Electrocardiogram

Presented byChinmoy Roy 08011503011

Meenu Singh 07711503011 ICE Department

Electrocardiography is the method of recording of an electrocardiogram (ECG)

ECG or EKG is the graphic recording of the electrical activities of the heart

Electrocardiograph is the machine that

records the ECG

It is an important diagnostic & prognostic tool for assessment of cardiovascular function

body fluids are good conductors of electricity

electrical changes occurring in the heart with each heart beat, are conducted all over the body & can be picked up form the body surface

ECG recorded at the body surface represents the algebraic sum of the action potential of the individual cardiac muscle fibers

The ECG is recorded to study the following parameters:

Anatomical orientation of the heart

Relative size of the chambers of the heart

A variety of disturbances of the rhythm & conduction

To detect ischemia of the myocardium, if present

The location, extent & progress of myocardial infarction

The effects of altered electrolyte concentration

The influence of certain drugs like digitalis

Evaluation of electrical pacemaker function

Requirements: ECG machine

Cardiac jelly

ECG paper

ECG leads

ECG leads Direct leads

Leads applied directly to the surface of the heart

These leads are used to record cardiac activities during cardiac surgery or during an experiment

Indirect leads Leads applied away form the heart to record the

cardiac activities

Different indirect leads are limb leads, chest leads

Limb leads (bipolar & unipolar) Bipolar limb leads Bipolar standard limb leads are original leads selected

by Einthoven to record electrical potential on frontal plane

electrodes are attached to right arm, left arm, & left foot another electrode is applied to the right leg, which acts as a

ground wire to prevent external disturbance during recording

Lead I: between right arm (negative electrode) & left arm (positive electrode)

Lead II: between right arm (negative electrode) & left leg (positive electrode)

Lead III: between left arm (negative electrode) & left leg (positive electrode)

Augmented limb leads (unipolar limb leads) positive electrode is connected to one limb, &

negative electrode to the other two through high resistances

There are three augmented limb leads aVR: between right arm (positive electrode) & left

arm + left leg (negative electrode) aVL: between left arm (positive electrode) & right

arm + left leg (negative electrode) aVF: between left leg (positive electrode) & right

arm + left arm (negative electrode)

Unipolar chest leads

six chest leads are used routinely; V1 to V6 (V7-V9)

The reference electrode is connected to the right arm, left arm & left leg through a high resistance.

V1: in the right fourth intercostal space at the right border of the sternum

V2: in the left fourth intercostal space at the left border of the sternum

V3: at the midpoint between V2 & V4

V4: in the left fifth intercostal space on the midclavicular line

V5: in the left fifth intercostal space on the anterior axillary line

V6: in the left fifth intercostal space on the mid-axillary line

V7: in the left fifth intercostal space on the posterior axillary line

V8: in the left fifth intercostal space on the posterior scapular line

V9: in the left fifth intercostal space on the back just left to the spine

Abnormalities of rhythm Tachycardia

fast heart rate (>100 bpm)

Bradycardia slow heart rate (<60 bpm)

Sinus arrhythmia ↑ heart rate during inspiration & ↓ during

expiration

Arterial extrasystole an abnormal focus of impulse generation in atria

may discharge sporadically giving atrial extrasystoles & corresponding P waves in the ECG

First degree block when the P-R interval ↑ 0.20s

Second degree block when the P-R interval ↑ 0.35 to 0.45s

Third degree block complete block of the impulse from the atria into

the ventricles occurs

Atrial tachycardia This is similar to atrial extrasystoles except that

the abnormal focus generates impulses at a regular rate

Atrial flutter causes a rapid rate of contraction of the atria,

usually between 200 & 350 beats per minute

Atrial fibrillation If the abnormal focus of impulse generation

discharge at a rate exceeding 300 per min

Ventricular extrasystole It occur because a capillary muscle may fire an

impulse before normal impulse reaches the ventricles, leading to premature contraction (extrasystole) of ventricles.

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