The effect of obesity on mid-term survival following coronary artery bypass surgery

Several studies have shown no significantly increased risk of in-hospital mortality for obese patients after coronary artery bypass grafting (CABG). However, the effect of obesity on mid-term survival has not been adequately studied. We set out to examine whether mid-term survival following CABG is affected by obesity.

We performed a retrospective study of 4713 consecutive patients undergoing isolated CABG between April 1997 and September 2001. Body mass index (BMI) was used as the measure of obesity, with 3429 patients categorised as non-obese (BMI<30 kg/m(2)), and 1284 patients as obese (BMI> or = 30 kg/m(2)). Patient records were linked to the National Strategic Tracing Service, which records all deaths in the community, to establish current vital status. Deaths occurring over time were described using Kaplan-Meier techniques. To control for differences in patient characteristics, we used Cox proportional hazards analysis to calculate adjusted hazard ratios (HR) and 95% confidence intervals (CI).

Three hundred and thirty (7.0%) deaths occurred during the study period, with a mean follow-up of 2.4+/-1.4 years. The crude HR of mid-term mortality for obese patients was 1.09 (95% CI 0.86-1.39; P=0.457). After adjustment for core pre-operative factors, the adjusted HR of mid-term mortality for obese patients was 1.28 (95% CI 1.01-1.64; P=0.048). The adjusted freedom from death in the obese patients at 30 days, 1, 2, 3, and 4 years was 97.9, 95.9, 94.2, 92.4 and 90.5%, respectively, compared with 98.4, 96.8, 95.5, 94.0 and 92.5% for the non-obese patients.

Although in-hospital mortality after CABG does not seem to be adversely affected by obesity there appears to be a significant increase in mortality in obese patients during a 4-year follow-up period.