METHODS
This was a retrospective, observational study utilizing a prospectively maintained institutional database. All isolated bioprosthetic surgical aortic valve replacements (SAVRs), performed at our center using either a bovine or porcine valve, from 2010 to 2020 were included. Patients who underwent mechanical aortic valve replacement (AVR) were excluded. Patients with a history of prior AVR were also excluded, as were patients who underwent concomitant operations such as coronary artery bypass grafting (CABG) or mitral valve repair/replacement. Definitions and terminology were consistent with the Society of Thoracic Surgeons (STS) database. This study was approved by the Institutional Review Board of the University of Pittsburgh on 4/17/2019 (STUDY18120143), with written consent being waived.
The primary aim of the study was to compare long-term survival between patients who underwent SAVR using a bovine versus porcine bioprosthetic valve. Secondary outcomes of interest included postoperative clinical outcomes, echocardiographic data, all-cause readmission rates, and aortic valve reintervention rates. Follow-up data was obtained from the clinical warehouse that contains all long-term survival data for patients undergoing cardiac surgery at the University of Pittsburgh Medical Center. Vital status data from the clinical warehouse was cross-referenced with the Social Security Death Index.
Primary stratification was between the bovine valve group and the porcine valve group. Continuous variables were presented as mean ± standard deviation for normally distributed data, or median and interquartile range (IQR) for non-normally distributed data. Categorical data were reported by frequency and percentage. Normally distributed continuous variables were analyzed using the student’s t-test, while non-normally distributed continuous variables were analyzed with the nonparametric Mann-Whitney U test. The Chi-squared or Fisher’s exact test was used to compare categorical variables between groups, as appropriate. A 1:1 propensity-score matched analysis was performed using greedy nearest-neighbor matching, incorporating baseline characteristics. The quality of the match was determined by standardized mean differences (SMD), with <0.1 considered indicative of an adequate balance.7 Postoperative outcomes in the matched cohorts were compared. Survival estimates were generated using Kaplan-Meier methods and compared between the two matched cohorts using log-rank statistics. Stratified Cox proportional hazards regression was used for the multivariable analysis of mortality in propensity-matched pairs. Cumulative incidence functions were calculated for all-cause readmissions and for aortic valve reinterventions. Death was treated as a competing risk for both readmissions and reinterventions. All statistical analyses were performed using either STATA, version 16.1 (Stata Corporation, College Station, TX) or R programming language version 4.1.0 (R Foundation for Statistical Computing, Vienna, Austria). All tests were 2-sided with an alpha level of 0.05 designated to indicate statistical significance.