Results
During the study period, 404 patients underwent isolated mini-AVR. There were 222 patients with a non-obese BMI who were excluded from the study. The final study population included 182 patients: 106 (58.2%) with Class I obesity, 42 (23.1%) with Class II obesity, and 34 (18.7%) with Class III obesity. The total study population had a median (IQR) BMI of 34.0 (31.7-37.4) kg/m2.
Baseline demographic and clinical characteristics amongst patient cohorts are described in Table 1. The prevalence of diabetes mellitus correlates with obesity class, with the proportion of diabetic patients increasing from Class I to Class II and from Class II to Class III (Class I 33.0% [n=35] vs. Class II 33.3% [n=14] vs. Class III 55.9% [n=19]; p=0.049). The Society of Thoracic Surgeons (STS) predictive risk of mortality (PROM) score also increases with increasing obesity class (Class I 1.03% [0.70-1.92%] vs. Class II 1.39% [0.96-2.22%] vs. Class III 1.86% [1.22-2.41%]; p=0.028). The proportion of patients with hypertension does not differ between cohorts (p=0.687). Most patients were of Caucasian race, with all African American and Asian patients falling into the Class I obesity cohort. Patient race was not statistically different between obesity classes (p=0.327).
Table 2 presents perioperative characteristics of the population stratified by patient cohort. There was no difference amongst cohorts in bypass or cross-clamp time (p=0.332 and p=0.784, respectively), ICU length of stay (p=0.180), or intraoperative or postoperative transfusion of blood products. Patients with Class II obesity demonstrated a less frequent requirement for postoperative packed red blood cell transfusions (Class I 12.3% [n=13] vs. Class II 0.0% [n=0] vs. Class III 14.7% [n=5]; p=0.018), but with no different rates of postoperative bleeding (Class I 0.94% [n=1] vs. Class II 0.0% [n=0] vs. Class III 5.88% [n=2]; p=0.131).
The postoperative length of stay (Class I 4.0 [3.0-6.0] days vs. Class II 4.5 [3.0-6.0] days vs. Class III 5.0 [4.0-6.0] days; p=0.098) and total direct costs (Class I $24,487 [$20,199-$27.480] vs. Class II $22,921 [$20,433-$27,740] vs. Class III $23,886 [$20,063-$33,800]; p=0.860) did not differ between obesity class cohorts (Figure 1). Postoperative 30-day mortality (Class I 2.83% [n=2] vs. Class II 0% [n=0] vs. Class III 0% [n=0]; p=0.763) did not differ between patient cohorts and was contextualized by in-hospital mortality and 30-day readmission rates that also failed to show between-cohort differences. Aside from postoperative atrial fibrillation, which was observed much more frequently in patients with Class II and III obesity (p<0.001), postoperative complication rates were comparable between cohorts (Figure 2).