What does the QRS complex represent in an ECG?

The QRS complex on an ECG represents ventricular depolarization, which is the electrical impulse that triggers the contraction of the ventricles. This complex is a crucial part of the cardiac cycle, as it reflects the moment when the electrical activity spreads through the ventricles, leading to their contraction and the subsequent pumping of blood to the lungs and the rest of the body.

During this phase, the atria have already depolarized and contracted, contributing to the filling of the ventricles prior to this electrical event. It is important to note that while the QRS complex only indicates ventricular depolarization, it also masks the repolarization of the atria, which occurs simultaneously but is not seen on the ECG due to the dominance of the QRS waveform.

The other choices focus on different aspects of cardiac electrical activity. Atrial depolarization is represented by the P wave, atrial repolarization is typically not distinctly visible on a standard ECG, and ventricular repolarization is represented by the T wave. Understanding the roles of each component in the ECG provides essential insights into cardiac function and rhythm.