Which electrophysiological event does the QRS complex represent?

The QRS complex on an electrocardiogram (ECG) primarily represents ventricular depolarization, which is the process of the ventricles of the heart becoming electrically activated. This event leads to the contraction of the ventricles, allowing them to pump blood to the lungs and the rest of the body.

During depolarization, sodium ions rush into the cardiac muscle cells, causing a movement of electrical charge that triggers contraction. The QRS complex is typically a prominent and sharp feature on the ECG, reflecting the rapid and significant electrical activity occurring in the ventricles as compared to other events in the cardiac cycle.

In contrast, atrial depolarization is represented by the P wave, atrial repolarization is hidden within the QRS complex itself, and ventricular repolarization is indicated by the T wave. Hence, the QRS complex's role in representing ventricular depolarization is a crucial aspect of understanding the cardiac conduction system and interpreting an ECG.