The Accuracy of Transit Time Flow Measurement in Predicting Graft Patency after Coronary Artery Bypass Grafting

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Abstract
Objective: Transit time flow measurement (TTFM) is a method used to assess intraoperative blood flow after vascular anastomoses. Angiography represents the criterion standard for the assessment of graft patency after coronary artery bypass grafting (CABG). The purpose of this study was to compare flow measurements from TTFM to diagnostic angiography. Methods: From October 9, 2009, to April 30, 2012, a total of 259 patients underwent robotic-assisted CABG procedures at a single institution. Of these, 160 patients had both TTFM and either intraoperative or postoperative angiography of the left internal mammary artery to the left anterior descending coronary artery graft. Transit time flow measurements were obtained after completion of the anastomosis and after administration of protamine before chest closure. Transit time flow measurement assessment included pulsatility index, diastolic fraction, and flow (milliliters per minute). Angiograms were graded according to the Fitzgibbon criteria. The patients were grouped according to angiographic findings, with perfect grafts defined as FitzGibbon A and problematic grafts defined as either Fitzgibbon B or O. Results: Overall, there were 152 (95%) of 160 angiographically perfect grafts (FitzGibbon A). Of the eight problematic grafts, five were occluded (Fitzgibbon O) and three had significant flow-limiting lesions (FitzGibbon B). Two patients had intraoperative graft revision after completion angiography, one had redo CABG during the same hospitalization, and five were treated with percutaneous coronary intervention. A significant difference was seen in mean ± SD flow (34.3 ± 16.8 mL/min vs 23.9 ± 12.5 mL/min, P = 0.033) between patent and nonpatent grafts but not in pulsatility index (1.98 ± 0.76 vs 1.65 ± 0.48, P = 0.16) or diastolic fraction (73.5% ± 8.45% vs 70.9% ± 6.15%, P = 0.13). Conclusions: Although TTFM can be a useful tool for graft assessment after CABG, false negatives can occur. Angiography remains the criterion standard to assess graft patency and quality of the anastomosis after CABG.

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