Antiarrhythmic effects of cibenzoline Thirty-three patients with ventricular tachyarrhythmias were referred for evaluation of their arrhythmias using programmed electrical stimulation to guide antiarrhythmic therapy. Cibenzoline succinate, a new antiarrhythmic agent, was compared to procainamide in patients with ventricular tachycardia. Cibenzoline was given intravenously, initially 1.0 mg/kg, then in 1 mg/kg increments to a maximum of 3.0 mg/kg, during electrophysiologic testing. The results were compared to procainamide, which was also administered intravenously to 1000 and then to 1500 mg. Cibenzoline provided protection against ventricular tachycardia induction in 16 of 33 patients. The PR interval increased 13%, QRS duration widened 26%, and QT, interval was prolonged by 7%. There was a 9% fall in mean arterial blood pressure. Procainamide prevented ventricular tachycardia induction in 21 out of 31 patients tested. The PR interval increased 1 l%, QRS duration widened 27%, and QT, interval prolonged by 8%. Cibenzoline was given orally to 13 patients for chronic treatment. Chronic oral cibenzoline therapy after a mean follow-up of 8.8 months caused a reduction of ventricular ectopy from 666 to 190 beats/hr. Ventricular tachycardia events decreased per Holter monitor recording from 6 to 0.6. Cibenzoline therapy was discontinued in 5 of 13 patients due to break-through arrhythmias (nonsustained ventricular tachycardia on Holter monitor and recurrence of sy,mptoms). Cibenzoline may be an effective antiarrhythmic agent in selected patients. (AM HEART J lOg:827, 1985.) Dennis S. Miura, M.D., Ph.D., Gad Keren, M.D., Vilma Torres, M.D., Brenda Butler, B.A., Keiko Aogaichi, M.D., and John C. Somberg, M.D. Bronx, N.Y. Cibenzoline succinate (Cipralan) or Z-(2,2-diphenyl- cyclopropyl)imidazoline succinate is a new antiar- rhythmic agent which is not chemically related to other known antiarrhythmic agents. The antiar- rhythmic efficacy of cibenzoline has been demon- strated in several animal and clinical studies. Ciben- zoline has been shown to cause a prolongation of the effective refractory period, a decrease in the rate of rise of the action potential, a prolongation in re- polarization, and blockade of the slow calcium chan- nel. These finding have led Millar and Vaughan Williams1~2 to propose that the drug fits into three of four classes in their classification of antiarrhythmic drugs. The antiarrhythmic effects of cibenzoline have been demonstrated in isolated preparations in the Harris dog model.3 Studies using programmed electrical stimulation techniques to determine drug From the Cardiology Division, Department of Medicine, Albert Einstein College of Medicine. Supported in part by a grant from Hoffmann-La Roche, Inc., and by an Established Investigatorship (Dr. Somberg) from the American Heart Association. Received for publication July 5, 1984; revision received Sept. 10, 1984; accepted Oct. 22, 1984. Reprint requests: John C. Somberg, M.D., Division of Cardiology, Albert Einstein College of Medicine, 1300 Morris Park Ave., F-208, Bronx:, NY 10461. efficacy have shown cibenzoline to be effective in a canine modeL4 Its clinical efficacy has been reported in the suppression of ventricular arrhythmias, and it has been noted to have few clinical side effects on oral administration5m8 Cibenzoline has also been reported to be effective in prolonging the refractory period of an accessory pathway in a patient with Wolff-Parkinson-White syndrome.s Programmed electrical stimulation techniques have been used by a number of investigators as a rapid method to assess the efficacy of antiarrhyth- mic therapy in patients with life-threatening ven- tricular tachyarrhythmias.‘O-l5 Using this method, we tested the antiarrhythmic efficacy of cibenzoline in patients with a history of symptomatic ventricular tachycardia. This study reports the acute antiar- rhythmic efficacy of cibenzoline compared to a conventional antiarrhythmic agent, procainamide. METHODS Patient population. Thirty-three patients (22 men and 1 I women) were studied (Table I). The age range was from 34 to 80 years, with a mean of 61.6 t 1.9 @EM). They were referred to our laboratory for selection of antiar- rhythmic therapy. Six patients were referred after resusci- tation following a cardiac arrest. Seventeen patients had documented symptomatic ventricular tachycardia on Holter monitor recording or coronary care unit monitoring 827