Ann Thorac Surg 2003;76:2118-2120
© 2003 The Society of Thoracic Surgeons
How to do it
A technique for evaluating competitive flow for intraoperative decision making in coronary artery surgery
Gil Bolotin, MD, PhD*a,
Alan P. Kypson, MDa,
L. Wiley Nifong, MDa,
W. Randolph Chitwood, Jr, MDa
a Department of Surgery, Brody School of Medicine, East Carolina University, Greenville, North Carolina, USA
Accepted for publication March 25, 2003.
* Address reprint requests to Dr Bolotin, Department of Surgery, Brody School of Medicine, East Carolina University, 600 Moye Blvd, Greenville, NC, USA 27858
e-mail: boloting{at}mail.ecu.edu
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Abstract
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The effect of native coronary competitive flow on the patency of arterial and saphenous vein grafts is controversial. We use a simple intraoperative technique to evaluate competitive flow that allows us to make informed intraoperative decisions regarding anastomotic quality, vessel runoff, and competing native coronary blood flow.
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Introduction
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Coronary artery grafting to minimally and moderately stenotic target vessels may lead to competitive flow between the native vessel and the graft. Critical stenoses of more than 80% generally minimize competitive coronary graft flow as fixed inflow to the distal vessel has expended vasodilatory reserves and thus, any supplemental distal flow will be measured in the graft. Because of regional variations in stenotic lesions and this integrated physiologic phenomenon, controversy exists regarding the implication of competitive flow on the patency of left internal mammary artery bypass grafts [1, 2]. Data regarding radial and composite internal mammary artery grafts suggest that the degree of stenosis in the native coronary artery significantly influences the graft patency rate [3, 4]. Moreover, in reoperations, new arterial grafts may subtend large segments of myocardium and provide inadequate perfusion after minimally stenotic old vein grafts are ligated. Thus, both native and competitive flow, as well as myocardial demands, must be considered when assessing perfusion adequacy. Competitive flow is a multifactorial phenomenon, and therefore, even an estimation of impact remains difficult, especially if based alone on preoperative coronary angiography. The simple intraoperative technique is effective for measuring and evaluating native and competitive graft flow, and it is an important tool for intraoperative decision making.
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Technique
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The Butterfly Flowmeter (Medi-Stim AS, Oslo, Norway) is used to measure graft flow routinely in all off pump coronary artery bypass patients and selectively in pump coronary artery bypass grafting operations. To estimate competitive flow after grafting, measurement of graft flow is performed both with the native coronary open and after the proximal coronary artery is closed for several seconds. Either Silastic or MyOcclude clip occluders (Medtronic, Inc, Minneapolis, MN) are deployed to temporarily and safely obliterate proximal native vessel flow. Again flow is measured when the native proximal vessel is reopened. Accordingly, we can distinguish between inferior flow secondary to either a poor anastomosis or suboptimal coronary run-off versus decreased flow due to native coronary competition. Studies are done under stable physiologic conditions just before the chest is closed. If flow is good when the native vessel is occluded, we consider the anastomoses optimal. However, if flow levels drop when the occluder is removed from the coronary artery, then competitive flow exists and the decrement is secondary to a noncritical native vessel stenosis and not the anastomosis. Careful attention is paid to the flow tracing to be sure that the diastolic component is present, especially in studies with noncritical native stenoses. An appropriate size flow probe must be selected for these measurements, and these tracings help to optimize vessel-probe approximation.
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Case reports
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Patient 1
A 72-year-old man underwent off pump coronary artery bypass left internal mammary artery (LIMA) to the left anterior descending coronary artery (LAD) for 70% proximal LAD stenosis. The LAD was found to be of good quality and it was a 1.5-mm vessel. The anastomosis was performed uneventfully. Upon completion of the anastomosis, a 22 mL per minute flow was measured in the LIMA (Fig 1A).
The proximal Silastic (Medtronic, Inc) suture then was tightened to occlude the proximal native LAD with flow in the LIMA increasing to 48 mL perminute (Fig 1B). After the Silastic (Medtronic, Inc) suture was released again, LIMA flow returned to 23 mL per minute (Fig 1C). Therefore we surmised that the anastomosis was optimal and the relative low flow was due to native vessel competitive flow. No graft was added and the postoperative recovery of the patient was uneventful.
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Fig 1. Left internal mammary artery (LIMA) flow (A) after the completion of the LIMA to the left anterior descending coronary artery (LAD) anastomosis, (B) with the proximal LAD closed, and (C) during the reopening of the proximal LAD native vessel.
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Patient 2
A 64-year-old man underwent off pump coronary artery bypass of the LIMA to the LAD and saphenous vein graft (SVG) to obtuse marginal. The LAD was 1 mm and of poor quality with multiple noncritical lesions. After completion of the anastomosis, minimal flow was detected in the LIMA. However, after the proximal LAD Silastic (Medtronic, Inc) snare was tightened, flow in the LIMA increased to 15 mL/min. Thus we concluded that the poor graft flow was due to a combination of a poor target vessel and competitive flow. In order to increase the LAD blood supply, and as a preventative treatment for possible LIMA closure due to low flow, a short segment of SVG was added to the distal LAD. After occluding the LIMA graft, vein graft flow was then measured to be 20 mL/min and was considered to be sufficient for this small and diseased LAD, despite the presence of competitive flow. The patient’s postoperative recovery was uneventful with no electrocardiographic signs of ischemia.
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Comment
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The technique described in this article is very simple and allows accurate intraoperative measurements of competitive graft flow. This method can distinguish between low flow due to poor anastomotic technique or poor target runoff vessel, as well as competitive flow effects from a minimally stenotic native coronary vessel. Either re-anastomosis or placement of another graft to the same coronary vessel should be considered when flow remains low after these maneuvers. In presence of major competitive flow, the decision should be made according to the graft type and physiology. SVG are less sensitive to competitive flow [5, 6], in situ mammary artery characteristics are controversial [1, 2], whereas radial arteries and composite mammary arteries have been reported to have a higher risk of failure in the presence of competitive flow [3, 4]. Using these surgeon friendly methods, additional characterization of reactive hyperemic flow reserves in the distal coronary bed may help define the competitive physiology more accurately in both primary and reoperative coronary patients. Moreover, by alternatively closing either the proximal native vessel or the distal one, the surgeon can assess the retrograde as well as the antegrade patency of the graft. We recommend the intraoperative studies to define competitive flow in any graft that appears to have inferior flow characteristics at the end of the operation.
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References
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- Kawasuji M., Sakakibara N., Takemura H., Tedoriya T., Ushijima T., Watanabe Y. Is internal thoracic artery grafting suitable for a moderately stenotic coronary artery?. J Thorac Cardiovasc Surg 1996;112:253-259.[Abstract/Free Full Text]
- Pagni S., Storey J., Ballen J., et al. Factors affecting internal mammary artery graft survival: how is competitive flow from a patent native coronary vessel a risk factor?. J Surg Res 1997;71:172-178.[Medline]
- Maniar H.S., Sundt T.M., Barner H.B., et al. Effect of target stenosis and location on radial artery graft patency. J Thorac Cardiovasc Surg 2002;123:45-52.[Abstract/Free Full Text]
- Moran S.V., Baeza R., Guarda E., et al. Predictors of radial artery patency for coronary bypass operations. Ann Thorac Surg 2001;72:1552-1556.[Abstract/Free Full Text]
- Hamada Y., Kawachi K., Yamamoto T., et al. Effect of coronary artery bypass grafting on native coronary artery stenosis. Comparison of internal thoracic artery and saphenous vein grafts. J Cardiovasc Surg (Torino) 2001;42:159-164.[Medline]
- Otaki M., Lust R.M., Sun Y.S., et al. Experimental supplemental vein grafting and hypoperfusion syndrome. Ann Thorac Surg 1995;59:1423-1428.[Abstract/Free Full Text]
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Abstract
Introduction
