Materials and Methods
This is a retrospective cohort study of all adult patients (≥ 18 years of age) who underwent isolated minimally invasive aortic valve replacement at a single academic medical center between January 1, 2015 and June 5, 2020 (Robert Wood Johnson University Hospital, New Brunswick, New Jersey). This center has an average annual surgical volume of 15,000 cases performed out of twenty-two operating rooms; approximately 1,600 are cardiac surgical procedures, with 1,400 open cases and 200 transcatheter valves procedures per year. The data source for the study is the cardiac surgery database of the academic center, developed according to The Society of Thoracic Surgeons (STS) Adult Cardiac Database version 2.81 definitions. The database contains patient demographics, baseline clinical and perioperative characteristics, in-hospital outcomes, and 30-day outcomes. This study was approved by the Institutional Review Board at the academic center.
Minimally invasive aortic valve replacement (mini-AVR) patients included those who underwent aortic valve replacement through partial sternotomy or right minithoracotomy. Patients were selected for minimally invasive valve surgery versus conventional full sternotomy based upon shared decision-making between the surgeon and the patient. The study population was stratified into three cohorts by patient BMI according to the Centers for Disease Control and Prevention adult obesity classifications: Class I (BMI 30.0 to < 35.0 kg/m2), Class II (BMI 35.0 to < 40.0 kg/m2), and Class III (BMI ≥ 40.0 kg/m2). Patients with a non-obese BMI (< 30 kg/m2) and those who underwent additional concomitant procedures (e.g. , double valve replacement) were excluded from the study.
Baseline patient demographic, clinical, and perioperative characteristics were recorded and compared between cohorts. Primary outcomes of postoperative length of stay, mortality within 30 days after surgery, and total direct costs were evaluated. To contextualize 30-day mortality, in-hospital mortality and 30-day readmission were analyzed as secondary outcomes. Postoperative complications of atrial fibrillation, acute renal failure, bleeding requiring transfusion, delayed extubation, circulatory support with intra-aortic balloon pump, and stroke were assessed as tertiary outcomes.
Continuous and categorical variables are presented as median and interquartile range (IQR: 25th to 75th percentiles) and frequencies and percentages, respectively, and compared using the Kruskal–Wallis one-way analysis of variance test or Fishers exact test with the Freeman-Halton extension.8 Statistical significance was accepted at ap value of less than 0.05.