What defines the P wave in an ECG?

The P wave in an ECG is defined by atrial depolarization. This is the initial phase of the cardiac cycle where the atria contract and push blood into the ventricles. During this phase, the electrical activity that stimulates the contraction of the atrial muscles is represented by the upward deflection seen in the P wave on an electrocardiogram. This depolarization is crucial for proper heart function as it precedes the contraction of the atria, allowing for efficient blood flow into the ventricles.

In contrast, other options such as atrial repolarization, ventricular depolarization, and ventricular repolarization refer to different phases of the cardiac cycle. Atrial repolarization occurs after the P wave and is typically masked by the larger QRS complex that represents ventricular depolarization. Ventricular depolarization, represented by the QRS complex, is related to the contraction of the ventricles, while ventricular repolarization is signified by the T wave. Understanding the significance of the P wave is essential for interpreting ECGs and assessing cardiac health.