Increase of respiratory sinus arrhythmia after administration of diltiazem despite reduction of blood pressure

Power spectral analysis of heart rate variability was used to study the effects of the calcium channel blocker diltiazem and the β-receptor blocker metoprolol on the parasympathetic nervous system. The area under the curve of the high frequency range (f=0.18-0.35 Hz) during controlled respiratory frequency (f=0.25 Hz) was used as a quantitative probe of parasympathetic activity. 24 male patients with proven coronary heart disease and normal left ventricular function (LVEF>60%), mean age 60±9 years, were studied 2 weeks after chronic treatment with diltiazem (3×60 mg) or metoprolol (3×60 mg). 12 patients received diltiazem, 12 patients received metoprolol. After acute administration of diltiazem blood pressure was reduced but parasympathetic activity was significantly higher as compared with the initial measurement. The same effect was seen for metoprolol where a significant lower heart rate was present after acute administration of the drug. The relative enhancement of the vagal influence on heart rate may contribute to the beneficial effects of both drugs in patients with coronary heart disease