Effect of digitalis in patients with paroxysmal atrioventricular nodal tachycardia

Atrioventricular (A-V) conduction, ventriculo-atrial conduction and mechanism of tachycardia were studied by programmed electrical stimulation before and after the administration of ouabain in 15 patients suffering from paroxysmal supraventricular re-entrant tachycardia. In 13 patients the tachycardia circuit was confined to the A-V node. In two patients the stimulation study showed that an accessory pathway was used in a ventriculo-atrial direction during tachycardia. Ouabain lengthened the effective and functional refractory period of the A-V node and A-V nodal transmission time in all patients in whom this could be studied. Only six patients showed lengthening in ventriculo-atrial conduction time or refractory period of the ventriculo-atrial conduction system. In seven patients no tachycardia could be initiated after ouabain. The width of the zone of atrial premature beats able to initiate tachycardia (the tachycardia zone) narrowed in five patients, showed no change in two patients, and increased in one patient. In these eight patients the tachycardia zone shifted to longer premature beat intervals. Ouabain resulted in slowing of cardiac rate during tachycardia. Both patients who used an accessory pathway during tachycardia showed no change in width of their tachycardia zone following ouabain administration. Seven patients were restudied two weeks after chronic oral administration of digoxin. The results were similar to those obtained following ouabain administration. This indicates that in patients suffering from paroxysmal A-V nodal tachycardia the effect of chronic oral digoxin administration can be predicted from the study of the effect of ouabain during programmed stimulation of the heart.