What is indicated by the Q wave on an ECG?

The Q wave on an electrocardiogram (ECG) is significant as it represents the initial negative deflection that occurs during the depolarization of the ventricles. This wave is part of the QRS complex, which collectively reflects the electrical activity associated with the contraction of the ventricles.

Specifically, the Q wave is often associated with the depolarization of the interventricular septum, the wall dividing the left and right ventricles. This portion of the heart depolarizes first due to the conduction pathway provided by the bundle of His and the Purkinje fibers, leading to the contraction of the heart muscle.

It's important to distinguish this from other waves on the ECG: atrial depolarization corresponds to the P wave, ventricular repolarization is depicted by the T wave, and the QRS complex as a whole, including the Q wave, denotes ventricular depolarization, not just the specific Q wave itself. Therefore, recognizing the Q wave’s role in septal depolarization is critical for interpretations of cardiac function and can also help in diagnosing certain conditions, such as previous myocardial infarctions.