Vagal reinnervation in the long term after orthotopic heart transplantation

Background: Sympathetic reinnervation after orthotopic heart transplantation (HTx) has become an accepted phenomenon, particularly in long-term transplanted patients. Parasympathetic reinnervation, however, still remains questionable. Methods: In 38 HTx recipients, mean age of 51.6 +/- 9.7 years (range, 29 to 70 years), with a time span after HTx of 4.6 +/- 2.8 years (0.5 to 10.5 years), we stimulated carotid baroreceptors using periodic neck suction at low (0.1 Hz) and high (0.2 Hz) frequencies to test sympathetic and vagal responses, respectively. Respiratory rate was fixed at 0.25 Hz. We simultaneously recorded surface electrocardiogram, finger blood pressure, respiration and neck pressure signals while patients rested in the supine position. Time series of RR intervals, respiration, and neck and blood pressures were generated and subjected to spectral analysis. Results: All patients demonstrated a 0.25-Hz peak in RR-interval spectrum, caused by non-autonomic respiratory sinus arrhythmia. Thirteen patients (5.2 +/- 3.5 years after HTx; range, 0.9 to 10.2 years) showed a baroreflex-induced sharp peak at 0.1 Hz in RR-interval power spectrum during 0.1-Hz neck suction, indicating sympathetic reinnervation. However at 0.2-Hz neck suction, 4 of the 13 sympathetically reinnervated patients displayed a baroreflex-induced 0.2-Hz peak, which could be suppressed with atropine administration-strong evidence for vagal reinnervation. Conclusions: Non-invasive carotid baroreflex stimulation is an appropriate tool to prove restoration of autonomic control after orthotopic HTx. Sympathetic reinnervation parallels parasympathetic reinnervation in long-term transplanted patients.