Sympathetic rhythmicity in cardiac transplant recipients

Background - Variability of R-R interval and muscle sympathetic nerve activity (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 in normal humans is associated with an increased LF component of the R-R interval and MSNA. Patients with severe heart failure have high sympathetic activity 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 interval, and respiration in 9 patients with heart transplants, 9 chronic heart failure patients, and 9 normal control subjects, all closely matched for age, sex, and body mass index. MSNA (bursts per minute) was higher in patients 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). However, the LF and HF oscillations in MSNA in patients with heart transplants were comparable to those evident in the control subjects. Conclusions - Cardiac transplantation does not reduce MSNA. However, LF oscillations in sympathetic activity are restored after transplantation such that the MSNA oscillatory profile is similar to that observed in normal subjects.