[Increased vagal activity after administration of the calcium antagonist diltiazem in patients with coronary heart disease].

The effects of the calcium channel blockers diltiazem on the parasympathetic nervous system were studied by using spectral analysis of heart rate variability, and were compared with the effects of the beta-receptor blocker metoprolol. The area under the curve of the high-frequency range (f = 0.18-0.35 Hz) during controlled respiratory rate (f = 0.25 Hz) was used as a quantitative index of parasympathetic activity. Twenty-four male patients with proven coronary artery disease and normal left ventricular function (LVEF > 60%) were studied 2 weeks after chronic treatment with diltiazem (3 x 60 mg daily) or metoprolol (3 x 50 mg daily) before and after administration of the drug. Twelve patients received diltiazem and 12 patients metoprolol. After administration of diltiazem the peripheral systolic blood pressure was reduced, but the parasympathetic activity was significantly higher than compared with the initial measurement. The same effect was seen for metoprolol, but a significant lower heart rate was present after administration. The relative area under the high-frequency range significantly increased at rest, by 110% after diltiazem and 70% after metoprolol. Diltiazem and metoprolol enhance the vagal influence at the heart, thereby leading to an enhancement of barosensitivity and of the respiratory sinus arrhythmia. This action may contribute to the beneficial effects of both drugs in patients with coronary artery disease.