Noninvasive Assessment of Sudden Death Risk After Myocardial Infarction - Results of the REFINE Study.
Presentation Start/End Time:	Friday, May 11, 2007, 11:30 AM -11:44 AM
Location:	403
Author Block:	Derek V. Exner, MD, MPH, Katherine M. Kavanagh, MD, Darlene Ramadan, RN, BSN, Sandeep G. Aggarwal, MD, Catherine Noulett, RN, Michael P. Slawnych, MD, PhD, Allie Van Schaik, RN, L. Brent. Mitchell, MD, Sajad Gulamhusein, MD, Henry J. Duff, MD, on behalf of the Risk Estimation Following Infarction, Noninvasive Evaluation (REFINE) Investigators. Libin Cardiovascular Institute of Alberta, Calgary, AB, Canada, University of Alberta, Edmonton, AB, Canada
Introduction: Myocardial infarction (MI) survivors are at risk for serious arrhythmias, particularly those with residual LV dysfunction. While the ICD reduces mortality late after an MI, no survival benefit with has been demonstrated with ICD therapy early post-MI. The accurate identification of patients at risk for serious arrhythmias early after an MI remains elusive. We sought to assess whether impaired autonomic function plus abnormal electrical substrate would accurately identify patients at risk serious arrhythmias early after an MI. Methods: From May 2001 to July 2004 322 patients with a recent MI and LV dysfunction (median EF 0.40) underwent testing in the initial 4 weeks and again at 10-14 weeks post-MI. This included exercise-induced spectral repolarization alternans (TWA), followed by 30 min high-resolution ECG recording from which signal averaged QRS width and modified moving average TWA were assessed. Patients then underwent baroreflex testing followed by a 24-hour ECG recording from which heart rate variability and heart rate turbulence were measured. Compared to past studies, more sensitive cut-points were utilized in order to enhance diagnostic accuracy. The primary outcome was cardiac death or resuscitated cardiac arrest. Results: There were 22 cardiac deaths and 7 cardiac arrests over 47 months of follow-up. None of the noninvasive tests reliably identified patients at risk in the initial 4 weeks post-MI. All tests, apart from QRS width, predicted outcome when assessed at 10-14 weeks post-MI. The most predictive combinations were moderately impaired baroreflex sensitivity or heart rate turbulence plus abnormal TWA. All combinations predicted a 4-fold or higher risk among patients with abnormalities in autonomic function and electrical substrate versus the remaining patients (over 20% risk of cardiac death or cardiac arrest at 4-years with versus less than 5% without abnormalities in both). Conclusions: Abnormalities in both autonomic function and electrical substrate occur in 25-30% of post-MI patients with residual LV dysfunction. This combination identifies patients at high risk for serious arrhythmias and cardiac death.