Differential characteristics of neural circulatory control - Early versus late after cardiac transplantation

Background-Reappearance of low-frequency (LF) (+/-0.10 Hz) oscillations in RR interval (RR) after cardiac transplantation is indicative of sympathetic efferent reinnervation. We hypothesized that restored LF oscillations in R R in heart transplant recipients (HTRs) are linked to oscillations in muscl e sympathetic nerve traffic (MSNA). Methods and Results-RR, RR variability, and MSNA were recorded 5 +/-2 month s (n=7, short-term HTRs) and 138 +/-8 months (n=7, long-term HTRs) after he art transplantation and compared with matched hypertensive patients (n=7). A coherence function determined the coupling between LF oscillations in MSN A and RR. RR variance did not differ between short-term and long-term HTRs. However, LF variability was only 1 +/-0.5 ms(2) in the short-term HTRs but was 15 +/-8 ms(2) in the long-term HTRs (P <0.05). Normalized LF variabili ty was also higher in the long-term HTRs (40 +/- 14 normalized unites) vers us the short-term HTRs (6 +/-3 normalized united, P <0.05) but did not diff er from the LF variability of the hypertensive patients. Long-term HTRs wer e taking less cyclosporine (P <0.01) but had higher MSNA than the short-ter m HTRs (62 +/-7 versus 31 +/-7 burst/min, respectively, P <0.05). Coherence between LF oscillations in MSNA and RR was similar in the long-term HTRs ( 0.59 +/-0.11) and the hypertensive patients (0.60 +/-0.07) and was 3-fold g reater than in the short-term HTRs (0.20 +/-0.06, P <0.05). Conclusions-Cardiac reinnervation after long-term heart transplantation is characterized by a restoration of the coherence between LF oscillations in RR and MSNA. Higher MSNA in long-term than in short-term HTRs suggests that time elapsed after cardiac transplantation may be a major determinant of s ympathetic excitation in heart transplant recipients.