A ventricular tachycardia with left bundle branch block morphology typically suggests origin from which ventricle?

• A. Right ventricle
• B. Left ventricle
• C. Atria
• D. Atrioventricular node

Answer: (A)

In ventricular tachycardia, the shape of the QRS complex on the surface ECG reflects where in the ventricles the impulse starts and how it spreads. If the tachycardia shows a left bundle branch block pattern, it means the right ventricle is firing first and the impulse then propagates to the left ventricle. The left ventricle is activated later, producing QRS complexes that resemble a left bundle branch block. Therefore, a VT with left bundle branch block morphology points to origin from the right ventricle. If the origin were in the left ventricle, you’d expect a right bundle branch block pattern. Origins in the atria or AV node aren’t responsible for a ventricular tachycardia with this ventricular activation pattern.