Electrophysiological studies in the denervated transplanted human heart. Response to trial pacing and atropine.

To date, no studies have documented the conduction characteristics of the atrioventricular conduction system in the transplanted human heart. Three patients who had undergone cardiac transplantation 1—2 years previously formed the basis of this study. All were functional class I symptomatically and had normal hemodynamics and coronary arteriograms at the time of study. Each patient was in sinus rhythm with a normal P-R interval and QRS configuration. None was taking medications known to affect the atrioventricular conduction system. Using the His bundle technique, all were shown to have normal base-line atrium-His bundle (AH) and His bundle-ventricle (HV) conduction times. Recordings were made of both the donor (AD) and the recipient (AR) electrograms. The AD rate was more rapid than the AH rate by an average of 24 beats/min. Right atrial pacing to a rate of 170 beats/min resulted in a progressive lengthening of the AH interval to an average of 205 msec, a result comparable to that in normal patients. At the cessation of rapid pacing, AD recovery time averaged 770 msec, which is normal. The administration of 1-2 mg of atropine increased the AR rate by an average of 28% but did not alter the AD rate; the AH intervals did not change. We conclude that (1) the normal AH intervals at rest and the increased AH intervals during pacing demonstrate the inherent conduction delay imposed by the atrioventricular node independent of autonomic influence, (2) the AD recovery time after overdrive is an inherent property of the AD sinus node, and (3) the absence of change in the AD rate or the AH interval after administration of atropine suggests that parasympathetic reinnervation has not occurred in these patients.