Each beat of a heart begins with an electrical impulse originating in the sinoatrial (SA) node. This impulse spreads through the upper heart chambers (atria), causing them to contract, is briefly delayed in the atrioventricular (AV) node, and then spreads through the lower chambers (ventricles).

An electrocardiogram (ECG) is a recording of this impulse as it travels through the heart. This recording can be displayed continuously on a monitor or printed to paper for analysis. Measurements of this tracing provide valuable information about heart function.

This diagram illustrates ECG waves and intervals as well as standard time and voltage measures on the ECG paper.

ECG Diagram

A rhythm screen can be done by placing the contacts on the patients chest. ECG machine ECG Tracing Printing an ECG

A complete 6 lead ECG can be done by clipping leads to each limb. ECG Tracing Diagram