Relationship between QRS fragmentation on electrocardiogram and myocardial scar characterization on cardiac magnetic resonance imaging in patients with ischemic and non-ischemic cardiomyopathy.

Fragmented QRS (fQRS) on electrocardiogram (ECG) may reflect myocardial fibrosis in both ischemic and non-ischemic cardiomyopathy. Gray zone on cardiac magnetic resonance (CMR), which represents a heterogeneous interface between dense scar and viable myocardium, is a known predictor of appropriate implantable cardioverter-defibrillator (ICD) shocks or death. The relationship between fQRS and myocardial scar on CMR remains poorly studied and may improve risk stratification for ICD therapy. This study aimed to evaluate the relationship between fQRS and scar core/gray zone by CMR late gadolinium enhancement (LGE), and to determine whether fQRS predicts benefit from ICD therapy. We included 388 adults who underwent CMR followed by ICD implantation for primary or secondary prevention between 2005 and 2018 at two tertiary centers. ECGs were assessed for fQRS and CMR images were independently evaluated. The primary endpoint was a composite of all-cause mortality or appropriate ICD shock. Mean age was 61 ± 13 years and mean left ventricular ejection fraction (LVEF) was 32%. LGE was present in 69% and fQRS in 28%. fQRS was associated with greater scar burden on visual LGE assessment (p=0.036), but not with quantitative LGE measures (2SD, 4SD, FWHM) or gray zone. Over a median follow-up of 61 months, 36% experienced the primary outcome. In multivariable analysis adjusting for LVEF and other prognosticators, fQRS was not independently associated with the primary outcome (HR 0.85; 95% CI: 0.67-1.08; p = 0.20). In conclusion, fQRS is associated with scar burden by visual assessment but does not provide incremental predictive value for ICD benefit.