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.