Effects of 4 antiarrhythmic drugs on sinoatrial conduction time in isolated and blood-perfused dog atria.

We examined the effects of four antiarrhythmic drugs (quinidine, disopyramide, procainamide and propranolol) on sinus cycle length (SCL), sinoatrial conduction time (SACT) measured by a constant atrial pacing technique, and atrial developed tension (DT), using isolated blood-perfused dog atrial preparations. When an infusion rate of 10-40 micrograms/min of quinidine, disopyramide or procainamide was continuously given into the sinus node artery and propranolol at a rate of 1-4 micrograms/min, all the agents prolonged SCL and SACT, and reduced DT dose-dependently, but not in the same fashion. Propranolol caused almost a parallel action in prolongation of SCL and SACT, and reduction of DT in increasing doses. Quinidine, disopyramide and procainamide caused negative inotropic and chronotropic effects with only a small prolongation of SACT in a relatively small dose. At larger doses, quinidine and disopyramide produced a relatively more marked prolongation of SACT than procainamide. In the doses used, quinidine, disopyramide and procainamide caused relatively small depression of DT in contrast to propranolol. The order of potencies for inducing a prolongation of SACT was propranolol greater than quinidine = disopyramide greater than procainamide.