ABSTRACT
OBJECTIVE: To investigate whether heart rate variability(HRV) can assess exercise ability in patients with cardiac syndrome X(CSX). METHODS: A total of 246 subjects(55.2 ± 12.2 years, 68.3% male), who were diagnosed with CSX by the positive exercise stress test and normal coronary angiogram in Cardiovascular Department of the Second Affiliated Hospital of Harbin Medical University from March 2016 to August 2017 were enrolled. The 24-hour dynamic ECG monitoring was used to analyze HRV for long-time frequency domain analysis. The HRV power spectrum index included total power(TP),very low frequency(VLF), low frequency(LF) and high frequency(HF). RESULTS: VLF, LF and TP, but not LF/HF, were higher in the patients with good exercise capacity(≥90% of the age predicted maximal heart rate). After accounting for age, sex, systolic blood pressure and heart rate, VLF, LF and TP remained significantly associated with good exercise capacity. In addition, increased VLF, LF and TP were also associated with increased exercise duration, rate-pressure product, and heart rate recovery. In subgroup analysis, VLF, LF and TP demonstrated similar predictive values related to exercise capacity across various subpopulations, especially in the young. CONCLUSION: In patients with CSX, HRV is independently associated with exercise capacity, and is an independent predictor of ischemic tolerance in CSX patients, which can be used as an important index for evaluating the exercise ability of CSX patients.