[Electrophysiological effects of the combined administration of digoxin and propranolol in man].

The electrophysiological effects of the combined administration of digoxin and propranolol were studied in 40 patients, compared with the effects of digoxin alone and considered in relation to anomalies of the conduction pathways. The cycle of the sinus node was only lengthened by digoxin in patients who had an anomaly of sinus node function. In contrast the addition of propranolol always increased it (from 1 109 +/- 53 ms to 1 232 +/- 58 ms). Sinus node recovery time was only increased by combined administration (from 1 331 +/- 101 ms to 1 450 +/- 68 ms). Changes in sino-atrial conduction intervals were not very marked. The AH interval was increased by digoxin (from 97 +/- 4 ms to 109 +/- 6 ms), with propranolol exerting a synergistic effect (119 +/- 6 ms). When there was pre-existing supra-His block only combined administration increased the conduction defect. The HV interval and QRS duration were not altered. The effective atrial refractory period was increased by combined administration (from 264 +/- 10 ms to 304 +/- 14 ms) except in subjects who had supra-His block. The effective refractory period of the AV node (385 +/- 26 ms) was increased by digoxin (450 +/- 37 ms). This effect was potentiated by propranolol (478 +/- 34 ms) except in those subjects who had supra-His block. In three cases in which there were two conduction pathways at A V node level the refractory periods of the rapid and slow pathways were increased by digoxin, with a synergistic effect from propranolol. The ventriculo-atrial conduction time changed from 151 +/- 24 ms to 172 +/- 22 ms following digoxin, then to 193 +/- 34 ms after the addition of propranolol.