Effects of enalapril maleate on heart rate variability: a pilot study.

The effects of enalapril maleate on heart rate variability, an indicator of cardiac autonomic function, were evaluated by nonspectral analysis in 12 patients with standard deviation in the R-R interval for each 5-minute period for 24 hours (SDANN) of 80 msec or less. A 24-hour electrocardiogram was recorded before treatment and after 2 weeks of treatment with enalapril. No significant difference was observed in the mean R-R interval on 24-hour electrocardiography between the pretreatment and the posttreatment periods (824 +/- 84 msec vs 834 +/- 83 msec). The SDANN increased significantly (P < 0.01) between the pretreatment period (62.8 +/- 13.7 msec) and the posttreatment period (87.1 +/- 31.2 msec), as did the standard deviation of the R-R interval during the two monitoring periods (P < 0.001). However, no significant difference was observed in the mean value of the standard deviations of the R-R interval for 5 minutes; the proportion of adjacent R-Rs with a difference of more than 50 msec; or the root-mean square of the difference in successive R-Rs in the pretreatment period as compared with the posttreatment period. Causal blood pressure at rest decreased significantly (P < 0.05) after treatment with enalapril (124 +/- 17/66 +/- 7 mmHg) as compared with the pretreatment period (140 +/- 24/75 +/- 13 mmHg). Enalapril may be useful for maintaining normal autonomic nerve activity, preventing sudden cardiac death, and enhancing quality of life in our stressful society.