Minimally invasive mitral valve surgery in high-risk patients: operating outside the boxplot

(i) To establish who is at high risk for mitral surgery. (ii) To assess the performance of minimally invasive mitral valve surgery in high-risk patients by presenting early and late outcomes and compare these with those of the non-high-risk population.

We reviewed our database of prospective data of 1873 consecutive patients who underwent minimally invasive mitral surgery from 2003 to 2015. To establish an unbiased definition of risk cut-off, we considered as high-risk the 'outliers of risk' identified using boxplot analysis in relation to EuroSCORE II.

Two hundred and five patients were outliers, with 98 as minor (EuroSCORE II ≥ 6%) and 107 as major outliers (EuroSCORE II ≥ 9%). Outliers accounted for several different comorbidities. Nineteen patients died while in hospital (9.2%); different postoperative complications were observed. Outliers had a significantly lower mean survival time and a higher risk of cardiac-related death than the general population; however, the worst outcomes were observed in major outliers. No statistically significant difference was found with regard to the need for mitral reintervention and the degree of mitral regurgitation at follow-up.

Boxplot analysis helped to achieve an internal definition of risk cut-off, starting from EuroSCORE II ≥ 6%. Minimally invasive mitral surgery in these outliers of risk was associated with acceptable early and long-term results; however, major outliers with EuroSCORE II ≥ 9% may benefit from catheter-based procedures.