The application of intraoperative transit time flow measurement to accurately assess anastomotic quality in sequential vein grafting

Abstract

Objectives: Intraoperative transit time flow measurement (TTFM) is widely used to assess anastomotic quality in coronary artery bypass grafting (CABG). However, in sequential vein grafting, the flow characteristics collected by the conventional TTFM method are usually associated with total graft flow and might not accurately indicate the quality of every distal anastomosis in a sequential graft. The purpose of our study was to examine a new TTFM method that could assess the quality of each distal anastomosis in a sequential graft more reliably than the conventional TTFM approach.

Methods: Two TTFM methods were tested in 84 patients who underwent sequential saphenous off-pump CABG in Beijing An Zhen Hospital between April and August 2012. In the conventional TTFM method, normal blood flow in the sequential graft was maintained during the measurement, and the flow probe was placed a few centimetres above the anastomosis to be evaluated. In the new method, blood flow in the sequential graft was temporarily reduced during the measurement by placing an atraumatic bulldog clamp at the graft a few centimetres distal to the anastomosis to be evaluated, while the position of the flow probe remained the same as in the conventional method. This new TTFM method was named the flow reduction TTFM. Graft flow parameters measured by both methods were compared.

Results: Compared with the conventional TTFM, the flow reduction TTFM resulted in significantly lower mean graft blood flow (P < 0.05); in contrast, yielded significantly higher pulsatility index (P < 0.05). Diastolic filling was not significantly different between the two methods and was >50% in both cases. Interestingly, the flow reduction TTFM identified two defective middle distal anastomoses that the conventional TTFM failed to detect. Graft flows near the defective distal anastomoses were improved substantially after revision.

Conclusions: In this study, we found that temporary reduction of graft flow during TTFM seemed to enhance the sensitivity of TTFM to less-than-critical anastomotic defects in a sequential graft and to improve the overall accuracy of the intraoperative assessment of anastomotic quality in sequential vein grafting.

Keywords: Anastomotic quality; Sequential saphenous coronary artery bypass grafting; Transit time flow measurement.

Figure 1:

Schematic diagram for transit time flow measure (TTFM). (A) Conventional TTFM. Flow probe was placed a few centimetres above a target anastomosis in a sequential graft. (B) Flow reduction TTFM. An atraumatic bulldog clamp was placed at the graft a few centimetres distal to a target anastomosis, and flow probe was placed a few centimetres above the target anastomosis in a sequential graft.

Figure 2:

Comparison of flow parameters measured by the two methods. (A) Comparison of mean blood flow between the conventional transit time flow measurement (TTFM) and the flow reduction TTFM. (B) Comparison of pulsatility index (PI) between the conventional TTFM and the flow reduction TTFM. The graft flow and PI were measure at the middle distal anastomoses to Di, OM and PLV by the two methods. Mean blood flow and PI were calculated from the total patients. Pair-wise Student's t-test was performed to compare the values from the two methods. *P < 0.05, the flow reduction TTFM vs the conventional TTFM. ***P < 0.001, the flow reduction method vs the conventional TTFM.