NEW ORLEANS – Long-term data from the Radial Artery Patency Study show that radial arteries, compared with saphenous veins, are associated with reduced rates of functional and complete graft occlusion in patients undergoing coronary artery bypass surgery.
In addition, radial arteries are associated with lower rates of graft disease, lead author Dr. Stephen E. Fremes said during a late-breaking trial session at the annual meeting of the American College of Cardiology.
The issue of which conduit provides the best long-term graft outcomes has been a subject of lengthy debate. Several trials have indicated that radial-artery grafts are no better than saphenous-vein grafts, including a recently published Veterans Affairs (VA) study showing similar 1-year graft patency among 757 patients undergoing first-time, elective coronary artery bypass grafting (JAMA 2011;305:167-74).
One-year data previously published from the Radial Artery Patency Study (RAPS) showed that complete graft occlusion was significantly reduced in radial-artery grafts compared with saphenous-vein grafts (8.2% vs. 13.6%), but that partial graft occlusion was similar (12.3% vs. 14.3%) between the two conduits (N. Engl. J. Med. 2004;351:2302-09).
When Dr. Fremes was asked how to reconcile the results of RAPS with those from the recent VA study, he replied that the VA study was conducted almost exclusively in men (99%), vein grafts performed better than predicted, and there were very high rates of evidence-based medicine. Adherence to evidence-based medicine was good in RAPS, but the trial accrued much earlier, from November 1996 to January 2001. The mean age of the 269 patients in the current analysis was 60 years, and 15% were women.
RAPS enrolled 561 patients with isolated triple-vessel disease and a left ventricular fraction of more than 35% from 12 Canadian centers and one in New Zealand. Randomization was unique in that it was performed within patients and not between patients, explained Dr. Fremes, head of the cardiovascular surgery division at Sunnybrook Health Sciences Centre and research director at the Schulich Heart Centre at Sunnybrook, Toronto. Patients were randomized to receive either a radial artery to the right coronary territory and a saphenous vein to the circumflex territory or a saphenous vein to the right coronary territory and a radial artery to the circumflex territory.
Late angiography was performed on 440 patients at 1 year and on 269 patients at a mean of 7.6 years after surgery. Grafts were considered occluded if they had a TIMI (Thrombolysis in Myocardial Infarction) score of 0-2, and were considered patent with a TIMI score of 3.
At 5 years, the primary end point of functional graft occlusion was significantly decreased in radial-artery grafts at 12%, compared with saphenous-vein grafts at 18.8% (odds ratio, 0.64), Dr. Fremes said. Significantly fewer radial-artery grafts also became completely occluded at 9%, compared with saphenous-vein grafts at 18% (OR 0.50).
Among 164 patients who had completely patent grafts at follow-up, graft stenosis was similar for both conduits for proximal and distal anastomotic lesions. There were fewer graft-body lesions at 6.7% in radial arteries, vs. saphenous veins at 15.2% (OR 0.42). Consequently, radial-artery grafts were significantly less likely to be either stenotic or completely occluded at 22%, compared with saphenous-vein grafts at 34% (OR 0.58), he said.
Target vessel stenosis, an important risk factor for graft occlusion at 1 year, was evaluated in a subgroup analysis. Target vessels with stenosis were classified a priori as those with 70%-89% narrowing and those with at least 90% narrowing. Although graft occlusion was reduced almost 50% for either graft in target vessels with at least 90% narrowing, radial-artery grafts had much lower functional (8.8%) and complete (6.3%) occlusion rates, as did saphenous-vein grafts (14.6% and 14.5%, respectively), in the more severely narrowed vessels.
The incidence of cardiac death beyond 1 year was 5%, of nonfatal myocardial infarction was 1.5%, and of major adverse cardiac events was 15%. Dr. Fremes pointed out that the clinical event findings were descriptive rather than explanatory since each patient received both graft types.
Overall survival in the entire cohort was 96% at 5 years, 91% at 7.5 years, and 78% at 10 years. Event-free survival was 95%, 90%, and 78%, respectively.
During the panel discussion of the study, Dr. James McClurken, professor and vice-chair of surgery at Temple University in Philadelphia, said, "This [study] lends credence to utilizing the radial artery, with obvious caveats that it is important to place it in highly obstructed vessels so there is not competitive flow and to maintain patency for the longest period of time.
"This is not quite as good as internal-mammary artery patency data, but certainly better than vein-graft data."