Antiarrhythmic effects of three new drugs, propafenone, tocainide, and SUN 1165, were examined using three canine ventricular arrhythmia models, i.e., digitalis, adrenaline and two-stage coronary ligation arrhythmias. The effects of procainamide, disopyramide, lidocaine, and phenytoin, class 1 antiarrhythmic drugs, on digitalis arrhythmia were also examined. The minimum effective plasma concentrations of all these drugs for each arrhythmia model were determined for a quantitative comparison. Propafenone and tocainide suppressed all the arrhythmias, while SUN 1165 suppressed digitalis and coronary ligation arrhythmias. The minimum effective plasma concentrations of propafenone for digitalis, adrenaline, 24-h coronary ligation, and 48-h coronary ligation arrhythmias were 1.8 +/- 0.7, 0.58 +/- 0.20, 3.5 +/- 0.3, and 3.6 +/- 0.9 micrograms/ml, respectively, and those of tocainide were 6.2 +/- 2.1, 23.7 +/- 9.0, 11.4 +/- 0.5, and 8.6 +/- 2.9 micrograms/ml, respectively (mean +/- standard deviation, n = 6-7). The minimum effective concentrations of SUN 1165 for digitalis, 24-h coronary ligation, and 48-h coronary ligation arrhythmias were 0.92 +/- 0.19, 2.5 +/- 0.4, and 1.2 +/- 0.4 micrograms/ml. The minimum effective concentrations for digitalis arrhythmias were 1.7 +/- 0.4 micrograms/ml for disopyramide, 10.1 +/- 2.4 micrograms/ml for procainamide, 3.5 +/- 1.6 micrograms/ml for lidocaine, and 11.3 +/- 3.0 micrograms/ml for phenytoin. Digitalis arrhythmia seems to be a useful model for detecting class 1 drugs, as it was suppressed by all the class 1 Na-channel blocking antiarrhythmic drugs, while class 2 beta adrenergic blockers and class 4 Ca-channel blockers had no effect. Also, not all the class 1 drugs suppressed coronary ligation and adrenaline arrhythmias.

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Using two-stage coronary-ligation-, digitalis- and adrenaline-induced ventricular arrhythmias in beagles, antiarrhythmic effects of AN-132 were examined, and the minimum effective plasma concentration for each arrhythmia model was determined. AN-132 suppressed all the arrhythmias, and the minimum effective plasma concentrations for arrhythmias induced by 24-hour coronary ligation, 48-hour coronary ligation, digitalis, and adrenaline were 3.4-4.6, 1.5-2.3, 0.83, and 9.3 micrograms/ml, respectively. The concentration for adrenaline-induced arrhythmia was significantly higher than that of 24-hour coronary ligation arrhythmia, and it was also higher than that of digitalis arrhythmia. This pharmacologic profile is similar to those of pirmenol and mexiletine. Since AN-132 had no deleterious effects on the hemodynamics and the central nervous system, it may become a clinically useful antiarrhythmic drug.

Abstract-Antiarrhythmic effects of a new beta 1 selective adrenoceptor blocker, betaxolol, were examined in comparison with those of atenolol using two canine ventricular arrhythmia models (adrenaline arrhythmia and digitalis arrhythmia). Both betaxolol and atenolol suppressed adrenaline arrhythmia, and the minimum effective plasma concentration of betaxolol for this arrhythmia model was deter mined to be less than 10 ng/ml.However, on digitalis arrhythmia, both beta blockers were ineffective, even though the high doses used in these experiments, 3 mg/kg for betaxolol and 5 mg/kg for atenolol, showed significant hypotensive effects.The present results suggest that betaxolol and atenolol may be expected to be clinically effective on arrhythmias related to increased sympathetic tone.