THE ACTION OF QUINIDINE ON THE COLD BLOODED HEART

¹ From the Departments of Medicine and Physiology, University of Rochester School of Medicine and Dentistry, Rochester, New York

Studies made on driven strips of turtle auricle and ventricle have shown that quinidine does not alter significantly the absolute refractory period. The refractory period and the Q-T interval have again been found to be practically equal, and this holds both normally and under quinidine action. The threshold for electrical stimuli is raised promptly and in consequence conduction in muscle is slowed, in about the same proportion. The drug slows the rate of beating of the heart of the pithed turtle and of the isolated frog heart. The P-R interval of the rhythmically driven turtle heart, in situ or isolated, is not appreciably lengthened at a time when conduction in auricle and ventricle is markedly slowed. Variation of Q-T interval with rate of beating is the same after the drug as before. It is concluded that the principal effects of the drug can be ascribed to rise of threshold and its consequences. Therapeutic use of the drug is indicated primarily in the re-entrant tachycardias, for in them slowing of conduction within the muscle may permit the normal pacemaker to re-establish control.