Abstract
BACKGROUND: Left ventricular (LV) reverse myocardial remodeling occurs following septal myectomy in hypertrophic obstructive cardiomyopathy (HOCM), but it remains unclear whether diffuse fibrosis is reversible during this period. Extracellular volume fraction (ECV) and indexed extracellular volume (iECV) are important surrogate markers of diffuse myocardial fibrosis. This study aimed to investigate whether diffuse myocardial fibrosis in HOCM can regress after myectomy. METHODS: A prospective cohort study was conducted among patients with HOCM. All subjects underwent clinical assessment (clinical history, 6-min walk test, biochemical analysis), echocardiography, and cardiovascular magnetic resonance preoperatively and 6months after septal myectomy. RESULTS: A total of 43 patients (52±14years, 23 female) were included in the analysis. At 6months post-myectomy, there were significant within-person decreases in LV mass index (101.0 [82.5-121.0] to 85.8 [66.7-100.0]g/m(2); p<0.001), indexed cell volume (68.6 [53.2-82.6]mL/m(2) to 54.0 [4(2).6-62.0]mL/m(2); p<0.001) and iECV (26.5 [22.4-30.1]mL/m(2) to 21.2 [18.7-26.4]mL/m(2); p<0.001). Conversely, ECV (28.2±3.3% to 30.2±2.8%; p<0.001) and late gadolinium enhancement mass (4.5 [0.2-8.2]g to 8.7 [2.1-12.8]g; p<0.001) increased. These changes were accompanied by improvement of New York Heart Association functional class, 6-min walk test results, N-terminal pro-B-type natriuretic peptide, and high-sensitivity cardiac troponin T. CONCLUSION: Six months after septal myectomy, both cellular hypertrophy and diffuse fibrosis are reversible in HOCM, while focal fibrosis does not regress. These changes are accompanied by improvement of exercise parameters and laboratory biomarkers, revealing the plastic nature of diffuse fibrosis in HOCM and its potential as a therapeutic target.