Ultra-short-term heart rate variability for early risk stratification following acute ST-elevation myocardial infarction.

OBJECTIVES: To evaluate the prognostic significance of early ultra-short-term heart rate variability (HRV) measurement in patients admitted for ST-elevation myocardial infarction (STEMI).
METHODS: HRV was calculated retrospectively from the standard admission and discharge 10-second ECG of 196 consecutive patients with STEMI. Reduced HRV was defined as standard deviation of N-N intervals (SDNN) <9.5 (25th percentile). Data regarding all end points were obtained 2 years after discharge for all patients.
RESULTS: Patients' age was 60.9 +/- 13 years and 21% were female. Admission SDNN was lower than discharge SDNN (20.2 +/- 18 vs. 34.2 +/- 31.1, respectively; p = 0.001). Admission and discharge SDNN positively correlated with survival (r = 0.16, p = 0.03 and r = 0.15, p = 0.04, respectively), but were not predictive of other cardiovascular end points. Reduced admission SDNN was associated with increased mortality at 1 and 6 months, and 1 and 2 years after admission, while discharge SDNN was associated only with 1- and 2-year mortality. Using multivariate analysis, adjusted for potential confounders, admission SDNN <9.5 was found to be an independent risk factor for 2-year mortality (odds ratio = 2.9, 95% confidence interval = 1.12-7.56; p = 0.028).
CONCLUSIONS: Reduced HRV, recorded from admission and discharge ECG, appears to be a significant and independent predictor of all-cause mortality in patients with STEMI.