Methods
Settings and Patient population
Institutional electronic medical records from a tertiary care center in the United States were queried for patients who had mitral valve surgery for mitral regurgitation (MR) caused degenerative mitral valve disease between January 2011 and December 2016. Patients with MR due to pathology other than degenerative (endocarditis, hypertrophic obstructive cardiomyopathy, ischemic, and functional MR) were excluded from the analysis. Patient demographics, baseline characteristics, and other risk factors were recorded. Operative reports were reviewed by a research resident (S.Y.) trained by the senior author (A.G.). Mortality data were retrieved from the hospital electronic record system on the date of censoring (02/22/2020). Of note: hospital mortality data is updated monthly from the Connecticut state vital statistics which captures subjects who died within the state. The Institutional Review Board at Yale University approved this study. IRB protocol ID: 2000020356, approval date: 2/13/2019. Need for written patient consent was waived by the IRB.
Definitions
Experienced surgeon was defined as a surgeon who performed an average of ≥25 mitral valve surgeries/year (all mitral valve pathologies) throughout the study period, surgeons with <25 were defined as less experienced8. Valve pathology was defined according to leaflet involvement (posterior leaflet, anterior leaflet or bi-leaflet prolapse). Residual MR was defined as mild MR or less on intraoperative transthoracic echocardiogram (ECHO) at end of operation. Repair complexity was defined by a technical score summing the number of techniques used in the repair: Simple repairs used only a single technique, moderate repairs used 2-4, and complex repairs used 5 or more9. Recurrent MR was defined as moderate or higher MR on any follow-up ECHO.
Outcomes
The primary outcome of the study was successful valve repair versus replacement. Secondary outcomes included recurrent MR, reoperation for recurrence, and mortality.
Statistical analysis
Differences in patient characteristics according to surgeon experience were compared with two-tailed t-tests for continuous variables and Fisher’s exact tests for categorical variables. Multivariable logistic regression analysis was performed to identify independent risk factors for MR recurrence by 2-year follow-up. Survival analysis for mortality was performed with Kaplan-Meier curve and Cox proportional hazard model. To identify variables to be included in the model, we first compared patients who died to patients who were still alive on the day of censoring and variables with P values ≤0.02 were included in the model. These variables are patient’s age at the time of surgery, surgeon experience, valve replacement vs repair, hypertension, dyslipidemia, diabetes mellitus (DM), atrial fibrillation, congestive heart failure (CHF), chronic lung disease, and urgent/emergent operation. P value of <0.05 and 95% confidence interval (CI) were used to define statistically significant differences. Analyses were conducted using Microsoft Excel 2019 and Prism 8.2 (GraphPad Software, San Diego, CA), and SAS 9.4 (SAS Institute Inc, Cary, NC).