Electropharmacology of Diltiazem in a Chronic Canine Myocardial Infarction, Ventricular Tachyarrhythmia Model
The electropharmacology of diltiazem was evaluated in 11 dogs with chronic myocardial infarction susceptible to the initiation of sustained ventricular tachyarrhythmias (VTs) using programmed pacing. Dogs were studied open chest under pentobarbital anesthesia both before and after either 0.2 (N = 5), 0.4 (N = 5) or 0.8 mg/kg (N = 5) intravenous diltiazem infused over 5 mimutes. Two doses were studied in 4 dogs. The maximal changes in heart rate, AH, HV and QTc intervals, QRS duration and sinus node recovery time were determined. Mean transmyocardial conduction times from endocardium to epicardium, and excitability thresholds and ventricular refractory periods in both normal and infarct tissue were also determined. Although diltiazem had significant doserelated effects on the heart rate, AH interval and sinus node recovery time at these dosages, diltiazem had no significant effect on the transmyocardial conduction times, excitability thresholds or ventricular refractory periods of either normal or chronically infarcted myocardium. Correspondingly, di1tiazem also failed to prevent the initiation of either ventricular tachycardia or fibrillation by programmed pacing in any of these 11 dogs.
KeywordsRefractory Period Ventricular Tachyarrhythmia Normal Site Effective Refractory Period Chronic Myocardial Infarction
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