Paradoxical effects of pirenzepine on parasympathetic activity in chronic heart failure and control

We studied the effect of intravenous pirenzepine (3 mg) in normal subjects (n=15, 43+/-16 years old) and in patients with chronic heart failure (n=15, 61+/-12 years old) to assess the effect of low-dose pirenzepine on vagal a ctivity. R-R intervals and the standard deviations, low-frequency power (LF : In ms(2), 0.04-0.15 Hz), high-frequency power (HF: In ms(2), 0.15-0.40 Hz ) and the ratio of low- to high-frequency power (LF/HF ratio) were measured 10 min before and after pirenzepine using a Holter analysis system. Pirenz epine was found to cause a significant increase in the R-R interval from 90 3+/-112 to 956+/-129 ms in the control group (P<0.0001) and from 927+/-141 to 958+/-168 ms in patients with chronic heart failure (P<0.01). Pirenzepin e also increased HF significantly from 4.29+/-0.32 to 5.16+/-0.38 In ms(2) in the control group (P<0.0001) and from 4.04+/-0.16 to 4.48+/-0.24 In ms(2 ) in the chronic heart failure group (P<0.05). Pirenzepine did not signific antly alter the LF/HF ratio in either group. We emphasize that pirenzepine appears to have a vagoinimetic effect in patients with chronic heart failur e and that it may be useful for augmenting vagal control of the heart in so me patients with chronic heart failure. (C) 1999 Elsevier Science Ireland L td. All rights reserved.