Overdrive Suppression in the Transplanted Heart: Effect of the Autonomic Nervous System

To assess the influence of the autonomic nervous system upon the recovery of the normal human sinus node, the responses to overdrive pacing at multiple cycle lengths of the denervated donor heart sinus nodes of 18 human cardiac transplant recipients were compared to the responses of those 18 patients' innervated, remnant atria and of 20 control subjects with normal sinus node function. The mean average spontaneous sinus cycle length of the donor atria (643 ± 78 msec [SD]) was significantly shorter than that for either the innervated recipient (822 ± 171 msec) or the control atria (840 ± 204 msec). The longest sinus node recovery time occurred after overdrive pacing at cycle lengths of 400 msec or less in 94% of the donor atria, but in only 28% of the recipient atria (p < 0.01) and 10% of the control atria (p < 0.0001). Secondary postpacing cycles were longer than the initial postpacing pause after at least one pacing intervention in only 6% of the donor, but in 78% of the recipient (p < 0.01) and 45% of the control atria (p < 0.01). Curves describing the relationship between the corrected sinus node recovery time and the cycle length of overdrive pacing were smooth and predictable in 72% of the donor atria, but in only 17% of the recipient (p < 0.01) and 20% of the control atria (p < 0.01). In transplant patients pacing was performed for both 60and 15-second overdrive periods; recovery phenomena were qualitatively and quantitatively the same for the two durations of pacing. We conclude that the cardiac autonomic nervous system has considerable influence on the postpacing recovery phenomenon of the normal human sinus node. This may account, in part, for the insensitivity of the sinus node recovery time in detecting sinus node dysfunction.