In an ECG with wide complex tachycardia, which of the following clues most strongly supports the diagnosis of ventricular tachycardia? 

A. Atrial-ventricular dissociation 

B. Classic right bundle branch block pattern 

C. Irregularly irregular rhythm with changing QRS complexes 

D. QRS duration >120 msec 

E. Slowing of rate with carotid sinus massage

The answer is A. (Chap. 277) Atrial-ventricular dissociation is a classic finding in ventricular tachycardia. Physical examination may show jugular vein cannon a waves when the atria contracts against a closed tricuspid valve, and the ECG will manifest this with atrial capture and/or fusion beats. Other findings on ECG of ventricular tachycardia include QRS duration >140 msec for right bundle branch pattern in V1 or >160 msec for left bundle morphology in lead V1, frontal plane axis –90 to 180 degrees, delayed activation during initial phase of the QRS complex, and bizarre QRS pattern that does not mimic typical right or left bundle branch block QRS complex patterns. An irregularly irregular rhythm with changing QRS complexes suggests atrial fibrillation with ventricular preexcitation. Carotid sinus massage, aimed at increasing vagal tone and slowing AV node conduction, is not effective at slowing ventricular tachycardia because the reentrant focus is below the AV node.