What does the P wave represent in an electrocardiogram?

The P wave in an electrocardiogram (ECG) is specifically associated with atrial depolarization. This phase represents the electrical activity that triggers the contraction of the atria, allowing blood to flow into the ventricles. During this process, sinoatrial (SA) node impulses spread through the atrial muscle tissue, causing it to depolarize. As a result, the P wave appears as the first deflection on the ECG tracing, typically depicted as a small, upward curve.

Atrial depolarization is a critical part of the cardiac cycle, as it sets the stage for ventricular filling prior to the subsequent contraction of the ventricles, reflected in the QRS complex of the ECG. Understanding the P wave's role helps in interpreting various cardiac abnormalities and their potential underlying causes.