Impact of Diabetes on Graft Patency and Progression of Proximal Coronary Stenosis After Coronary Bypass Surgery

BACKGROUND: Patients with diabetes experience diminished survival after coronary artery bypass grafting (CABG), despite comparable long-term graft patency to patients without diabetes. Reduced survival may be related to accelerated progression of native coronary disease proximal to the graft in patients with diabetes, reducing native flow reserve in the case of progressive graft failure. This phenomenon has not been previously investigated. METHOD: Patients referred for CABG at the Royal Melbourne Hospital were included if both their preoperative and postoperative coronary angiography reports were available. Study outcomes were patency of internal mammary artery (IMA), radial artery (RA) and saphenous vein grafts (SVG); and progression of proximal stenosis in grafted coronary arteries that were non-chronic total occlusions (non-CTO), stratified by diabetic and non-diabetic status. On postoperative angiography, a patent graft demonstrated contrast opacification, and a progressive native lesion demonstrated an absolute increase in preoperative stenosis severity of ≥20 percentage points or development of a new occlusion. Analyses were performed with an exchangeable Generalised Estimating Equations (GEE) multivariable binary logistic regression model. RESULTS: Postoperative angiography occurred mostly for symptoms between August 1997 and March 2020. Overall, 250 patients with diabetes and 497 patients without diabetes received 858 grafts (312 IMA, 461 RA, 85 SVG) and 1,433 grafts (561 IMA, 719 RA, 153 SVG), respectively. Mean follow-up was at 8.7±5.6 years after surgery. Overall graft patency was not different between patients with and without diabetes, 90.6% vs 88.5% (odds ratio [OR]=1.35, 95% confidence interval [CI]=0.89-2.04; p=0.161). Among patients with diabetes, arterial graft (IMA+RA) patency remained stable over time (OR=0.98, 95% CI=0.93-1.03; p=0.339) and was superior to SVG, 92.0% vs 77.6% (OR=2.94, 95% CI=1.41-6.11; p=0.004), for which the odds of patency declined by 17% with each postoperative year (OR=0.83, 95% CI=0.73-0.94; p=0.002). Of the grafted non-CTO coronary arteries, progression of proximal stenosis occurred more frequently in patients with diabetes compared to patients without diabetes, 62.1% vs 53.7% (OR=1.34, 95% CI=1.03-1.74; p=0.03). CONCLUSIONS: Diabetes did not impact overall graft patency, but was associated with accelerated progression of proximal stenosis in grafted coronary arteries. The SVG demonstrated progressive decline in patency, which may heighten the risk of myocardial ischaemia in patients with diabetes due to reduced flow reserve from the native circulation. In contrast, arterial grafts demonstrated durable patency over time and may promote sustained myocardial protection in patients with diabetes.