Prognostic Significance of Heart Rate Variability During the First 24 Hours of Acute Myocardial Infarction: A 5-Year Follow-up Study

Abstract

Background: The prognostic value of heart rate variability (HRV) measured within the first 24 hours of acute myocardial infarction was assessed in 94 consecutive patients. Methods: The mean of standard deviation of normal R-R intervals for all 5-minute segments (SDNN index), the width of the R-R interval histogram at 10% and 50% of the peak, and three frequency-domain measures of HRV (low frequency [LF], high frequency [HF], and LF/HF ratio) were calculated from a continuous ECG recording taken within the first hours of admission and their prognostic value for long-term events was studied. Results: During the follow-up period (56.7 ± 5.9 months) 6 sudden and 7 nonsudden cardiac deaths occurred. Time-domain measurements of HRV were lower in patients with sudden death (SDNN index: 27.0 ± 20.2 vs 47.5 ± 20.7 ms in survivors, P < 0.001). LF and HF power, but not the LF/HF ratio, were also inversely associated with sudden death. No significant differences were found between survivors and patients with nonsudden cardiac death. After adjustment for other clinical covariates, LF and HF power remained significantly associated with sudden death. Conclusion: We conclude that heart rate variability measured within the first 24 hours of myocardial infarction is a strong predictor of sudden death during subsequent follow-up.