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Rates of death, heart attack and stroke were similar at five years for people who underwent coronary artery bypass graft (CABG) using one or both mammary arteries.
Bypass surgery involves grafting another blood vessel to bypass the narrowed or blocked artery to improve blood flow to the heart muscle. The left mammary (internal thoracic) artery is often used. Previous research had shown outcomes may be improved by using both left and right mammary arteries but bilateral procedures are more complicated.
This trial found no difference in early mortality or vascular outcomes although wound complications and sternum (breastbone) reconstructions were more common among people who had a bilateral bypass.
The trial is on-going, with planned follow-up to ten years. The comparative costs of the two operations, including management of complications, would need to be considered alongside clinical outcomes before considering change in practice.
Why was this study needed?
Coronary heart disease, where the arteries supplying the muscle have become narrowed or blocked, affects around 2.3 million UK adults. Procedures for coronary heart disease include implanting a small tube or inserting a balloon to widen the artery and restore blood flow to the heart. Coronary artery bypass grafting is a common operation where surgeons take a section of another blood vessel to “bypass” the narrowed section of coronary artery. Vein grafts are commonly used, but using an internal thoracic (mammary) artery has been shown to potentially give better long term graft function.
Evidence from observational studies suggested that bypasses using both left and right mammary arteries (bilateral) led to fewer deaths in the 10 years following the operation than just using the left artery. The bilateral procedure has not been widely adopted because it is more complex, with higher risk of complications with the wound to the sternum. Also because the evidence was observational there was a risk of bias or confounding.
Therefore this randomised controlled trial was conducted to provide high quality evidence about long-term outcomes following bilateral internal thoracic grafts.
What did this study do?
The Arterial Revascularisation Trial (ART) trial randomly assigned 3102 people who were due to undergo grafting, to have either single or bilateral internal thoracic artery grafts. Participants were recruited from 28 centres in seven countries, 15 of these centres were UK-based.
People who had previously undergone cardiac bypass surgery, only needed one vessel bypassing or also needed heart valve surgery were excluded from the trial.
Surgeons had to have experience of performing 50 or more bilateral bypass operations, and be proficient in both procedures, to mitigate the risk that results could be skewed by surgeon experience.
Surgery was recommended to take place within six weeks of randomisation, so that participants’ clinical condition did not change considerably between randomisation and surgery.
What did it find?
- There was no significant difference in mortality rate at five years for people who received bilateral (134 people, 8.7%) or single bypass (130, 8.4%) hazard ratio 1.04 (95% confidence interval [CI], 0.81 to 1.32).
- The overall combined outcome of death, heart attack or stroke five years after surgery was also similar for bilateral bypass (189 events, 12.2%) and single bypass groups (198 events, 12.7%) hazard ratio, 0.96 (95% CI, 0.79 to 1.17).
- Sternal wound complications were significantly more common among people undergoing bilateral bypass (54 people, 3.5%) compared with the single bypass group (29, 1.9%) (P = 0.005).
What does current guidance say on this issue?
NICE guidelines on management of unstable angina and heart attack without ST-segment elevation (2013) recommend that patients are offered either surgical bypass or the alternative non-surgical procedure of percutaneous coronary intervention to improve blood flow to the heart. The discussion around choice of procedure should take into account findings from imaging of the heart arteries (angiography), any other medical conditions, and potential benefits and harms to the individual.
NICE do not give specific recommendations around choice of graft if surgery is selected.
What are the implications?
This trial indicates that mortality and cardiovascular outcomes are comparable with single and bilateral internal thoracic artery bypass five years after surgery. However, sternal wound complications are much higher following bilateral bypass.
The ART trial is on-going, and the benefits of arterial grafting may only be evident after several years, so the results at 10 years’ follow-up will be important. The trial does not consider the comparative costs of the initial operations or subsequent costs, in particular management of sternal complications and possible repair.
The full clinical and cost outcomes associated with these procedures are needed before any changes to practice can be considered.
Citation and Funding
Taggart DP, Altman DG, Gray AM, et al; ART Investigators. Randomized Trial of Bilateral versus Single Internal-Thoracic-Artery Grafts. N Engl J Med. 2016;375(26):2540-9
This project was funded by the British Heart Foundation and Medical Research Council.
Bibliography
NHS Choices. Coronary heart disease. London: Department of Health; 2014.
NHS Choices. Coronary artery bypass graft. London: Department of Health; 2015.
NICE. Unstable angina and NSTEMI: early management. CG94. London: National Institute for Health and Care Excellence; 2013.
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