Effects of cardiac denervation on atrioventricular nodal accommodation and hysteresis

Conduction through the atrioventricular (AV) node is significantly altered by changes in autonomic tone. AV nodal accommodation (time-dependent changes in AV nodal conduction after a sudden change in atrial cycle length) and AV nodal hysteresis (asymmetry of AV nodal accommodation after directionally opposite atrial pacing cycle length changes) have been characterized in humans. Studies in dogs after cardiac transplantation suggest that the rapid phase of AV nodal accommodation is altered following ablation of neural input to the AV node. To determine if cardiac denervation alters AV nodal accommodation and hysteresis in humans, 13 patients after orthotopic cardiac transplantation and 12 control patients with normal AV nodal function were studied. Atrial pacing was performed for 1 minute at different pacing cycle lengths and AH or AV intervals were measured after cycle length changes. The rapid phase of accommodation is defined as the time required for the AV interval to reach 75% of the final AV interval. During abrupt changes from long to short pacing cycle lengths, the rapid phase of accommodation took 3.2 +/- 1.0 and 4.3 +/- 1.0 beats in control subjects and transplant patients, respectively (p = not significant [NS]). When going from short to long pacing cycle lengths, the rapid phase of accommodation took 1.7 +/- 1.2 and 2.1 +/- 1.8 beats in control subjects and transplant patients, respectively (p = NS). Hysteresis of 1.5 +/- 1.3 and 2.1 +/- 1.4 beats was noted in the control and transplant groups, respectively (p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)