We compared the abilities of three different calcium (Ca2+) entry blockers, verapamil, diltiazem and felodipine to abolish ouabain-induced ventricular ectopy (100 × ectopic/total beats, VE) in anesthetized, closed-chest dogs. Ventricular tachycardia (VT) was produced in anesthetized, bilaterally vagotomized, closed-chest dogs by an average dose of 65 ± 19 μg/kg ouabain. 30 min after establishing VT, either verapamil (25–50 μg/kg + 5–10 μg/kg/min), diltiazem (50–100 μg/kg + 20–50 μg/kg/min), felodipine (3 μg/kg + 0.3 μg/kg/min) or saline was administered for another 30 min. Verapamil, at the higher dose utilized, practically abolished ouabain-induced VT (97 ± 3 to 8 ± 19% VE); diltiazem was moderately effective (96 ± 4 to 50 ± 8% ectopy) at 100 μg/kg, and felodipine exerted no antiarrhythmic effects in this model. All three Ca2+ entry blockers lowered mean aortic pressure, felodipine lowering this parameter most prominently. Thus, these structurally and electrophysiologically dissimilar Ca2+ entry blockers differed in their abilities to abolish the digitalis glycoside-induced arrhythmias in vivo. The superiority of verapamil may be related to its multiple, additional electrophysiologic effects.
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