Background: The guidelines recommend mitral valve repair whenever possible in patients undergoing surgical treatment for active infective endocarditis of the native mitral valve. However, the impact of causative microorganisms in relation to treatment strategies, especially Staphylococcus aureus, has not been studied. In this study, we aimed to compare the outcomes of mitral valve repair versus replacement in patients with native mitral valve infective endocarditis caused by methicillin-susceptible Staphylococcus aureus.

Methods: Consecutive patients with definitive active infective endocarditis of the native mitral valve caused by methicillin-susceptible Staphylococcus aureus undergoing cardiac surgery between 2012 and 2022 were selected. Patients were classified according to the treatment received in two groups: repair and replacement. Inverse propensity treatment weighting was employed to correct for confounders. The endpoints were all-cause mortality, incidence of recurrent endocarditis, reoperation rate, and event-free survival at two-year follow-up.

Results: Among 170 operated-upon patients with active infective endocarditis of the native mitral valve, 44 cases were caused by methicillin-susceptible Staphylococcus aureus. A total of 23 patients underwent mitral valve repair and 21 patients received mitral valve replacement. Weighted 30-day mortality in the repair group was 43%, versus 27% in the replacement group (p = 0.15). Two-year mortality increased to 57% in the repair group and 32% in the replacement group (p = 0.02). Three patients developed recurrent endocarditis in the repair group, while no recurrent endocarditis occurred in the replacement group. Three patients in the repair group required reoperation due to recurrence and one patient in the replacement group underwent re-operation due to paravalvular leakage. Weighted two-year event-free survival was 29% in the repair group and 59% in the replacement group (p < 0.01).

Conclusions: Mortality in patients with mitral valve infective endocarditis caused by Staphylococcus aureus is extremely high, especially in patients undergoing mitral valve repair. The risk of recurrent endocarditis and mid-term mortality seems to be higher in mitral valve repair, resulting in poor event-free survival during two-year follow-up. However, the sample size was likely insufficient for drawing definitive conclusions.