Compared efficacy of quinidine, amiodarone and diltiazem on both nomotopic and ectopic automaticity in the rat heart

The effect of quinidine, amiodarone and diltiazem have been studied on both nomotopic (isolated right atria) and ectopic automaticity (induced by a local injury in the isolated right ventricle) in the rat heart. The efficacy of these three drugs, measured by the corresponding ID25, was diltiazem greater than quinidine greater than amiodarone on atrial rate and amiodarone greater than quinidine greater than diltiazem on ectopic ventricular automaticity. A depression of isolated right atria rate (sinus node function) could be regarded as an adverse effect of the drug tested (toxicity-index). On the other hand, the reduction of ectopic ventricular automaticity by the antiarrhythmic agent is considered as desired effect (effectiveness-index). We conclude that this method might be useful to evaluate the effectiveness-toxicity ratio, as a first experimental step in the development of new antiarrhythmic drugs with a direct action on cardiac tissue.