Original article
Cardiovascular
Relationship of Body Mass Index With Outcomes After Coronary Artery Bypass Graft Surgery

https://doi.org/10.1016/j.athoracsur.2007.03.017Get rights and content

Background

A debate exists whether obesity is a risk factor for operative mortality after coronary artery bypass graft surgery (CABG). The contradictory findings in the literature may largely be attributable to the variety of methodological approaches used to model the association between body mass index (BMI) and post-CABG outcomes. This study aims to investigate this association, and to uncover possible explanations for the lack of consensus across prior studies.

Methods

Data were prospectively collected on 80,792 patients who underwent a CABG procedure during a 14-year period at the 45 Department of Veterans Affairs cardiac surgery programs. Generalized additive models were used to estimate the relationship of BMI and outcomes after a CABG procedure.

Results

We found that the relationship of BMI with post-CABG mortality and morbidity is U-shaped with the minimum risk located around a BMI of 30 kg/m2, indicating that patients classified as overweight have the lowest risk, and those in the lower end of the obese range do not have seriously elevated risk. This U-shape relationship is significantly nonlinear and robust to adjustment for other risk factors.

Conclusions

This study demonstrates that BMI is an independent predictor of mortality and morbidity after CABG surgery. Previous studies that model BMI linearly or as categories cannot accurately capture this U-shaped relationship and are unlikely to find a significant contribution by including BMI. Further research is needed to determine the mechanisms of risk for patients with low and high BMI and whether interventions to modify BMI may improve patient outcomes.

Section snippets

Material and Methods

The Department of Veterans Affairs (VA) Continuous Improvement in Cardiac Surgery Program (CICSP) prospectively collects patient-level risk, procedural, and outcome data on all patients undergoing cardiac surgery at the 45 VA cardiac surgical centers. The goal of the CICSP is to provide performance reports to VA-based clinical care team members for use in self-assessment and self-improvement quality of care initiatives. A description of this complete database and the variables captured has been

Results

The distributions across BMI classes of these risk factors for the patients included in this analysis are displayed in Table 1. Of the 80,792 patients, 887 (1.1%) were classified as underweight (BMI < 18.5), 18,130 (22.4%) were normal weight (18.5 ≤ BMI < 25), 34,063 (42.2%) were overweight (25 ≤ BMI < 30), 19,391 (24.0%) were obese (30 ≤ BMI < 35), and 8,321 (10.3%) were morbidly obese (BMI ≥ 35). Increasing BMI was associated with younger age, lower rates of smoking and chronic obstructive

Comment

The primary goal of this study was to estimate the risks of death and major complications as nonlinear functions of BMI during the period directly after CABG surgery. We found that the relation between BMI and post-CABG outcomes was significantly nonlinear, and when BMI was tested as a linear function or using a category for obesity, it did not result in a significant predictor in the model. Risks were higher in the extremes of BMI, with minimum risk occurring near a BMI of 30 kg/m2. Adjustment

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