Abstract 1919: Arrhythmic Risk in MADIT II Patients: Role of Infarct size and Heterogeneity
Background: Patients with prior myocardial infarction (MI) meeting MADIT II criteria (LV ejection fraction (EF) < 30% and prior MI) are at increased risk of lethal ventricular arrhythmias (VT). Heterogeneous tissue substrate for inducible VT on electrophysiologic study (EPS) has been proposed (Wu et al) as a zone of “gray” myocardium (GZ) outside the infarct core on delayed enhancement cardiac MRI (DE CMR). However, only limited series have been studied and the relationship of GZ to outcomes is unknown.
Methods: We recruited 59 patients meeting MADIT II criteria. Forty-three underwent EPS at intake and CMR (Siemens Sonata) with DE and volumetric functional imaging was performed. Using research software (Siemens Corporate Research), MI was defined by signal 2SD above mean remote signal intensity. Maximal MI signal intensity was determined and GZ size assessed with thresholds of 50% and 75% of MI signal intensity. GZ mass was compared to inducibility of sustained monomorphic VT at EPS and to a combined clinical endpoint that included EPS inducibility and follow-up arrhythmic events (sudden death, late EPS inducibility, documented VT, valid ICD firings) Mean follow-up was 20.5 ± 8.5 months. Absolute and normalized MI sizes were also assessed.
Results: GZ size was associated with inducibility at EPS using a maximal signal intensity threshold of 75% (p = 0.01), but not 50 % (Table⇓). For both 75% and 50% thresholds there were strong trends towards association of GZ size with an abnormal combined endpoint (50%:18.4 ± 16.16g vs. 11.56 ± 7.03 g, p = 0.0528; 75%: 42.16 ± 23.18g vs. 26.68 ± 12.61g, p = 0.0755). However absolute MI size was more closely associated with an abnormal outcome (56.17+31.1 g vs. 35.83+14.59 g, p = 0.0075).
Conclusions: Gray zone size may be an important determinant of inducibility of VT at EPS. However, absolute infarct size appears to be more closely associated with overall arrhythmic risk.