Electrophysiological evidence of reinnervation of the transplanted human heart

Beat-by-beat heart rate (HR) changes during exercise were studied in two young and fit heart-transplanted humans at different time intervals following transplantation. Upon the start of the exercise, a slow gradual increase in HR was seen during the early experiments after the transplantation, whereas an immediate rapid increase in HR was observed during the later experiments. From standard ECGs obtained 32 months after transplantation, two P waves at somewhat different rates could be identified in both subjects, probably arising from donor and recipient sinoatrial nodes, respectively. The two P wave rate changes during and following exercise were very similar. We conclude that these changes in the HR pattern and ECG must be due to reinnervation of the donor hearts, most likely by parasympathetic cardiac fibers.