What is indicated by a P wave on an ECG?

A P wave on an electrocardiogram (ECG) is indicative of atrial depolarization, which is the first electrical event that occurs in the cardiac cycle. During this phase, the sinoatrial (SA) node generates an electrical impulse that spreads through the atria, causing them to contract and pump blood into the ventricles. The P wave reflects this process, allowing healthcare providers to assess the electrical activity of the heart accurately. Understanding the significance of the P wave is crucial for interpreting the ECG, as it provides insight into atrial function and overall cardiac health.

The other options represent different cardiac events that do not correspond to the activity reflected by the P wave. For instance, ventricular contraction occurs after the P wave and is associated with the QRS complex, while ventricular repolarization corresponds to the T wave. Atrial repolarization, though it occurs, is typically not visible on the ECG due to its electrical activity being masked by the larger QRS complex.