As a domain expert in cardiology with a focus on electrophysiology, I can explain the P wave in an electrocardiogram (ECG). The P wave on an ECG is a crucial part of the heart's electrical activity that is recorded during an ECG. It represents the depolarization of the atria, which is the process by which the atrial muscle fibers become excited and prepare to contract. This depolarization occurs as electrical impulses spread through the atria from the sinoatrial (SA) node, which is the natural pacemaker of the heart, to the atrioventricular (AV) node. The P wave is typically the first wave seen on an ECG and precedes the QRS complex, which represents the depolarization of the ventricles. The wave of atrial repolarization, which is the return of the atrial muscle fibers to their resting state after depolarization, is usually not visible on the ECG because it has a low amplitude and is often obscured by the larger QRS complex. In summary, the P wave is a vital indicator of atrial activity and can provide important diagnostic information regarding the heart's rhythm and conduction. read more >>

Atrial and ventricular depolarization and repolarization are represented on the ECG as a series of waves: the P wave followed by the QRS complex and the T wave. The first deflection is the P wave associated with right and left atrial depolarization. Wave of atrial repolarization is invisible because of low amplitude.read more >>