Scar heterogeneity on cardiovascular magnetic resonance as a predictor of appropriate implantable cardioverter defibrillator therapy

Background: Despite the survival benefit of implantable-cardioverter-defibrillators (ICDs), the vast majority of patients receiving an ICD for primary prevention do not receive ICD therapy. We sought to assess the role of heterogeneous scar area (HSA) identified by late gadolinium enhancement cardiovascular magnetic resonance (LGE-CMR) in predicting appropriate ICD therapy for primary prevention of sudden cardiac death (SCD). Methods: From September 2003 to March 2011, all patients who underwent primary prevention ICD implantation and had a pre-implantation LGE-CMR were identified. Scar size was determined using thresholds of 4 and 6 standard deviations (SD) above remote normal myocardium; HSA was defined using 3 different criteria; as the region between 2 SD and 4 SD (HSA(2-4SD)), between 2SD and 6SD (HSA2-6SD), and between 4SD and 6SD (HSA(4-6SD)). The end-point was appropriate ICD therapy. Results: Out of 40 total patients followed for 25 +/- 24 months, 7 had appropriate ICD therapy. Scar size measured by different thresholds was similar in ICD therapy and non-ICD therapy groups (P = NS for all). However, HSA(2-4SD) and HSA(4-6SD) were significantly larger in the ICD therapy group (P = 0.001 and P = 0.03, respectively). In multivariable model HSA(2-4SD) was the only significant independent predictor of ICD therapy (HR = 1.08, 95% CI: 1.00-1.16, P = 0.04). Kaplan-Meier analysis showed that patients with greater HSA(2-4SD) had a lower survival free of appropriate ICD therapy (P = 0.026). Conclusions: In primary prevention ICD implantation, LGE-CMR HSA identifies patients with appropriate ICD therapy. If confirmed in larger series, HSA can be used for risk stratification in primary prevention of SCD.