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.