Studies on the preventive method of lowered ventricular fibrillation threshold during experimental acute myocardial infarction. A comparison between disopyramide phosphate and lidocaine.

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Abstract
The prophylactic effect of disopyramide phosphate on ventricular fibrillation in acute myocardial infarction was investigated. Lidocaine and disopyramide phosphate (DP) were compared in terms of their effects on the lowered ventricular fibrillation threshold in experimental myocardial infarction produced by coronary ligation in dogs. The effect of lidocaine i.v. + infusion appeared promptly and the ventricular fibrillation threshold exceeded control levels from 45 min onwards (P < 0.01). The i.m. injection of lidocaine was effective in a dose of 10 mg/kg. The minimally effective blood level was 1.7 .mu.g/ml. DP 5 mg/kg i.v. produced a tendency towards recovery from 15 min onwards. After 30 min, the ventricular fibrillation threshold was significantly higher than control (P < 0.01). DP 5 mg/kg i.m. was initially effective after 45 min. The effect was significant from 1 h and 30 min onwards, compared with control (P < 0.01). The minimally effective blood level was 2.4 .mu.g/ml. DP 2 mg/kg i.m. produced a tendency towards recovery but the difference from the control was not significant. In equivalent i.m. doses, DP was more potent than lidocaine in increasing the ventricular fibrillation threshold. In the aforementioned doses, DP did not cause any marked changes in PQ interval or QT time in ECG. The i.m. injection of DP is apparently a hopeful clinical treatment to prevent ventricular fibrillation in the very early stages of acute myocardial infarction.