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Guidelines for development and use of transluminally placed endovascular prosthetic grafts in the arterial system

1995; Elsevier BV; Volume: 21; Issue: 4 Linguagem: Inglês

10.1016/s0741-5214(95)70198-2

1097-6809

Frank J. Veith, William M. Abbott, James S.T. Yao, Jerry Goldstone, R. A. White, Dorothy Abel, Michael D. Dake, Calvin B. Ernst, Thomas J. Fogarty, K.W. Johnston, Wesley S. Moore, Arina van Breda, George Sopko, Paul Didisheim, Robert B. Rutherford, Barry T. Katzen, D. Craig Miller,

Vascular Procedures and Complications

The feasibility of placing prosthetic grafts within the arterial tree by inserting them via a remote site, guiding them intraluminally to the appropriate location, and fixing them there with attachment systems, such as a variety of expandable stents, has been demonstrated in animals and human beings. 1Parodi JC Palmaz JC Barone HD. Transfemoral intraluminal graft implantation for abdominal aortic aneurysms.Ann Vasc Surg. 1991; 5: 491-499Abstract Full Text PDF PubMed Scopus (2797) Google Scholar, 2Laborde JC Parodi JC Clem MF et al.Intraluminal bypass of abdominal aortic aneurysm: feasibility study.Radiology. 1992; 184: 185-190Crossref PubMed Scopus (166) Google Scholar, 3Chuter TAM Green RM Ouriel K Fiore W DeWeese JA Transfemoral endovascular aortic graft placement.J VASC SURG. 1993; 18: 185-197Abstract Full Text Full Text PDF PubMed Scopus (176) Google Scholar There is a potential for these transluminally placed endovascular grafts (TPEGs) aaAt present, these include a variety of graft-stent combinations. However, these guidelines apply to other devices that will have or develop blood impervious walls and that may be inserted via intraluminal routes to provide prosthetic support or replacement of a diseased arterial wall. Devices that involve autologous tissue (e.g., stents and a vein graft) are also a variety of TPEG. Another variety is TPEGs used in the systemic or portal venous systems. Although some generalities in these guidelines apply to these autologous and venous TPEGs, they will not be dealt with specifically in this document. Throughout these guidelines the terms TPEG, stented graft, and stent graft are used interchangeably, although it is recognized that TPEG has a broader meaning because not all of these devices will necessarily include a stent component per se.aaAt present, these include a variety of graft-stent combinations. However, these guidelines apply to other devices that will have or develop blood impervious walls and that may be inserted via intraluminal routes to provide prosthetic support or replacement of a diseased arterial wall. Devices that involve autologous tissue (e.g., stents and a vein graft) are also a variety of TPEG. Another variety is TPEGs used in the systemic or portal venous systems. Although some generalities in these guidelines apply to these autologous and venous TPEGs, they will not be dealt with specifically in this document. Throughout these guidelines the terms TPEG, stented graft, and stent graft are used interchangeably, although it is recognized that TPEG has a broader meaning because not all of these devices will necessarily include a stent component per se.to provide improved treatment for a variety of arterial lesions, including aneurysms, traumatic injuries, and arteriosclerotic occlusions, and TPEG repairs of all three kinds of lesions have been carried out at various levels of the arterial tree with short-term success. 1Parodi JC Palmaz JC Barone HD. Transfemoral intraluminal graft implantation for abdominal aortic aneurysms.Ann Vasc Surg. 1991; 5: 491-499Abstract Full Text PDF PubMed Scopus (2797) Google Scholar, 4Cragg AH Dake MD. Percutaneous femoropopliteal graft placement.Radiology. 1993; 187: 643-648PubMed Google Scholar, 5Marin ML Veith FJ Panetta TF et al.Percutaneous transfemoral stented graft repair of a traumatic femoral arteriovenous fistula.J VASC SURG. 1993; 18: 298-301Google Scholar, 6Parodi JC, Barone HD, Schonholz C, Marin ML, Panetta TF, Cynamon J, Veith FJ. Endovascular insertion of balloon expandable stented grafts to treat peripheral arterial lesions: initial experience in man. Proceedings of the XXI World Congress of the International Society for Cardiovascular Surgery, Sept. 13-15, 1993;Lisbon, Portugal.Google Scholar, 7Marin ML Veith FJ Panetta TF et al.Transfemoral stented graft treatment of occlusive arterial disease for limb salvage: a preliminary report.Circulation. 1993; 88 ([Abstract]): I-11PubMed Google Scholar, 8Marin ML Veith FJ Panetta TF et al.Transfemoral endoluminal stented graft repair of popliteal artery aneurysm.J VASC SURG. 1994; 19: 754-757Abstract Full Text Full Text PDF PubMed Scopus (191) Google Scholar, 9May J White G Waugh R Yu W Harris JM Transluminal placement of a prosthetic graft-stent device for treatment of subclavian aneurysm.J VASC SURG. 1993; 18: 1056-1059Abstract Full Text Full Text PDF PubMed Scopus (136) Google Scholar, 10Volodos NL Karpovich IP Troyan VI et al.Clinical experience of the use of self-fixing synthetic prostheses for remote endoprosthetics of the thoracic and abdominal aorta and iliac arteries through the femoral artery and as intraoperative endoprosthesis for aorta reconstruction.Vasa. 1991; 33: 93-95PubMed Google Scholar, 11Marin ML Veith FJ Panetta TF et al.Transluminally placed endovascular stented graft repair for arterial trauma.J VASC SURG. 1994; 20: 466-473Abstract Full Text Full Text PDF PubMed Scopus (270) Google Scholar, 12Marin ML Veith FJ Cynamon J et al.Transfemoral endovascular stented graft treatment of aorto-iliac and femoropopliteal occlusive disease for limb salvage.Am J Surg. 1994; 168: 156-162Abstract Full Text PDF PubMed Scopus (80) Google Scholar, 13Parodi JC. Endovascular repair of abdominal aortic aneurysms.Adv Vasc Surg. 1993; 1: 85-106Google Scholar, 14Moore WS Vescara CL. Repair of abdominal aortic aneurysm by transfemoral endovascular graft placement.Ann Surg. 1994; 220: 331-341Crossref PubMed Scopus (155) Google Scholar, 15White GH Weiyun Y May J Stephen MS Waugh RC. A new nonstented balloon-expandable graft for straight or bifurcated endoluminal bypass.J Endovasc Surg. 1994; 1: 16-24Crossref PubMed Scopus (62) Google Scholar, 16Scott RAP Chuter TAM. Clinical endovascular placement of bifurcated graft in abdominal aortic aneurysm without laparotomy.Lancet. 1994; 343: 413Abstract PubMed Scopus (53) Google Scholar, 17Yusuf SW Baker DM Chuter TAM Whitaker SC Wenham PW Hopkinson BR. Transfemoral endoluminal repair of abdominal aortic aneurysm with bifurcated graft.Lancet. 1994; 344: 650-651Abstract PubMed Scopus (84) Google Scholar Because TPEG repairs can be performed less invasively, their risks and costs may be less than those of standard vascular graft operations. They will therefore be extremely attractive to both patients and physicians, and consequently there will be enormous pressure to develop and use these devices rapidly. The purpose of this document is to foster the development of safe, effective devices for performing TPEG repairs of various arterial lesions at all levels of the arterial tree. To this end, it will provide guidelines for the careful and structured evaluation and monitoring that are necessary to document the safety, efficacy, and effectiveness bb Safety is defined as freedom from complications or intrinsic device failure; efficacy is defined as the ability of the device to restore the vascular wall and luminal integrity, to prevent aneurysm expansion and rupture, or to maintain luminal patency; and effectiveness is defined as the ability to extend patient survival and limb or organ function by preventing aneurysm expansion and rupture or by maintaining arterial flow through the diseased segment of the artery.bb Safety is defined as freedom from complications or intrinsic device failure; efficacy is defined as the ability of the device to restore the vascular wall and luminal integrity, to prevent aneurysm expansion and rupture, or to maintain luminal patency; and effectiveness is defined as the ability to extend patient survival and limb or organ function by preventing aneurysm expansion and rupture or by maintaining arterial flow through the diseased segment of the artery.of these devices in various settings before they undergo widespread clinical use. Although these guidelines are not a regulatory document, they are intended to help avoid premature and potentially harmful usage of TPEGs. TPEGs can be divided into those that are covered single stent devices ccA covered single stent is one to which a prosthetic graft, which is or will become imprevious to blood, if fixed so that the graft covers a portion or all of the internal or external surface of the stent after its expansion within a blood vessel. Some devices of this variety may incorporate stentlike components within a graft matrix to provide an integrated unit: others may consist of a stent alone that becomes impervious to blood.and end fixation devices, which comprise a prosthetic graft fixed with a stent orother attachment system at both ends. Variants of the latter are bifurcated Y grafts or branched grafts with attachment devices at all three ends and long grafts stented at one end and with no stent or a suture anastomosis at the other end. Further division of TPEGs can be based on the characteristics of the device, specifically the nature of the delivery system (e.g., sheath/no sheath, over a wire/not over a wire, etc.), the nature of the attachment or fixation system and method (balloon-expandable, spring-expandable, or mechanically expandable stent or other device, with or without hooks for fixation to the vessel wall, and the nature of the graft or covering material component (knitted polyester [ [Dacron]d,dDacron is a trademark of DuPont Co., Inc., Wilmington, Del. It refers to the polyester, polyethyleneterephthalate. Throughout these guidelines the generic term, polyester, will be used for this material.,woven polyester [Dacron],d polytetrafluoroethylene [PTFE] or other developmental prosthetic material). Because different characteristics and properties of TPEGs may be required to treat different forms of arterial disease in different parts of the arterial tree, usage must be defined on the basis of lesion location and lesion pathology. Safety, efficacy, and effectiveness must at least be considered separately for each device and each usage. This document provides guidelines for evaluating TPEGs according to usage categories defined by the following vessel sizes and locations: the thoracic and suprarenal aorta, large arteries (infrarenal aorta, iliac, innominate, common carotid and subclavian), and medium-sized arteries (femoral, popliteal, axillary, visceral, renal, coronarye,eCoronary, carotid, and vertebral devices will have special problems relating to the end organs they supply and technical challenges to obtain access. Appropriate monitoring of end organ function, that is, the heart or brain, will be required with devices used in these arteries.vertebral,e and carotid bifurcation and branchese); and for devices to be used to treat aneurysms, traumatic lesions (false aneurysms, arteriovenous fistulas, mural injuries), stenotic and occlusive lesions, and dissections and intramural hematomas. Usage categories other than these may be required on the basis of pathologic, anatomic, or physiologic characteristics of the patient or lesion being treated. For example, some aneurysmal, traumatic, or ulcerating atherosclerotic lesions may cause distal embolization as their only manifestation. The suitability of such lesions for TPEG treatment might need to be evaluated separately. For purposes of demonstrating safety, efficacy, and effectiveness, each specific device should be considered for evaluation in a specified-sized artery in one or more locations with similar defined disease. However, it is possible that a given device will be safe and effective in several different sized arteries, in different locations, and even for the treatment of different types of lesions. Accordingly, it will be acceptable to evaluate and demonstrate safety, efficacy, and effectiveness of a given device by studies in which that device is used in more than one location or for more than one type of lesion. In such circumstances a satisfactory rationale and justification for combining usage categories must be provided. All studies should be designed to demonstrate statistically valid conclusions within one or more subdivisions of this categorization system. Because TPEGs require vascular surgical skills and catheter-guidewire-imaging skills to insert and deploy, the clinical teams involved in their development and initial testing in patients should consist of individuals with the highest levels of expertise in both of these modalitiesf.fSeparate training and credentialing guideline documents for individuals who can perform vascular surgery and endovascular procedures have been prepared by various specialty organizations.18Moore WS Treiman RL Hertzer NR Veith FJ Perry MO Ernst CB Guidelines for hospital privileges in vascular surgery.J VASC SURG. 1989; 10: 678-682PubMed Scopus (32) Google Scholar, 19String ST Brener BJ Ehrenfeld WK et al.Interventional procedures for the treatment of vascular disease: recommendations regarding quality assurance, development, credentialing criteria, and education.J VASC SURG. 1989; 9: 736-739PubMed Scopus (8) Google Scholar, 20Spies JB Bakal CW Burke DR et al.Guidelines for percutaneous transluminal angioplasty.Radiology. 1990; 177: 619-626PubMed Google Scholar, 21Levin DC Becker GJ Dorros G et al.Training standards for physicians performing peripheral angioplasty and other percutaneous peripheral vascular interventions.Circulation. 1992; 86: 1348-1350Crossref PubMed Scopus (81) Google Scholar, 22White RA Fogarty TJ Baker WH Ahn SS String ST Endovascular surgery credentialing and training for vascular surgeons.J VASC SURG. 1993; 17: 1095-1102Abstract Full Text Full Text PDF PubMed Scopus (42) Google Scholar, 23Spittell JA Creager MA Dorros G et al.Recommendations for peripheral transluminal angioplasty: training and facilities.J Am Coll Cardiol. 1993; 21: 546-548Abstract Full Text PDF PubMed Scopus (62) Google Scholar The general principles expressed in these documents should also apply to this guideline document.This means that individuals possessing skills and experience in vascular surgery ggProcedures performed for lesions of the thoracic aorta may require the participation of individuals skilled and credentialed in cardiothoracic surgery, especially if it appears that cardiopulmonary bypass may be necessary to manage device complications.and interventional radiology must be involved in and responsible for the efforts of these developmental centers. Usually this combination of skills will require two or more individuals, a vascular surgeon and an interventional radiologist who work smoothly together as a team, although it is possible that one individual will possess the requisite skills and experience to perform all parts of the procedure. It is recommended that developmental or research centers testing these devices be staffed by integrated teams of vascular surgeons and radiologists, coordinated by a single individual who is familiar with vascular disease and natural history and all standard treatment alternatives and who bears overall patient responsibility. To deal optimally with unexpected problems, procedures carried out on patients should be performed in a procedural room that is equipped with digital imaging fluoroscopy and that has all the appropriate equipment and personnel to carry out open arterial operations. In light of current designs, approaches, and clinical experience and because the possibility that large artery injury, occlusion, or rupture may require immediate emergency operation, procedures conducted on the thoracic or abdominal aorta, the iliac arteries, or other aortic branches should be performed in a room that has appropriate imaging devices and equipment and staff to carry out emergency major vascular or cardiovascular surgery. (See the section on "Requirements For Facilities in Which TPEGs Will Be Used Clinically" for further details regarding equipment requirements.) In addition, these centers should have inpatient radiologic and vascular surgical services experienced in performing the full range of standard arteriography, catheter-directed angioplasty and stent placement, and all vascular and cardiothoracic operations. They should also have the outpatient facilities, noninvasive vascular diagnostic laboratories, radiology services, and support staffs to perform the high-quality imaging techniques needed for accurate and thorough patient follow-up evaluation. Centers involved in these studies must demonstrate a commitment to long-term follow-up. It should be recognized that some properties of TPEGs may differ from those required of standard grafts or stents used to treat similar lesions in similar locations. Because TPEGs will be inserted from a remote site and guided into position, there are clear advantages to reducing their unexpanded cross-sectional diameter or "profile" as much as possible. In this way the requirement that they be introduced through an open arteriotomy in a large-caliber artery will be minimized. Thus devices with a low profile offer clear advantages in terms of feasibility and applicability. However, making the TPEG thin and flexible to achieve a low, unexpanded profile may require a thinner graft with reduced strength. Currently it is not known whether TPEGs need the same burst strength or porosity characteristics as a standard arterial graft. A TPEG that will be placed within the unsupported lumen of an aortic aneurysm must have adequate strength and durability to withstand aortic pressures and flows, although it may not have to meet the same safety factors required of standard aortic grafts with regard to these parameters. In addition, a TPEG intended for use in the treatment of unruptured aneurysms may not require the same porosity specifications as a standard graft used to treat the same condition. Because the endoluminally inserted device will be contained within the intact aneurysm sac, greater porosity may be tolerable because transinterstitial bleeding will be contained by the aneurysm wall until fibrin deposition occludes the pores. Moreover, a TPEG placed within a stenotic or occluded artery may receive structural support from the surrounding arterial wall, thereby allowing the use of grafts with different physical properties (e.g., decreased wall thickness and strength). Long-term experimental and clinical studies will be required to settle these issues. In contrast, some endoluminally placed grafts may require unusual characteristics not needed with standard grafts. Examples include physical properties that contribute to an intact and fixed friction seal at junction points with host arteries, to developing rapid and secure impermeability to blood in ruptured aneurysms and traumatic arteriovenous fistulas, or to resisting compression when a TPEG is placed within occluded arteries. When TPEGs and appropriate systems for their insertion are developed and are believed to be suitable for treatment of specific lesions in specified locations, the following general guidelines are recommended for preclinical and clinical testing before the devices are brought into widespread usage. For any device, the evaluation must consist of four phases: bench testing, (structural/mechanical), preclinical (animal) testing, clinical testing-feasibility, and clinical testing-comparative performance. However, in identifying appropriate testing for any device, consideration must be given to the mode(s) of failure and its/their effect on the performance of the device. For the graft portion of the device, this should consist of essentially the same tests of physical properties, such as strength, durability, porosity, kink resistance, suture holding abilityh,hIf an open surgical anastomosis may be required at one end.flexibility, and longitudinal and radial stretchability, as are required for a currently standard or proposed new arterial prosthesis. 24Standards for vascular graft prostheses. The Association For The Advancement Of Medical Instrumentation, Arlington, Va1986Google Scholar, 25Abbott WM Callow A Moore W Rutherford R Veith FJ Weinberg S Evaluation and performance standards for arterial prostheses.J VASC SURG. 1993; 17: 746-756Abstract Full Text Full Text PDF PubMed Google Scholar, 26Guidance For The Preparation of Research and Marketing Applications For Vascular Graft Prostheses (Draft). Prosthetic Devices Branch, Division of Cardiovascular, Respiratory and Neurological Devices, Office of Device Evaluation, Rockville, Md1993Google Scholar The possibility also exists that modified requirements may need to be developed for new graft materials that may be developed and used for TPEGs. In addition, the stent portion or attachment system of a TPEG device will have to be evaluated for the various characteristics important to its function, such as inertness in blood, lack of toxicity, absence of metal fatigue, flexibility, compression resistance, and other physical properties that contribute to a leak-proof seal and secure fixation at junction points with arteries. 27Guidance For The Submission of Research and Marketing Applications For Interventional Cardiology Devices: PTCA Catheters, Atherectomy Catheters, Lasers, Intravascular Stents (Draft). Interventional Cardiology Devices Branch, Division of Cardiovascular Respiratory and Neurology Devices, Office of Device Evaluation, Rockville, Md1993Google Scholar Finally, the delivery system of a device will require bench testing to demonstrate appropriate maneuverability, kink resistance, radiopacity, and marker visibility to be effective in the clinical setting in which it will be used. Successful animal implantation of all TPEG devices, by use of the same introduction systems and localization and deployment methods that will be used in patients, should be required before clinical trials can be undertaken. Successful implantation includes the ability to visualize and deploy the device by techniques similar to those that will be required in patients; the firm fixation of the device at the site of original implantation; and acceptable freedom from leakage, migration, vessel wall erosion, thrombosis, excessive intimal hyperplasia with luminal narrowing, and distal embolization. There should also be acceptable freedom from other complications related to the fixation component or stent, particularly those with hooks or spikes. The duration of observation in animal testing should be for a minimum of 6 months before clinical tests can be undertaken. Longer studies may be needed if synthetic materials not currently in use in the vascular system are involved. The TPEG should be inserted in animal models at similar although not necessarily identical anatomic locations to those intended for use in patients. Every effort should be made to use animal models that mimic as closely as possible the clinical problem being addressed. Device insertion techniques and endpoints studied should parallel those that will apply in the clinical setting as much as possible. Imaging techniques, such as angiography or intravascular ultrasonography (IVUS), that provide visualization and localization of the fixation device and the graft are important parameters to evaluate in these studies. It is recognized, however, that animal models have several limitations in evaluating TPEGs. First, the commonly available large animal models (dogs, pigs, or sheep) have arteries that are smaller than comparable arteries in human beings. Calves are larger, and their arteries better approximate the size of human arteries, but their rapid growth limits their utility for anything other than short-term studies. Second, it is not possible to produce in animals arterial lesions that are comparable to those in patients, with the possible exceptions of traumatic arteriovenous fistulas, false aneurysms, and aortic dissections. 28Moon MR Dake MD Pelc LR Liddell R Castro LJ Mitchell RS Miller DC. Intravascular stenting of acute experimental type B dissections.J Surg Res. 1993; 54: 381-388Abstract Full Text PDF PubMed Scopus (59) Google Scholar Although animal models with fusiform polyester cloth aneurysms have been described 2Laborde JC Parodi JC Clem MF et al.Intraluminal bypass of abdominal aortic aneurysm: feasibility study.Radiology. 1992; 184: 185-190Crossref PubMed Scopus (166) Google Scholar, 3Chuter TAM Green RM Ouriel K Fiore W DeWeese JA Transfemoral endovascular aortic graft placement.J VASC SURG. 1993; 18: 185-197Abstract Full Text Full Text PDF PubMed Scopus (176) Google Scholar, 29Balko A Piaseck GS Shah DM Carney WI Hopkins RW Jackson BT. Transfemoral placement of intraluminal polyurethane prosthesis for abdominal aortic aneurysm.J Surg Res. 1986; 40: 305-309Abstract Full Text PDF PubMed Scopus (176) Google Scholar, 30Mirich D Wright KC Wallace S et al.Percutaneously placed endovascular grafts for aortic aneurysms: feasibility study.Radiology. 1989; 170: 1033-1037PubMed Google Scholar and have some limited applicability, good models of true aneurysms and arteriosclerotic occlusive disease do not exist. Accordingly, animal studies have limited applicability in predicting the outcome of TPEGs in treating some human arterial lesions. Furthermore, it may be necessary to test some devices in more than one animal model to address all concerns (e.g., long-term implants in dogs with acute studies in calves to study clinical-sized devices). All animal studies should include gross and histologic evaluation and, if possible, angiographic evaluation, computed tomography (CT) scanning with contrast, magnetic resonance imaging (MRI), and/or IVUS to document device, luminal, and arterial wall structure and relationships. All the animals involved in these studies must receive humane care in compliance with the "Principles of Laboratory Animal Care" formulated by the National Society for Medical Research and the Guide for the Care and Use of Laboratory Animals (NIH Publication No. 86-23, revised 1985) prepared by the National Academy of Sciences. Clinical testing must demonstrate the safety, efficacy, and effectiveness of TPEGs in the treatment of human arterial diseases. Separate studies may be needed for each usage category and each artery size and lesion described in the "Generalities" section. However, it is possible that some devices will be suitable for treating multiple categories of lesions. Therefore it may be appropriate to combine lesion sites and pathologic categories for clinical testing when this can be supported and justified. This is particularly likely when treatment of uncommon lesions is being considered. Clinical testing will be divided into two phases: feasibility testing and comparative performance testing. This should demonstrate that insertion of a TPEG device is possible in a given disease state in a given location and that the device functions safely and effectively for at least 6 months. These tests must include comparative preprocedural and postprocedural noninvasive measurements of the distal circulation and, in the case of aneurysms, their size before and 3 and 6 months after TPEG placement. These measurements include lower extremity segmental systolic pressures and pulse volume recordings (or Doppler waveform measurements) and ultrasound, contrast-enhanced CT scanning, MRI, and/or IVUS measurements of aneurysm size. iiThese measurements should permit accurate definition of wall, clot, and lumen (flowing blood) dimensions.They must be available in at least 10 patients and should be supplemented by appropriate imaging studies to demonstrate device patency, confinement of flowing blood to the graft lumen, and freedom from leakage, migration, and aneurysm enlargement. jjIn the descending thoriacic aorta, transesophageal echo may be useful for these evaluations.Preplacement, completion, and 6 months postplacement arteriographic confirmation should be provided in at least one half of the patients and preferably in all. However, if other less invasive modalities can provide accurate equivalent information, arteriographic study may be unnecessary. There are two types of feasibility studies. In both, protocols should be consistent with Institutional Review Board (IRB) and Food and Drug Administration (FDA) standards and regulations. In the first type of feasibility study, standard usage, the TPEG treatment is offered to patients who are candidates for standard operative abdominal aneurysm repair, 25Abbott WM Callow A Moore W Rutherford R Veith FJ Weinberg S Evaluation and performance standards for arterial prostheses.J VASC SURG. 1993; 17: 746-756Abstract Full Text Full Text PDF PubMed Google Scholar standard operative graft or balloon angioplasty/stent treatment of occlusive lesions, or standard surgical repair of traumatic lesions or peripheral aneurysms for the usual indications. In this setting, the patient must be prepared for and willing to undergo the standard procedure if the TPEG placement is impossible or unsuccessful or has a complication. In general, if the aorta or iliac arteries are involved or if limb salvage is the indication, patients having these initial TPEG procedures should have them performed in a location that is equipped and staffed for emergency operative repair. In the second form of feasibility study, high-risk usage, patients who are unsuitable for or at high risk for the standard treatment may be offered the new TPEG treatment as an option. kkThere is some disagreement over the ethical merits of demonstrating feasibility in patients for whom no surgical rescue procedure is available if the untested device fails. These guidelines cannot resolve this disagreement. Ideally, some prior experience or other evidence should be available to suggest feasibility before high risk usage of a new TPEG device is undertaken. High-risk usage protocols must have risk factors or criteria clearly defined and objectively documented to avoid overly liberal use.In the case of abdominal aneurysm repair, these can be patients with large, threatening aneurysms whose operative risk is excessive, for example, in excess of 3 to 4 times normal, on the ba