Clinical electrophysiological properties of penbutolol: a non-selective beta-blocking agent.

The electrophysiological effects of the beta-adrenergic blocking agent penbutolol (4 mg i.v.) were studied in 15 patients by means of intracardiac recording using the extra-stimulus technique and rapid atrial pacing. The following effects were observed. (1) Significant prolongation of the sinus cycle length (16%). (2) Significant prolongation of the AV-nodal conduction time during sinus rhythm (12%). (3) Significant prolongation of the AV-nodal conduction time with increasing atrial pacing rate (16--29%). At 150/min, 4 of 7 patients with intact AV-conduction under baseline conditions developed second degree AV-block 15 to 30 min after penbutolol administration. (4) Significant prolongation of the effective refractory period of the AV-node (19%). Penbutolol had no effect on the intraventricular conduction, on intraatrial conduction or on the corrected sinus node recovery time.