| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Ann Thorac Surg 2002;74:S1818-S1820
© 2002 The Society of Thoracic Surgeons
a Department of Cardiovascular and Thoracic Surgery, Stanford University School of Medicine, Stanford, California, USA
* Address reprint requests to Dr Mitchell, Department of Cardiothoracic Surgery, Falk Cardiovascular Research Center, Stanford University School of Medicine, Stanford CA, 94305-5247, USA
e-mail: rsmitch{at}stanford.edu
Presented at the Aortic Surgery Symposium VIII, May 2–3, 2002, New York, NY.
Abstract
The treatment of thoracic aortic pathology is complicated by the morbidity of the surgical procedure, and the comorbidities encountered in an elderly population. Stent grafts have now been used for approximately 10 years for the treatment of thoracic aneurysmal disease, management of aortic dissections, intramural hematoma, and giant penetrating ulcers, and for traumatic aortic tears, with impressive early results. However, these efforts have been significantly limited by the lack of a commercially available stent graft specifically designed for the thoracic aorta, the lack of real long-term follow-up, and the failure of experience in the abdominal aorta to translate to the thoracic aorta. Nevertheless, significant and even unique therapies have been enabled by stent graft technology for the treatment of the above-mentioned diseases. It is likely that, with more sophisticated technology and improved understanding of thoracic aortic pathology, stent graft use will expand, and its utility will be further clarified.
The exact role for stent graft technology for treatment of disease of the thoracic aorta remains undefined. In part, this is secondary to the relatively short time period for which it has been utilized, and also the relative paucity of centers that have investigated its use. Unlike stent grafts for abdominal aortic aneurysms, no stent graft specifically designed for the thoracic aorta has been generally available during this period. Nevertheless, we will attempt to define the utility of stent grafts for the various thoracic aortic pathologies.
Descending thoracic aortic aneurysms
As thoracic aortic aneurysms have become more ubiquitous, with an incidence approaching 10 cases per 100,000 patient-years [1], so has the demand for less invasive strategies. Many centers have documented the feasibility of stent graft repair for descending thoracic aortic aneurysms, and some agreement exists regarding the major anatomic constraints necessary to assure success. These include landing zones of normal aorta 1.5 cm or greater in length distal to the left subclavian artery (or left common carotid artery if the left subclavian artery is to be sacrificed), and proximal to the celiac axis. Depending on the device available, straighter segments have been more successfully treated than acutely angled segments, especially if the angle of curvature exceeds 60o from the transverse arch. Access through femoral and iliac arteries is facilitated by a vessel diameter greater than 7 mm, again dependent on the specific device.
Endoleaks significantly limit the efficacy of these stent grafts. They may be characterized as type I endoleaks, which occur at anastomotic junctions of aorta and stent graft, and which allow the aneurysm sac to remain pressurized. Type II endoleaks result from back-bleeding branch vessels within the aneurysm sac. Although their prognostic significance has not been defined, they certainly portend an ominous outcome if they are associated with aneurysm sac expansion. Type III endoleaks occur at stent graft junctions, and require repair, usually by insertion of another stent graft segment. Finally, type IV endoleaks occur through the stent graft fabric, and also allow continued pressurization of the aneurysm sac. Unfortunately, unlike the abdominal aorta, in which the infrarenal portion is predominantly disposed toward aneurysm formation, degeneration in the thoracic aorta is more diffuse in nature, and, in time, likely to involve the entire thoracic aorta. Total aortic replacement, either by surgical or endovascular procedures, is unlikely to proceed as a single stage. Thus, progression of disease at attachment sites is likely to result in type I endoleaks during long-term follow-up. The exact incidence of this problem will be apparent only as long-term studies become available.
Aortic dissections
Aortic dissections likely represent the greatest opportunity, and also the greatest challenge, for this emerging stent graft technology. Currently, the majority of patients with acute uncomplicated type B aortic dissections are treated medically with antiimpulse therapy. Those who present with visceral ischemia undergo a central aortic repair, previously associated with surgical mortality rates of 50% to 70% [1]. Improved imaging afforded by high-resolution, contrast-enhanced, spiral computed tomography scanning now allows identification of the malperfusion mechanism, nicely illustrated by Williams and associates [2]. Dynamic obstruction is caused by compression of the true lumen by the pressurized false lumen. Conversely, static obstruction is caused by local intimal tears at branch vessel orifices. This differentiation is significant, because in a previous study, all dynamic obstructions could be relieved by stent graft coverage of the primary intimal tear, redirecting flow into the true lumen. Similar therapy was successful in reversing static obstructions in only about 40% of cases, necessitating further interventional techniques (septal fenestration or orifice stenting). A major advantage of endovascular techniques in preference over a central aortic operation is that the malperfusion can be assessed immediately after stent graft placement, and if incompletely relieved, can be immediately fixed in the catheterization laboratory with interventional methods. An additional if unexpected benefit of these procedures is elimination of the false lumen during follow-up in approximately 80% of cases. Although the future for these techniques appears bright, many questions remain. Although it is possible that all patients will benefit from coverage of the primary intimal tear (PIT), we currently recommend stent grafts only for patients with complicated dissections, namely those with rupture or impending rupture, intractable pain, malperfusion, and sudden increase in aortic size to greater than 4.5 to 5.0 cm. However, in the acute setting, the dissected vessel is fragile, and injury during stent graft insertion is an easily imagined complication of unknown magnitude. The ability to cover the PIT is also an issue, especially for large tears immediately adjacent to the left subclavian artery.
Palma and associates [3] in Brazil have reported a series of 70 patients with type B aortic dissections repaired with a stent graft. Procedural success was achieved in 65 patients (92%), with only two deaths. Surgical conversion was required in the 5 patients in whom a proximal endoleak could not be repaired. In approximately 50% of patients, the PIT was within 2 cm of the left subclavian artery orifice. In 30% of patients, it was between 2 and 6 cm from the orifice, and it was more distal in the remaining 20%. Two patients required emergent surgical conversion due to aneurysm expansion, and 3 other patients underwent elective surgical repair to eliminate torrential false lumen flow. Residual flow in the false lumen below the diaphragm persisted in approximately 20% of patients due to more distal fenestrations. At a mean follow-up of 29 months, survival was 91%.
Although these are impressive results, they represent a group with a long-standing interest and expertise in aortic dissections. Whether these results can be translated into more generalized utility is unknown. Also unknown is the long-term durability of these stent graft repairs. Pseudoaneurysms of the distal arch have been reported secondary to stent graft erosion, and Ninomiya and associates [4] have described intimal perforations at the distal implant site arising late in aortic dissections. Other concerns include the timing of the intervention, and the necessity for complete coverage of the PIT.
Type A dissections represent an interesting subset for utilization of this stent graft technology. Kazui and associates [5] have described an aggressive ascending and arch replacement technique, including a distal elephant trunk, for the management of acute type A aortic dissections. Given their very acceptable early results, this technique may become the preferred operation for Marfan patients as well as younger, good-risk patients with significant expectation of longevity. Other surgeons [6] have advocated adding a stent graft inserted through the open arch in an effort to eliminate the patent false lumen in the descending thoracic aorta. The safety and long-term benefit of these procedures clearly remain undefined.
Intramural hematomas and giant penetrating ulcers also represent an attractive substrate for stent graft management. Surgical repair has incurred significant morbidity, and the necessary extent of resection is unclear for those with diffuse involvement. Although stent graft coverage of any intimal ulcer is an attractive concept, diffuse disease is generally present, and aortic dissections extending into the arch and ascending aorta are a recognized complication. The suitability for stent graft repair in these diffusely degenerated aortas remains undefined.
Aortic trauma
Blunt injury to the aortic isthmus is another entity seemingly ideally suited to stent graft repair. For many of these patients with hepatic and splenic lacerations and closed head injuries, heparinization and extracorporeal support may be contraindicated. Conservative nonsurgical management is problematic, because at present, we have no way to differentiate those intimal injuries that will progress to uncontrolled hemorrhage from those with a more benign clinical course. The ability to introduce a stent graft to cover the intimal tear, if only to stabilize the injury until it can be properly addressed after other multiple organ injuries have healed, would be a major benefit.
However, these injuries merit special consideration. Because these usually occur in younger patients with normal-sized aortas, the aortic dimension is usually substantially less than that seen in the patient with a thoracic aortic aneurysm. This would necessitate having on-site grafts of smaller dimensions, and generally requiring a lower profile, because they must be introduced through small iliac and femoral arteries. Additionally, it is likely that the left subclavian artery would have to be covered in the majority of cases (> 80%) in order to effect a proximal hemostatic seal, with unknown long-term consequences. Again, long-term performance data and graft availability need to be assessed.
Conclusions
Clearly, this stent graft technology is an intriguing concept for the management of complex thoracic aortic disease. Unlike the abdominal aorta, the disease process frequently involves the entire thoracic aorta, although it may not become manifest during the same treatment interval. Thus, it is likely that disease progression in previously untreated areas of the thoracic aorta will provoke type I endoleaks at previously hemostatic attachment sites. Late erosions of dissection flaps may mandate reinterventions months or years after the initial procedure. Although there has been great enthusiasm for thoracic stent grafting as a new paradigm, I suspect the lasting paradigm for this technology will be eternal vigilance, because long-term follow-up will be mandatory for these patients to discover and correct late failures and complications.
References
This article has been cited by other articles:
|
|
 |
|
  S. D. Moffatt-Bruce and R. S. Mitchell Endovascular Therapy for the Treatment of Thoracic Aortic Disease Card. Surg. Adult, January 1, 2008; 3(2008): 1299 - 1308. [Full Text]
|
|
|
|
 |
|
 M. Doss, J. P. Wood, J. Balzer, S. Martens, H. Deschka, and A. Moritz Emergency endovascular interventions for acute thoracic aortic rupture: Four-year follow-up J. Thorac. Cardiovasc. Surg., March 1, 2005; 129(3): 645 - 651. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. P. Carrel, P. A. Berdat, I. Baumgartner, H.-P. Dinkel, and J. Schmidli Combined Surgical and Endovascular Approach to Treat a Complex Aortic Coarctation Without Extracorporeal Circulation Ann. Thorac. Surg., October 1, 2004; 78(4): 1462 - 1465. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Doss, J. Balzer, S. Martens, J. P. Wood, G. Wimmer-Greinecker, H.-G. Fieguth, and A. Moritz Surgical versus endovascular treatment of acute thoracic aortic rupture: a single-center experience Ann. Thorac. Surg., November 1, 2003; 76(5): 1465 - 1470. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 N. R. Tai and K. D Boffard Thoracic trauma: principles of early management Trauma, April 1, 2003; 5(2): 123 - 136. [Abstract] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ANN THORAC SURG | ASIAN CARDIOVASC THORAC ANN | EUR J CARDIOTHORAC SURG |
| J THORAC CARDIOVASC SURG | ICVTS | ALL CTSNet JOURNALS |
