Abnormalities of the P Wave and PR Interval

The P wave represents atrial depolarization, as well as the start of the cardiac electrical cycle. Atrial activation is normally initiated in or immediately around the sinoatrial (SA) node in the superior right atrium and proceeds toward the left atrium and the atrioventricular (AV) node. The terms right and left atrial abnormality are preferred to such labels as right and left atrial enlargement, hypertrophy, overload, and conduction delay, as the P-wave changes attributed to these states are not specific for just one, and substantial crossover exists. Biatrial abnormality manifests as a combination of the findings seen with right atrial abnormality and left atrial abnormality. The PR interval represents the time from the start of atrial activation to the onset of ventricular activation and can be shortened or lengthened by factors that affect the speed of conduction from the atria to the ventricles.