Eur J Cardiothorac Surg 1998;14:476-479
© 1998 Elsevier Science NL
Can visual assessment of flow waveform morphology detect anastomotic error in off-pump coronary artery bypass grafting?1
Saad F. Jaber,
Steven C. Koenig,
Bobby BhaskerRao,
Daniel J. VanHimbergen,
Paul A. Spence
Jewish Hospital Cardiothoracic Surgical Research Institute, 500 S. Floyd Street, Department of Surgery, University of Louisville, Louisville, KY 40202, USA
Received 16 March 1998;
received in revised form 19 August 1998;
accepted 1 September 1998.
Corresponding author. Tel.: +1 502 8524838; fax: +1 502 8524868.
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Abstract
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Objective: Flow probes are being used for intraoperative assessment of anastomotic quality during off-pump coronary artery bypass grafting (CABG). We conducted a survey with the cooperation of 19 international surgeons to assess the ability of surgeons to detect anastomotic errors by evaluating mean flow and flow waveform morphology. Material and methods: Mongrel dogs underwent mammary to left anterior descending (LAD) grafting. Mean graft flow and flow wave morphology for varying degrees of anastomotic stenoses were recorded using transit-time flow probes. A questionnaire consisting of ten different recorded flow tracings and the corresponding mean flows were given to 20 surgeons from around the world. The surgeons were asked to determine the degree of stenosis and whether they would re-do the anastomosis based upon the mean flow and the flow tracings. Results: All of the 19 surgeons that responded were able to clearly identify a highly stenotic graft (>90% stenosis). However, 24% would re-do a fully patent anastomosis, 58% accepted an anastomosis with moderate stenosis, and 72% accepted anastomoses with severe stenosis. Conclusions: Evaluation of flow tracing morphology and/or mean flows can be used to reliably detect nearly occluded anastomoses (>90% stenosis). However, surgeons should be cautious in assessing anastomoses with lesser degrees of stenosis, as they may be more difficult to reliably interpret.
Key Words: Anastomotic quality • Off-pump coronary artery bypass grafting • Flow probes
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Introduction
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The quality of anastomosis in coronary artery bypass grafting (CABG) surgery is currently the critical issue for `off pump' and minimally invasive procedures. A variety of flow measurement techniques are being used for intraoperative assessment of anastomotic quality
[1]
[2]. These techniques are being accepted with increasing frequency worldwide, despite the lack of a definitive scientific study to support their use. Prompted by a graft failure from a minimally invasive CABG procedure, in which a transit-time flow probe was used to assess anastomotic quality, we launched clinical and laboratory studies to evaluate the effectiveness of using mean flow and flow waveform morphology for assessment of anastomotic quality.
A questionnaire consisting of sample flow tracings with their respective means was developed using data obtained from animal studies. The questionnaire was sent to 20 cardiovascular surgeons, experienced in off-pump CABG, from all over the world (North and South America, Asia and Europe). They were asked to determine the quality of the anastomosis by assessing flow morphology and mean flows (note: the identities of survey participants have been kept confidential). This brief communication summarizes the results of this survey.
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Materials and methods
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An animal model (mongrel dog) was developed for grafting the right and/or left internal mammary arteries (IMA) to the left anterior descending (LAD) coronary artery without the benefit of cardiopulmonary bypass (`off pump'). A transit-time flow probe (Transonic, Ithaca, NY) was placed around the IMA. Flow tracings were then obtained with the LAD occluded and with varying degrees of stenosis in the IMA. Stenosis was created by strategically placing a suture through the anastomosis site, thereby reducing the cross-sectional area. The degree of anastomotic stenosis was verified by post-operative angiography. All animals received humane care in compliance with the `Guide for the Care and Use of Laboratory Animals' published by the National Institutes of Health (NIH publication 85–23, revised 1985) and with approval by the University of Louisville Institutional Animal Care and Use Committee.
A questionnaire was developed using ten flow tracings (
Fig. 1 ). The selected flow tracings came from grafts with various degrees of stenosis ranging from patent to nearly occluded. Twenty cardiovascular surgeons were asked to assess the quality of anastomosis by rating the degree of stenosis as either patent (0–15%), moderate (25–50%), severe (50–85%), or occluded (>90%). They were also asked to determine whether they would accept or re-do the graft based upon flow tracing morphology and the corresponding mean flow.
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Fig. 1. Questionnaire containing flow tracings and mean flows for LAD to IMA graft with LAD closed and varying degrees of anastomotic stenosis.
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Results
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Nineteen of the twenty cardiovascular surgeons completed the questionnaire. All of the surgeons surveyed were able to detect a highly stenotic graft (>90% stenosis). However, 24% of the surgeons would have redone a fully patent anastomosis, 42% accepted an anastomosis with moderate (25–50%) stenosis and 72% accepted an anastomosis with severe (50–85%) stenosis (
Fig. 2
). A summary of the results of the survey for each case is provided in Table 1, where the `true' degree of stenosis, mean flow and the percentage of surgeons who would have accepted the graft are shown.
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Fig. 2. Percentage of surgeons accepting anastomosis with patent (<10%), moderate (25–50%), severe (50–85%), or nearly occluded (>90%) stenosis.
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Table 1. `True' degree of stenosis, mean graft flow and percentage of surgeons who would accept the anastomosis for each flow tracing case
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Discussion
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Off-pump CABG offers many potential advantages including decreased incidence of stroke, less blood transfusion requirements, reduced cost and shorter hospital stay
[3]. However, the construction of a patent anastomosis on the beating heart is technically demanding, despite the growing use of cardiac stabilizers and pharmacologic agents to slow heart rate. Angiography is considered the `gold standard' technique for assessment of anastomotic quality in CABG surgery. However, it is costly, invasive and not available in most operating rooms for immediate intraoperative analysis.
A variety of flow measurement techniques have been introduced that provide the surgeon with continuous flow tracings and mean graft flow, which have been used to assess anastomotic quality
[4]. Transit-time flow probes are the most commonly used devices, as they are relatively easy to use intraoperatively and they have been shown to be highly accurate
[1]. The presence of predominantly diastolic flow in the flow tracing is considered to be a sign of `good' anastomotic quality, while the presence of a high peak systolic component and the absence of diastolic flow are considered signs of `poor' anastomotic quality. The role and effectiveness of these probes in detecting intermediate (moderate to severe) anastomotic stenosis have not been well established
[5].
In this study, grafts with moderate to severe stenosis still showed a predominant diastolic component as would be seen in a patent graft. The mean graft flow was also found to be misleading. For example, the mean graft flow was 21 ml/min in a patent graft (Case 3,
Fig. 1), but a 22 ml/min mean flow was recorded in a severely stenotic graft (Case 5,
Fig. 1), which 95% of the surgeons surveyed would have accepted (Case 5, Table 1). Conversely, all of the surgeons accepted a severely stenotic anastomosis with a mean flow of 17 ml/min, but only 63% accepted a patent anastomosis with a mean flow of 16 ml/min. This leads us to believe that visual evaluation of flow and/or mean flow in grafts with intermediate stenosis may not be a reliable technique in assessing anastomotic quality. This belief is supported, in part, by the large percentage of surgeons who would have accepted a severely stenotic anastomosis and those who were divided over what they would do with a moderately stenotic anastomosis.
The questionnaire served as a critical first step in determining whether flow morphology and/or mean flows correlate with anastomotic quality. Clearly, the results of the questionnaire demonstrated that all surgeons surveyed were able to detect highly stenotic/occluded grafts (>90%). However, a large proportion of surgeons missed the grafts with severe stenosis (50–85%), which should serve as a warning to surgeons to exercise caution in evaluating anastomotic quality based upon visual assessment of waveform morphology and/or mean graft flow. The ability to detect severely stenotic grafts would be extremely valuable, because these grafts are likely to require anastomotic revision. The importance of diagnosing grafts with moderate stenosis is less crucial as it has been shown that these grafts are capable of remodeling and can be fully patent on repeat angiography
[6].
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Conclusion
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Evaluation of flow tracing morphology and/or mean flows can help the surgeon detect nearly occluded (>90% stenosis) anastomoses intraoperatively, thus allowing the surgeon to re-do the graft. However, current flow measurement techniques may not be as reliable a method for assessing intermediate stenosis. In view of this finding, we are investigating alternative analysis techniques, such as pattern recognition and neural networks, that have shown promising potential.
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Acknowledgments
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Supported by a grant from Jewish Hospital Heart and Lung Institute, Louisville, KY, USA.
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Footnotes
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Presented at the 3rd MIDCAB meeting, Utrecht, the Netherlands, September, 1997. 
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References
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- Supramanian V.A. Less invasive arterial CABG on a beating heart. Ann Thorac Surg 1997;63:S68-S71.
- Louagie Y.A., Haxhe J.B., Buche M., Schoevaerdts J.C. Intraoperative electromagnetic flowmeter measurements in coronary artery bypass grafts. Ann Thorac Surg 1994;57:357-364.[Abstract]
- Calafiore A.M., Teodori G., Di Giammarco G. Minimally invasive coronary artery surgery: the last operation. Semin Thorac Cardiovasc Surg 1997;9(4):305-311.[Medline]
- Calafiore A.M., Di Giammarco G., Teodori G. Midterm results after minimally invasive coronary surgery (the last operation). J Thorac Cardiovasc Surg 1998;115:763-771.[Abstract/Free Full Text]
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Abstract
Introduction
