Background:Although minimally invasive mitral valve surgery via a right minithoracotomy (MICS-mitral) is widely performed, no tool to evaluate its risk has been reported. We sought to establish MICS-mitral risk calculators using a national clinical database for selection of appropriate patients.

Methods and Results:Between 2008 and 2015, 3,240 patients (mean age 59±14 years, males 1,950) underwent a MICS-mitral procedure in Japan and were registered in a national clinical database. We examined mortality and composite outcome (operative mortality, stroke, reoperation for bleeding) using multivariate analysis, then developed a risk calculator for each using stepwise analysis. Operative mortality was 1.1% and the composite outcome rate was 5%. In multivariate analysis, risk factors for operative mortality were shown to be age, respiratory dysfunction, thoracic aortic disease, myocardial infarction, body mass index >30, NYHA class IV, moderate or severe aortic regurgitation, mitral valve replacement, multiple valve surgery, and annual cases <10. ROC curve analysis of our prediction formulas for mortality and composite outcome revealed an area under the curve for operative mortality of 0.877 (95% confidence interval: 0.82–0.94, P<0.01) and for composite outcome of 0.665 (95% confidence interval: 0.62–0.71, P<0.01).

Conclusions:We developed risk calculator formulas using risk factors associated with both operative mortality and composite outcome. The present risk calculator formula is useful for patient selection and may influence future applications for this procedure.