[Anti-arrhythmic and cardiodepressive effects of anti-arrhythmia agents].

With the exception of amiodarone (class III), which lengthens the action potential, all agents available for the treatment of tachyarrhythmias produce negative inotropic effects. The antiarrhythmic action of class I antiarrhythmic drugs is due to an impaired Na channel recovery and a prolongation of the refractory period. The same mechanism results in the negative inotropic effects of these agents. A decrease in the intracellular Na concentration, and hence in the intracellular Ca concentration via the Na/Ca exchange system produces a decrease in force of contraction. The negative inotropic effect of class I antiarrhythmic drugs is particularly pronounced in those agents (e.g., quinidine) which interact with Na channels for a relatively long period of time. The negative inotropic effects of beta-adrenoceptor blocking agents (class II) and of calcium-channel inhibitors (class IV) is mainly due to an inhibition of the slow Ca inward current, as are the antiarrhythmic effects of these agents. In conclusion, the negative inotropic effects of antiarrhythmic agents are due to different mechanisms. Thus, the cardiodepressive effects of these drugs may be increased in an additive manner when these agents are combined to increase their antiarrhythmic effectiveness.