Invasive and non-invasive quantification of myocardial fibrosis in primary mitral regurgitation: prognostic implications for post-operative remodelling, symptom burden and exercise capacity

Abstract Chronic primary mitral regurgitation (MR) exposes the left ventricle (LV) to volume overload and is associated with evidence of fibrosis on non-invasive imaging. It is not known whether fibrosis predicts outcome from surgery. This study aimed to 1) quantify myocardial fibrosis on histology and non-invasive imaging, 2) investigate any association between fibrosis and LV size and function, 3) determine the impact of fibrosis on post-operative outcome. Methods In a prospective observational multicentre study, 105 patients with severe MR (N=65/32/8 NYHA Class I/II/III respectively; mean age 63.1±13.4 years; male 73%; VO2max 91.2±22.4%) had multiparametric cardiac magnetic resonance (CMR), symptom assessment (Minnesota Living with Heart Failure Questionnaire (MLHFQ)) and cardiopulmonary exercise testing before and at 9 months following repair. Patients consented for up to 3 intraoperative LV biopsies for histological collagen volume fraction (CVF) quantification. Results 234 LV biopsies were feasible from 86 patients with median CVF of 14.6% [IQR 7.4–20.3]. Fibrosis was present even in NYHA Class I patients (13.6% [6.3–18.8]), and was significantly higher than the 3.3% [2.6–6.1] obtained from 8 autopsy controls without cardiac disease (P