Effect of Digoxin on Atrioventricular Conduction Studies in Patients with and without Cardiac Autonomic Innervation

The effect of digoxin on atrioventricular (A-V) conduction-was compared in five patients with an intact cardiac autonomic nervous system (Group I) and seven patients who had undergone cardiac transplantation (Group II), in whom we have previously shown the transplanted heart to be completely denervated.Small decreases in the atrial effective refractory period (ERP) (from 262 ± 12 to 254 ± 11 msec) and atrial functional refractory period (FRP) (from 304 ± 12 msec to 298 + 12 msec) were observed in Group I patients after digoxin, but these changes were not significant. However, significant increases in the A-V nodal ERP (from 315 ± 18 msec to 351 ± 17 msec, P < 0.05), and A-V nodal FRP (from 426 ± 42 to 460 ± 46 msec, P < 0.01) were produced by digoxin and were unrelated to changes in cycle length. In Group II patients with denervated hearts, changes in atrial ERP (from 246 4 to 243 ± 6 during spontaneous sinus rhythm; from 204 ± 10 to 216 ± 8 msec during atrial pacing) and atrial FRP (from 311 ± 12 to 316 + 11 msec during spontaneous sinus rhythm; from 254 ± 12 to 260 ± 10 msec during atrial pacing) were not significant. However, in contrast to the Group I patients, the digoxin-induced changes in A-V nodal ERP (from 280 ± 22 to 297 ± 18 msec during atrial pacing) and FRP (from 368 ± 18 to 377 18 msec during spontaneous sinus rhythm; from 334 ± 13 to 346 ± 16 msec during atrial pading) were also statistically insignificant. Our results demonstrate that the electrophysiologic effects of digoxin on atrioventricular conduction in man are most marked in the atrioventricular node and are dependent on cardiac innervation.