From Pages to Practice
Published May 30, 2018
As a second-year general surgery resident, I spent one month rotating on the cardiac surgery service. I had the opportunity to observe a variety of operations, including valve replacements, aortic root replacements, and of course, coronary-artery bypass grafting (CABG). The graft of choice where I trained was the left internal mammary artery (LIMA) and the saphenous vein. I remember physician assistants harvesting saphenous-vein grafts in the legs while the rest of us prepped the chest to prepare the heart for grafting. Radial-artery grafts were almost never used because they require different positioning, often take longer, and might increase risk for hand ischemia. Further, no studies have convincingly showed a benefit to using radial-artery grafts.
In this week’s issue of NEJM, Guadino et al. report the results of a patient-level combined analysis of six randomized controlled trials comparing radial-artery grafts and saphenous-vein grafts for CABG. Although prior randomized controlled trials have shown differences in angiographic patency between the two types of grafts, the individual studies were underpowered to detect differences in clinical outcomes. In the era of data sharing, this research group was able to combine patient-level data from several randomized controlled trials to attain sufficient power to detect differences in clinical events.
All studies compared long-term (≥2 years) outcomes in patients randomized to receive either radial-artery grafting or saphenous-vein grafting to supplement LIMA grafting during isolated CABG surgery. The primary outcome was a composite of major adverse cardiac events, including death, myocardial infarction, and repeat revascularization. The individual components of the composite outcome were also analyzed. The secondary outcome was graft patency at protocol-defined follow-up angiography.
The pooled analysis compared 534 patients who received radial-artery grafts and 502 patients who received saphenous-vein grafts. Baseline characteristics were comparable between the two groups. Interestingly, none of the studies used endoscopic harvesting of either the saphenous vein or the radial artery. The mean follow-up time was 60±30 months.
Overall, the radial-artery graft was associated with a significantly fewer major adverse cardiac events (the primary outcome) compared with the saphenous-vein graft (25 vs. 39 events per 1000 patient-years; hazard ratio=0.67; 95% CI, 0.49-0.90, P=0.01). Analysis of individual components of the composite primary end-point indicated that radial-artery grafts were associated with a slightly lower incidence of myocardial infarction (6 vs. 9 per 1000 patient-years; HR=0.72; 95% CI, 0.53-0.99; P=0.04) and repeat revascularization (9 vs. 17 per 1000 patient-years; HR=0.50; 95% CI, 0.40-0.63; P<0.001). However, rates of all-cause death did not differ (15 vs 17 per 1000 patient-years; HR=0.90; 95% CI, 0.59-1.41; P=0.68). Consistent with prior trials, radial-artery grafts had longer patency; rates of graft occlusion were 19 versus 46 events per 1000 patient-year in the radial-artery graft and the saphenous-vein graft groups, respectively. Subgroup analysis showed a small clinical benefit in patients younger than 75, women, and patients without renal insufficiency.
Although this combined analysis does show improvement in clinical outcomes with radial-artery grafts, benefits were modest at best and rates of all-cause death did not differ. Rates of radial-artery grafting in the U.S, are low compared with rates of LIMA with supplemented saphenous-vein grafting, and it’s unlikely that this study will have an immediate effect on that practice. Deputy editor John Jarcho comments, “This analysis gives strong support to the potential advantages of using a radial-artery graft over a saphenous-vein graft as the second bypass vessel after the internal thoracic artery. Concern persists, however, about the technical aspects of radial-artery harvesting and about possible adverse effects of the procedure. This study does suggest that a single large randomized trial might confirm a benefit of use of the radial artery in CABG procedures.”