CHICAGO – With more than 15 years of follow-up from two related trials, the best conduit for the second most important target vessel in coronary artery bypass grafting (CABG) appears to be resolved.
The radial artery (RA) graft is linked with a lower risk of major adverse cardiac events (MACE) relative to a saphenous vein (SV) or the free right internal thoracic artery (FRITA).
On the basis of these findings, “a radial artery graft should be considered in all isolated CABG operations unless there are contraindications,” reported David L. Hare, MBBS, director of research in the department of cardiology, University of Melbourne.
For the primary graft, there is general agreement that the left internal thoracic artery (LITA) is the first choice for the left anterior descending vessel, but the optimal graft for the second most important target has never been established, according to Dr. Hare.
Almost 25 years ago, two randomized controlled trials called RAPCO-RITA and RAPCO-SV were initiated to address the question. There is now 15 years of follow-up for both of the RAPCO (Radial Artery Patency and Clinical Outcomes) trials, which were presented together at the American Heart Association scientific sessions.
Two trials conducted simultaneously
The RAPCO-RITA trial randomized CABG patients less than 70 years of age (less than 60 years in those with diabetes) to grafting of the second target vessel with an RA or FRITA graft. The RAPCO-SV trial randomized those 70 years or older (60 years or older with diabetes) to an RA or SV graft.
The two primary endpoints were graft patency at 10 years and a composite MACE at 10 years. The assessment of the MACE endpoint, which consisted of cardiovascular mortality, acute myocardial infarction, and coronary revascularization, was later amended to include a comparison at 15 years.
Ten-year patency results, favoring the RA in both studies, were previously published in. In the new data presented at the meeting, the RA was associated with a significant reduction in MACE relative to the comparator graft in both studies.
“The main driver was a reduction in all-cause mortality,” Dr. Hare reported.
In RAPCO-RITA, 394 patients were randomized with follow-up data available for all but 1 patient at 15 years. Similarly, only 1 patient was lost to follow-up among the 225 randomized in RAPCO-SV. In both studies, baseline characteristics were well balanced.
MACE curves separate at 5 years
In RAPCO-RITA, the MACE survival curves began to separate at about 5 years and then gradually widened. By 15 years, the lower rate of MACE in the RA group (38% vs. 48%) translated into a 26% relative reduction (hazard ratio, 0.74; P = .04).
In RAPCO-SV, the pattern was similar, by 15 years, the rates of MACE were 60% and 73% for the RA and SV groups, respectively, translating into a 29% relative reduction (HR, 0.71; P = .04).
There was no heterogeneity in benefit across prespecified subgroups such as presence or absence of diabetes, gender, or age. In RAPCO-RITA, there was 8% absolute and 31% relative reduction in all-cause mortality. In RAPCO-SV, the absolute and relative reductions were 11% and 26%.
When the trial was initiated, Dr. Hare hypothesized that RITA would prove more durable than RA, so the outcome was not anticipated.
“This is the first randomized controlled trial program to address the question,” said Dr. Hare, who noted that there have been numerous retrospective and case control analyses that have produced mixed results in the past.