Graft Patency Doesn’t Explain Poorer Long-Term Survival in CABG Patients with Diabetes

Diabetes doesn’t compromise the long-term patency of grafts used in coronary artery bypass graft surgery (CABG), yet long-term survival is worse in CABG patients with diabetes than in those without diabetes. Those are the seemingly incongruous findings of a very large observational study from a Cleveland Clinic database examining CABG outcomes according to patients’ diabetes status over more than two decades of follow-up.

The study, published in the Journal of the American College of Cardiology (JACC) in August (2017;70:515-524), yielded another important finding: While internal thoracic artery (ITA) graft patency remained high and stable over time across the cohort, saphenous vein graft patency declined progressively for diabetic and nondiabetic patients alike.

“Little was known about how diabetes affects long-term patency of bypass grafts,” says study co-author Faisal Bakaeen, MD, a Cleveland Clinic cardiothoracic surgeon. “Contrary to our hypothesis, diabetes did not influence long-term graft patency. Notably, our findings also lead to the conclusion that ITA grafts should be used whenever possible — regardless of patients’ diabetes status — because of their excellent patency even 20 years after CABG surgery.”

In an accompanying editorial in JACC, two experts from the U.K. wrote that these findings on diabetes’ differing effects on graft patency and survival raise the possibility of a “diabetic paradox” in CABG.

The editorialists — David P. Taggart, MD, PhD, and Umberto Benedetto, PhD — congratulated the study’s authors for the size and scope of their investigation: “In view of the number of patients, angiograms, and duration of follow-up, the current study gives the most definitive resolution to date to the conflicting evidence of the effects of diabetes on graft patency,” they wrote. The study “is particularly important,” they added, since the incidence of diabetes is rising sharply, with 25 to 60 percent of CABG recipients now having diabetes, depending on geography.

Study in brief: Nearly 16,000 angiograms compared

Indeed, that wide prevalence of diabetes in the CABG population prompted the investigation, Dr. Bakaeen explains.

He and colleagues mined the extensive Cleveland Clinic cardiovascular disease registry to identify all patients who underwent primary isolated CABG at the institution from 1972 through 2010 (N = 57,961). Of these, 1,372 patients with pharmacologically treated diabetes and 10,147 control patients without diabetes met inclusion criteria for adequate preoperative and postoperative angiographic data. These patients collectively had 15,887 postoperative angiograms that were assessed for comparative graft patency at one, five, 10 and 20 years of follow-up.

ITA graft patency was found to be stable over time and comparable in patients with and without diabetes at all follow-up time points, with patency rates above 90 percent at 20 years. By contrast, saphenous vein graft patency declined over time to similar degrees in patients with and without diabetes, down to patency rates just above 40 percent at 20 years.

Despite these similar patency rates in the diabetic and nondiabetic cohorts, long-term patient survival was significantly higher among those without diabetes (P < .0001). Divergence between the groups began by five years and increased steadily thereafter. By 20-year follow-up, survival was 58 percent in the nondiabetic group versus 35 percent in the diabetic group.

So what explains the survival difference?

Further studies are needed to better determine the factors that reduce long-term survival of bypass patients who have diabetes, Dr. Bakaeen notes, but he says we now know lower graft patency is not one of those factors. “It appears that worse survival in this group is likely to be related to a higher comorbidity burden, more-progressive atherosclerosis and the complications of diabetes,” he observes.

He adds that future studies should also aim to evaluate the impact of diabetes on long-term patency of additional bypass conduit types, such as radial, gastroepiploic and inferior epigastric artery grafts.

For their part, the authors of the accompanying JACC editorial noted that the study’s “seminal” message may be the differing patency of venous and arterial grafts over two decades of follow-up across the entire cohort. “[These findings] underpin the practice of those surgeons who have consistently argued for the use of more arterial grafts because of their much superior patency over the long term,” they wrote.