Comparative study of the effect of the calcium antagonist nifedipine, the beta receptor blockers acebutolol and propranolol and their combination on electrophysiologic parameters in the human

It is well known that in the isolated atrium, nifedipine, verapamil and diltiazem slow down the spontaneous frequency and conduction velocity in the sinus- and in the atrioventricular node. Using therapeutic doses in man, we studied the influence of the calcium-antagonist nifedipine, the beta-blockers acebutolol and propranolol and a combination of these on sinus-node parameters (spontaneous cycle length AA, sinus-node recovery time SNRT, corrected sinus-node recovery time CSNRT, sinoatrial conduction time SACT), and on the intracardiac conduction time (PA-, AH-, HV-interval). Both beta-blockers slowed the spontaneous frequency of depolarization of the sinus-node, but lengthened sinus-node recovery time and sinoatrial conduction time (acebutolol: AA + 6% n.s.; SNRT +5% n.s.; CSNRT +2% n.s.; SACT +33% s.; propranolol: AA +9% n.s.; SNRT +15% s.; CSNRT +37% n.s.; SACT +32% n.s.). Simultaneously PA-, AH and HV-interval lengthened (acebutolol: PA +16% n.s.; AH +7% s.; HV +15% s.; propranolol: PA +19% n.s.; AH +16% s.; HV +9% s.). Nifedipine caused essentially no change in sinus-node parameters nor in intracardiac conduction time in man (AA -11% s.; SNRT -12% s.; CSNRT -7% n.s.; SACT +35% n.s.; PA +4% n.s., AH -2% n.s.; HV +5% n.s.). This is in contrast to results obtained in the isolated atrium, and is different from other calcium-antagonists such as verapamil, gallopamil and diltiazem. The effect of acebutololinduced beta-blockade is not intensified by nifedipine (AA -3% n.s.; SNRT -6% s.; CSNRT -12% s.; SACT -19% n.s.; PA -5% n.s.; AH +3% n.s.; HV +9% n.s.).