Blunt aortic injury (BAI) is a life-threatening complication

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1 Blunt Traumatic Aortic Transection: The Endovascular Experience Victoria P. Orford, MBBS (Hons), Noel R. Atkinson, FRACS, Ken Thomson, MD, Peter Y. Milne, FRACS, William A. Campbell, FRACS, Andrew Roberts, FRACS, John Goldblatt, FRACS, and James Tatoulis, FRACS Cardiothoracic Surgery Unit, Vascular Surgery Unit, Department of Radiology, Royal Melbourne Hospital, Vascular Surgery Unit, The Alfred Hospital, and Vascular Surgery Unit, Austin and Repatriation Medical Centre, Melbourne, Victoria, Australia Background. Thoracic aortic transection resulting from blunt trauma is usually fatal. It is almost always associated with multiple, complex, nonaortic injuries that could be adversely affected by standard surgical repair of the aorta. Endovascular stenting techniques offer these patients a less physiologically disruptive treatment option. We studied the feasibility and safety of endovascular stent graft placement for treatment of acute traumatic aortic transection. Methods. Between 1994 and 2001, 9 patients were treated emergently for aortic transections with stent graft placement. The first patient had a custom-made prototype, and the other 8 patients had the Cook-Zenith thoracic stent graft implanted. All were polyestercovered Z-stent construction and deployed through a femoral 20- to 24-F delivery sheath. Results. Stent graft placement successfully sealed the aorta in all patients. One patient died as a result of a cerebrovascular accident. One patient required a brachial thrombectomy to relieve arm ischemia. The remaining eight patients were alive and without complications during the follow-up period (mean 21 months). Conclusions. Endovascular repair for acute aortic transection is a safe, effective, and timely treatment option. It may be the treatment of choice in patients with extensive associated injuries. (Ann Thorac Surg 2003;75:106 12) 2003 by The Society of Thoracic Surgeons Presented at the Thirty-eighth Annual Meeting of The Society of Thoracic Surgeons, Fort Lauderdale, FL, Jan 28 30, Address reprint requests to Dr Orford, Cardiothoracic Surgery Unit, The Royal Melbourne Hospital, Grattan St, Parkville, Victoria 3050 Australia; victoria.orford@mh.org.au. Blunt aortic injury (BAI) is a life-threatening complication of chest trauma. In a study of 387 blunt trauma deaths [1], it was cited as the second most common cause of death after head injury. It is an injury of rapid deceleration and is strongly associated with motor vehicle accidents. Approximately 85% of patients die at the accident scene [2, 3], and of the 10% to 15% of patients who arrive at hospital alive, 20% will die of aortic rupture [2]. Therefore, considerable attention is paid to rapid diagnosis and treatment, with surgical repair being the standard method of treatment. Rarely is BAI an isolated injury [2]. The problem faced by aortic surgeons is that these associated injuries are often serious, if not life threatening in their own right. Many of these injuries can be compromised by various aspects of standard surgical repair of the aorta, including positioning, thoracotomy, single-lung ventilation, systemic anticoagulation, cardiopulmonary bypass, and aortic cross-clamping. Since 1991, when Parodi and associates [4] described their first clinical experience of endovascular stenting in abdominal aortic aneurysms, there has been a growing interest in stent grafting as an alternative to traditional surgery, particularly in patients with serious comorbidities. Dake and colleagues [5] took this technology to the thoracic aorta and have reported an extensive series of chronic aneurysms repaired by using stent grafts. More recently they studied a group of patients with traumatic thoracic aortic aneurysms, both acute and chronic, with promising results [6]. In this series, we report our experience of acute traumatic transections of the aorta, all treated emergently with endovascular stent graft placement. The purpose of our study was to demonstrate that stent graft technology is a safe, effective, and feasible treatment option in the acute setting of BAI. Material and Methods Patient Selection From August 1994 to March 2001, 9 patients underwent repair of a traumatic aortic transection with the use of stent grafts. The cause of the injury in all cases was rapid deceleration from blunt trauma (Table 1). Five patients suffered motorcycle trauma, three were caused by automobile accidents, and one was a trotting sulky mishap. The patients were aged 26 to 91 years (mean, 52 years). Six were male. In 8 patients the BAI was diagnosed in the emergency This article has been selected for the open discussion forum on the CTSNet Web site: by The Society of Thoracic Surgeons /03/$30.00 Published by Elsevier Science Inc PII S (02)04331-X

2 Ann Thorac Surg ORFORD ET AL 2003;75: BLUNT TRAUMATIC AORTIC TRANSECTION Table 1. Patient Characteristics Patient No. Age (y) Sex Mechanism of Injury Interval From Diagnosis to Repair Indication 1 35 M Motorcycle accident 48 hours/27 days Past pleurodesis 2 91 M Motor vehicle accident 8 hours Age, closed head injury 3 47 M Motorcycle accident 7 hours Spinal cord injury 4 57 M Motorcycle accident 5 hours Closed head injury, pulmonary contusions, fractured C F Motorcycle accident 7 hours Fractured pelvis, multiple compound fractures 6 44 M Trotting sulky collision 12 hours Pulmonary contusions, respiratory failure 7 26 M Motorcycle accident 6 hours Pulmonary contusion, open fracture pelvis 8 61 F Motor vehicle accident 4 hours Pulmonary contusion, myocardial contusion 9 79 F Motor vehicle accident 24 hours Subdural hematoma, pulmonary contusions, fracture and dislocation C4/5 107 CARDIOVASCULAR F female; M male. room using computed tomographic angiography after clinical suspicion was raised by symptomatology, chest radiograph findings, or the mechanism of injury. The ninth patient was diagnosed using intraoperative transesophageal echocardiography during an orthopedic procedure, and he subsequently underwent computed tomographic angiography. Indications for the stent graft procedure were the presence of serious comorbidities that made open surgical repair extremely high risk. The most common of these comorbidities were severe pulmonary contusions, closed head injury, and spinal or spinal cord injury. Indications for endovascular repair softened during the 7-year study period as endoluminal graft technology evolved (Table 2). The first patient in our series had a history of previous pleurodesis. Open repair through a thoracotomy was attempted and abandoned because of extensive adhesions and poor access to the aorta. He subsequently had Table 2. Associated Injuries in Study Population Injury Type Number of Patients Pulmonary contusions 7 Multiple rib fractures 5 Closed head injury 4 Fractured pelvis 4 Lower limb fracture 4 Upper limb fracture 3 Lumbar spine 3 Maxillofacial fracture 2 Cervical spine 2 Thoracic spine 1 Spinal cord 1 Small bowel 1 Other abdominal 1 Brachial plexus 1 a bridging Palmaz stent (Cordis, NJ) placed for signs of developing aortic obstruction. The contained false aneurysm remained stable, perhaps supported by the periaortic adhesions from the past pleurodesis. A prototype, covered stent graft was then constructed by Dr. Michael Dake of Stanford University Medical Center, Palo Alto, California, and implanted 27 days later. Stent Graft Details The dimensions used for stent graft sizing were determined on the basis of computed tomographic angiography and angiographic images (Fig 1). The graft was oversized by 20% compared with the normal, adjacent aorta. In our series, average stent graft diameter was 24 mm (range 22 to 28 mm), and average length was 110 mm (range 50 to 120 mm). With the exception of the first patient in the series who had a custom prototype, the remaining 8 patients had aortic repair using the Cook-Zenith Thoracic Stent Graft (Cook Australia, Brisbane, Australia). The graft is of a Vascutec polyester weave, covered stainless steel Z-stent construction and is deployed through a 20- to 24-F delivery sheath. In the current graft design, the proximal end is covered and has stainless steel hooks protruding through the graft fabric (Fig 2), which anchor the graft directly to the aortic wall. This protects against distal stent graft migration during high-velocity systolic blood flow. Full deployment of the top stent (with spikes) is released by pulling a trigger wire once optimal graft position is confirmed. Technique Informed consent was obtained from all patients or from the next of kin. All nine procedures were performed in the angiography suite because of the high-quality imaging required for the procedure. All patients received general anesthesia and endotracheal intubation. Lowdose systemic heparin was administered at approxi-

3 108 ORFORD ET AL Ann Thorac Surg BLUNT TRAUMATIC AORTIC TRANSECTION 2003;75: Fig 1. Preoperative angiogram showing a pseudoaneurysm of the descending thoracic aorta as a result of blunt trauma. A calibration catheter can be seen in situ with markings at 1-cm intervals. guide wire. The sheathed stent graft was advanced until the tip was just proximal to the site of the transection. Stent graft position was then confirmed using digital subtraction angiography with injection through the left subclavian artery catheter. The sheath was then retracted over the graft, resulting in partial deployment of the self-expanding stent graft, with the proximal anchoring spikes not yet engaging the aortic wall. Further aortograms were performed and the stent graft moved longitudinally as required. A separate trigger wire was then removed to complete the opening of the top stent. This allowed the metal spikes to engage the aorta above the transection site. A compliant 30-mL latex balloon (Cook Australia, Queensland, Australia) was then expanded inside the stent graft to ensure an adequate seal with the aortic wall. This resulted in approximately 30 seconds of aortic occlusion, which was well tolerated in all patients. Completion digital subtraction angiographic aortography was performed to confirm good graft position and to look for the presence of a leak around the graft (endoleak), suggesting inadequate isolation of the pseudoaneurysm (Fig 3). An adequate seal was achieved in all patients without the use of additional stents. Finally, the femoral access site was repaired. Heparin was not reversed. No further anticoagulation was provided in the postoperative period. In some of the early procedures, intravenous adenosine was used to achieve temporary cardiac standstill during graft deployment. This was found to be unnecessary and was not done in later patients. mately 100 U/kg. Operating theater and cardiopulmonary bypass facilities were available for conversion to open repair if required. Vascular access was obtained by surgical exposure of the common femoral artery in all patients. A retrograde cannulation of the femoral artery was performed, and a 180-cm J wire (Boston Scientific, Boston, MA) was inserted and passed into the thoracic aorta. A 5-F, 100-cm calibration pigtail catheter (Cook Australia, Queensland, Australia) was then inserted over the J wire. Digital subtraction angiography was performed with Ultravist contrast (Schering Pty, Alexandra, Australia) to show the anatomy, size of the aorta, and morphology of the pseudoaneurysm. Most patients also had a left brachial artery sheath inserted and a J wire and catheter advanced into the aortic arch and left subclavian artery. The purpose of this access was twofold first for identification of the left subclavian artery during graft positioning and second to enable proximal forward-flow aortography. A long Amplatz Super Stiff guide wire (Boston Scientific, Boston, MA) was then inserted through the femoral sheath. The Cook-Zenith stent graft was flushed with heparin saline solution. The stent graft delivery system (20 to 24 F) was inserted under fluoroscopic control over the Amplatz Fig 2. Proximal covered Z-stent of the Cook-Zenith thoracic stent graft. Note the stainless-steel spikes protruding through the graft material. They anchor the graft to the aortic wall.

4 Ann Thorac Surg ORFORD ET AL 2003;75: BLUNT TRAUMATIC AORTIC TRANSECTION Fig 3. This completion angiogram shows successful exclusion of the pseudoaneurysm by the stent graft. Follow-Up A plain chest radiograph was obtained as a record of the stent graft skeleton and position. Follow-up imaging involving computed tomographic angiography was routinely performed before discharge from the hospital. Further computed tomographic angiographic examinations were performed at 6 and 12 months after the procedure and annually thereafter. Results In all 9 patients the aortic tear was located at the aortic isthmus or proximal descending aorta. All were treated acutely, and 8 of the 9 patients had stent graft repair within 24 hours of diagnosis (range 4 to 24 hours, mean 9 hours). The relatively short time to graft implantation was made possible by stocking a range of graft sizes at the major regional trauma hospitals. The first patient in our series was, as previously described, bridged to stent graft repair using an uncovered stent, which was placed within 48 hours of diagnosis. Because the technology was in its prototype stage, the definitive stent graft repair was not undertaken until 27days later. Common femoral or external iliac artery access was used in all patients. Stent graft deployment was successful in all 9 patients, and the aortic tear was successfully bridged and sealed in all cases. It is recommended that there be 15 to 20 mm of normal aorta proximally (the landing zone), in which to anchor the stent graft. In all of our patients the transection was in the descending thoracic aorta within 5 cm of the left subclavian artery. In 7 patients there was at least 15 mm of normal aorta between the left subclavian artery and the transection. In 2 patients it was necessary to accept partial coverage of the left subclavian artery in order to obtain an adequate landing zone. There were no periprocedural complications and no conversions to open repair. There was one early death in the series. The patient, a 91-year-old man, was involved in a high-speed motor vehicle accident, with profound hypotension and loss of consciousness at the scene. Glasgow Coma Score was 9 on arrival in the emergency room. He also suffered severe facial injuries, which required endotracheal intubation. The aortic stent graft procedure was uncomplicated, but the patient failed to regain consciousness in the intensive care unit. Although a computed tomographic scan of his brain on admission showed no acute changes, subsequent computed tomographic scanning performed on day 10 after admission showed a left occipital cerebrovascular accident. The patient died 11 days after admission. It is not known whether the etiology of this event was related to the primary trauma event or the stent graft procedure itself. There was no other death in the series. There was one major complication. One patient in whom the left subclavian artery was partially covered by the stent graft developed a cool, pulseless, but viable left hand on her fourth postoperative day. A successful left brachial artery thrombectomy was performed for a thrombus that appeared to propagate from the site of an intraoperative 7-F brachial sheath. Circulation was restored successfully and has remained patent at followup. Subsequent to this, we have used smaller, 5-F brachial access sheaths. The other patient in whom the subclavian artery was partially covered did not develop any symptoms or signs of ischemia. No other major or minor complications were observed, including no bleeding, paraplegia, infection, embolization, renal or respiratory failure, or myocardial infarction. During the follow-up period (range, 3 to 82 months; mean, 21 months), 8 of the 9 patients were alive, without any complications. In particular, there was no evidence of stent graft failure, leak, or distal migration. In all cases, the pseudoaneurysm sac has regressed. Comment 109 Blunt aortic injury has been shown as the second most common cause of death from blunt trauma, after head injury [2]. The standard treatment for aortic transection is open surgical repair using a variety of techniques; from the clamp-and-sew technique, to various forms of shunting, to partial or even full cardiopulmonary bypass. The mortality rate from emergent open surgical repair of BAI ranges from 15% to 30% in contemporary studies [2, 7, 8]. Reported mortality rates from stent graft thoracic aortic repairs range from 0% to 9% [6, 10, 11], but these procedures have been performed in patients with aortic pathology (mostly chronic aneurysms), and most were done electively. Endovascular stent graft technology has been used successfully in the infrarenal aorta since 1991 and in the thoracic aorta since Williams and associates [9] used Z-stents covered with polytetrafluoroethylene in a canine model of acute aortic rupture and concluded that stent graft treatment of aortic rupture was feasible. In the early part of our series, stent graft repair of BAI was the therapeutic option of last resort and was used only in patients whose history, age, or coexisting injuries precluded open repair. As the technology has evolved, it has become more accessible and easier to use, CARDIOVASCULAR

5 110 ORFORD ET AL Ann Thorac Surg BLUNT TRAUMATIC AORTIC TRANSECTION 2003;75: and so the indications for stent graft repair of BAI have softened significantly. There are several aspects of open aortic repair that can be affected by, or have an effect on, coexisting nonaortic injuries, rendering the operative risk prohibitively high. These can include lateral patient positioning in patients with spinal or spinal cord injuries; thoracotomy and single-lung ventilation in the presence of significant pulmonary contusions; and high-level systemic heparinization with closed head injuries, solid organ abdominal injury, or major fractures. A meta-analysis of studies of surgical treatment of acute traumatic rupture of the aorta found a higher mortality rate in patients who received systemic heparinization (18.2%) compared with those who did not receive heparin (11.9%) [13]. The physiologic effect of cardiopulmonary bypass and the systemic inflammatory response it invokes should not be underestimated in these patients, as many develop multiple organ failure. The use of the aortic cross-clamp not only decreases end-organ perfusion to various structures, such as the spinal cord, gut, and kidneys, but also increases intracranial pressure. This increase in intracranial pressure is particularly important in patients with BAI, where approximately half have a coexistent head injury. Stent grafts minimize or eliminate many of these factors that are so essential to open repair. The patient is positioned supine, and thoracotomy or one-lung ventilation is not necessary. There is significantly less anticoagulation and no aortic cross-clamping. The physiologic derangement associated with cardiopulmonary bypass is also absent. The use and duration of aortic crossclamping has been associated with postoperative paraplegia, particularly in the clamp-and-sew technique [2, 12], with incidence of 2% to 20% [13]. Mitchell and coworkers [11] reported a series of 82 chronic and acute aortic aneurysms that were repaired with a stent graft. The overall paraplegia rate in that series was 3.6%, and paraplegia was more common in those who had combined thoracic and abdominal aortic grafts. Other series using stent grafts, including our own, have reported no paraplegia [6, 10]. This should not, of course, be extrapolated to mean a zero risk of paraplegia with this procedure, as stent graft repair of aortic pathology does not allow for reimplantation of intercostal arteries. However, more than 90% of BAI occur at or around the isthmus of the thoracic aorta where there are few strategic intercostal arteries. These injuries are also able to be repaired using a relatively short stent graft, thereby minimizing the number of intercostal arteries excluded from the circulation. A stent graft requires 15 to 20 mm of normal aorta above the tear or pseudoaneurysm to allow for snug application against the wall and hence a seal. It can be difficult to find the required length of normal aorta proximal to the tear and yet remain distal to the origin of the left subclavian artery. Because of that problem, two patients in our series had to have partial covering of the left subclavian artery by the stent graft. As previously described, one of those patients developed left brachial Fig 4. This picture demonstrates the flexibility of the Cook-Zenith thoracic stent graft. This is achieved by varying the distance between rigid Z-stents and allows the graft to mold to the curve of the thoracic aorta. artery thrombosis; however, we believe this condition was more related to the large brachial access sheath used than to the partial subclavian occlusion. This hypothesis is supported by the fact that after thrombectomy, the patient has had normal circulation in the left arm, despite the stent graft position being unchanged. The other patient with partial left subclavian occlusion suffered no adverse effects. When there is an inadequate length of normal aorta between the left subclavian artery and the aortic pathology, there are several options available to the surgeon. The first is to cover the subclavian artery as required and adopt a wait-and-see policy regarding the status of the left arm. The presence of subsequent ischemia will depend on the adequacy of collateral flow from various sources, including the left vertebral artery through the circle of Willis. Most patients will require no further intervention and will suffer no ischemic symptoms. Inevitably, however, a few patients will require a

6 Ann Thorac Surg ORFORD ET AL 2003;75: BLUNT TRAUMATIC AORTIC TRANSECTION left carotid subclavian artery bypass, which is a relatively simple procedure. Another option is to use a graft with a prefashioned side hole through the graft material, which can be positioned over the origin of the subclavian artery. We did not encounter any other major morbidities in our series, including complications such as perigraft leak, graft migration, bleeding, infection, distal embolization, myocardial infarction, or renal failure; however, the number of patients in our series was small. One of the challenges in using stent graft technology in the proximal thoracic aorta is the curve of the distal arch, which can be highly angulated. In previous series of thoracic stent grafts, problems with the device being too rigid to negotiate such a curve have been reported. This has sometimes resulted in a poor proximal seal and subsequent perigraft leaks [6]. The Cook device used in 8 of 9 cases in this series now has three grades of flexibility allowing contouring to the curved aorta. This is achieved by varying the distance between the rigid Z-stents. We encountered no proximal graft leaks using this device (Fig 4). The relatively large gauge of the graft delivery device can be of concern in patients with small-caliber or tortuous femoral and iliac vessels. Although the delivery sheath is semirigid, by carefully negotiating tortuous iliac arteries first with a stiff guide wire, these vessels often can be straightened enough to feed the stent graft with minimal hazard. If the femoral vessels are too small in caliber or have significant atheromatous disease, it is possible to use iliac arteries or even the distal aorta for access. Patients with extreme aortic size can be difficult to treat acutely. At present, the two major trauma hospitals in our city stock a selection of thoracic stent grafts ranging from 22 to 42 mm in diameter. In most patients, this range enables endograft implantation to occur emergently. Any graft outside this size range would require special delivery or custom manufacturing, which would delay implantation by approximately 1 week. Although the longevity of the stent grafts is still not known, midterm results up to 10 years are promising. We have occasionally placed stent grafts in younger patients with BAI. If durability becomes an issue in the future, these patients could require elective removal of the stent graft. In certain patients this might still be preferable to an emergent open repair, which can carry a relatively high morbidity and mortality risk. The trauma patient who receives a BAI presents a high surgical risk. Stent graft repair is an evolving technology that offers a safe and effective alternative to standard surgical repair. Our limited experience also shows that it can be used in the acute trauma setting, with an acceptable time between diagnosis and repair. Further follow-up is mandatory, however, particularly in relation to graft durability, before this technology can be recommended to all patients. If stent graft repair continues to fulfil its promise as a valuable tool in aortic surgery, it could become the treatment of choice in severely injured patients with BAI. References Smith RS, Chang FC. Traumatic rupture of the aorta: still a lethal injury. Am J Surg 1986;152: Fabian TC, Richardson JD, Croce MA, et al. Prospective study of blunt aortic injury: multicenter trial of the American Association for the Surgery of Trauma. J Trauma 1997;42: Parmley LF, Mattingly TW, Manion TW, et al. Nonpenetrating traumatic injury of the aorta. Circulation 1958; 17: Parodi JC, Palmaz JC, Barone HD. Transfemoral intraluminal graft implantation for abdominal aortic aneurysms. Ann Vasc Surg 1991;5: Dake MD, Miller DC, Semba CP, et al. Transluminal placement of endovascular stent grafts for the treatment of descending thoracic aortic aneurysms. N Engl J Med 1994; 331: Kato N, Dake MD, Miller DC, et al. Traumatic thoracic aortic aneurysm: treatment with endovascular stent-grafts. Radiology 1997;205: Turney SZ, Attar S, Ayella R, Cowley RA, McLaughlin J. Traumatic rupture of the aorta: a five-year experience. J Thorac Cardiovasc Surg 1976;72: Cowley RA, Turney SZ, Hankins JR, Rodriguez A, Attar S, Shanskar BS. Rupture of the thoracic aorta caused by blunt trauma. J Thorac Cardiovasc Surg 1990;100: Williams DM, Andrews JC, Chee SS, Marx MV, Abrams GD. Canine model of acute aortic rupture: treatment with percutaneous delivery of a covered Z stent work in progress. J Vasc Interv Radiol 1994;5: Rousseau H, Soula P, Perreault P, et al. Delayed treatment of traumatic rupture of the thoracic aorta with endoluminal covered stent. Circulation 1999;99: Mitchell RS, Miller DC, Dake MD. Stent-graft repair of thoracic aortic aneurysms. Semin Vasc Surg 1997;10: Marin ML, Veith FJ, Cynamon J. Initial experience with transluminally placed endovascular grafts for the treatment of complex vascular lesions. Ann Surg 1995;222: Von Oppell UO, Dune TT, De Groot MK, Zilla P. Traumatic aortic rupture: twenty-year metaanalysis of mortality and risk of paraplegia. Ann Thorac Surg 1994;58: CARDIOVASCULAR DISCUSSION DR ALAN D. HILGENBERG (Boston MA): I enjoyed your presentation. I agree that stent grafting will be the way most traumatic aoric disruptions are treated once we have grafts and delivery systems that are easy to use. I have two questions. Were there any patients in whom you intended to place a stent graft but were unable to because of proximity to the left subclavian artery? Second, are there any patients in whom you would not use this technique because you were concerned about fragility of the pseudoaneurysm and the possibility of rupture during instrumentation for placement of the graft? DR ORFORD: In this study there were no exclusions because of proximity to the left subclavian artery. There will be patients in whom the location of the transection will require either partial

7 112 ORFORD ET AL Ann Thorac Surg BLUNT TRAUMATIC AORTIC TRANSECTION 2003;75: or total covering of the left subclavian artery. This provokes concern from many surgeons. However, as described in the article, this does not seem to present as great a problem as was feared. In our experience of all thoracic stent grafts, ischemia of the left arm is rare. When it occurs it can be corrected by the relatively simple carotid-to-subclavian artery bypass. Yes, there is a small theoretical risk of rupture of the pseudoaneurysm during placement of the stent graft. However, the open technique has real risks of rupture during the exposure and control of the aorta. The passage of the guide wires, catheters, and graft delivery system is controlled and done with high-quality imaging. Most patients with aortic transection will have a relatively normal aorta above and below the area of the pseudoaneurysm. Overall aortic fragility should not be a problem. DR J. ERNESTO MOLINA (Minneapolis, MN): This method will be become ideal if it is effective. I have several questions. When we tried to insert larger-size graft sizes like the ones you used, as you indicated, the size of the recipient vessel, the common femoral artery, the external iliac artery, had to be large enough to take it. So, in some cases, did you have to expose the iliac arteries, the common iliac, to pass this device upwards? The second question pertains to the material. I believe that what you were using is still woven graft Dacron. Have you tried any of the Gore-Tex? It seems to be thinner and easier to deploy. The other question is, have you used ultrasound to position the graft? That is what we were doing. It looks like you position the graft using aortography or arteriography. And we use ultrasound, which works remarkably well, and you do not have to use contrast medium. And finally, have you tried to anchor the grafts in the lip of the left subclavian artery, or have most of the grafts been anchored below that level? In the thoracic aorta it is easier to have a dislodgement or migration of the graft versus the infrarenal type of repairs. DR ORFORD: We did not need to expose the iliac arteries in any of our cases. All had common femoral, external iliac arteries of at least 8 mm in diameter. This size will accept the 20- to 24-F delivery system. Exposure of the common iliac arteries could be needed if the femoral arteries are too small or tortuous. That has been more of an issue in our patients with degenerative aneurysms. These Cook-Zenith grafts have a Dacron fabric cover and we have not used PTFE. We have, on occasion, used transesophageal echocardiography, but we have not used intravascular ultrasound. We accept that it is a valid method of guiding the positioning of the graft and identification of the pathology. These Cook-Zenith grafts have quite effective anchoring spikes. We have not tried to use the orifice of the left subclavian artery as an anchor site. In our series distal displacement has not occurred. DR JOHN S. IKONOMIDIS (Charleston, SC): You present a study of 9 patients who underwent endovascular repair. They are transections from three hospitals over an 8-year period. I would think that there must have been more than 8 patients with traumatic aortic tears in three institutions over this time period. What is the denominator? DR ORFORD: I cannot give a precise number of all aortic transections seen at the three hospitals over the 8 years. In the early stages, this technique was used in the minority of cases and usually where other injuries made open repair extra risky. Later on, with experience and more confidence, the percentage of cases treated with a stent graft increased. The denominator would be of the order of 40 to 50 cases. Fabian s large series of 274 patients with aortic transection obtained by 50 centers over 2.5 years demonstrates that no one sees a large number of these injuries because of the high prehospital mortality rate. DR ANDREW CARNEY (Chicago, IL): My question is regarding the construction of the stent. Is it self-expanding or is it expanded with a balloon? And if it is expanded by a balloon, does the balloon cover the entire length of the stent or just one end? Can you use the entire length of the stent balloon on the straight of the aorta? When it comes to the curve, does the inflated balloon create problems? DR ORFORD: It is a self-expanding stent. A 30-mL compliant latex balloon is used to mold the stents at the end of deployment. This balloon is relatively short and is used to try to ensure complete apposition of the top stent within the aorta above the transection. We have not had problems negotiating the aortic curve with this balloon.