Bilateral mammary artery grafting increases postoperative mediastinitis without survival benefit in obese patients

The prevalence of obesity has risen in the last decade, increasing the percentage of obese patients who undergo cardiac surgery. Deep sternal wound infection (DSWI) is a rare but devastating postoperative complication, more often encountered in the obese population. DSWI is also associated with the use of bilateral internal mammary artery (BIMA), particularly in this high-risk population. The aim of this study is to determine the short-term and long-term outcomes following BIMA revascularization in obese patients.

This is a single-centre retrospective cohort study using prospectively collected data including all obese patients who underwent coronary artery bypass grafting (CABG) surgery between April 1991 and April 2014. Preoperative demographic characteristics, operative and postoperative variables were taken from the computerized database of the hospital. A propensity score matching was conducted for the short- and long-term outcomes in the entire study population.

Results showed that 5608 patients with a body mass index of ≥30 kg/m² underwent CABG during the studied period. After propensity scoring, 494 patients receiving BIMA were matched to 5089 patients receiving single internal mammary artery (SIMA). All preoperative characteristics were comparable except for a higher prevalence of left ventricular dysfunction and left main disease as well as higher mean EuroSCORE in the SIMA group. In the postoperative period, short-term mortality was comparable in the two groups (P = 0.68). In-hospital DSWI was also comparable (P = 0.10). However, when considering DSWI occurring after hospitalization (median time; 19 days), the latter was significantly lower in the SIMA than in the BIMA group (1.1 vs 3.2%; P < 0.0001). For long-term survival, no difference was observed between the BIMA and SIMA groups after appropriate matching (P = 0.22).

In obese patients, CABG surgery using BIMA instead of SIMA increased the risk of postoperative DSWI, without improving survival. According to our results, short-term postoperative risks of infection associated with BIMA are not offset by longer-term benefits in that patient population. Special care should be exerted when selecting conduits for myocardial revascularization in obese patients.