Effects in conscious dogs of ajmaline,propranolol, amiodarone and verapamil on right ventricular anodal strength-interval curves

We studied the effect of antiarrhythmic drugs on the right ventricular anodal strenth-interval curve in the conscious dog. The anodal strenth-interval curve differs from its cathodal homologue by a shorter refractory period, a higher late diastolic threshold and the existence of a dip corresponding to a period of rhythmic vulnerability. The dogs were equipped with permanent ventricular electrodes; the heart was driven at a constant frequency by left ventricular stimulation and the anodal extra-stimulus was delivered on the right ventricle. This technique allowed us to determine the variations in the effective refractory period, the interventricular conduction (IVC) and the specific curve thresholds (late diastolic threshold, LDT, minimal dip level, Sm, maximal post dip threshold, SM). Ajmaline, a quinidine-like drug, significantly increased IVC and all the thresholds. Only high doses lengthened the effective refractory period. Propranolol, a β-blocking agent significantly increased Sm. The intrinsic effect of amiodarone, a non-specific anti-adrenergic drug and a potent anti-anginal substance seemed to result in a significant increase in LDT, Sm, SM. Verapamil, a calcium antagonist only caused a significant increase in SM. Therefore, each of the four drugs studied, belonging to a different group of teh Vaughan Williams classification, acted in a different way on the anodal strengh-interval curve. This study clarified the mechanisms by which these drugs exert their antiarrhythmic effect.