Concealed retrograde bypass tracts and enhanced atrioventricular nodal conduction. An unusual subset of patients with refractory paroxysmal supraventricular tachycardia.

The clinical and electrophysiologic features of eight patients with unusually rapid, medically refractory paroxysmal supraventricular tachycardia are described. Exercise induction of tachycardia and functional bundle branch block patterns during tachycardia were common. Tachycardia resulted from anterograde enhanced atrioventricular nodal conduction combined with retrograde conduction by a concealed left atrial-left ventricular accessory pathway producing rates ranging from 200 to 300 beats/min. Management and late follow-up study were characterized by generally unsuccessful electrophysiologic-pharmacologic testing and inconsistent rhythm control with continued drug therapy. Three patients underwent successful surgical interruption of the concealed accessory pathway, with elimination of recurrent tachycardias. These patients represent a unique subgroup with an identifiable electrophysiologic basis for unusually rapid tachycardias, potentially benefiting from invasive study and aggressive therapy.