How Does Transit-Time Flowmetry Compare to Angiography?
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.
The mean flow in Group 1 was 44.0 ± 25.4 ml/min; the mean flow in Group 2 was 23.4.0 ± 10.0 ml/min. Diastolic-dominant flow patterns were observed in both groups; the ratio of peak diastolic flow to peak systolic flow was the same for both groups. Pulsatility index (PI) was the same and acceptable in both groups.
The LIMA-LAD grafts were patent when high graft flow was accompanied by diastolic dominance. When there was vasospasm without any anastomotic problems, a lower graft flow with an acceptable PI and diastolic filling could be observed. When flow was less than 10 mL/min with a high pulsatility index, angiographic evaluation was required to clarify the cause of the poor flow pattern to avoid unnecessary graft revision.
This paper highlights the usefulness of both quantitative and functional modalities: intraoperative transit-time flow measurement for graft function and intraoperative angiography to help determine the cause of poor graft flow; anastomotic failure, graft kinking, thrombosis of the anastomosis, severe vessel spasm, dissection of the LIMA.