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

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.

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).

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.

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.