Atrioventricular block after administration of atropine in patients following cardiac transplantation

Background. Atropine is widely used as a parasympatholytic agent during diagnostic and therapeutic procedures, We observed an unexpected paradoxical response to atropine after cardiac transplantation. Method. In a study investigating the occurrence of autonomic reinnervation after cardiac transplantation, atropine, at 0.015 mg/kg body weight, was given intravenously to 23 patients (mean age, 56+/-8 years) 98 days to 6.4 years after transplantation. Results. Two patients experienced a witnessed syncope 40 and 150 min after administration of atropine. Second-degree atrioventricular (AV) block was documented in the first patient immediately afterward, and third-degree AV block was seen on 24-hr electrocardiogran monitoring in the second patient, A third patient developed documented AV block 15 min after atropine but experienced no sequelae because of a previously implanted pacemaker. Conclusions. Although the underlying mechanism is not clear, these findings suggest that atropine may paradoxically cause high-degree AV block in patients after transplantation. Accordingly, it should be used with caution and appropriate monitoring in these patients.