What indicates the onset of ventricular depolarization on an EKG?

The onset of ventricular depolarization on an EKG is represented by the QRS complex. This complex reflects the electrical activity that occurs as the ventricles prepare to contract. During the QRS complex, electrical impulses travel through the ventricles, causing them to depolarize and subsequently leading to their contraction, which is crucial for pumping blood effectively to the body.

The other features of an EKG represent different aspects of heart activity. The P wave indicates atrial depolarization, while the T wave represents ventricular repolarization—the return of the ventricular muscle cells to their resting state following contraction. The J point serves as a point of reference between the end of the QRS complex and the beginning of the ST segment, but it does not denote the actual event of depolarization. Therefore, the QRS complex is the correct indicator for the onset of ventricular depolarization, outlining its significance in EKG interpretation.