Abstract
The precise relation between heart rate variability (HRV) and autonomic re-innervation has not been established explicitly in patients after orthotopic heart transplantation (OHT), but can be inferred from the fact that the HRV is reduced immediately after OHT and may increase gradually with time. The aim of this study was to investigate the residual HRV in patients about 1–2 years after OHT, as compared with patients after coronary artery bypass graft (CABG) surgery. Thirteen patients who had received OHT and 14 patients who had received CABG surgery were recruited. HRV analysis was performed and the HRV measures in supine position were compared between these two groups of patients. We found that the mean (mRRI), standard deviation and coefficient of variation of RR intervals, total power, very low frequency power (VLFP), low frequency power, high frequency power (HFP), normalized VLFP (nVLFP) and low-/high-frequency power ratio in the OHT group were all significantly decreased, while the heart rate (HR) and normalized HFP (nHFP) were significantly increased, as compared with the CABG group. The decrease in HRV was more severe in the VLFP region. A smaller nVLFP and a greater nHFP were associated with a smaller mRRI and a larger HR in the OHT patients. The slope of the power law relation of HRV became positive in OHT patients, instead of negative in CABG patients. We conclude that patients after OHT have residual HRV which were characterized by severely depressed time and frequency domain HRV, increased HR and nHFP, decreased nVLFP, and positive slope of the power-law relation of HRV. The use of nHFP as the indicator of vagal modulation and the use of nVLFP as the indicator of renin-angiotensin modulation, thermoregulation and vagal withdrawal must be careful in the OHT patients.
Highlights
Spontaneous beat-to-beat fluctuation in heart rate (HR) reflects the ongoing modulation of sinus node activity through several cardiovascular control mechanisms [1]
We found that the mean, standard deviation and coefficient of variation of RR intervals, total power, very low frequency power (VLFP), low frequency power, high frequency power (HFP), normalized VLFP and low-/high-frequency power ratio in the orthotopic heart transplantation (OHT) group were all significantly decreased, while the heart rate (HR) and normalized HFP were significantly increased, as compared with the coronary artery bypass graft (CABG) group
By using heart rate variability (HRV) analysis, we found that the patients after OHT had smaller time and frequency domain HRV measures than those of the patients after CABG, except that the HR and normalized HFP (nHFP) of the OHT patients were greater than those of CABG patients
Summary
Spontaneous beat-to-beat fluctuation in heart rate (HR) reflects the ongoing modulation of sinus node activity through several cardiovascular control mechanisms [1]. This fluctuation in heart rate is termed heart rate variability (HRV), and can be quantified by the mathematical technique of power spectral analysis, which calculates the frequency contents of the time-varying signals and plots the power of the frequency bands as a function of frequency. The very-low frequency range reflects the renin-angiotensinaldosterone modulation and vagal withdrawal [5,6,7], and the ultra-low frequency range is often used in the power law relationship [8]. Reduced cardiac vagal modulation has been reported in patients with coronary artery disease (CAD) [13, 14], and the reduction in the cardiac vagal modulation was found to correlate with the angiographic severity, independent of previous myocardial infarction, location of diseased coronary arteries, and left ventricular function [15]
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