Which ECG clues suggest ventricular tachycardia in a patient with structural heart disease?

• A. Narrow QRS tachycardia with rapid rate.
• B. ECG shows frequent P waves with atrial activity preceding QRS.
• C. Wide QRS, abnormal morphology, AV dissociation, capture or fusion beats.
• D. Short PR interval with delta waves.

Answer: (C)

In a patient with structural heart disease, ventricular tachycardia is most strongly suggested when the ECG shows signs that the rhythm originates in the ventricles rather than being driven from the atria. The hallmark clues are a wide QRS complex with abnormal morphology, indicating activation that bypasses the normal His-Purkinje system; AV dissociation, where atrial activity occurs independently of the ventricular rhythm; and capture or fusion beats, where occasional normal or hybrid QRS complexes appear during the tachycardia. These features together are highly specific for VT in this clinical setting. By contrast, a narrow QRS tachycardia favors a supraventricular mechanism with aberrant conduction, atrial activity preceding the QRS points to an atrial origin, and a short PR interval with delta waves suggests preexcitation rather than VT.