Which ECG finding most strongly suggests ventricular tachycardia over a supraventricular tachycardia with aberrant conduction?

• A. AV dissociation or capture/fusion beats
• B. P waves dissociated from QRS complexes
• C. Narrow QRS complexes with a regular rhythm
• D. Short PR interval with wide QRS

Answer: (A)

The important idea is that signs showing independent ventricular activity point to ventricular tachycardia rather than a supraventricular rhythm with aberrant conduction. AV dissociation means the atria and ventricles beat on their own clocks, so P waves march through at a rate that does not dictate the QRS rhythm. This independence is a strong, specific clue that the ventricular rhythm is originating within the ventricles themselves, not being driven by a supraventricular impulse. Capture beats (a ventricular beat that’s momentarily “captured” by an atrial impulse) and fusion beats (a hybrid of VT and normal conduction) are additional, highly specific indicators that ventricular activation is coming from a separate focus rather than from the atrial rhythm conducting through the AV node. Together, these findings make VT much more likely.

Other patterns are less definitive. A regular rhythm with narrow QRS complexes suggests a supraventricular origin with normal or only mild aberrancy. A wide QRS with a short PR interval can occur with pre-excitation or other non-VT mechanisms and doesn’t by itself prove VT. While dissociation of P waves from QRS can occur, it’s the combination of true AV dissociation and capture/fusion phenomena that most strongly points to VT.