Diffuse and regional patterns of myocardial fibrosis in hypertrophic cardiomyopathy occur independently of each other and have distinct clinical associations

Abstract

Purpose: Previously, in hypertrophic cardiomyopathy (HCM), only dense regional fibrosis could be identified by cardiac magnetic resonance (CMR) imaging with late gadolinium enhancement (LGE) sequences. Recently, post-contrast T1 mapping has also enabled quantification of diffuse myocardial fibrosis. We sought to explore relationships between both patterns of myocardial fibrosis and several clinical parameters in a typical cohort of patients with HCM. Methods: We performed contrast-enhanced CMR on 123 patients (67% male, mean age 51±14 years) with documented HCM. Regional myocardial fibrosis was evaluated by LGE sequences, and diffuse fibrosis by post-contrast T1 mapping. Correlations between both patterns of fibrosis and patients' clinical characteristics, CMR-derived LV volumetric data and echocardiographic findings were investigated. Results: LGE consistent with HCM was observed in 88% of patients with a mean quantity of 4.6±6.3% of total LV mass, and mean post-contrast myocardial T1 time was 495±81 ms. LGE extent correlated with LV ejection fraction (r = -0.48, p < 0.01) whereas T1 time did not. Conversely, T1 time correlated with E/e' (r = -0.46, p < 0.01) whereas LGE extent did not. Patients with LV outflow tract obstruction had less LGE (3.1±5.6% vs. 6.9±7.5%, p < 0.05), but similar T1 times. Patients with exertional dyspnoea had shorter T1 times (485±84 ms vs. 521±71 ms, p < 0.05), but similar LGE extent. No relationship was observed between LGE and post-contrast T1 time. Conclusions: In HCM, regional and diffuse patterns of myocardial fibrosis occur independently of each other and exhibit distinct clinical associations. Regional fibrosis is associated with reduced LV systolic function and the absence of LV outflow tract obstruction, whereas diffuse fibrosis is associated with higher LV filling pressures and the presence of exertional dyspnoea.