What does the QRS complex represent in an ECG?

The QRS complex on an ECG represents ventricular depolarization, which is a crucial part of the cardiac cycle. During ventricular depolarization, the electrical impulse travels through the ventricles, causing them to contract and pump blood to the lungs and the rest of the body.

This complex typically appears as a series of downward and upward deflections on the ECG tracing, and it reflects the rapid spread of the electrical signal across the ventricular myocardium. The width and morphology of the QRS complex can provide valuable information about the conduction system of the heart. For instance, a wide QRS complex may indicate a delay in conduction, such as in the case of a bundle branch block.

In contrast, the other choices reflect different cardiac events. Atrial depolarization is represented by the P wave, ventricular repolarization is indicated by the T wave, and delays in conduction at the AV node are not directly represented by the QRS complex. Understanding the role of the QRS complex is vital for interpreting ECGs and diagnosing various cardiac conditions.