What does the P wave in an ECG represent?

The P wave in an electrocardiogram (ECG) specifically represents atrial depolarization. This is the electrical activity that initiates contraction of the atria, leading to the movement of blood from the atria into the ventricles. The P wave is the first deflection of the ECG tracing, indicating that the sinoatrial (SA) node, which is the natural pacemaker of the heart, has triggered this depolarization.

When the heart's electrical impulse travels through the atrial myocardium, it causes the atrial muscles to contract, and this is visually represented on the ECG as the P wave. Understanding the P wave is crucial in evaluating heart function and identifying potential dysrhythmias, as alterations in the shape or duration of the P wave can indicate underlying issues such as atrial enlargement or rhythm disturbances.

In contrast, the other choices refer to different phases of the cardiac cycle: ventricular depolarization corresponds to the QRS complex, while ventricular repolarization is represented by the T wave. Atrial repolarization, while it does occur, is typically not represented distinctly on the ECG due to its obscured appearance within the QRS complex.