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Heart sounds

sounds at low frequency (< 100 Hz) that occur at regular intervals which arise

form the oscillation of the heart and/or the large arteries and from the tension of

the myocardium and/or the closure of valves

Ischemia

deficiency in blood circulation

Mean electric axis

(cardiac vector) graphical representation of QRS complex from 6 frontal plane

leads (I, II, III, aVR, aVL, aVF) reconstructed from the instantaneous vectors rep-

resenting ventricular depolarization.

Myocardial Infarct

necrosis of myocardium due to interruption of blood supply to a certain area

Phonocardiogram

measurement of heart oscillations using a mechanic-electrical transducer (micro-

phone)

Sokolow-Lyon Index

electrocardiographic index used in diagnosis of left ventricular hypertrophy

Stenosis

restriction or narrowing in a blood vessel or heart valve

Transition zone

in the Wilson measurement, the time when S=R (normally between V2 and V5.

Valvular regurgitation

the inability of a valve to close properly leading to a back current