Observed versus expected morbidity and mortality in patients undergoing mitral valve repair

Objectives: Mitral valve repair (MVP) is the gold standard treatment for degenerative mitral regurgitation. With the expansion of transcatheter technologies, this study compares the outcome of MVP in low-risk and non-low-risk patients to serve as a benchmark. Methods: This retrospective, single-institution study examined all patients who underwent MVP for primary mitral regurgitation from 2005 to 2018. Patients were stratified into 2 risk categories: low-risk [Society of Thoracic Surgeons (STS) Predicted Risk of Mortality (STS-PROM) ≤2%] and non-low risk (STS-PROM > 2% or age > 75), with a subgroup of very low risk (STS-PROM ≤1%, age <75). Results: A total of 1207 patients were included, and 1053 patients were classified as low risk and 154 as non-low risk. The non-low-risk group was significantly older, more likely to be female, and had a higher comorbidity burden than the low-risk group (all P < 0.01). For the low-risk group, the observed-to-expected (O:E) STS mortality ratio was 0.4 and the composite morbidity and mortality ratio was 0.6, whereas for the non-low risk, the O:E mortality was 1.5 and the composite morbidity and mortality was 0.9. When the subgroup of very low-risk group was assessed, the mortality O:E ratio was 0. Conclusions: The observed composite morbidity and mortality of patients undergoing MVP were persistently lower in low-risk patients, mainly driven by the very low-risk group. The excellent outcome of MVP in low-risk patients should be validated on a national level to determine how transcatheter technologies can be utilized in these patients.