The Acute-Phase Heart Rate Variability in Acute Coronary Syndrome-The Implications of Different Analyses

Abstract

Purpose: Heart-rate variability (HRV) is non-stationary. HRV is traditionally analyzed by power spectrum (low/high frequency (LF/HF) ratio). Detrended fluctuation analysis (DFA) deduces HRV to a simple fractal scaling exponent alpha. Previously, HRV studies focused on post-MI and chronic heart failure. The decreased DFA alpha is associated with mortality. The acute-phase HRV has not been elucidated. We intended to evaluate acute-phase HRV of acute coronary syndromes (ACS), in comparison with non-ACS subjects.Methods: Our study had two parts: simulation of acute stress on non-ACS volunteers and the prospective observation in patients of ACS. We assessed 1-hour ECO of volunteers taking three designated intensity of exercise and patients in the acute stage of ACS. All ECO data were analyzed by DFA and power spectrum. The results of HRV were evaluated by univariate analysis.Results: The 30 volunteers got elevated DFA alpha while the intensity of exercise increased (0.95±0.050 to 1.07±0.084 to 1.20±0.083, p＜0.05). The fractal properties of 33 ACS patients correlated with the complexity of post-MI course (1.004±0.0080 in non-complicated vs. 1.216±0.058 in complicated p＜0.05). There was no significance when the fractal scaling exponent was categorized by age, type of ACS and other variables. The LF/HF ratio did not differ in any clinical perspective but between RCA/LCx and LAD groups (4.23±2.34/4.987 vs. 1.87±1.06, p＜0.05).Conclusions: DFA can be used to study the acute-phase HRV in ACS, while the traditional power spectral analysis failed. The increased a value derived from DFA may imply unresolved cardiac stress which demands further attention.