If ventricular tachycardia originates in the left ventricle, what is the expected morphology in lead V1?

• A. Left bundle branch block pattern with positive QRS in V1
• B. Right bundle branch block pattern with negative QRS in V1
• C. Right bundle branch block pattern with positive QRS in V1
• D. Left bundle branch block pattern with negative QRS in V1

Answer: (C)

The main idea is that the QRS shape during ventricular tachycardia reflects where the tachycardia starts. If the VT originates in the left ventricle, the activation spreads from left to right, producing a pattern on the ECG that resembles a right bundle branch block. In lead V1, a right-bundle–like pattern typically shows a positive QRS complex, because the net depolarization vector is directed toward V1. So left-ventricular origin gives a QRS in V1 that is positive, fitting a right-bundle–block–type morphology.

If the tachycardia came from the right ventricle, you’d expect a left-bundle–block–type pattern, often with a negative QRS in V1, which is not the case here.