Rationale: Heart transplantation involves afferent and efferent cardiac denervation resulting in altered heart rate responsiveness and variability. Cardiac autonomic function has been assessed previously in heart transplant recipients (HTR) using heart rate variability (HRV). HTR have commonly shown reduced HRV; however, there is research to support reinnervation in some HTR. Limited information exists regarding the HRV of other noncardiac organ transplant recipients (OTR). This information would provide important insights into the effects of common treatment (eg, immunosuppressive therapy or surgery) strategies for orthotopic transplant patients.
Objective: The purpose of this investigation was to evaluate indices of HRV in HTR, OTR, and age- and activity-matched healthy controls.
Methods: We assessed 13 HTR, 33 OTR (liver, n = 12; kidney or double kidney, n = 10; lung or double lung, n = 7; kidney and pancreas, n = 2; bone marrow, n = 2) and 31 controls. Short-term (5 minutes) HRV was determined using time- and frequency-domain analyses in the supine position. For frequency-domain analysis, low-frequency HRV (LF, 0.004-0.15 Hz), high-frequency HRV (HF, 0.15-0.5 Hz), and LF(HF ratio analyses were used. For time-domain analysis, standard deviation of the normal-to-normal (NN) intervals (SDNN), square root of the mean-squared differences of successive NN intervals (RMSSD), and proportion derived by dividing the number of interval differences of successive N-N intervals greater than 50 milliseconds by the total number of NN intervals (pNN50) were obtained.
Results: Resting heart rates were highest in the HTR (84.7 +/- 10.2 bpm), while both transplant groups (OTR (72.7 +/- 11.6 bpm) had higher resting heart rates than the controls (60.0 +/- 7.7 bpm, P = .00). The sympathetic indicator LF was significantly higher in OTR (738.8 +/- 937.3 ms2) compared to the HTR (102.9 +/- 255.3 ms2) and the controls (91.2 +/- 62.3 ms2). Time domain indicators of parasympathetic activity (SDNN, RMSSD, and pNN50) were all significantly higher in the controls than in the HTR (P < .05). However, the HTR and OTR did not differ in the parasympathetic measures RMSSD and pNN50.
Conclusion: OTR demonstrated significantly elevated indices of sympathetic activity compared to HTR and controls. This finding may reflect the effects of organ transplant therapy (such as immunosuppressive therapy and/or surgery) on cardiac autonomic function. As anticipated, the HTR did not exhibit elevated sympathetic indices. However, the similarities between OTR and HTR in parasympathetic indices may indicate the possibility of some parasympathetic reinnervation in the HTR.