Abstract 2145: Recovery of Cardiac Autonomic Dysfunction after Acute Myocardial Infarction as a Predictor of Fatal of Near-Fatal Arrhythmic Events

Abstract

Background. Changes in cardiac autonomic function have been documented after myocardial infraction (MI), but their significance is unknown. We assessed the amount of recovery of autonomic dysfunction after MI and its significance among the patients with depressed left ventricular ejection fraction (LVEF ≤ 0.40 - CARISMA and ≤ 0.50 - REFINE). Methods and Results. Changes in heart rate variability (dHRV) and turbulence (dHRT) were measured from 24-hour ECG recordings performed 5–21 days and again at six weeks post-MI in 312 patients included in the Cardiac Arrhythmias and Risk Stratification after Myocardial Infarction (CARISMA) study. The primary endpoint was sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) recorded by an implantable device. Non-arrhythmic death was a secondary endpoint. HRV and HRT measures increased significantly from baseline to six weeks post-AMI (p<0.001 for dHRV and p=0.017 for dHRT slope). The patients with attenuated recovery of autonomic function had a higher incidence of VT/VF events (n=25), e.g. those with a dHRT slope < 2.0 ms/RRi (optimized cut-off) had a hazard ratio of 10.2 (95% CI from 1.35 to 77.9, p=0.03) of experiencing the VT or VF. The change of very-low (dVLF) and low-frequency (dLF) spectral components also predicted the VT/VF events (p=0.03 for dVLF and p=0.02 for dLF). Only one patient with a dHRT slope ≥2.0 mm/RRi (n=79) experienced VT/VF event (negative accuracy 99%). Validation was performed in the Risk Estimation Following Infarction Non-invasive Evaluation (REFINE) post-MI population (n=322). Of the 24 fatal or non-fatal cardiac arrests that occurred in REFINE, all but two were identified by a lack of improvement in HRT slope as defined in CARISMA (negative accuracy 98%). The risk of fatal or non-fatal cardiac arrest was 7.0-fold (95% CI from 1.6 to 29.6; p = 0.009) higher in patients without improvement in HRT. Lack of improvement in HRT was not predictive of non-arrhythmic death in either post-MI population. Conclusions. Autonomic function undergoes a substantial improvement early after MI, which is associated with vulnerability to VT or VF. A marked recovery of autonomic dysfunction protects from the occurrence of fatal or near-fatal arrhythmic events after MI despite depressed LVEF