Abstract
OBJECTIVE: To clarify the effects of being underweight on clinical outcomes after coronary artery bypass grafting (CABG) and possible associated sex differences. METHODS: The study population included 5914 patients who underwent their first isolated CABG; patients with acute myocardial infarction were excluded. Clinical outcomes within and beyond 30 days after CABG were compared across groups on the basis of preoperative body mass index (BMI): underweight (BMI <18.5; n = 318), normal (18.5 ≤ BMI < 25; n = 3835), overweight (25 ≤ BMI < 30; n = 1580), and obese (BMI ≥30; n = 181). RESULTS: The cumulative 30-day incidence of all-cause death was 3.2%, 1.2%, 0.4%, and 1.1% in the underweight, normal, overweight, and obese groups, respectively (log-rank P < .001). This trend was more prominent in men than in women (4.0%, 1.3%, 0.4%, and 1.6%, log-rank P < .001; 1.7%, 0.9%, 1.1%, and 0.0%, log-rank P = .74). The cumulative 5-year incidence of all-cause death >30 days after CABG was significantly greater in the underweight group (27.1%, 16.6%, 10.1%, and 6.5%; log-rank P < .001). The greater risk of being underweight and the lower risk of being overweight or obese relative to normal were significant for all-cause death (adjusted hazard ratio, 1.22 [95% confidence interval, 1.00-1.49]; 0.77 [0.68-0.89]; and 0.63 [0.42-0.95], respectively). Furthermore, the excess mortality risk of being underweight relative to normal was significant in men (1.32 [1.03-1.68]) but not in women (1.14 [0.80-1.63]) (interaction P = .01). CONCLUSIONS: Being underweight was associated with increased short- and long-term mortality after CABG, especially in men, whereas being overweight or obese was associated with decreased long-term mortality after CABG.