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 therapeutic and supratherapeutic ranges would be a valuable diagnostic tool, particularly in delirious and unconscious patients.

SETTING

108 patients treated with amitriptyline, 8 patients treated with doxepin, 10 patients 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 rather independent of heart rate, the patients showed significantly decreased heart rate variability parameters (p < 0.0001), as compared with the normal subjects. Of the patients presenting delirious symptoms 6 showed coefficients of variation more than 4 standard deviations below the mean control value.

CONCLUSIONS

As heart rate variability can be 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.