Impact of Myocardial Fibrosis on the Left Ventricular Reremodeling after Subannular Repair for Type-IIIb Functional Mitral Regurgitation

 

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Objectives: The treatment of type-IIIb functional mitral regurgitation (FMR) is still controversial and those patients who benefit most from the FMR correction are not sufficiently determined. Although standardized subannular repair in the FMR treatment seems to significantly improve long-term stability of MV repair, postoperative left ventricular (LV) reremodeling occurs not in every patient. We aimed to correlate MRI-detected myocardial fibrosis at baseline with LV reremodeling after FMR repair.

Methods: We identified 43 consecutive type-IIIb FMR patients, who underwent FMR repair including papillary muscle repositioning and had preoperative cardiac MRI examination. Cardiac MRI examination included myocardial fibrosis quantification by T1 mapping (ms) and extracellular volume (ECV, %) calculation. All patients were followed by transthoracic echocardiography at our institution at 6 months, 1 year, and 2 years postoperatively. Primary endpoint was the relationship between myocardial fibrosis, at baseline and postoperative LV reremodeling (defined as LVEF improvement >  10%). Secondary endpoint was the association between myocardial fibrosis and clinical outcomes (survival and adverse cardiac events during follow-up).

Results: All 43 patients (mean age 65.1 ± 11.3 years, 57.4% male, mean LVEF 36.7% ± 9.0%) underwent surgical FMR repair including standardized subannular repair. Preoperative myocardial fibrosis revealed T1 mapping values of 1067.3 ± 80.0 ms and ECV values of 29.7 ± 3.5%. At 6 months postoperatively, follow-up echocardiography showed no recurrent MR32 and LVEF improvement in the whole study cohort (39.2 ± 9.5% vs. 36.7 ± 9.0%, p = 0.019). A total of 11 (26%) patients showed LVEF improvement >  10% at 6-month follow-up (LVEF recovery group), while the remaining 32 (74%) patients had no such improvement (LVEF nonrecovery group). Baseline ECV values were significantly higher in the LVEF nonrecovery group (31.7 ± 2.4% vs. 27.8 ± 1.0%, p = 0.035), while there was no difference in baseline T1 values between the groups (1,062.8 ± 42.8 vs. 1,050.6 ± 37.9 ms, p = 0.279). Furthermore, we found a strong linear correlation between ECV values at baseline at LVEF change after the FMR surgery (R2 = 0.624, p = 0.02).

Conclusion: MRI-based myocardial fibrosis quantification by ECV may help to identify those FMR patients who have the highest potential for LV reremodeling and therefore benefit most from the standardized FMR correction, including subannular repair.