Isradipine is a new dihydropyridine calcium antagonist reported to have minimal effects on cardiac electro–physiology. Of 19 patients with normal cardiac electrophysiological profiles, 11 received isradipine intravenously at doses of 0.0010, 0.0020, 0.0040 and 0.0080 mg–kg‐1 (0.0150 mg–kg‐1 total dose), and eight received verapamil intravenously at 0.0125, 0.0250, 0.0500 and 0.1000 mg–kg‐1 (0.1875 mg–kg‐1 total dose). One patient experienced hypotension several minutes after receiving the third isradipine dose. With isradipine, systolic blood pressure (BP) decreased from 154 ± 24 to 151 ± 22, 143 ± 25, 133 ± 19 and 124 ± 17 mmHg, respectively. Diastolic BP decreased from 83 ± 10 (baseline) to 80 ± 12, 76 ± 10, 74 ± 7 and 68 ± 9 mmHg, respectively. With verapamil, systolic BP changed from 132 ± 20 (baseline) to 135 ± 29, 132 + 24, 130 ± 25 and 115 ± 17 mmHg, respectively, and diastolic BP changed from 80 ± 14 to 84 ± 14, 81 ± 9, 78 ± 6 and 73 ± 5 mmHg, respectively. Isradipine had no significant effect on the PR, QRS, QT and QTc intervals, nor were there changes in the atrial–His (AH) and His–ventricle (HV) intervals, atrioventricular nodal effective refractory period, Wenckebach cycle length or sinus node recovery time. Similarly, verapamil at the doses studied did not significantly affect PR, QRS, QT, QTc, AH or HV intervals. However, with verapamil, the Wenckebach cycle length changed significantly from 394 + 82 (baseline) to 448 ± 93 ms. Despite the significant fall in BP with isradipine, heart rate did not change significantly. These results support the electrophysiological neutrality of isradipine on the cardiac conduction system.
