Predicting Midterm Coronary Artery Bypass Graft Failure by Intraoperative Transit Time Flow Measurement

Background: Transit time flow measurement has been accepted as a valuable tool to predict early coronary artery bypass graft failure immediately after surgery. However, if the graft is patent in the early postoperative period, the ability of transit time flow measurement to predict midterm graft failure is unknown. Methods: Midterm postoperative angiography was performed between 1 and 4 years after surgery for 104 grafts, which were evaluated by intraoperative transit time flow measurement and confirmed to be fully patent in early postoperative angiography. Results: Of the 104 grafts, 21 grafts were found to have a new, midterm occlusion or worsening of stenosis. Univariate analysis revealed that a lower mean flow (odds ratio 0.96 per flow unit, mL/min, p < 0.001) and a higher percentage of backward flow (odds ratio 1.08 per percentage point, p < 0.05) measured by transit time flow measurement was a risk factor for predicting midterm graft failure. An increasing interval between the surgery and the midterm angiography was also a predictive risk factor (odds ratio 1.06 per month, p < 0.05). In the multivariate stepwise logistic regression analysis, a lower mean flow was found to be the independent risk factor for midterm graft failure (p < 0.01). A venous graft and an increasing interval between surgery and midterm angiography were also found to be possible risk factors. Conclusions: Transit time flow measurement provides a good prognostic index, not only for the immediate term but also for the midterm follow-up. A graft with intraoperative lower mean flow, and especially with a higher percentage of backward flow, should be carefully monitored, even if it was initially anatomically patent.