Cardiac electrophysiologic properties of intravenous isradipine in patients with sick sinus syndrome

Isradipine is a new dihydropyridine calcium antagonist with powerful vasodilating properties. Although therapeutic concentrations do not affect myocardial contractility in vivo, in vitro studies have demonstrated a negative chronotropic action with only minor dromotropic influence. In humans with normal sinus and atrioventricular node function, even in the presence of beta-blockade, such a negative chronotropic effect could not be proved. No data are available on the effects of isradipine on a compromised sinus node. Therefore, the effect of intravenous isradipine at 0.3 μg/kg/minute for 30 minutes was studied in seven patients with the clinical signs of a sick sinus syndrome. Mean arterial blood pressure decreased from 126 ± 21 to 113 ± 15 mm Hg (p <0.05). Spontaneous sinus cycle length decreased from 969 ± 22 to 843 ± 161 msec (p <0.05). Changes in sinoatrial conduction time, sinus node recovery time, and corrected sinus node recovery time were not significant. Changes in atrioventricular node functional refractory period, the atrial-His interval, the His-ventricle interval, and Wenckebach point were not significant. Also, effective. Also, effective refractory periods of atrium and ventricle, and QRS duration changed but not significantly. The QT interval decreased (419 ± 45 to 405 ± 44 msec; p <0.05), and there was a slight (not significant) increase of QTc interval (429 ± 41 to 443 ± 37 msec; not significant). It is concluded that isradipine in hemodynamically effective doses has no depressant effect on sinus and atrioventricular node function in patients with sick sinus syndrome.