The document discusses electrocardiography (ECG). ECG reflects the electrical activity of the heart and is useful for detecting arrhythmias, myocardial infarction, and other abnormalities. It involves recording the electrical activity of the heart using electrodes placed on the limbs and chest. The recording is done on graph paper and represents time on the horizontal axis and voltage on the vertical axis. Key aspects of the ECG waveform like the P, QRS, and T waves are described along with what each represents in terms of cardiac electrical activity and muscle function. Normal values for intervals like the PR and QT intervals are also provided. Finally, some common indications for ECG are listed.

1. Electrocardiography
Prepared By:
Barsha Silwal

2. The Heart
• All heart muscle is capable of
conducting an electrical impulse
and initiating a spontaneous
electrical discharge. .
• Calcium is major cation
responsible for cardiac
contraction.

3. ECG
ECG reflects the electrical activity of cardiac cells & useful to
detect arrythmia, MI & other abnormality.

4. Cont’d
ECG — A galvanometer & electrodes with four limb leads and
six chest leads which record electrical activity of heart on graph
paper with divisions.
• ECG recorders & monitors are standardized at a speed of
25mm/sec.

5. Cont’d
• Electrocardiographic paper: A
graph paper with each small
square measuring 1mm X 1mm.
• Time is measured on horizontal
(X) axis & voltage on Y axis.
• Each small square represents
0.04seconds.
• Five small squares make up one
large square representing 0.20
seconds.

6. Cont’d
In 12 lead ECG
Chest leads-6 (V1,V2,V3,V4,V5&V6 ) Electrode positioned in
the
• V1-4th intercostal space (ICS) in the right sternal border.
• V2-4th ICS in the left sternal border.
• V3- Midway between V2&V4.
• V4-5th ICS in the left midclavicular line.
• V5- Same level as V4, anterior axillary line.
• V6-Same level as V4 & V5, midaxillary line.

7. Cont’d

8. Cont’d
P wave Represents atrial contraction(depolarization).
QRS complex Represents ventricular contraction (depolarization) and is
composed of 3 waves, the Q, R & S. Q wave is the first negative
deflection. R wave is the first positive deflection after the P wave. S wave
is the negative deflection following R wave. It is about 0.08 to 0.12 sec,
represented by 3 small squares.

9. Cont’d
• ST segment representing early ventricular relaxation
(repolarization). Elevated ST segment in MI & depress ST
segment in myocardial ischemia.
• T wave Represents ventricular repolarization. Usually
positive, rounded, & slightly Asymmetric.
• U wave Results from slow repolarization of ventricular
Purkinje fibers. More common in lead V3. Due to
Hypokalemia.

10. Cont’d
PR interval :Measured from the
beginning of P wave to the beginning
of QRS complex. The normal PR
interval is 0.12 - 0.2 sec. The time it
takes for the impulse to spread from
atria to ventricles.
QT interval :Represents total time
required for ventricular depolarization
& repolarization. Normal QT interval
is 0.32 to 0.4sec.

11. Indications
• Myocardial Infarction& other types of CAD such as angina
• Cardiac dysrhythmias
• Cardiac enlargement
• Electrolyte disturbances
• Inflammatory diseases of the heart (RHD & myocarditis)
• Effects on the heart by drugs, such as antiarrhythmics.

12. Cont’d

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16. Cont’d