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Department of Cardiothoracic Surgery, John Radcliffe Hospital, Headley Way, Oxford OX3 9DU, United Kingdom
(Email: bala1log{at}doctors.org.uk).
Coronary artery bypass grafting (CABG) ideally mandates the use of objective technology to confirm graft patency. With the increasing use of off-pump CABG and arterial grafting, both of which are considered technically demanding, interest in intraoperative graft patency assessment has progressively evolved in recent years. Several qualitative and quantitative methods have been used to detect intraoperative graft failure. The most common quantitative technique in current clinical use is transit time flowmetry (TTFM).
D’Ancona and colleagues [1] have described the clinical application of TTFM in a large series and proposed the use of flow waveform morphology and derived values such as the mean flow and pulsatility index to determine graft patency. After this, several groups have examined the reliability of TTFM to detect graft failure [2–4]. In our experience, we found that when comparing intraoperative fluorescence imaging with TTFM, reliance on TTFM alone would have prompted unnecessary graft revision in 3.8% of grafts (10% of patients) [3].
Tokuda and colleagues [5] present a retrospective analysis of TTFM flow values from a selected group of patients during a 4-year period. The strength of this study is the availability of postoperative angiography at 3 months for comparison.
The receiver operating characteristic curve analysis was performed for the graft flow values to determine the optimal cut off criteria for identifying graft failure. A dominant systolic flow pattern was found to be a risk factor only for grafts to the left coronary artery (LCA) territories. This may be explained by the fact that the flow profile of grafts to the right coronary territory tends to have a predominantly balanced systolic–diastolic flow pattern attributed to a lower right ventricular transmural pressure gradient. Importantly, the analysis shows a wide range of positive predictive value from 0.31 to 0.80 for the proposed cut off values for identifying graft failure. This clearly corroborates with our existing knowledge that intraoperative assessment based on TTFM alone may be unreliable, especially in low flow situations. In particular, this study demonstrates that a critical limitation of these cut off values is the uncertainty in confirming patency of grafts to the LCA territories. This is a crucial issue because patency of internal mammary artery grafts to the left side is prognostically significant.
These facts support the value of additional qualitative information, such as that available from intraoperative fluorescence imaging with quantitative information from TTFM to enhance the accuracy of confirming graft patency.
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