Q wave represents depolarization of which cardiac structure?

• A. Depolarization of the right atrium
• B. Depolarization of the interventricular septum
• C. Depolarization of the ventricular apex
• D. Depolarization of the left atrium

Answer: (B)

The Q wave marks the initial phase of ventricular depolarization, specifically the interventricular septum. When the impulse travels through the heart, the septum depolarizes from left to right, producing a small negative deflection on the ECG. This early septal activity creates the Q wave in many leads, especially those oriented toward the left heart.

In contrast, the atria depolarize first to form the P wave, so atrial depolarization is not what the Q wave represents. The ventricular apex depolarizes later as the wavefront moves toward the apex, contributing to the larger R waves seen in the lower chest leads, not the initial Q wave. So the Q wave corresponds to septal depolarization, not atrial or apical depolarization.