Generation of the normal electrocardiogram

Relation between cardiac depolarization, ventricular repolarization, and the appearance of the normal electrocardiogram, including the P wave, QRS complex, ST segment, and T wave. The PR interval can be prolonged by disease from the atria to the Purkinje fibers (steps 2 to 4). The SA node is not seen on the surface ECG due to its small mass; its activity is inferred from the P wave, which reflects atrial activation.