Electrocardiogram

Electrocardiography (ECG) is a technique that uses an electrocardiograph to record the graphical representation of the electrical activity changes produced by the heart during each cardiac cycle from the body surface. During a normal cardiac cycle, each myocardial cell undergoes depolarization followed by repolarization, thereby generating an action potential. Under normal circumstances, myocardial cell depolarization proceeds in an orderly fashion, with the sinoatrial node depolarizing first, then sequentially conducting to the atria, atrioventricular node, and ventricles. The electrical signal propagates throughout the heart in the form of a depolarization wavefront. The small electric fields generated by this wavefront can be detected on the body surface, and the signals recorded by the electrocardiograph constitute the electrocardiogram.