Abstract
The direct myocardial depressant effects of lidocaine, ajmalin, propranolol and quinidine were determined in vitro in isolated right ventricular papillary muscles and spontaneously beating right atria of the cat. In concentrations similar to therapeutically effective serum levels, the average depression in contractile force produced by each drug was: lidocaine 1%, ajmalin 1.9%, Propranolol 3.5%, and quinidine 8.3%. Similarly, the reduction in spontaneous atrial rate was: ajmalin 4.5%, Propranolol 5%, and quinidine 11%. The minimal depressive effects of lidocaine and ajmalin confirm their relative safety in patients as compared to quinidine. The combination of the direct myocardial depressant effects and beta blocking effects of propranolol suggest that this drug, as well as quinidine, must be used with caution in patients with heart failure.
