DECREASED R-R VARIATION - A CRITERIUM FOR OVERDOSAGE OF TRICYCLIC PSYCHOTROPIC-DRUGS

Objective: Since intoxication with tricyclic antidepressants is common , a supplementary screening method for differentiation between therape utic and supra-therapeutic ranges would be a valuable diagnositc tool, particularly in delirious and unconscious patients. Setting: 108 pati ents treated with amitriptyline, 8 patients treated with doxepin, 10 p atients treated with clozapine, and 72 normal control subjects matched for age and sex were tested for heart rate variability while resting. Results: Considering time and frequency derived measures, which are r ather independent of heart rate, the patients showed significantly dec reased heart rate variability parameters (p < 0.0001), as compared wit h the normal subjects. Of the patients presenting delirious symptoms 6 showed coefficients of variation more than 4 standard deviations belo w the mean control value. Conclusions: As heart rate variability can b e easily calculated, this measurement is suggested as a useful tool to quickly exclude or support the diagnosis of chronic intoxication with tricyclic antidepressants or clozapine.