ELECTROPHYSIOLOGIC ASSESSMENT OF CALCIUM-CHANNEL BLOCKERS IN TRANSPLANTED HEARTS - AN EXPERIMENTAL-STUDY

The effects of calcium channel blockers on automaticity, conduction, a nd refractoriness were studied in a model of heterotopic heart transpl antation in dogs, which combined an innervated heart (recipient) and a denervated one (donor). Following the surgical procedure, 0.2 mg/kg v erapamil (n = 10), 0.15 mg/kg diltiazem (n = 10), or 5 mu g/kg + 30 mu g/kg/h nifedipine (n = 10) was administered intravenously. In basal s ituation and after drUg administration, each heart was assessed for AV interval, cycle length, sinoatrial conduction time, atrioventricular node antegrade block point, and atrioventricular node and ventricular refractory periods; electrocardiographic PR and QT intervals and QRS c omplexes; systemic arterial, pulmonary artery, central venous, and pul monary capillary wedge pressures; and cardiac output. The depressor ef fects of these calcium channel blockers on automaticity, refractorines s, and conduction were more intense in the transplanted hearts, very p ossibly because of the absence of adrenergic reflexes mediated by the autonomic nervous system; in particular, verapamil produced a great de pression of sinus automaticity in a large number of cases.