Cardiac effects of atropine in patients treated with antidepressive medication

Abstract

It is often suggested that atropine should be avoided in patients on treatment with tricyclic or tetracyclic antidepressants. It is feared that the strong anticholinergic side effects of these drugs could exaggerate the effects of atropine on the heart. In a controlled prospective study, 31 patients on treatment with tri- or tetracyclic antidepressants were given atropine in incremental doses. ECG-changes and changes in heart rate were recorded and compared to a control group. Atropine 2 micrograms/kg was administered in 60 sec. intervals up to a total dose of 10 micrograms/kg. The patients on antidepressant treatment had a higher incidence of common anticholinergic side effects (dryness of mouth, accommodation disorders, constipation) due to the anticholinergic properties of the antidepressants. In addition, the basal heart rate of these patients was significantly higher compared to the control group (81/min vs. 73/min). After administration of 2 and 4 micrograms/kg of atropine the patients of the control group showed a 5% resp. 4% decrease in heart rate. 26% of these patients developed conduction disturbvances. These changes could be explained by the parasympathetic effect of low doses of atropine. They were less pronounced in the patients on treatment with antidepressants. Here, only the administration of 2 micrograms/kg of atropine led to a 2% decrease in heart rate. Only 6% of these patients developed conduction disturbances. Both groups showed an increase in heart rate when higher doses of atropine were administered (8 and 10 micrograms/kg). However, the increase in heart rate after administration of 10 micrograms/kg was significantly less in the patients on antidepressant treatment compared to the control group (11.4% vs. 16.2%). There were no changes of blood pressure during these investigations. The results of this study suggest that the anticholinergic properties of tri- and tetracyclic antidepressants include an increase in basal heart rate, but do not render the heart more susceptible to the cardiac effects of atropine.