Quantitative Assessment of Diffuse and Replacement Myocardial Fibrosis in Hypertrophic Cardiomyopathy Using T1, T2 Mapping, and Extracellular Volume

Background. Hypertrophic cardiomyopathy (HCM) is a genetically determined myocardial disease characterized by heterogeneous left ventricular hypertrophy and progressive myocardial remodeling. Myocardial fibrosis plays a central role in disease progression and adverse outcomes. Late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) is widely used to detect replacement fibrosis; however, it is insensitive to diffuse interstitial fibrosis. Quantitative T1 mapping and extracellular volume fraction (ECV) assessment may provide earlier and more comprehensive characterization of myocardial fibrosis. Aim. To assess native T1 mapping, ECV, and T2 mapping in pediatric and adult patients with symmetric and asymmetric forms of HCM and to evaluate their relationship with myocardial morphology, left ventricular function, and the extent of LGE. Materials and methods. Eighty-five patients with HCM underwent CMR at 1.5 T, including cine imaging, LGE, native and post-contrast T1 mapping (MOLLI), and T2 mapping. Patients were stratified by age (children and adults), morphological phenotype (symmetric vs asymmetric HCM), and LGE extent (0 %, <15 %, >15 %). Quantitative mapping parameters were compared between groups. Results. Elevated native T1 and ECV values were observed in both adults and children with HCM, including patients without detectable LGE, indicating the presence of diffuse interstitial fibrosis. The highest T1 and ECV values were found in patients with LGE greater than 15%, reflecting the coexistence of diffuse and replacement fibrosis. No significant differences in native T1 or ECV were identified between symmetric and asymmetric HCM phenotypes despite greater wall thickness, higher prevalence of obstruction, and more frequent LGE in the asymmetric form. T2 values showed no evidence of myocardial edema. Global left ventricular systolic function remained preserved in both age groups. Conclusions. Native T1 mapping and ECV provide sensitive quantitative markers of diffuse myocardial fibrosis in HCM, detecting early remodeling even in the absence of LGE. While LGE reflects advanced replacement fibrosis, T1-based techniques allow a more complete assessment of myocardial fibrotic burden and may support earlier and more refined risk stratification in patients with HCM.