The Action of Procaine and Procaine Amide on the Heart

Abstract

The depressant action of procaine on the heart muscle has been the subject of several clinical and experimental studies (Wiggers and Wegria, 1940;Burstein, 1946;Uhley and Wilburne, 1948; Schaffer et al., 1950). Procaine was found useful in the treatment of cardiac arrhythmias occurring in anesthetized patients during cardiac surgery. However, its usefulness in the management of clinical arrhythmias in conscious patients has been found to be greatly limited because of its effects on the central nervous system. More recently, procaine amide was introduced (Mark et al., 1951; Newman and Clark, 1951) and both clinical and experimental observations have suggested that this drug is effective in abolishing various types of cardiac arrhythmias and that it is more suitable for clinical purposes than procaine (Berry et al., 1951;Kinsman et al., 1951;Schlachman et al., 1951; Stearns et al., 1952;Enselberg and Lipkin, 1952;Zapata-Diaz et al., 1952; Shack et al., 1952;Lucas and Short, 1952). The present study was undertaken in order to evaluate the effects of procaine and procaine amide on the heart in the experimental animal and to assess the effectiveness of procaine amide in abolishing clinical arrhythmias. In a few cases a comparison was attempted of the relative value of procaine amide and quinidine. EXPERIMENTAL OBSERVATIONSA total of 35 experiments were performed in cats under dial anxsthesia. Electrocardiograms were recorded before and at frequent intervals after the administration of procaine hydrochloride (1% solution) or procaine amide (pronestyl, Squibb). The blood pressure and respiration were continuously recorded on a kymograph.The Effects ofProcaine and Procaine Amide Alone. Eleven cats received procaine and six cats procaine amide by the intravenous route. Single doses of 5-10 mg. per kg. of either drug produced no significant changes in the electrocardiogram, blood pressure, or respiration. Amounts between 15 and 25 mg. per kg. of procaine or procaine amide given in single or in divided doses at 10-minute intervals produced depression of the S-T segment with lowering of the T wave in about 50 per cent of the experiments and transient widening of the QRS complex in every experiment. Further increase in the dosage resulted in progressive widening of the QRS complex in every experiment; various degrees of heart block in about 90 per cent and ectopic beats in one-third of the experiments. An example is shown in Fig. 1. The sequence of events was similar in both groups, but whereas the early changes appeared after comparable doses of procaine and procaine amide on a weight basis (between 15 and 25 mg. per kg.), much larger doses of procaine amide were necessary to produce irreversible widening of the QRS complex, heart block, and ectopic rhythm. These latter changes appeared after an average dose of 30 mg. per kg. of procaine and 100 mg. per kg. of procaine amide.Lowering of the blood pressure was much more gradual when procaine amide was given and in two experiments up to 60 and 90 mg. per kg., respectively...