Phenylephrine (Neo-synephrine) Terminated Ventricular Tachycardia

Five cases of recurrent, wide QRS complex tachycardia which could be terminated with phenylephrine are presented. These cases fulfilled all accepted criteria for ventricular tachycardia. Carotid sinus massage with and without edrophonium hydrochloride had no effect on the ventricular activity but selectively slowed the atrial rate in cases of atrioventricular (A-V) dissociation, or blocked retrograde conduction in cases of A-V association. The mechanism of action of phenylephrine remains unclear.These cases have many possible implications. Two of the most important are: 1) phenylephrine may be useful in terminating certain cases of ventricular tachycardia; 2) termination of an unknown, regular, wide QRS complex tachycardia by phenylephrine, and possibly other pressors, can no longer be taken as proof of a supraventricular mechanism.