The bronchodilator terbutaline enhances digitalis-induced arrhythmia

The hypothesis that beta 2-sympathomimetics augment digitalis-induced arrhythmias and antagonize its positive inotropic action was tested in isolated, electrically driven guinea-pig left atria. Alone, 0.3 mM terbutaline enhanced myocardial force generation but did not induce dysrhythmia. Terbutaline shortened the time to the onset of 3 microM ouabain-induced arrhythmia by approximately 75% from 19.7 +/- 3.2 minutes to 5.7 +/- 1.2 minutes (p less than 0.005). The enhancement of arrhythmias appeared to be the result of triggering ouabain-induced delayed afterdepolarizations (DAD) into overt arrhythmia. The effect of terbutaline was antagonized by blocking cardiac beta-adrenoceptors with propranolol. Terbutaline did not affect the ability of ouabain to increase myocardial contractility.