Abstract 2031: Risk Assessment Following a Myocardial Infraction: Additive Value of Heart Rate Turbulence, Repolarization Alternans, and Deceleration Capacity.
Background: No benefit from prophylactic implantable cardioverter defibrillator (ICD) therapy has been demonstrated in patients soon after a myocardial infarction (MI). Reliable identification of patients at risk of serious arrhythmias early post-MI is required to guide appropriate prophylactic ICD therapy.
Methods & Results. A cohort of 322 patients with left ventricular ejection fraction (EF) values < 0.50 in the initial week post-MI were followed a median of 47 months. Serial assessment of autonomic tone (including heart rate turbulence [HRT] and deceleration capacity [DC]), electrical substrate (including repolarization alternans [TWA]), and EF was performed, and interpreted blinded. The primary outcome was cardiac death or resuscitated cardiac arrest. Mortality was a secondary outcome. Testing in the initial month post-MI did not reliably identify patients at risk. Testing beyond 8 weeks after the index MI did. Beyond 8 weeks post-MI the combination of HRT + TWA using Holter methods plus an EF < 0.50 (17% of the population) identified patients with a 6.1-fold (95% CI 2.8, 12.9) higher risk of the primary outcome after adjustment for important covariates. The sensitivity of this approach was 54% and the positive accuracy was 27%. When assessed at the same time point, the combination of HRT + TWA + DC plus an EF < 0.50 (9% of population) predicted a 9.0-fold higher adjusted risk of the primary outcome (95% CI 3.8, 21.4), with a sensitivity of 39% and positive accuracy of 38%. Similar results were observed for all-cause mortality. In comparison, the elevated independent risk identified by an EF < 0.35 at least 8 weeks post-MI was only 3.0-fold (95% CI 1.5, 6.4), with a sensitivity of 40% and predictive accuracy of 19%.
Conclusions: The presence of impaired HRT, abnormal TWA, with or without abnormal DC reliably identifies patients early post-MI with mild or greater LV dysfunction at greatly increased risk of serious events. The use of HRT + TWA enhances sensitivity, while the use of HRT + TWA + DC optimizes predictive accuracy. Holter-based assessment was superior to EF alone. Ongoing studies are required to assess whether these Holter measures can be used to select patients likely to benefit from prophylactic ICD therapy in the early post-MI period.