Protamine-induced hypotension and bradycardia in a cardiac transplant patient

The potential for functional reinnervation of the transplanted heart in man is controversial. We report the sudden onset of bradycardia in a cardiac transplant patient following a period of hypotension subsequent to the administration of protamine. Possible mechanisms underlying this response, including reinnervation of the transplanted heart, are assessed.

Eight weeks after cardiac transplantation, a patient returned to hospital for a left femoral-tibial artery bypass vein graft. The patient was anaesthetized using general anaesthesia. Upon completion of the procedure, protamine was administered to reverse the heparin-induced anticoagulation. Although administration of a 5.0 mg "test-dose" appeared to be without cardiovascular effect, after an additional 20.0 mg, blood pressure decreased from 98/52 to 62/40 mmHg. After blood pressure reached its nadir, heart rate decreased precipitously from 57 to 29 beats.min-1.

This report demonstrates that heart rate can change considerably in patients who have undergone cardiac transplantation. It is argued that the change in heart rate observed in the present report cannot be explained by reinnervation of the transplanted heart, as the patient had undergone transplantation only eight weeks previously. Rather, we suggest that the change was mediated by mechanisms intrinsic to the transplanted heart and extrinsic to the CNS.