Consistency of Multicenter Measurements of Heart Rate Variability in Survivors of Acute Myocardial Infarction

Heart rate variability (HRV) analysis from 24-hour ambulatory ECG has been widely used in risk stratification of patients after myocardial infarction (MI). The accuracy of HRV assessment is known to potentially vary when different commercial systems are used. However, the consistency of HRV measurements has never been fully investigated. Twenty-six post-MI patients (mean age 59 +/- 8 years, 22 men) were studied, of whom 13 succumbed to sudden cardiac death (SCD) within 1 year and 13 remained alive for at least 3 years (MI survivors). Each patient had a 24-hour Holter ECG recorded before hospital discharge. HRV analysis was performed four times from the same recordings using three different Holter tape analysis systems (Marquette, Reynolds, and CardioData) by four independent operators (CardioData system was used twice, once in the United Kingdom and once in the United States). Mean normal-to-normal RR intervals (mNN) and 3 HRV parameters (SDNN, RMSSD, and HRV triangular index [HRVi]) were derived from each recording. The consistency of mNN and HRV measurements was evaluated by coefficient of variance (CV) and by the Bland-Altman method. The results demonstrated that (1) all indices measured by different systems were statistically similar (P = NS) except the measurement of RMSSD (P = 0.01), (2) the measurements of mNN were highly reproducible with a maximum mean difference of 1.8 +/- 13.8 ms and maximum limits of agreement from -14.6 to +15.6 ms. The maximum mean differences were--1.8 +/- 1.4 unit and 4.4 +/- 9.6 ms for HRVi and SDNN, respectively, and RMSSD was less reproducible with a maximum mean difference of--11.1 +/- 11.5 ms, and limits of agreement from -16.2 to +9.6 ms; and (3) the consistency of mNN (CV 0.9% +/- 0.9%) was significantly higher than that of HRVi, SDNN, and RMSSD (P < 0.0001). The consistency of HRVi was similar to that of SDNN (4.8% +/- 2.1% vs 5.7% +/- 4.8%, P = 0.4), and the consistency of RMSSD (26.6% +/- 13.3%) was significantly lower than that of the other measurements (P < 0.00001). In conclusion, the measurements of mNN by different analytical systems are the most consistent among the parameters studied. The global 24-hour measurements of HRV (SDNN and HRVi) are highly reproducible, whereas the measurement of short-term HRV components (RMSSD) is significantly less reproducible.