Reliability of heart rate variability measurements in patients with a history of myocardial infarction
Résumé
Despite a well established prognostic value in cardiac patients, heart rate variability (HRV) indexes have been little used in the clinical setting. Poor reliability of the measurements might be a possible explanation. In this study we assessed the reliability of short-term HRV indexes in post myocardial infarction (MI) patients. We studied 61 MI patients (50 males, mean age±SD: 59±8 yrs, LVEF: 46±6 %), who underwent a 5+5min ECG recording during spontaneous and paced breathing, on two consecutive days. Standard time- (SDNN, RMSSD) and frequency-domain (LF and HF power and LF/HF) indices of HRV were computed. Absolute and relative reliability were assessed respectively by the 95% limits of random variation and by the intraclass correlation coefficient (ICC). The agreement between the two measurements in classifying patients at low or high risk, according to different cut-points, and the sample size needed to detect a clinically relevant change, were also assessed. During spontaneous breathing, individual changes in test-retest measurements ranged from –41% to +61% (SDNN, best case) and from -76% to +316% (LF/HF, worst case). The ICC ranged from 0.72 to 0.81. Most patients (79 – 90%) were assigned to the same class by the two measurements. Paced breathing did not improve reliability. Short-term HRV parameters in MI patients may exhibit large day-to-day variations, making the detection of treatment effects in individual patients difficult. However, the ICC values and the analysis of consistency of classification between repeated tests indicate that HRV measurements fulfil the criteria required to be used for diagnostic or classification purposes.
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