During cardiac contraction changes of electrical potential occur in each muscle cell. The electro-cardiograph (ECG) does not record these detailed changes but records the potential difference between two points on the body surface that face various parts of the heart. Willem Einthoven (1860-1927), a Dutch physiologist, was the first person to record these potentials, using a string galvanometer.

Nowadays thermionic valves are used to amplify the current and the various machines available are highly refined. For many years the only leads used were those that re¬corded the potential difference between electrodes placed on the limbs, the so-called standard bipolar leads, but unipolar leads are now used. These are based on the principle that the heart lies at the centre of an equilateral triangle that may be represented by the right arm, left arm, and left leg on the surface of the body. If these points are joined together no current flows and they may be connected to one pole of the machine; the remain¬ing electrode can be used to explore the potential existing over the surface of the chest and limbs. These leads are called V leads. Each cycle of activity within the heart shows corresponding electrical changes on the ECG and these are recorded photographically or by a direct writing machine. Electrocardiographs are extremely useful in diagnosing cardiac arrhythmias, conduction defects, and cardiac infarction  Willem Einthoven (1860-1927), a Dutch physiologist is the first person to record....

Compiler: C.K.Mohamed/Tellicherry