FFR and Competitive Flow in CABG Surgery
Sebastian P. Vaughan-Burleigh, BA (Hons)1, David P. Taggart, MD, PhD2.
1University of Oxford, Oxford, United Kingdom, 2Department of Cardiovascular Surgery, University of Oxford, Oxford, United Kingdom.
OBJECTIVE: Competitive flow is considered responsible for much of early arterial graft failure. Predicting competitive flow is difficult by angiography, yet angiography is usually the investigation of choice for guiding surgical strategy in CABG. This work addresses the possibility of a role for FFR measurements in CABG decision-making, specifically focusing on avoiding competitive flow.
METHODS:A PubMed and clinicaltrials.gov search was performed using the terms ["coronary artery bypass graft" AND "fractional flow reserve"]. After exclusion criteria 13 studies were selected for review. RESULTS: 1) FFR values correlate with early graft patency rates, but increased graft occlusion does not impact clinical outcomes. Current evidence shows no excess of mortality or angina in patients who have occluded grafts on functional native vessels. Occluded grafts may maintain no-flow anatomical patency and act as collaterals recruited when increased flow demand is caused by native vessel disease progression. 2) FFR appears useful in guiding surgical strategy and a cut-off value of <0.75 for target vessel grafting is associated with no excess of mortality. Very limited evidence suggests that redefining disease functionally instead of anatomically may produce improved outcomes for patients downgraded to PCI. 3) FFR cannot account for all factors reducing graft patency. Diffuse disease produces unreliable FFR measurements, and for the same FFR value graft occlusion is significantly higher on diffusely compared to focally stenotic vessels.
CONCLUSIONS:FFR values correlate with early graft patency rates and grafts to non-significantly occluded vessels have significantly reduced patency rates. There is conflicting evidence regarding the utility of FFR measurements in clinical practice; FFR measurements appear useful for guiding surgical strategy but do not alter clinical outcomes. The studies included are severely limited by lack of randomization, short follow-up times, and low rates of angiographic follow-up to assess graft patency. Despite prospective evidence, no randomised data for FFR and angiography guided versus angiography guided CABG exists, and the disparity amongst current evidence advocates a trial to investigate this.
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