The electrophysiologic effects of nisoldipine in the conscious dog

The electrophysiologic effects of nisoldipine, 10 to 100 micrograms/kg, were studied in eight conscious nonsedated chronically instrumented dogs. No change in blood pressure or electrophysiologic measurements followed 10 micrograms/kg nisoldipine. Following 30 micrograms/kg, the mean arterial pressure was decreased from 116 +/- 9 to 105 +/- 10 mm Hg (means +/- SD) and the sinus cycle length decreased from 536 +/- 101 to 428 +/- 75 (msec) without changes in PR, AH, HV intervals, atrioventricular (AV) nodal conduction, or sinus node recovery times. After 100 micrograms/kg, the mean blood pressure was further reduced (87 +/- 17 mm Hg), the sinus cycle length further decreased (378 +/- 71 msec), and the AV nodal effective and functional refractory periods shortened (178 +/- 59 to 148 +/- 43 and 178 +/- 59 to 148 +/- 43 msec, respectively), as did the sinus node recovery time (corrected and uncorrected) and the QT and QTc intervals. No significant changes in atrial or ventricular pacing thresholds, atrial or ventricular refractory periods, or in the HV interval were observed. Nisoldipine, a nifedipine derivative, did not significantly change electrophysiologic parameters in intact conscious animals when given in doses which did not alter blood pressure. When nisoldipine produced significant vasodilatation, the enhancement of AV nodal conduction observed probably reflects a balance of the direct effect of nisoldipine and opposing autonomic activity.