Arrhythmogenic dose of acetylstrophanthidin unchanged by beta-sympathomimetics in conscious dogs.

The enhanced arrhythmogenic risk of combined treatment with cardiac glycosides and beta-sympathomimetics is referred in some textbooks, but only a few detailed studies on in vivo models are available. We therefore investigated this problem in conscious dogs in an intraindividual study. We determined the dose of acetylstrophanthidin (intravenous infusion of 5 mcg/kg per min), which provoked ventricular premature beats with and without concomitant treatment with the partial beta-agonistic compounds doxaminol (3 mg/kg p.o.), prenalterol (0.4 or 1.0 mg/kg p.o.) or isoprenaline (0.31 +/- 0.100 mcg/kg per min). In some dogs a coronary artery was narrowed in order to reduce the coronary blood supply. The arrhythmogenic dose of acetylstrophanthidin was nearly the same in all the groups investigated (range from 52.1 +/- 5.66 to 59.9 +/- 3.23 mcg/kg). Whereas the arrhythmogenic dose of acetylstrophanthidin was unchanged by beta-sympathomimetics, the combination of the glycoside and each of the beta-agonistic drugs increased the contractile force more than did either single compound. We therefore conclude that the arrhythmogenic risk of the combination of glycosides and beta-sympathomimetics may be--at least in experimental models--less than has been suggested in the past.