Signs of vagal reinnervation 4 years after heart transplantation in spectra of heart rate variability

Several investigators have shown signs of possible sympathetic but not parasympathetic reinnervation in heart transplanted patients. Spectral analysis of heart rate and blood pressure variability is a noninvasive tool appropriate to detect a functional autonomous reinnervation to the heart. In a follow-up study, 13 patients after heart transplantation (HTx) were investigated, mean age 50.6 ± 8.5 years, 18 healthy volunteers were selected as control group. For each patient two recordings were performed which took part 14 ± 5 months respectively 42 ± 8 months after HTx. ECG and systolic blood pressure (SBP) have been recorded simultaneously for 5 min in supine position during controlled respiratory rate of 12 or 15 cycles/min. No graft rejection has been detected in the endomyocardial biopsy performed right after the recordings. Power spectral densities (PSD) were calculated for the beat-to-beat time series of RR-intervals (distance of two following QRS complexes) and SBPs. The area of PSD in the range of 0.05-0.17 Hz was defined as low frequency (LF) and that of 0.18-0.35 Hz as high frequency (HF). LF and HF are indicative of efferent sympathetic respectively parasympathetic activity at the sinus node. A significant increase of LF (226%) and HF (213%) during a mean period of 28 months could be found. No differences were to be shown for systolic blood pressure variability. Previous findings confirm that LF band increases 4 years after transplantation, suggesting a possible sympathetic reinnervation of the heart. On the other hand an increase of the HF band also suggests a parasympathetic reinnervation.