Vein Graft Failure In Coronary Artery Bypass Surgery
Pretreating a vein graft with edifoligide prior to coronary bypass graft surgery does not lower the rate of graft failure, according to a study in the November 16 issue of JAMA. This study is being released early to coincide with its presentation at the American Heart Association's annual meeting.
Coronary artery bypass graft (CABG) surgery is one of the most common surgical procedures performed in the United States, according to background information in the article. In appropriately selected patients, CABG surgery results in improved survival, relief of angina, and improved quality of life. Despite frequent use of artery grafts, vein grafts remain the most frequently used conduit. The long-term patency (duration of remaining open) of vein grafts is limited and graft failure has consequences similar to those of coronary artery disease: recurrent angina, myocardial infarction (MI), additional revascularization procedures, and premature death.
Neointimal hyperplasia (abnormal increase in the cells lining the inner wall of the blood vessel) leading to accelerated atherosclerosis and thrombosis is one proposed mechanism of vein graft failure. Neointimal hyperplasia begins as an adaptive response to the increased pressure and shear forces of arterial circulation. A new approach to inhibiting neointimal hyperplasia and preventing graft failure involves using edifoligide, which was developed to work via gene therapy to inhibit cell proliferation. For this study, scientists took each patient's harvested vein (that would be used for the graft) prior to CABG and treated the vein for 10 minutes with a pressure-mediated delivery system with either edifoligide or saline placebo.
John H. Alexander, M.D., M.S., of Duke University Medical Center, Durham, N.C., and his colleagues conducted the Project of Ex-vivo Vein Graft Engineering via Transfection (PREVENT IV) trial to assess the efficacy of edifoligide in preventing angiographic vein graft failure. The study included 3,014 patients undergoing primary CABG surgery with at least 2 planned vein grafts. The first 2,400 patients enrolled were scheduled for 12- to 18-month follow-up angiography. The patients were enrolled in the study between August 2002 and October 2003 at 107 U.S. sites.
A total of 1,920 patients (80 percent) either died (n=91) or underwent follow-up angiography (n=1,829). The scientists found that edifoligide had no effect on the primary end point of per patient vein graft failure (436 [45.2 percent] of 965 patients in the edifoligide group vs. 442 [46.3 percent] of 955 patients in the placebo group; or on any secondary angiographic end point, or on the incidence of major adverse cardiac events at 1 year (101 [6.7 percent] of 1,508 patients in the edifoligide group vs. 121 [8.1 percent] of 1,506 patients in the placebo group.
"Despite negative results, PREVENT IV provided many noteworthy lessons. First, an unusual approach to drug delivery was investigated in PREVENT IV; edifoligide was administered directly to the harvested vein graft prior to implantation. This type of specific, targeted application of a therapy to a specific tissue or organ may limit systemic toxicity and be a future direction of surgical intervention. Second, PREVENT IV includes and was powered to both a surrogate end point (angiographic vein graft failure) and a long-term clinical confirmatory end point (major adverse cardiac events). For important interventions believed to have long-term effects, this approach may allow beneficial therapies to be adopted earlier based on surrogate effects yet still ensure rigorous ultimate proof of safety and efficacy. Finally, the long-term clinical follow-up in PREVENT IV is being conducted centrally, from a single center, rather than by the 107 sites that enrolled patients and conducted angiographic follow-up and should result in considerable resource saving and perhaps more complete and systematic follow-up," the authors write.
"Failure of at least one vein graft is quite common within 12 to 18 months after CABG surgery. Eventhough safe and well tolerated, inhibition .with edifoligide is no more effective than placebo in preventing these events. Longer-term follow-up and additional research are needed to explain the mechanism and clinical consequences of vein graft failure and to improve the durability of CABG surgery," the scientists conclude.
(JAMA. 2005;294:2446-2454. Available pre-embargo to the media at www.jamamedia.org).