What does a QRS complex represent on an ECG?

The QRS complex on an ECG represents ventricular depolarization, which is a crucial phase in the heart's electrical cycle. During this phase, the ventricles are stimulated to contract, which is necessary for pumping blood throughout the body. The sequence of events that occurs includes the rapid conduction of electric activity through the ventricles via the Purkinje fibers, resulting in the muscular contraction of the ventricular walls.

In contrast, the other choices focus on different phases of the cardiac cycle. Atrial contraction is indicated by the P wave, which reflects the depolarization of the atria prior to their contraction. Atrial repolarization occurs simultaneously with the QRS complex but is usually not visually represented on an ECG due to its electrical activity being overshadowed by the larger QRS complex. Ventricular repolarization is represented by the T wave, which occurs after ventricular contraction and indicates the recovery phase of the ventricles. Understanding these components is essential for interpreting ECG readings effectively.