Electrocardiograph (ECG)

The electrical activity within the heart can be detected by attaching electrodes to the surface of the body. The pattern of electrical activity may be displayed on an oscilloscope screen or traced on paper. The apparatus used is an electrocardiograph and the tracing is an electrocardiogram (ECG).Electrocardiogram  is graphic record of the electric current produced by the excitation of the cardiac muscles. The instrument used to record the changes is an electrocardiograph. Waller (1887) first recorded the electrocardiogram but Einthoven (1903) studied ECG in details and is also considered “father of the electrocardiography“.The normal ECG tracing shows five waves which, by convention, have been named P, Q, R, S and T

The P Wave is a small upward wave that represents electrical excitation or the atrial depolarisation which leads to contraction of both the atria (atrial contraction). It is caused by the activation of SA node. The impulses of contraction start from the SA node and spread throughout the artia.The QRS Wave (complex) begins after a fraction of 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 its base. It represents ventricular depolarisation (ventricular contraction). It is caused by the impulses of the contraction from AV node through the bundle of His and Purkinje fibres and the contraction of the ventricular muscles. Thus, this wave is due to the spread of electrical impulse through the ventricles.The T Wave is dome-shaped which represents ventricular repolarisation (ventricular relaxation). The potential generated by the recovery of the ventricle from the depolarisation state is called the repolarisation wave. The end of the T-wave marks the end of systole.

Clinical Significance of Electrocardiograoph

Any deviation from the normal ECG shape indicates a possible abnormality or disease.

Enlargement of the P wave indicates enlargement of the atria. During atherosclerotic heart disease and rheumatic fever, the PR interval is lengthened. This is due to the inflammation of atria and AV 

The enlarged Q and R waves indicate a myocardial infarction (heart attack). The ST segment is elevated in acute myocardial infarction and depressed when the heart muscle receives insufficient oxygen.

T wave is flat when the heart muscles receive insufficient oxygen as in atherosclerotic heart disease. It may be elevated when the body’s potassium level is increased.