Electrophysiological Effects of a New Antiarrhythmic Agent, Nicainoprol, in Humans

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Abstract
The electrophysiological effects of nicainoprol, a new antiarrhythmic drug, were evaluated in a heterogeneous group of 23 patients aged 59 .+-. 15 (mean .+-. standard deviation) years. Nicainoprol was administered intravenously as a bolus of 1-2 mg/kg followed by continuous infusion at two dose levels. Electrophysiologic study was performed before and during the infusion at a steady-state drug level on each dose. The sinus node recovery time was unaltered in patients with normal sinus node function and was markedly prolonged in three of six patients with sinus node dysfunction. The intranodal conduction time (p < 0.01) and the infranodal conduction time (p < 0.001) increased, and the QRS duration (p < 0.05) lengthened significantly even during 1 mg/kg/h. During 2 mg/kg/h, these times were further prolonged and, in addition, the intra-atrial conduction time (p < 0.05), atrioventriuclar nodal effective and functional refractory periods (p < 0.01), as well as the Wenckebach cycle length (p < 0.001) also increased significantly. Similar depressant effects on the retrograde ventriculoatrial conduction system were also produced by nicainoprol. Retrograde His-atrioventricular nodal conduction was blocked in six of eight patients with this condition and was prolonged in the remaining two. Sustained supraventricular tachycardia was induced in seven patients, five of whom received nicainoprol during the tachycardia. The termination of supraventricular tachycardia was exclusively due to ventriculoatrial block in all five subjects, three with orthodromic circus movement tachycardia and two with atrioventricular nodal reentrant tachycardia of the slow-fast type. The reinducibility of supraventricular tachycardia could be prevented in five of seven patients. In contrast, there were only small changes of the right atrial and right ventricular refractoriness as well as of the heart rate corrected Q-T interval. It is concluded that nicainoprol acts on the antegrade and retrograde atrioventricular conduction system. Nicainoprol seems to be highly effective in termination and prevention of supraventricular reentrant tachycardias. It is safe and well tolerated without adverse reactions.