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Moffatt-Bruce S Di , Mitchell R Si . Endovascular Therapy for the Treatment of Thoracic Aortic Disease.
Cohn Lh, ed. Cardiac Surgery in the Adult. New York: McGraw-Hill, 2008:1299-1308.

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CHAPTER 55

Endovascular Therapy for the Treatment of Thoracic Aortic Disease

 Susan D. Moffatt-Bruce/ R. Scott Mitchell

HISTORY
NATURAL HISTORY AND SURGICAL OUTCOMES OF THORACIC AORTIC DISEASES
    Thoracic Aortic Aneurysms
    Thoracic Aortic Dissections
    Penetrating Atherosclerotic Ulcers and Intramural Hematomas of the Thoracic Aorta
    Thoracic Aortic Trauma
ENDOVASCULAR THERAPY OF THE THORACIC AORTA
    Technical Development
    Clinical Results Using Endovascular Stents for Thoracic Aortic Disease
        Thoracic aortic aneurysms
        Thoracic aortic dissection
        Penetrating atherosclerotic ulcers and intramural hematomas
        Thoracic aortic trauma
CONCLUSIONS
References

   INTRODUCTION
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Patients with thoracic aortic disease are a difficult population to treat, as they frequently consist of an aged population with multiple comorbidities. The modern surgical treatment of thoracic aortic diseases began in the 1950s when successful treatment using segmental resection and graft replacement was reported by Swan, Lam, DeBakey, and Etheredge.1–3 Thereafter, DeBakey and Cooley reported the first successful repair of an ascending aortic aneurysm using cardiopulmonary bypass.4 Our understanding of the pathophysiology and natural history of thoracic aortic disease has evolved, which has expanded our treatment choices.5,6 In addition, improvements in diagnostic capabilities, surgical techniques, and perioperative care have resulted in improved outcomes, even as the risk profile has increased. Nonetheless, operative intervention in this patient population frequently results in substantial mortality and long-term morbidity.7,8 The concept of using an endovascular stent-graft in patients with thoracic aortic disease emerged a decade ago, propelled by the desire to avoid surgical risk as well as to induce reconstructive modeling of the diseased aorta by initiating a natural healing process through exclusion and depressurization of the aneurysmal sac.9 In an effort to improve outcomes in the treatment of patients with thoracic aortic disease, endovascular stent-graft technology has rapidly followed applications on the abdominal aorta.10,11 Originally devised for high-risk patients with multiple comorbidities, thoracic stent-graft applications are being expanded to young and old patients with a variety of pathologies, including thoracic aortic aneurysms, aortic dissections, intramural hematomas, penetrating atherosclerotic ulcers, and thoracic aortic trauma.12–19 Initial reports using these endovascular stent-grafts have been encouraging, but long-term outcomes are unknown, and the necessity for long-term follow-up, with its attendant expense, has raised serious concern.20–22


   HISTORY
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Endovascular stent-graft technology was initially envisioned for use in abdominal aortic aneurysms.23 Introduced by Parodi, balloon expandable stents attached to the ends of a vascular tube graft were utilized to exclude the aneurysm sac. There were several attractive features of this concept, including the introduction of the device from a peripheral site, eliminating the necessity for an invasive laparotomy, the avoidance of aortic cross-clamping and its requisite physiologic perturbations, and minimizing respiratory complications. Lastly, hospital stay and recovery time could be potentially shortened.

At Stanford University Medical Center, a collaborative effort between interventional radiologists and cardiovascular surgeons proved highly synergistic, and resulted in the manufacture and clinical use of thoracic stent-grafts. Work had commenced years earlier with the use of uncovered stents for the repair of aortic dissections in an animal model. The stent-grafts were manufactured using self-expanding Gianturco Z stents (Cook Co., Bloomington, Ind), which were fastened together and then covered with a woven Dacron graft (Meadox-Boston Scientific, Natick, Mass; Fig. 55-1). Institutional review board (IRB) approval was initially obtained for a high-risk study using endovascular stentgrafts for the treatment of thoracic aortic aneurysms in patients who were deemed not to be surgical candidates.24 A total of 13 patients underwent transluminal endovascular grafting of thoracic aortic aneurysms with a mean diameter of 6.1 cm. The stent-grafts, custom-designed for each patient, were constructed of self-expanding stainless steel stents covered with woven Dacron grafts. Placement of these stents was successful in all patients with thrombosis of the aneurysm surrounding the stent occurring in 12 of the 13 patients. As reported, at 1 year there were no deaths, paraplegia, stroke, distal embolization, or infection.24 It was therefore concluded that these preliminary results demonstrated that endovascular stent-graft repair was safe in highly selected patients.


Figure 1
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  		Figure 55-1 First-generation stent-graft assembled from articulated Z stents and covered with a woven Dacron tube graft.

 
This feasibility trial led to the extension of the IRB approval for the treatment of 103 patients with thoracic aortic aneurysms.25 Of these 103 patients, 60% were unsuitable candidates for conventional open surgical repair and therefore deemed inoperable. Again, these patients underwent repair of a descending thoracic aortic aneurysm using "home-made" or first-generation stent-grafts fabricated from self-expanding Z stents covered with woven Dacron tube graft. Complete aneurysm thrombosis was achieved in 83% of patients. Early mortality was 9% and was significantly associated with preoperative cerebrovascular accidents and myocardial infarctions. Major perioperative morbidity included paraplegia in 3 patients, cerebrovascular accidents in 7 patients, and respiratory insufficiency in 12 patients. Treatment failure occurred in 38 of the 103 patients, and 5 patients required late operative therapy for endoleaks associated with aneurysm enlargement. Actuarial survival was 81% at 1 year and 73% at 2 years. Given the high-risk nature of this patient population, these first-generation results were deemed satisfactory. It was, however, recognized that mortality and morbidity occurred frequently and that long-term follow-up was necessary to fully define the efficacy of an endovascular approach in thoracic aortic aneurysm therapy. Subsequently, in 2004, midterm results were reported for these 103 patients treated with the first-generation stent-grafts.26 Overall actuarial survival was dismal; 82%, 49%, and 27% at 1, 5, and 8 years, respectively. However, the survival of the potentially operable candidates was 93% and 78% at 1 and 5 years, respectively, as compared to 74% and 31% at 1 and 5 years, respectively, in those patients designated as inoperable. In patients judged not to be surgical candidates, life expectancy, despite endovascular therapy, was therefore quite bleak, and has raised concerns whether any surgical therapy is appropriate for these patients. Further results revealed that 11 of the 103 patients suffered late aortic rupture at the site of endovascular treatment. This was a very sobering finding considering that open surgical graft replacement has been associated with durable long-term results with only a negligible late hazard of anastomotic problems. However, it must be remembered that this study involved the use of a relatively primitive first-generation device, with a fairly steep learning curve.

Extending the use of the endovascular stent-grafts to the treatment of complicated acute aortic dissections of the descending thoracic aorta, Dake and associates reported their findings in the New England Journal of Medicine in 1999.27 Again these stents were the first-generation "home-made" devices described above. Placement of the stents across the primary entry tears was technically successful in all patients, with correction of malperfusion. Complete thrombosis of the false lumen occurred in 79%. The early mortality rate was 16%, which reflected late referral, with established intestinal gangrene, and another patient with Ehlers-Danlos syndrome, perhaps a poor candidate for endovascular repair. Favorable clinical results persisted out to a mean follow-up of 13 months.

These pioneering efforts at the Stanford University Medical Center established some interesting concepts. Namely, that these were complex patients with complex aortic problems, and that endograft therapy for aneurysmal disease was effective, potentially with reduced morbidity, but with uncertain long-term durability. Improved results could likely be obtained with more sophisticated devices, and endograft repair could effectively reverse malperfusion syndromes in complicated type B aortic dissections.


   NATURAL HISTORY AND SURGICAL OUTCOMES OF THORACIC AORTIC DISEASES
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Thoracic Aortic Aneurysms

Approximately 50% of all thoracic aortic aneurysms are located in the descending aorta; these aneurysms commonly arise at the level of the left subclavian artery and are often atherosclerotic in nature.28 The size-rupture correlation has been demonstrated by studying the natural history of these aneurysms as reported by Clouse and associates, using the Olmstead County database, in which thoracic aortic aneurysms have an overall 5-year rupture risk of 30%.29 The Mount Sinai group has identified clinical variables that determine the risk for rupture, which include increasing age, presence of chronic obstructive pulmonary disease, maximal thoracic and abdominal aneurysm diameter, and the presence of pain.30 The Yale Aortic Diseases Group has documented rupture and dissection of ascending or arch aneurysms at a median size of 6 cm and descending or thoracoabdominal aneurysms at a median size of 7.2 cm.6 Furthermore, the Yale group has reported that the mean rate of rupture or dissection is 2% per year for small aneurysms, 3% for aneurysms 5.0 to 5.9 cm, and 6.9% for aneurysms of 6.0 cm and larger. Using proportional hazards regression, the odds ratio for rupture is more than 25 times higher in patients with aneurysms of 6.0 cm or greater than in those with aneurysms in the range of 4.0 to 4.9 cm.31

Open surgical graft replacement is the traditional treatment for these patients. The presence of comorbidities in this specific population increases the surgical risks, especially in the case of emergency intervention. However, with increasing experience, very good surgical morality rates in the 5 to 10% range have been reported from experienced centers.32–34 Similarly, paraplegia and paraparesis rates range from 3 to 16%, with predictive factors including extent of resection, emergency operation, renal dysfunction, distal circulatory support, and cerebrospinal fluid drainage.35–37 Nevertheless, 5-year survival rates between 60 and 80% have been achieved in recent surgical series.32–34

Thoracic Aortic Dissections

Acute aortic dissection is the most common catastrophe affecting the thoracic aorta, with many more people dying of rupture of dissections than of aneurysms. Although poorly understood, a primary intimal tear allows a high-pressure entry of blood into the subadventitial space, which then rapidly propagates proximally and distally. With the Stanford classification system, type A connotes involvement of the ascending aorta. The high mortality rate of 50% at 48 hours usually mandates emergent surgical repair. Conversely, type B dissections involve the descending thoracic aorta, and are typically managed with anti-impulse therapy, with surgical management reserved for those patients presenting with complications, namely intractable pain, rupture or impending rupture, or visceral or limb malperfusion syndromes.38–41

The Stanford group has compared the actual survival of medically and surgically treated type B dissection over a 36-year period. The actuarial survival estimates for all patients were 71%, 60%, 35%, and 17% at 1, 5, 10, and 15 years, respectively, and were similar for the medical and surgical patients.40 The hope for benefits of avoiding the late complications from false-lumen expansion following surgical repair was not demonstrated in this follow-up.

The utility of thoracic endografts in chronic dissections is even more unclear. Given the multiple septal fenestrations, and the relative immobility of the chronically dissected septum, it seems unlikely that stent-graft insertion could realistically confer any long-term benefits, with the possible exception of a very focal aneurysmal false-lumen dilation distant from septal fenestrations near the level of the diaphragm.

Penetrating Atherosclerotic Ulcers and Intramural Hematomas of the Thoracic Aorta

Penetrating atherosclerotic ulcers (PAUs) and intramural hematomas (IMHs) are distinct pathologic entities now being diagnosed with increasing frequency.42 PAUs probably represent rupture of an atherosclerotic plaque, with penetration into the internal elastic lamina of the aorta, and may be associated with proximal and distal progression of an intramural hematoma. Conversely, IMH not associated with a penetrating ulcer may result from the spontaneous rupture of aortic vasa vasorum that may initiate hemorrhage into the aortic media, and may progress to an intimal tear and classic aortic dissection.42

In the ascending aorta, IMH, with or without PAU, frequently progresses to frank dissection during the acute phase, and thus warrants early ascending aortic replacement. The highest mortality rate among patients with IMH is associated with ascending aortic involvement.43,44 Experience has therefore suggested that a more aggressive approach with early surgery is warranted in those patients who have ascending aortic involvement or in those who have a coexisting aneurysm with IMH.44

In the descending thoracic aorta, pure IMH in the absence of aneurysmal change is usually treated with aggressive control of hypertension. For IMH with PAU, increasing maximal depth and maximal diameter were both associated with disease progression, in addition to persistent pain and increasing pleural effusion.45 The risk of aortic rupture is higher among patients with PAU by almost 30% than with patients with type A or B dissection.42 However, the progression of PAU is slow and is associated with a low incidence of acute rupture or other life-threatening events. Among patients with PAU who are not treated surgically, the natural history would indicate that the majority of patients will have aortic enlargement with the formation of saccular or fusiform pseudoaneurysms and intramural thrombus.43

Thoracic Aortic Trauma

Trauma is the most common cause of nondegenerative disease affecting the thoracic aorta. According to autopsy series, 36 to 54% of disruptions occur at the aortic isthmus, 8 to 27% involve the ascending aorta, 8 to 18% occur in the arch, and 11 to 21% involve the distal descending aorta.46 Blunt trauma is commonly a catastrophic injury with only approximately 20% surviving to hospital admission. Mortality following admission ranges from 39 to 73% and is frequently the result of other major injuries.47 The other multiple injuries a patient may experience almost invariably limit operative approaches and timing. All operations involving the thoracic aorta pose some risk of ischemic injury to the spinal cord, which is a dreaded complication in a predominantly young population. In addition, the immediacy of the operation associated with traumatic injury may require inexperienced surgeons to deal with complex pathology.46 Fortunately, in the past decade there has been increased understanding, suggesting that for some patients without radiographic signs of impending rupture, that permissive hypotension may be an effective temporizing strategy, allowing operative intervention after a patient has recovered from serious brain or lung injury that may have compromised immediate operative management.


   ENDOVASCULAR THERAPY OF THE THORACIC AORTA
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Technical Development

The first stent-grafts used at Stanford were manufactured using 2.5-cm self-expanding Gianturco Z stents (Cook Co., Bloomington, Ind), which were fastened together and then covered with a woven Dacron graft (Meadox-Boston Scientific, Natick, Mass; see Fig. 55-1). These stent-grafts were oversized approximately 10 to 15% above the cross-sectional diameter ascertained by computed tomography (CT) in an effort to obtain sufficient radial force to achieve an endoseal and prevent stent-graft migration. A minimum of 2 cm of normal aorta was required for adequate fixation, otherwise referred to as the "landing zone," both proximally and distally. The covered stent was loaded into a delivery capsule which required femoral and iliac arteries greater than 8 mm to allow the introduction of a 28 F delivery sheath. This dilator contained a sheath that had been previously placed over a super-stiff guidewire and was positioned proximal to the point of deployment. Once this was achieved, the compressed stent-graft was advanced into the sheath and deployed by using a "pusher" rod. Devices were limited to a maximal diameter of 40 mm in that aortas larger than 37 mm in diameter were themselves aneurysmal and unlikely to serve as stable attachment zones. Other anatomic constraints of these early "home-made" or first-generation stent-grafts that precluded secure fixation included acute angulation at the distal arch, and severe sigmoid-like tortuosity coursing through the diaphragmatic crura, reflecting the relative inflexibility of these early delivery systems.

The advent of this new stent-graft technology required a new terminology for endoleaks that allowed blood to leak around or through the stent-graft, thus allowing the aneurysmal sac to remain pressurized. Type I endoleaks occur at the proximal or distal attachment sites, and signify a failure to achieve a hemostatic seal at these implantation sites.14,24,25 Type II endoleaks denote a communication between a branch vessel and the excluded aneurysm sac. These usually occur from a back-bleeding inferior mesenteric artery in the abdomen, or intercostal artery in the chest. Type III endoleaks originate from the middle graft sections, and are usually caused by disruption of graft-to-graft overlaps, or by leakage through the graft itself. Type IV endoleaks are characterized by an increase in size of the aneurysm sac in the absence of an identifiable patent branch vessel, variously referred to as "endotension."

Years of experience with endovascular abdominal aorta repair and follow-up of thoracic aortic repairs has yielded important information for improved stent-graft technology.11,48,49 Commercially produced second- and third-generation stent-grafts are more flexible and have a lower profile, and thereby allow use of a smaller introducer sheath in the femoral vessels. Experience has shown that tapered, flexible, over-the-wire delivery systems that are less than 20F in diameter rarely fail to traverse tortuous femoral or iliac arteries. Hooks at the proximal end of the stent-graft appear to provide the most secure means of attachment, but may be suboptimal for treating patients with acute dissections. It is likely that different grafts may be developed for different pathologies, with devices for dissections being devoid of hooks or uncovered metal components. For traumatic aortic lacerations, smaller device sizes are necessary, as these are usually nonatherosclerotic normal-sized aortas with small access vessels. Ideal device components have been broken down into three categories: delivery system, graft material, and metal frame.50 The delivery system should be of low profile, flexible for maneuverability, rigid enough to resist kinking, and hemostatic during use. The graft material should also be of low profile, strong and durable, and reasonably thin. The graft metal frame should provide high column strength and ductility, be compression and kink resistant from external forces, radiopaque, and corrosion and fatigue resistant. Nitinol is now used for the stent material in the majority of grafts and the graft material is usually polytetrafluoroethylene (PTFE) or polyester.

Currently, the Gore Excluder TAG system (W. L. Gore, Sunnyvale, Calif) is the only Food and Drug Administration (FDA)-approved graft. However, the Talent and Valiant systems (Medtronic, Sunrise, Fla) and the Zenith system (Cook-Cardiovascular, Bloomington, Ind) are being used with special release consents required (Fig. 55-2). These second-and third-generation endoprostheses are more flexible and have a lower profile with smaller delivery systems that can be inserted easily to treat a number of thoracic aortic pathologies.


Figure 2
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  		Figure 55-2 Second-generation commercially manufactured thoracic aortic stent-graft. The thoracic Excluder TAG system by W. L. Gore contains a thin-walled PTFE graft covered by a nitinol exoskeleton.

 
Clinical Results Using Endovascular Stents for Thoracic Aortic Disease

Thoracic aortic aneurysms

The Stanford group originally reported their outcomes of endovascular stent-graft placement in 13 patients back in 1994.24 These preliminary results demonstrated that endovascular stent-graft repair was safe in highly selected patients with descending thoracic aneurysms (Fig. 55-3). This paper was followed by a report of 103 patients treated with endovascular stent-graft technology as part of a 5-year clinical trial. Using first-generation "home-made" stent-grafts, early mortality was reported as 9%, but a stroke rate of 7% and paraplegia rate of 3% were also reported. More recently, the Stanford group has reported 5- and 10-year results and has identified risk factors for adverse late outcomes.26 Overall survival was 82%, 49%, and 27% at 1, 5, and 8 years. This included patients who were deemed both operable and inoperable. In the group of patients who were deemed operable and could have undergone open repair of their descending thoracic aneurysms, the survival was 93% and 78% at 1 and 5 years, compared with 74% and 31% in those deemed inoperable. Independent risk factors for death were older age, previous stroke, and designation as a nonoperative candidate. Freedom from aortic reintervention and treatment failure at 8 years was only 70% and 39%, respectively. Ultimately these findings suggested that by using the first-generation stent-grafts, good operative candidates had satisfactory outcomes. Conversely, those deemed inoperable had bleak outcomes, perhaps no better than if they had not been treated at all. Therefore the question of intervening at all in this cohort of patients comes into question, with many questions concerning resources and quality of life being asked. This study also revealed that late aortic complications were detected in nearly 30% of patients, which re-emphasizes the importance of follow-up serial imaging surveillance.


Figure 3
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  		Figure 55-3 (A) Angiogram of a descending thoracic aortic aneurysm suitable for stent-graft repair. (B) Angiogram illustrating successful exclusion of the aneurysm sac with a thoracic stent graft.

 
In January 2005 the phase II multicenter trial of the Gore Excluder TAG thoracic endoprosthesis results were reported.51 This multicenter prospective nonrandomized trial was conducted at 17 sites and compared results of stent-graft repair of descending thoracic aortic aneurysms in 140 patients with results of open repair in 94 patients. Strict inclusion and exclusion criteria attempted to ensure comparability of both groups. Follow-up CT scans were obtained at 1, 6, 12, and 24 months. For stent-graft patients, operative blood loss, renal failure, paraplegia, and mortality rates were all significantly less than for the open repair group. Interestingly, stroke rates were about equal in both groups. ICU stay and total hospital stay, and time to return to normal activity were 50% shorter for the stent-graft group than for those with open repair. Although stent-graft patients maintained an advantage from aneurysm-related mortality out to 2 years (97 versus 90%), interestingly, all-cause mortality was similar between groups at 2 years, which is similar to results of recent randomized trials in abdominal aortic aneurysm stent-graft trials.52

Ricco and colleagues have most recently reported on an independent nationwide study in France using a variety of endovascular devices to treat descending thoracic aortic aneurysms in the majority of cases.53 The Gore Excluder TAG (Gore) and Talent (Medtronic) devices were used in 84% of patients and an operative mortality of 10% was reported. A complication rate of 21% was reported, which included endoleaks in 16% of patients that were fatal in three patients. The 6-month survival rate was 86% and freedom from other complications (other than endoleak) was only 63% at 6 months. This study, involving 166 stent-graft repairs, performed in 29 centers and using 6 different types of endoprostheses, demonstrated that stent-graft repair of thoracic aortic disease could be performed with acceptable morbidity and mortality, at short-term follow-up. They do, however, qualify their conclusions by stating that endograft treatment of thoracic aortic aneurysms should continue to be used in an investigative setting.

Thoracic aortic dissection

For dissections originating distal to the origin of the left subclavian artery, referred to as Stanford type B dissections, aggressive antihypertensive therapy has been the mainstay of treatment.40 For complicated dissections, however, including rupture, impending rupture, intractable pain, rapid expansion, or malperfusion syndromes, surgical intervention is indicated. In these instances, however, surgical mortality has been reported to be as high as 50 to 60%. Endograft coverage of the primary intimal tear, redirecting flow into the true lumen, would appear to be an ideal application of this endograft technology. The Stanford group, with their colleagues in Mie University in Japan, reported the use of the first-generation stent-grafts in 19 patients with complicated type B aortic dissections. Placement was successful in all patients, and revascularization of ischemic branch vessels occurred in 76% of cases. There were three hospital deaths, two of which resulted from late referral, and one in a patient with Ehlers-Danlos syndrome who was perhaps untreatable by any modality. Although the follow-up was short, there were no incidences of aortic rupture or aneurysm formation, and a single-lumen aorta to the level of the stent-graft was achieved in the majority of patients27 (Fig. 55-4).


Figure 4
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  		Figure 55-4 (A) Intravenous contrast-enhanced CT scan of the upper abdomen demonstrating an aortic dissection with compression of the true lumen. (B) Angiogram of the thoracic aorta demonstrating a type B dissection involving the descending thoracic aorta. (C) CT scan of the abdomen and (D) angiogram of the descending thoracic aorta after stent-graft implantation into the true lumen in the proximal descending thoracic aorta.

 
More recently, Kato and associates reported their use of endovascular stent-grafts for the treatment of aortic dissections, both acute and chronic.54 Significant findings were that although 2 of the 38 treated patients died early, there were no late deaths during a mean follow-up of 27 months. Furthermore, early and late complication rates were 33% and 36%, respectively, in patients with acute dissections, whereas rates were 4% and 0%, respectively, in patients with chronic dissections. These complications included endoleak and aneurysmal degeneration of the aorta in 25% of patients. Only one case of paraplegia was reported. This group therefore concluded that acute dissections could be treated with endovascular stent-grafts but that stent-graft repair should be delayed for acute Stanford type B dissections without complications.

Currently, a randomized trial is underway to compare the 2-year outcome of uncomplicated Stanford type B aortic dissections treated by endovascular implantation of a Medtronic Talent stent-graft to best medical treatment. This trial, referred to as the INSTEAD trial (INvestigation of STEnt in patients with type B Aortic Dissection) will measure all-cause mortality as the primary outcome; secondary outcome variables will include conversion to stent and/or surgery, thrombosis of the false lumen, cardiovascular morbidity, aortic expansion, quality of life, and hospital stay. Given the relatively low 1-year mortality for uncomplicated type B dissections, the benefit for any interventional strategy may be difficult to prove. Results should be available in late 2006.55

Penetrating atherosclerotic ulcers and intramural hematomas

IMH of the aorta is attracting growing interest as a variant of aortic dissection.44 The evolution from IMH to overt dissection or rupture is not well understood and currently pure IMH of the descending thoracic aorta is not amenable to stent-graft repair. IMH of the ascending aorta is currently a surgically treatable disease with early intervention being warranted.43,44 IMH, however, is often associated with or even precipitated by PAUs of the descending thoracic aorta.42 Therefore, covering the PAU with a stent-graft may limit the progression of the IMH and allow healing to occur.19,42 Unfortunately, even with successful stent-graft implantation using both first- and second-generation grafts, retrograde aortic dissection, new ulcer formation, and endoleaks have been noted in a significant percentage of patients, emphasizing the diffuse and severe nature of this disease.56–59

The Stanford group has reported their mid-term results treating PAU of the descending thoracic aorta, with an average of 51 months of follow-up19 (Fig. 55-5). Using both first-generation and second-generation commercial devices, 26 patients were treated, 14 of whom were deemed nonoperative candidates. The primary success rate was 92% with actuarial survival estimates of 85%, 76%, and 70% at 1, 3, and 5 years, respectively. Perioperative mortality was 12%. Increasing aortic diameter and female gender were determinants of treatment failure. These risk factors reflect the importance of careful patient selection based on anatomic criteria and clinical factors. In addition, long-term follow-up with serial CT angiography is necessary to detect late complications.


Figure 5
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  		Figure 55-5 Three-dimensional CT scan of a giant penetrating ulcer involving the descending thoracic aorta that is perfectly suited to treatment with a thoracic stent-graft.

 
Thoracic aortic trauma

Aortic injuries secondary to nonpenetrating trauma are lethal lesions, with 80 to 90% of patients dying in the hour following the accident.60 Urgent surgical graft replacement of the aorta is the standard treatment, but these patients frequently have other major injuries, including closed head injuries, pulmonary contusions, and other solid organ injuries that limit open surgical repair. Several authors have reported the improved results of stent-grafts over open repair for these acute injuries.61,62 Although long-term durability may be a concern, there appear to be significant short-term benefits.62,63 The major difficulty at present is the absence of thoracic stent-grafts sufficiently small in diameter as to be appropriate for these relatively normal-sized aortas, frequently less than 20 to 22 mm in diameter. Because of these limitations, our current strategy is to allow permissive hypotension, intervening only for those patients with signs of impending rupture, those with increasing mediastinal hematoma or hemothorax, or persistent pain. For these patients, conventional repair is preferred, using heparin-bonded circuits, unless closed head injury or pulmonary contusions contradict. Stent-graft repair is utilized for those patients in whom a conventional repair could not be tolerated.

The Stanford group has reported on their mid-term results of stent-graft repair of chronic traumatic aneurysm of the descending thoracic aorta64 (Fig. 55-6). Among 15 patients treated with either first- or second-generation stent-grafts, deployment was successful in all patients without need for surgical conversion. No neurologic complications were reported. Actuarial survival estimates at 1 and 6 years were 93% and 85%. Freedom from reintervention on the descending thoracic aorta was 93% and 70% at 1 and 6 years, respectively. Freedom from treatment failure at 1 and 6 years was 87% and 51%, respectively. They therefore concluded that stent-grafts are safe in patients with chronic traumatic aneurysms, and are associated with satisfactory but not optimal mid-term durability. They state that younger, low-risk patients should be offered conventional, open surgery and stent-grafting should be reserved for those patients who are at prohibitive operative risk.64


Figure 6
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  		Figure 55-6 (A) Thoracic angiogram demonstrating a contained rupture of the descending thoracic aorta in a trauma victim. (B) Thoracic angiogram revealing repair of the aortic rupture with a thoracic stent-graft.

 

   CONCLUSIONS
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Despite the many advances in the field of endovascular surgery, stent-grafting the thoracic aorta remains in a developmental phase.20,65 This evolving technology has been applied to the treatment of thoracic aortic aneurysms, aortic dissections, IMHs, and PAUs, and traumatic injuries. The early outcomes are encouraging but middle- and long-term outcomes are a concern. Although device technology has certainly improved over the past 20 years, all devices are limited by their own structural flaws, lack of conformability, limited array of sizes, length of landing zones necessary to allow secure fixation, and structural integrity to withstand the severe physiologic milieu present in the thoracic aorta. Given the variable pathologies, it is likely that many different stent-graft configurations will be necessary for the various clinical indications.

Of utmost importance in the treatment of thoracic aortic pathology with stent-grafts is strict and dedicated follow-up. Patients need to be seen on a routine basis and new symptoms or findings need to be investigated. Serial CT angiography is an excellent tool to follow the areas of the thoracic aorta treated with the endograft, as well as to follow the evolution of the untreated portions of the aorta. Follow-up will allow endoleaks and device migration to be detected, and may further define the natural history of endovascular treatment strategies.

Diseases of the thoracic aorta pose a significant challenge to the surgeon because of the complexity of the disease and the characteristics of the patient population. Current literature supports the early advantage of endovascular technology in well-suited patients, but longer follow-up and results of ongoing trials will help define the indications for their use in the future.


   References
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