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 activity. R-R intervals and the standard deviations, low-frequency power (LF: ln ms2, 0.04–0.15 Hz), high-frequency power (HF: ln ms2, 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. Pirenzepine was found to cause a significant increase in the R-R interval from 903±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). Pirenzepine also increased HF significantly from 4.29±0.32 to 5.16±0.38 ln ms2 in the control group (P<0.0001) and from 4.04±0.16 to 4.48±0.24 ln ms2 in the chronic heart failure group (P<0.05). Pirenzepine did not significantly alter the LF/HF ratio in either group. We emphasize that pirenzepine appears to have a vagoinimetic effect in patients with chronic heart failure and that it may be useful for augmenting vagal control of the heart in some patients with chronic heart failure.