What does the QRS complex represent in an ECG reading?

The QRS complex in an electrocardiogram (ECG) primarily represents ventricular depolarization. This phase occurs when the ventricles are electrically stimulated, resulting in contraction. The large, sharp deflections of the QRS complex illustrate the rapid spread of electrical impulses through the ventricles, leading to their contraction and subsequent pumping of blood to the lungs and the rest of the body.

Understanding this component is crucial for recognizing both normal and abnormal heart rhythms. For instance, changes in the duration or morphology of the QRS complex can indicate various cardiac conditions, such as bundle branch blocks or ventricular hypertrophy.

While other components of the ECG represent different electrical activities of the heart—such as atrial depolarization seen in the P wave or ventricular repolarization illustrated by the T wave—the QRS complex specifically signifies the critical moment when the ventricles prepare to contract, making it a key indicator of cardiac function.