[Effect of nifedipine on sinus node and atrioventricular node function following autonomic blockade in the human]

The effect of intravenously administered nifedipine (7.5 micrograms/kg) on sinus node and atrioventricular (AV) node function was evaluated in 17 patients, 9 of whom had sinus node disease after autonomic blockade (propranolol 0.2 mg/kg and atropine 0.04 mg/kg i.v.). The patients' ages ranged from 18 to 77 years. After nifedipine there was a nonsignificant increase in the median values for sinus cycle length from 750 ms to 760 ms, for sinus node recovery time from 1150 ms to 1240 ms, for corrected sinus node recovery time from 440 ms to 460 ms, and for sinoatrial conduction time from 63 ms to 75 ms. Nevertheless, nifedipine produced a significant increase in the AV node refractory periods (median values): the effective refractory period lengthened from 300 ms to 305 ms (rate 100/min) and from 290 ms to 300 ms (rate 120/min) respectively. The functional refractory period increased from 380 ms to 400 ms (rate 100/min) and from 385 ms to 410 ms (rate 120/min) respectively. The Wenckebach period was significantly prolonged from 370 ms to 390 ms. We conclude, therefore, that in the absence of autonomic control intravenous administration of nifedipine exerts a mild depressive effect on AV node but not on sinus node function.