Physiology · Cardiac Physiology (Cycle, Output, ECG, Electrophysiology)

On a standard 12-lead ECG, the P wave is normally inverted in which of the following leads?

A Lead I
B Lead aVR ✓
C Lead II
D Lead V5

Correct answer: B. Lead aVR

Explanation

The P wave represents atrial depolarization, which spreads from the SA node downward and leftward. Lead aVR is oriented to the right shoulder, so the depolarization wave moves away from it, producing an inverted P wave. Leads II and V5 normally show upright P waves.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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