Lack of an aging effect on responses to disopyramide in rabbit ventricle. A brief note.

The hearts of older animals, including man, undergo physiological changes and exhibit an increased sensitivity to antiarrhythmic drugs which may be due in part to an increased sensitivity of the heart to the drug. Isolated perfused hearts from young (2-4 months) and old (43-63 months) rabbits were driven at 3 Hz and the electrical strength-interval relationship was determined by interposing a test stimulus at known intervals after every tenth driving stimulus. This revealed the diastolic threshold for stimulation and the effective refractory period. Disopyramide at therapeutic concentrations increased the effective refractory period in both young and old hearts to the same extent without significantly altering the diastolic threshold. Thus, the increased sensitivity of older animals to type I antiarrhythmic drugs is probably due to some factor other than increased cardiac electrophysiologic effects.