ABSTRACT
The purpose of this study was to investigate the effect of multiple doses of orally administered isradipine on atrioventricular nodal conduction in patients with first-degree atrioventricular block. Forty-eight patients with a P-R interval > or =0.22 seconds on a surface electrocardiogram (ECG) (first-degree atrioventricular block) with or without a bundle-branch block were randomized to one of four groups for 6 weeks of treatment with either placebo or 5.0 mg/d, 7.5 mg/d, or 10.0 mg/d isradipine. P-R interval prolongation was assessed at baseline and posttreatment using resting 12-lead ECGs and 24-hour Holter monitoring. The effect of isradipine on the following parameters were assessed: systolic and diastolic blood pressures, heart rate, respiration rate, oral temperature, and weight. Neither isradipine nor placebo treatment had a statistically significant treatment effect on the change from baseline in P-R interval, QRS duration, Q-T interval (uncorrected), or sinus heart rate at week 7 as measured by 12-lead ECG. All treatment groups, however, had small, statistically insignificant decreases from baseline in the mean P-R interval. The largest decrease (from 0.26 seconds at baseline to 0.22 seconds at week 7) was recorded for the 7.5 mg/d isradipine group, which also had the greatest posttreatment decreases in QRS duration, sinus heart rate, and systolic and diastolic blood pressures. The treatment groups did not differ significantly with respect to the change from baseline to study end in P-R interval prolongation or degree of atrioventricular block (as measured by 24-hour Holter monitoring), radial pulse rate, respiration rate, weight, or oral temperature. In this study, isradipine did not have a negative dromotropic effect on the atrioventricular node. The trend toward a posttreatment decrease in P-R interval suggests that isradipine may actually improve atrioventricular nodal conduction in patients with first-degree atrioventricular block and thus may be used safely in this population.
