Electrophysiological studies with multiple drugs in patients with atrioventricular re-entrant tachycardias utilizing an extranodal pathway

Eleven patients with recurrent paroxysmal tachycardia (PSVT) underwent electrophysiological studies. In each patient, initial study revealed re-entrant PSVT with antegrade conduction via the normal pathway and retrograde conduction via an extranodal pathway (Kent bundle). A temporary electrode catheter was left at the conclusion of initial study and PSVT induction was performed on subsequent days before and after the following intravenous drugs: ouabain 0.01 mg/kg (OU), propranolol 0.1 mg/kg (PRO), ouabain + propranolol (OU + PRO) and procainamide 750 mg (PA). In all patients, control studies prior to drug administration revealed the ability to induce sustained PSVT. In five patients, OU, PRO, or OU + PRO prevented induction of sustained PSVT by increasing atrioventricular (A-V) nodal refractoriness. In four of the patients (including one of the above), PA prevented induction of sustained PSVT: in one, by increasing His-Purkinje refractoriness, and in three by increasing refractoriness in the Kent bundle. Oral drug therapy based upon the above studies (8 pts) prevented recurrent sustained PSVT for a mean follow-up period of 9 ± 5 months. In the remaining three patients, all drugs failed to prevent induction of sustained PSVT. These patients were either treated with radio-frequency pacemakers or surgery. In conclusion, drug responses in patients with recurrent PSVT utilizing a Kent bundle are variable. Antiarrhythmic drugs may interfere with circus movements at the A-V node, His-Purkinje system, or Kent bundle. Chronic oral drug therapy based upon responses to electrophysiological studies with multiple drugs prevents recurrent sustained PSVT over a short-term followup period.