Attenuated recovery of heart rate turbulence early after myocardial infarction identifies patients at high risk for fatal or near-fatal arrhythmic events

BACKGROUND Autonomic dysfunction tends to improve over time after acute myocardial infarction (MI), but the clinical significance of autonomic remodeling is not well known. OBJECTIVE The purpose of this study was to test the hypothesis that the amount of recovery of autonomic function early after MI is associated with a risk for serious arrhythmias. METHODS The prognostic significance of autonomic remodeling after MI was assessed in one post-MI cohort [Cardiac Arrhythmia and Risk Stratification after Myocardial Infarction (CARISMA)] and validated in a second cohort [Risk Estimation After Infarction, Noninvasive Evaluation (REFINE)]. Changes in heart rate variability (Delta HRV) and heart rate turbulence (Delta HRT) were measured from 24-hour ECG recordings performed early (5-21 days) and later (6 weeks) after MI in CARISMA (n = 312). Delta HRV and Delta HRT were similarly measured from early (2-4 weeks) and later (10-14 weeks) post-MI recordings in REFINE (n = 322). RESULTS HRV and HRT increased over time in both cohorts. Attenuated recovery of autonomic function, defined as Delta HRT slope <2.0 ms/RR, was associated with a 9.4-fold (95% confidence interval 1.2-71.6; P = .03) higher risk of ECG-documented sustained ventricular tachycardia or ventricular fibrillation in CARISMA and a 7.0-fold (95% confidence interval 1.6-29.6; P = .009) higher risk of fatal or near-fatal events in REFINE. Changes in HRV and HRT were not predictive of nonarrhythmic death in either cohort. CONCLUSION Attenuated recovery of autonomic function early after MI consistently predicts a higher risk of fatal or near-fatal arrhythmic events. A lack of improvement in HRT early after MI appears to be a specific marker for serious arrhythmic events.