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The Accuracy of Transit Time Flow Measurement in Predicting Graft Patency After Coronary Artery Bypass Grafting
Patrick Walker, William T. Daniel, Henry A. Liberman, Chandan Devireddy, John D. Puskas, Vinod H. Thourani, Michael E. Halkos.
Emory, Atlanta, GA, USA.
OBJECTIVE: Transit time flow measurement (TTFM) is a method used to assess intraoperative blood flow after coronary anastomoses. Angiography remains the gold standard for the assessment of graft quality and flows after coronary artery bypass surgery (CABG). The purpose of this study was to compare flow assessments using TTFM using the Medistim probes and the VeriQ Flowmeter System (Medistim, ASA, Oslo, Norway) with diagnostic angiography.
METHODS: From 8/1/2010 to 4/30/2012, 200 patients underwent robotic-assisted CABG procedures. Of these, 160 patients had both TTFM and either intraoperative or postoperative angiography performed of the left internal mammary artery to left anterior descending coronary artery graft. TTFM measurements were obtained after completion of the anastomosis and after administration of protamine prior to chest closure. TTFM assessment included pulsatility index (PI), diastolic fraction (DF), and flow (ml/min). Angiograms were graded according to Fitzgibbon criteria as Fitzgibbon A, B, or O. Patients were grouped according to angiographic findings with patent grafts defined as FitzGibbon A and non-patent grafts defined as either Fitzgibbon B or O.
RESULTS: The mean age was 62.4±11.6 years and 114 (71.3%) patients were male. Overall, there were 152/160 (95.0%) angiographically patent grafts (FitzGibbon A). Of the 8 non-patent grafts, 4 were occluded (Fitzgibbon O) and 4 had significant flow-limiting lesions (FitzGibbon B). Three patients had graft revision after intraoperative angiography, 1 had redo CABG during same hospitalization, and 4 were treated with percutaneous intervention. TTFM revealed no significant differences between patent grafts and non-patent grafts in PI (1.98±0.76 vs. 1.65±0.48, p=0.23), DF (73.5±8.45 vs. 70.9±6.15, p=0.39) or flows (34.3±16.8cc vs. 23.9±12.5cc, p=0.09).
CONCLUSIONS: Although TTFM can be a useful tool for graft assessment after CABG, false negatives can occur. Angiography remains the gold standard to assess graft patency and quality of the anastomosis after CABG. For innovative revascularization strategies such as robotic-assisted CABG, angiographic assessment may be helpful during the surgeon’s early experience.
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