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Ann Thorac Surg 2001;72:S2258-S2259
© 2001 The Society of Thoracic Surgeons
a Division of Cardiothoracic Surgery, Beth Israel-Deaconess Medical Center, Harvard Medical School, 110 Francis Street, #LMOB Suite 2A, Boston, MA 02215, USA
e-mail: fsellke{at}caregroup.harvard.edu
Doctor Wolfe’s presentation very nicely describes several of the methods available to cardiac surgeons to assess graft patency and the quality of distal anastomoses both intraoperatively and postoperatively. The outcome of coronary bypass surgery depends largely on the adequacy of the anastomoses, both distally and proximally. It has been assumed that if you could perform anastomoses under direct vision, there would be little reason to believe that technical factors would contribute to the short-term or long-term closure of arterial or venous bypasses. However, with the advent of MIDCAB and OPCAB, this has really been questioned, and the reliability of nonassisted assessment of graft patency using direct vision as the only criterion has also been questioned. As Dr Wolfe mentioned, the use of electromagnetic flow probes has never really been found to add much to the clinical assessment of graft patency. There is wide variation in the readings, tempting the surgeon to always choose the highest as the true flow rate. Doppler flow probes add to the reliability of the assessment and provide a significant advance over electromagnetic flow probes. Use of the pulsality index, which is a ratio of the maximum flow velocity to the minimum flow velocity, can be used to identify problems with the distal anastomoses, and probably with greater reliability. In my hands, however, Doppler has added little to the clinical assessment using ECG and echocardiography intraoperatively. We use intraoperative transesophogeal echocardiography on virtually all patients, and I consider this to be a very good and valuable method for intraoperative assessment of the adequacy of revascularization.
Calibrated pump flow is a very easy way to assess the adequacy of a distal anastomosis. The perfusion pressure is brought up to about 100 mm Hg. A flow of more than 80 mL/min usually indicates a good anastomosis. A flow of less than 50 may indicate that there is a technical problem. I do not have much experience with thermal angiography. It does not seem to be an optimal method, as it is time consuming and fraught with problems. We are fairly liberal in our use of coronary angiography postoperatively. If there are unsuspected ECG changes associated with changes in regional wall motion on echocardiography, we promptly obtain a coronary angiogram. A normal coronary angiogram, which may be found in the majority of cases, allows one to address issues other than the technical quality of the anastomosis, such as coronary spasm, embolization, and poor myocardial protection.
We have not had much experience with pH probes, as advocated in this symposium by Dr Khuri and colleagues. I think it does have some value in complementing other methods described above, which are used to assess the adequacy of the anastomosis. I suspect there might be false positives and false negatives because, as Dr Wolfe mentioned, this method assesses the adequacy of the anastomosis. There are also factors other than the quality of the anastomosis that can contribute to the acidosis in the distal myocardial segments that are subtended by the new graft.
My personal approach is to assess the technical adequacy of the anastomosis first by using a syringe to infuse a blood containing solution, and assessing the resistance to flow. Consideration is given to redoing the anastomoses if I encounter increased resistance over what I would expect. I also use the pump flow rate through the graft, as measured by the perfusionist. Again, if the flow is more than 80 mL/min with a pressure of 100 mm Hg, the adequacy of the anastomosis is usually verified. As previously mentioned, I find TEE to be very valuable intraoperatively in concert with some of these other methods to assess graft flow. Although it is a very indirect method, the absence of a regional wall motion defect after cross clamp removal, even in the face of minor ECG changes, gives me confidence that graft closure or stenosis is probably not the problem.
Although there is no perfect method presently to assess the adequacy of graft patency or the adequacy of the distal anastomosis intraoperatively, one needs to develop a systematic approach for those cases in which problems are encountered. We use postoperative angiography fairly liberally, and we monitor TEE in nearly all cases. Significant new wall motion abnormalities on postoperative TEE are correlated with graft closure or narrowing, and angioplasty can be used to open the native circulation or, in certain cases, to reestablish patency of the vein bypasses. It is critical to attend to a stenosed graft promptly, before scarring or complete thrombosis has occurred.
Again, I would like to congratulate Dr Wolfe on an excellent review.
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