Sympathetic rhythmicity in cardiac transplant recipients

Background-Variability of R-R interval and muscle sympathetic nerve activit y (MSNA) occurs predominantly at a low frequency (LF, +/-0.1 Hz) and a high frequency (HF, +/-0.25 Hz) in normal humans. Increased sympathetic drive i n normal humans is associated with an increased LF component of the R-R int erval and MSNA, Patients with severe heart failure have high sympathetic ac tivity but decreased or absent LF power of both R-R and MSNA, We tested the hypothesis that this dysfunction in autonomic modulation in heart failure can be reversed by heart transplantation. Methods and Results-We performed spectral analysis of resting MSNA, R-R int erval, and respiration in 9 patients with heart transplants, 9 chronic hear t failure patients, and 9 normal control subjects, all closely matched for age, sex, and body mass index. MSNA (bursts per minute) was higher in patie nts with heart transplants (74+/-3) than either patients with heart failure (56+/-6) or normal subjects (40+/-4) (P<0.001), LF variability in the R-R interval was reduced in both heart transplant recipients and heart failure patients compared with the control subjects (P<0.01), The LF variability in MSNA was also nearly absent in the heart failure patients (P<0.01), Howeve r, the LF and HF oscillations in MSNA in patients with heart transplants we re comparable to those evident in the control subjects. Conclusions-Cardiac transplantation does not reduce MSNA. However, LF oscil lations in sympathetic activity are restored after transplantation such tha t the MSNA oscillatory profile is similar to that observed in normal subjec ts.