Incessant reciprocating atrioventricular tachycardia. Factors playing a role in the mechanism of the arrhythmia.

The case of a patient suffering from incessant supraventricular tachycardia is presented. The electrophysiological study showed the presence of an accessory atrioventricular (A-V) bundle with nodal-like properties and long conduction times. This structure was used as the retrograde arm of the tachycardia circuit. Tachycardia was intermittent at rest, but had a sustained character during slight exercise. Administration of atropine and isoproterenol failed to sustain the arrhythmia and spontaneous initiation during sinus rhythm was no longer observed. During handgrip exercise a sustained tachycardia developed immediately. During ventricular stimulation a dual atrial response to a single paced ventricular premature beat was repeatedly observed, proving the availability of two separate A-V pathways for retrograde conduction. The case illustrates the labile nature of this type of accessory pathway, and suggests that autonomic changes can play an important role in the initiation, maintenance, termination, or even spontaneous cure of tachycardia in patients with this anomaly.