The prophylaxis of AV nodal re-entry tachycardia.

1. Electrophysiology study and clinical follow-up were used to evaluate verapamil in the prophylaxis of refractory paroxysmal supraventricular tachycardia (PSVT) due to atrioventricular (AV) nodal re-entry in twenty-one patients. 2. Electrophysiologic variables and initiation and maintenance of re-entry were studied by programmed electrical stimulation before and after intravenous verapamil of 0.15 mg/kg. 3. Verapamil significantly increased AV nodal conduction time (AH interval), decreased the atrial pacing rate at which AV Wenckebach occurred and prolonged both effective and functional refractory periods of the AV node. 4. AV nodal re-entry was initiated in twenty out of twenty-one patients before intravenous verapamil. Re-entry could not be initiated in nine of the twenty patients after verapamil and was non-sustained in a further four patients. 5. Over a mean follow-up period of 20 months, seventeen of the twenty-one patients were symptomatically improved while taking oral verapamil 80-160 mg t.d.s. Of two patients who had no improvement on oral verapamil, one proceeded to surgical His bundle section. The patient in whom arrhythmia induction during electrophysiology study was only possible after intravenous verapamil had increased frequency of PSVT on the oral preparation. Two further patients had unacceptable side effects which necessitated cessation of the drug. 6. It was concluded that verapamil is a useful agent in prophylaxis of AV nodal re-entry and that observations during electrophysiology study may guide long-term management.