Clinicians at the University of Calgary, Alberta, Canada sought to evaluate transit-time flow (TTF) as a tool to detect technical errors in arterial bypass grafts intraoperatively and predict outcomes. They measured flow in 336 consecutive patients who had an average of 3.02 grafts each. Ninety-nine percent of these bypass grafts were arterial. Three parameters: pulsatility index (PI), flow (cc/min) and diastolic filling (DF) were measured in 990 of the total 1,000 grafts.
In 2010, the European Society of Cardiology (ESC) and European Association for Cardio-Thoracic Surgery (EACTS) Task Force on Myocardial Revascularization released guidelines on myocardial revascularization that state the following with respect to intraoperative graft flow patency assessment following bypass graft construction:
In his 2005 paper “Intraoperative Bypass Flow Measurement Reduces the Incidence of Postoperative Ventricular Fibrillation and Myocardial Markers after Coronary Revascularization,” Dr. Stefan Bauer from the Department of Cardiovascular and Thoracic Surgery, Heart Institute, Lahr/Baden, Germany, presents definitive data that demonstrate that intraoperative flow measurements for graft assessment during coronary artery bypass grafting (CABG) reduces ventricular fibrillation and postoperative complications.
Two case studies from Brody School of Medicine at East Carolina State University in Greenville, N.C., highlight the importance of checking for competitive flow by occluding the native coronary artery during intraoperative assessment of graft patency. The clinicians recognized that preoperative coronary angiography doesn’t adequately inform about competitive flow.
Measurement of blood flow during coronary artery bypass grafting (CABG) is not new.
Since the 1970s, electromagnetic blood flow meters have been available to surgeons. However, their use was problematic. Within the surgical suite, other OR apparatus or ambient electrical noise interfered with operation of the flow meters. To measure flow, electromagnetic flow probes had to have a tight (constrictive) contact around the vessel which could heat up vessels and also cause vasospasm. Also, they were not able to measure flow in internal mammary arteries that were becoming the first choices for a bypass grafts. Because of these problems with electromagnetic flowmeters, blood flow measurement during surgery fell into disfavor.
Saphenous veins are used for coronary artery bypass grafting (CABG) surgery. However, progressive neointimal hyperplasia contributes to considerable vein graft failure. Dr. J.H. Alexander, from Duke Clinical Research Institute, sought to assess the efficacy and safety of pretreating vein grafts with edifoligide for patients undergoing CABG in order to determine if it may prevent neointimal hyperplasia and vein graft failure.
A phase 3 randomized, double-blind, placebo-controlled trial at 107 U.S. sites with 3,014 patients undergoing primary CABG surgery with at least two planned saphenous vein grafts was conducted.
Dr. Matija Jelenc, a leading Slovenian surgeon, recognized that low mean bypass graft flow and a high pulsatility index measured by the transit-time flow measurement (TTFM) method are not specific for anastomotic stenosis, but also occur in the presence of competitive flow and poor coronary run-off.
He hypothesized that graft compliance is responsible for these changes and that flow measured at the proximal end of the coronary bypass can be viewed as a sum of the graft capacitive flow and the flow that passes through the distal anastomosis.
In a 2015 study that included 345 CABG patients who had had 982 intraoperative graft flow measurements, Copenhagen University surgeons sought to determine if transit-time flow measurement can be used to predict graft patency at one year post-op.
In a 2001 study, surgeons at Keio University School of Medicine, Tokyo, Japan assessed the validity of left internal mammary artery transit-time graft flows to the gold standard, angiography. Left internal mammary artery to left anterior descending coronary artery (LIMA-LAD) grafts were assessed intraoperatively with transit-time flowmetry and angiography in 30 CABG patients. The patients were separated into two groups from their intraoperative angiographic findings. One group of 18 patients exhibited patent grafts; the other group of 12 patients had grafts that appeared problematic.
A retrospective analysis of a multicenter randomized clinical trial conducted at 18 Veterans Affairs hospitals using the Randomized On/Off Bypass (ROOBY) trial data set examined one-year graft patency and intraoperative revision rates in 1,607 patients undergoing CABG based on intraoperative transit time flow assessment in 2,738 grafts.
Included in the analysis was frequency of flow probe use; intraoperative flow values and pulsatility index (PI) values; intraoperative revision rates with pre-revision and post-revision flow and PI values; one-year graft patency rates for the 1,710 (62.5 percent) grafts that underwent cardiac catheterization assessment and the sensitivity, specificity and positive and negative predictive values of using the transit-time flows to predict graft patency.