Effect of digitalis in patients with paroxysmal atrioventricular nodal tachycardia

Abstract

Atrioventricular (AV) 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 AV node. In 2 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 AV node and AV nodal transmission time in all patients in whom this could be studied. Only 6 patients showed lengthening in ventriculo atrial conduction time or refractory period of the ventriculo atrial conduction system. In 7 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 5 patients, showed no change in 2 patients, and increased in 1 patient. In these 8 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 2 wk after chronic oral administration of digoxin. The results were similar to those obtained following ouabain administration. This indicates that in patients suffering from paroxysmal AV 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.