ECG (ELECTROCARDIOGRAM)

Electric changes of the cardiac chambers follow a specific sequence.

These changes can be recorded with the help of an apparatus-electrocardiograph.

The record is called ECG.

It is represented as PQRST; where P = depolarisation of atria; QRS = depolarisation of ventricles and T = repolarisation of ventricles.

Defects in cardiac function or structure are recorded in the ECG.

For the purpose of recording, metal electrodes or leads are attached in each arm and leg with the help of straps after cleaning and putting a special jelly, which improves electrical conduction.

An additional electrode is placed on the chest with the help of a rubber suction cup.

Then, the electrocardiograph is switched on.

The electrical current of the heart is detected and amplified by the machine and is transmitted to the recording pen that draws a wavy line, called the deflection waves (electrocardiogram).

A normal electrocardiogram is composed of a P wave, a QRS complex and a T wave.

The QRS complex has three separate Q, Rand S waves.

The P wave is a small upward wave that indicates the depolarisation of the atria or the spread of impulse from the sinus node throughout the atria.

The second wave, i.e., the QRS complex, begins after a fraction of a second of the P wave.

It begins as a small downward deflection (Q) and continues as large upright (R) and triangular wave, ending as downward wave (S) at the base.

This is the expression of the ventricular depolarisation.

The potential generated by the recovery of ventricle from the depolarisation state is called the repolarisation wave.

In electrocardiography, P-Q interval (also called PR interval) is the time taken by the impulse to travel through atria, AV node and the rest of the conducting tissues.

During rheumatic fever and in arteriosclerotic heart disease (i.e., the formation of plaques and calcification), the P-Q interval lengthens.

This is due to the inflammation of atria and atrioventricular node.

The normal PR interval lasts for 0.16 second.

The enlarged Q and R waves are the indication of myocardial infarction.

The ST intervai is the representation of time between the end of the spread of impulse through ventricles and its repolarisation.

The S-T segment is elevated in acute myocardial infarction and depressed in a condition when the heart muscles receive insufficient oxygen.

The ventricular repolarisation is represented as T wave.

When the heart muscles receive insufficient oxygen, then the T wave is flattened.