Increased repolarization alternans following myocardial infarction is related to adverse left ventricular remodeling: Implications for risk assessment & use of defibrillator therapy.
Category:  09 Signal Average ECG/T-Wave Alternans
Presentation Time: Friday, 3:45 p.m. - 4:45 p.m.
Derek V. Exner, MD, MPH, Katherine Kavanagh, MD, Ryan Mitchell, BSc, Sandeep Aggarwal, MD, Mariko Shibata, BSc, Darlene Ramadan, RN, Henry Duff, MD, REFINE Investigators. University of Calgary, Calgary, AB, Canada
Presentation Number: P5-25
Poster Board Number: P5-25
Background. Post-myocardial infarction (MI) patients are at risk for sudden death, particularly those with residual left ventricular (LV) dysfunction. Defibrillator therapy is effective in reducing mortality in patients with severe LV dysfunction late post-MI, but is not a practical routine therapy. Further, a large randomized trial (DINAMIT) found that defibrillator therapy early post-MI did not favorably alter survival. Whether this relates to remodeling or other factors is unclear.
Need for accurate risk stratification. Enhanced prediction of sudden death risk post-MI patients is vital for both appropriate & cost-effective delivery of preventive strategies. Determining the optimal timing for risk assessment, evaluating the stability of test results over time, & understanding the mechanisms responsible for any variation in test results are all essential to optimizing risk assessment. Microvolt repolarization alternans or T wave alternans (TWA) appears to be a promising technique in post-MI patients.
Methods. A total of 290 patients with LV dysfunction (mean ejection fraction [EF] 0.39 ± 0.07) underwent serial TWA assessment at 4, 8 & 16 weeks post-MI using a commercial exercise treadmill testing system (Cambridge Heart Inc). Standard definitions of TWA positivity & negativity were used. EF values were reassessed at 8 weeks post-MI. Standard post-MI therapies were used (ASA 96%, beta-blocker 90%, ACE inhibitor or ARB 92%, & statin 83%).
Results. A 23% (0.09 absolute) increase in EF was evident by 8 weeks, indicating significant remodeling in many participants. A significant proportion of patients (15%) went from TWA negative to positive over the 16 weeks. Patients with alterations in TWA results had significantly smaller increases in mean EF (0.03 ± 0.14) than did patients with stable TWA results (0.09 ± 0.11; p=0.02).
Conclusion. Variability in TWA is evident in a sizable number of patients during the initial 16 weeks post-MI & is related to less LV remodeling. These data support limiting TWA assessment to the chronic post-MI phase.