Although the inotropic and dromotropic effects of cardiac glycosides in atrial fibrillation (AF) are well recognized, their action on AF itself is not clear. Accordingly, to determine whether cardiac glycosides prolong AF, the duration of electrically induced AF, atrioventricular conduction, and left ventricular function were assessed for 30 minutes before and for 30 minutes following intravenous administration of acetyl strophanthidin (AS), 20 micrograms/kg, in neurally intact, beta-blocked, and beta-blocked and vagotomized dogs. In the intact dog, AS, 20 micrograms/kg, increased peak dp/dt by 132 +/- 35 mmHg.sec-1, p less than 0.05, and slowed ventricular response by 16 +/- 7 min-1, p less than 0.05, but had a variable effect on AF duration. While the increased left ventricular peak dp/dt persisted for 15 minutes after AS, an increased duration of AF was evident only at 20 minutes, when the effects of AS on left ventricular (LV) inotropy were no longer apparent. Moreover, the subset of dogs that did not demonstrate prolongation of average duration of AF after AS had a greater increment of peak dp/dt than those that showed prolongation, 237 +/- 52 versus 53 +/- 31 mmHg.sec-1, p less than 0.05. An additional 20 micrograms/kg, which produced ventricular extrasystoles, prolonged AF duration when compared to both control and 30-minute measurements. Acetyl strophanthidin, 20 micrograms/kg, had a variable effect on duration of AF with beta-blockade but prolonged duration by 114 +/- 34%, p less than 0.05, with both vagotomy and beta-blockade.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals Atrial Fibrillation