Heart rate variation in patients treated with antidepressants. An index of anticholinergic effects?

The aim of the present study was to investigate whether heart rate variation as obtained simply from an electrocardiographic registration is influenced in subjects given antidepressive medication. The mean difference between consecutive R-R intervals (MCD) was reduced in patients (n = 23) treated with various doses of tri- or tetracyclic antidepressants [7.7 (1.8-32.3) ms in patients versus 24.8 (7.0-87.7) ms in controls]. Among those receiving 1.67 mg tricyclic antidepressant or more per kilogram body wt (n = 12) MCD was further reduced [5.0 (2.1-12.0) ms] with no overlapping of values as compared to controls (n = 9). In a subgroup of patients treated with clomipramine the MCD was related inversely to the dosage (R = 0.78, P less than 0.02). In an additional group of seven patients, MCD was reduced following a few days of treatment with antidepressants as compared to pretreatment values (P less than 0.02), indicating that the reduction is a result of therapy and not a concomitant of the affective state. We suggest that measurements of heart rate variation could be a useful tool to measure anticholinergic effects of antidepressants.