Influence of arrhythmogenic and antiarrhythmic agents on alternating current-induced arrhythmias in guinea-pig heart preparations.

: The method for inducing arrhythmias or asystole by the application of a 50 Hz alternating current (ac) has been applied to isolated guinea-pig left atria and papillary muscles in order to characterize arrhythmogenic and antiarrhythmic substances. Aconitine, BaCl2 (less than 2 mmol/l) and hypoxia decrease threshold of ac-arrhythmia and ac-asystole, in both tissues to a similar extent, whereas carbachol and BaCl2 (greater than 2 mmol/l) increase threshold. The calcium antagonists nifedipine and diltiazem lower threshold of ac-asystole but differ with respect to threshold of ac-arrhythmia, which is increased by 10(-6) mol/l diltiazem in left atria and papillary muscles by about 30% and remains nearly unaffected with nifedipine. The Na+-inhibitory substance flecainide reverses the decrease in threshold of ac-arrhythmia and ac-asystole brought about by aconitine. Threshold of ac-arrhythmia lowered by hypoxia is increased by diltiazem in a concentration-dependent manner, whereas decrease of threshold of ac-asystole is even augmented. Therefore, the method offers an opportunity of quantifying the action of arrhythmogenic agents at concentrations which are too low to induce arrhythmia, as well as to characterize the activity of antiarrhythmic drugs in the presence of arrhythmogenic substances.