Rapid autonomic tone regulation of atrioventricular nodal conduction in man.

The changes in P-P intervals and atrioventricular nodal (AVN) conduction during the Valsalva maneuver were studied in 17 patients. In spite of a significant decrease in the sinus P-P interval during phase II of the maneuver (733 +/- 143 to 520 +/- 86 msec, p less than 0.005) and prolongation during phase IV (884 +/- 171 msec, p less than 0.01), there was no change in the AH interval (control: 78 +/- 15: phase II: 76 +/- 15: phase IV: 72 +/- 14 msec, N.S.). In six patients consecutive P-P intervals during phase II were recorded in solid-state memory and were used to trigger pacing of the high right atrium at rest. This showed a significant increase in the AH interval (75 +/- 10 to 123 +/- 45 msec, p less than 0.05). Valsalva maneuver during constant rate atrial pacing resulted in a significant decrease in the AH interval during phase II (115 +/- 36 to 80 +/- 15 msec, p less than 0.001). During phase IV there was prolongation of the AH interval (156 +/- 58 msec) but in 11 patients (61%) a variable degree of Wenckebach periodicity appeared. Thus autonomic tone modulates the changes in AVN conduction induced during physiologic heart rate variation, resulting in maintenance of adequate 1:1 AVN conduction.