Electrocardiogram

An electrocardiogram, abbreviated as ECG, or EKG, is a test that captures a record of the heart's electrical activity.

It is performed by placing electrodes on the arms, legs, and chest and recording the electrical signals using an electrocardiograph.

A typical ECG has three peaks: the P wave, the QRS complex, and the T wave.

The P wave shows atrial depolarization as the action potential spreads from the sinoatrial node, causing atrial contraction.

The QRS complex, a triangular wave with downward deflections on either side, represents ventricular depolarization.

The P-R interval represents the time between atrial and ventricular depolarization.

The T wave indicates ventricular repolarization. It is flatter than the QRS complex as repolarization is slower.

The S-T interval represents the plateau phase of the ventricular contractile cells, while the Q-T interval represents a cycle of ventricular depolarization and repolarization.

Clinically, a larger P and high-voltage QRS may suggest atrial enlargement and ventricular enlargement, respectively.

Changes in the S-T and Q-T intervals may indicate myocardial infarction and repolarization abnormalities.