Heart Rate Variability Is Associated with Exercise Capacity in Patients with Cardiac Syndrome X.

Dai-Yin Lu,Shih-Hsien Sung,Wen-Chung Yu,Tse-Min Lu,Albert C Yang,Hao-Min Cheng,Chen-Huan Chen,Joseph Devaney

doi:10.1371/journal.pone.0144935

Abstract

Heart rate variability (HRV) reflects the healthiness of autonomic nervous system, which is associated with exercise capacity. We therefore investigated whether HRV could predict the exercise capacity in the adults with cardiac syndrome X (CSX). A total of 238 subjects (57±12 years, 67.8% men), who were diagnosed as CSX by the positive exercise stress test and nearly normal coronary angiogram were enrolled. Power spectrum from the 24-hour recording of heart rate was analyzed in frequency domain using total power (TP) and spectral components of the very low frequency (VLF), low frequency (LF) and high frequency (HF) ranges. Among the study population, 129 subjects with impaired exercise capacity during the treadmill test had significantly lower HRV indices than those with preserved exercise capacity (≥90% of the age predicted maximal heart rate). After accounting for age, sex, and baseline SBP and heart rate, VLF (odds ratio per 1SD and 95% CI: 2.02, 1.19–3.42), LF (1.67, 1.10–2.55), and TP (1.82, 1.17–2.83) remained significantly associated with preserved exercise capacity. In addition, increased HRV indices were also associated with increased exercise duration, rate-pressure product, and heart rate recovery, independent of age, body mass index, and baseline SBP and heart rate. In subgroup analysis, HRV indices demonstrated similar predictive values related to exercise capacity across various subpopulations, especially in the young. In patients with CSX, HRV was independently associated with exercise capacity, especially in young subjects. The healthiness of autonomic nervous system may have a role in modulating the exercise capacity in patients with CSX.

Highlights

Cardiac syndrome X (CSX), a clinical condition characterized by exertional angina, exercise induced myocardial ischemia, and normal coronary angiogram [1], is associated with coronary microvascular insufficiency [2]
From 2009 to 2013, a total of 238 subjects who have sinus rhythm, myocardial ischemia documented by the exercise stress test, and consequent normal or nearly normal coronary angiogram on the basis of the visual inspection by two experienced cardiologists were enrolled to the present analysis
No doubt patients with good exercise capacity experienced longer exercise test duration, and they achieved higher METs and Bruce treadmill test stage. (Table 2) The baseline systolic blood pressure (SBP) and pulse pressure (PP) were lower and heart rate was higher in patients with good exercise capacity

Summary

Introduction

Cardiac syndrome X (CSX), a clinical condition characterized by exertional angina, exercise induced myocardial ischemia, and normal coronary angiogram [1], is associated with coronary microvascular insufficiency [2]. It has been shown that regular physical activity or exercise training may reverse the autonomic neural remodeling in subjects with CAD, myocardial infarction, or heart failure [11,12,13] with resultant improvement in the clinical outcomes [14]. HRV indices were not always related to physical activity or exercise tolerability in patient [15] or in the general population [16]. It remains unknown whether the cardiac autonomic function modulates exercise capacity in CSX patients. We investigated the association between HRV and exercise capacity in the patients with CSX

Methods

Results

Discussion

Conclusion