Heart rate variability as a means of assessing prognosis after acute myocardial infarction. A 3-year follow-up study.

The present study evaluated the prognostic value of heart rate variability after acute myocardial infarction in comparison with other known risk factors. The cut-off points that maximized the hazards ratio were also explored. Heart rate variability was assessed with 24 h ambulatory electrocardiography in 74 patients with acute myocardial infarction, 4 +/- 2 days after hospital admission and in 24 healthy controls. Patients were followed for 36 +/- 15 months. During follow-up, 18 patients died, nine suffered a non-fatal infarction and 20 underwent revascularization procedures. Heart rate variability was higher in survivors than in non-survivors (P = 0.005). This difference was found at higher statistical levels when comparing non-survivors vs controls (P = 0.0002). A similar statistically significant difference was also found between survivors vs controls (P = 0.04). Patients suffering non-fatal infarction and cardiac events (defined as death, non-fatal infarction or revascularization) had a lower heart rate variability than those without (P = 0.03 and P = 0.03, respectively). With multivariate regression analysis, decreased heart rate variability independently predicted mortality and death or non-fatal infarction. The presence of a left ventricular ejection fraction < 40% and a history of systemic hypertension were, however, stronger predictors. The cut-off points that maximized the hazards ratio using the Cox model differed from those reported by others. Decreased heart rate variability independently predicted poor prognosis after myocardial infarction. However, the cut-off points that should be used in clinical practice are still a matter for further investigation.