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Ann Thorac Surg 2001;72:1562-1565
© 2001 The Society of Thoracic Surgeons
a Division of Cardiovascular Surgery, Keio University School of Medicine, Tokyo, Japan
Accepted for publication June 12, 2001.
* Address reprint requests to Dr Shin, Division of Cardiovascular Surgery, Keio University School of Medicine, 35 Shinanomachi, Shinjuku–ku, Tokyo 160-8582, Japan
e-mail: h-shin{at}sc.itc.keio.ac.jp
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Abstract |
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Methods. The left internal thoracic artery (LITA) anastomosed to the left anterior descending artery (LAD) was assessed intraoperatively with both transit-time flowmetry and graft angiography in 30 patients. The patients were stratified into two groups based on intraoperative angiographic findings. In 18 patients (group A), the LITA and the LAD were well filled with contrast medium and the anastomosis was widely patent. In the other 12 patients (group B), spastic LITA or LAD was observed. Postoperative angiography was also performed before discharge from the hospital.
Results. The mean graft flow was 44.0 ± 25.4 mL/min in group A and 23.4 ± 10.0 mL/min in group B (p = 0.0129). Diastolic-dominant flow pattern was observed in both groups, and the ratio of peak diastolic flow to peak systolic flow and the percent diastolic time-flow integral were not statistically different between the groups. The pulsatility index was almost the same between the two groups and was acceptable in both. Postoperative angiography revealed that all grafts were patent without spasm or anastomotic stenosis.
Conclusions. LITA graft status is satisfactory when high graft flow with diastolic dominance is obtained. When there is vasospasm but no anastomotic problems, decreased graft flow with an acceptable pulsatility index and diastolic augmentation is observed.
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Introduction |
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The purpose of this prospective study was to assess the validity of TTFM performed on left internal thoracic artery (LITA) grafts (the most important coronary artery bypass graft) by comparing transit-time graft flow characteristics with simultaneously obtained angiographic results.
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Material and methods |
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TopAbstractIntroductionMaterial and methodsResultsCommentReferences |
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Assessment of each graft was performed just before the sternal closure under stable hemodynamic conditions. Flowmetry of the LITA was performed using a transit-time flowmeter (CardioMed CM2005; MediStem AS, Oslo, Norway) and a 2-mm or 3-mm probe, depending on the LITA size. The mean flow (mF) and the flow curve were obtained directly from the flowmeter. The mean flow index (mFI) was calculated from the mF and body surface area to take account of body size. The following three variables were determined by analyzing the flow curve using an image processing and analysis software (Socion Image Beta 4.02 for Windows; Socion Corporation, Fredrick, MD; Fig 1): the pulsatility index [PI = (maximum flow - minimum flow)/mean flow]; the ratio of peak diastolic flow to peak systolic flow (pFd/pFs); and the percent diastolic time-flow integral ([%DTFI] indicates the ratio of diastolic antegrade graft flow volume to the total antegrade graft flow volume).
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For all patients, the results of intraoperative angiography were compared with those of postoperative coronary angiography performed 14 ± 3 days after surgery, before discharge from the hospital (Fig 2). The patients were stratified into two groups based on intraoperative angiographic findings. In 18 patients (group A), the LITA and the LAD were well filled with contrast medium, their vessel walls were smooth, and the anastomosis was widely patent. In 12 patients (group B), spastic LITA or LAD was observed but no anastomotic stenosis was seen. In this study, when long segmental luminal narrowing of 50% or more that was not recognized in preoperative and postoperative angiograms was observed in intraoperative angiograms, the vessel was defined as spastic.
Statistical analysis
All data are expressed as the mean ± standard deviation. Differences between groups were determined using the unpaired Student’s t test. Values of p less than 0.05 were regarded as statistically significant.
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Results |
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Flowmetry was performed for a few minutes in all patients. The hemodynamic conditions at the time of flowmetry were stable; no abnormal electrocardiographic changes were seen on the monitor in any patients. The mean arterial pressure in groups A and B at the time of flowmetry was 69 ± 7 mm Hg and 74 ± 12 mm Hg, respectively, and heart rate was 88 ± 17 beats per minute and 80 ± 11 beats per minute, respectively. The mean arterial pressure and heart rate were not significantly different between the two groups.
The mF in groups A and B was 44.0 ± 25.4 mL/min and 23.4 ± 10.0 mL/min, respectively; the difference between the groups was significant (p = 0.0129). The difference in mFI values between the groups was also significant (group A, 26.8 ± 13.9 mL · min-1 · m-2; group B, 13.5 ± 4.7 mL · min-1 · m-2; p = 0.0036). The two groups’ PI values were almost the same and were both acceptable. In both groups, the blood supply from the LITA to the LAD was dominant during the diastolic phase, as indicated by pFd/pFs and %DTFI. There was no difference in the degree of dominance between the groups. Values of mF, mFI, PI, pFd/pFs, and %DTFI for the two groups are shown in Table 1.
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Comment |
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In the present study, we examined whether TTFM accurately reflects the status of LITAs anastomosed to LADs, by comparing TTFM results with those of intraoperative and postoperative angiography. If this type of flowmetry accurately represents graft status, including status of the anastomosis, it will enable surgeons to identify and correct problems intraoperatively, making the goal of 100% early graft patency achievable.
Most studies examining the reliability of TTFM are based on comparison of its results with those of postoperative angiography or intraoperative clinical signs such as electrocardiographic changes. We believe that comparison with simultaneous angiography is the correct basis for determining reliability of TTFM, because graft status may change before postoperative angiography and intraoperative clinical signs do not always correlate with flowmetric results [3]. Indeed, in our study, long segmental narrowing of the LITA or the LAD was frequently observed on the intraoperative coronary angiograms. In contrast, on the postoperative coronary angiograms of all patients, the LITAs and the LADs were well filled with contrast medium and their vessel walls were smooth.
It is generally believed that high flow with diastolic augmentation indicates good graft status, and that low flow or a systolic-dominant pattern suggests graft problems. This view is generally correct but not necessarily true in every case. The values of mF, mFI, pFd/pFs, and %DTFI were large in group A, with satisfactory angiographic results. This finding supports the general hypothesis that high flow with diastolic augmentation equates with good graft status. However, when there was vasospasm despite absence of anastomotic stenosis, the flow values mF and mFI were not conclusively indicative of good anastomotic status. On the other hand, when the anastomosis was not stenotic, diastolic-dominant flow was observed even when there was vasospasm, as indicated by pFd/pFs and %DTFI.
It has been reported that PI is a good indicator of the quality of the anastomosis. The absolute PI value at which severe anastomotic stenosis was indicated has varied among investigators. D’Ancona and associates [4] reported that the PI value indicating an anastomotic problem was 5 or greater. In our study the PI values of the two groups were almost the same and both were acceptable. Thus, PI may not be influenced by vasospasm.
The flow curve is a product of many factors, including the status of the anastomosis, the degree of vasospasm, the quality of the graft and native coronary artery, and the degree of proximal stenosis of the revascularized coronary artery. Although it is clear that intraoperative flowmetry provides important information that helps determine whether or not the surgical procedure has been done correctly, it is not clear in the present study whether TTFM can definitively identify anastomotic problems. Clinically, we interpret our intraoperative flowmetry results as follows. When high-volume biphasic flow with diastolic augmentation is recorded, the graft status is fair. When relatively low flow (between 10 and 20 mL/min) with a low PI value and diastolic augmentation is recorded, the flow pattern itself is not critical because decreased flow is likely secondary to vasospasm, which occurs frequently just after grafting [7], or to small size of the graft or native coronary. If low flow is due to vasospasm, repeated measurements with topical administration of vasodilators will show a subsequent increase in flow. When flow is poor (less than 10 mL/min), diastolic augmentation is weak, or the PI value is unacceptably high, angiographic evaluation is required to clarify the cause of the poor flow pattern and to decide whether the anastomosis must be revised, although we did not experience this type of poor flow pattern in the present series. D’Ancona and associates [4] reported that, in 3 (8.1%) of 37 grafts revised owing to unsatisfactory graft flow characteristics, they observed no abnormal findings at revision and flow characteristics remained unchanged after revision. We believe that intraoperative angiography is a useful method for clarifying the cause of flow deterioration (for example, anastomotic failure, kinking of the graft, dissection of the LITA, thrombosis of the anastomosis, or severe vessel spasm) and avoiding unnecessary graft revision.
There are some limitations to this present study. The number of patients was too small to produce an absolutely definitive conclusion. Flow characteristics in cases of severe anastomotic stenosis or occlusion were not assessed. The degree of vasospasm and quality of LITAs and LADs were not quantified. For all these reasons, future investigations are needed.
In conclusion, findings of transit-time flowmetry, used as a method of noninvasive intraoperative assessment, were compared with those of intraoperative graft angiography in LITA graft anastomosed to the LAD. Vasospasm is frequently observed in both the LITA and the LAD. Good flow with diastolic augmentation suggests good graft status. When there is vasospasm but no anastomotic problems, graft flow may decrease but maintenance of an acceptable pulsatility index and diastolic augmentation is likely.
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