Es. Kaufman et al., EFFECTS OF DIGOXIN AND ENALAPRIL ON HEART PERIOD VARIABILITY AND RESPONSE TO HEAD-UP TILT IN NORMAL SUBJECTS, The American journal of cardiology, 72(1), 1993, pp. 95-99
To test the effects of digitalis and angiotensin-converting enzyme inh
ibition on the RR interval variability in an electrocardiogram, 20 nor
mal subjects were given digoxin 0.25 mg, enalapril 10 mg, and placebo
twice daily in a randomized, double-blind, crossover study. Continuous
24-hour electrocardiographic recordings obtained on day 5 of each tre
atment were analyzed and several time domain and power spectral measur
es of heart period variability were calculated. Digoxin markedly incre
ased (up to 51%) indexes of vagal modulation of heart period without c
hanging mean RR interval. Enalapril did not change any measure of hear
t period variability despite a modest hypotensive effect. To determine
the effect of each treatment on the response to orthostatic stress, 1
0 subjects also underwent 15 minutes of 60 head-up tilt; power spectra
were calculated for 15 minutes at 0-degrees and at 60-degrees of tilt
. Neither active treatment affected the response to head-up tilt.