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Ann Thorac Surg 1996;62:695-696
© 1996 The Society of Thoracic Surgeons
DR HENDRICK B. BARNER (St. Louis, MO): Doctor Emery is to be congratulated for beautifully presenting this initial multiinstitutional experience with a new prosthetic coronary graft, which is increasingly needed at this time of rising numbers of reoperations in older patients who may lack autogenous conduit or have contraindications to harvesting of available conduit. On the other hand, there is increasing favorable experience with arterial conduits, which have the potential to reduce the need for such a prosthetic graft. Emery and associates have not maximally utilized arterial conduits, which reflects their desire to gain experience with this new device and perhaps reluctance to harvest additional arterial conduits in high-risk patients.
The concept of creating an arteriovenous fistula to maintain a higher rate of flow has been employed in peripheral vascular reconstruction with polytetrafluoroethylene conduits as well as nonautogenous biologic conduits. The rationale of maintaining a higher flow rate to promote conduit patency in low-flow situations is a valid one, although its success has been limited in lower extremity vascular reconstructions where local venous hypertension may complicate outcome and where perfusion pressure has not been characterized.
The unique feature of the Perma-Flow graft is the Venturi flow resistor, in effect a 2-mm stenosis to limit flow through the 5-mm conduit to 400 mL/min and to maintain adequate coronary perfusion pressure in the graft. These hemodynamic principles are sound and appear to provide an advantageous conduit, which creates a central arteriovenous fistula that is well tolerated.
A potential problem with the Perma-Flow graft is the known tendency for intimal hyperplasia to occur at the anastomosis of polytetrafluoroethylene grafts. This occurrence, which may result in anastomotic stenosis or occlusion, has been investigated experimentally in an effort to find deterrents. Thus far medical treatment of this phenomenon has not been particularly successful. Placement of an interposition cuff of vein at the anastomosis has reduced intimal hyperplasia experimentally and has improved long-term clinical patency, perhaps by reducing compliance mismatch between the polytetrafluoroethylene and the grafted artery.
Thus I would ask Dr Emery, is there any evidence that closure of 3 of 13 grafts at 1 year has been related to anastomotic intimal hyperplasia? Has any prophylactic treatment been directed at preventing anastomotic intimal hyperplasia in the patients that you have studied? Is interposition of a venous cuff or segment of vein at the coronary anastomosis a reasonable option, or would this increase the complexity of the operation to an unacceptable level?
DR EMERY: Thank you, Dr Barner. The issue of hyperplasia of the anastomosis remains to be answered. The phase II study has been designed to study patients at 1 week and at 1 year, along the lines of the Veterans Administration 207 study, such that we will be able to hopefully determine if hyperplasia is present. We have no late deaths, so we have no postmortem examinations and thus have not been able to examine the distal anastomoses of any patient late after construction. We have found, though, that in the anastomoses that have closed, much as the one I showed, there has developed more extensive disease of the native artery, which may have led to some distortion of the anastomosis. Hyperplasia may also be inhibited by the presence of a high flow through the prosthesis because of the arteriovenous fistula. This in and of itself may inhibit buildup. Second, we are giving all the patients aspirin. Recently Noel Mills has initiated a project to review platelet aggregation score for the phase II patients because of the inactivity of aspirin on platelets in some 40% of people who take it. So we are looking at this suggestion in terms of the phase II study, which actually began in October and now has 2 patients enrolled.
As regards the venous cuff, Dr Grinnan and Dr Mills discussed that in New Orleans at last year's meeting. It was thought that such an addition might add mobility to the anastomosis in that the polytetrafluoroethylene is fairly stiff and could roll or kink if there were an interposed flexible segment between the stiff polytetrafluoroethylene and the beating action of the heart. We thought that we should not take that step in the early studies.
Related Article
Ann. Thorac. Surg. 1996 62: 691-695.
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