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EDITORIAL |
Division of Vascular & Endovascular Surgery, Department of Surgery, University of Hong Kong Medical Centre, Hong Kong
Yiu-Che Chan, FRCS, Email: ycchan88{at}hotmail.com, University of Hong Kong Medical Centre, Department of Surgery, South Wing, 14th Floor K Block, Hong Kong.
With advances in endovascular technology and stent graft improvement over the past decade, it might be only a matter of time before pure endovascular management of ascending aortic dissection becomes a viable option. Successful endovascular stent graft repair of thoracic aortic dissection involving the ascending aorta and aortic arch requires a sufficient proximal landing zone with a portion of healthy aorta for the stent graft to fix and seal, while preserving aortic valvular competence, coronary and supra-aortic perfusion.
The outcome of conventional open surgery for Stanford type A aortic dissection with replacement of the ascending aorta (with or without the arch) depends heavily on preoperative cardiopulmonary comorbidities and perioperative complications; perioperative mortality and neurological complications may be significant, especially in the elderly.1 These procedures are challenging even in expert hands and require sternotomy, extracorporeal cardiopulmonary bypass, or deep hypothermic circulatory arrest. Currently, adjunctive open surgical extra-anatomical supra-aortic bypasses are required to provide an adequate proximal landing zone for an endovascular stent graft (hybrid approach) in patients unfit for conventional open surgical repair or those who have unfavorable pathoanatomy for endovascular treatment alone.2 Whilst hybrid surgery increases the therapeutic armamentarium for the management of aortic dissection, there is a continuing search for a pure endovascular solution for type A aortic dissection.
To date, there are only a handful of reports of pure endovascular treatment of type A aortic dissection; most of these are isolated case reports and small clinical series, with early to midterm results. Straight stent grafts were used initially. In most type A dissections, the entry tear is located in the ascending aorta, but there is a small subset (4%–20%) of type A dissections in which the entry tear is located in the descending thoracic aorta, and retrograde dissection extends back into the ascending aorta. Kato and colleagues3 reported successful endovascular stent graft treatment in 10 patients (7 with acute and 3 with subacute dissection) in whom the entry tears were located in the descending thoracic aorta.3 Patients were considered suitable only if they had a distance between the left subclavian artery and the entry tear of at least 0.5 cm, with no signs of severe cardiac tamponade, aortic regurgitation, or coronary ischemia.3 The first reported case of true type A dissection with an entry tear in the ascending aorta was from China in 2003: 2 silk-covered stainless steel Z-stents were successfully used to treat a patient with Marfan syndrome and acute type A dissection with the tear in the ascending aorta.4 A similar patient was described by Zhang and colleagues;5 despite initially successful stent graft treatment, this patient developed severe aortic valve regurgitation with progressive chest discomfort and shortness of breath 21 months later, and eventually required a Bentall operation.5 Inhken and colleagues6 reported the successful use of a Gore Excluder stent graft above the coronary arteries and flush with the origin of the brachiocephalic artery, to treat a frail 89-year-old patient with acute type A dissection. Zimpfer and colleagues7 deployed a custom-made covered stent graft distal to the coronary arteries and proximal to the brachiocephalic trunk (controlled by transesophageal echocardiography) to treat acute type A aortic dissection.7 This was the first procedure to be performed with temporary ventricular pacing to decrease the cardiac output and consequently minimize the risk of dislodging the stent graft during deployment.7 Senay and colleagues8 reported a case of acute type A dissection associated with a flap arising just above the right coronary artery. This patient was treated with a coronary stent followed by deployment of a Medtronic endovascular stent just distal to the sinus of Valsalva and just proximal to the brachiocephalic trunk.
The application of fenestrated and branched stent grafts for complex thoracoabdominal aneurysms and juxtar-enal abdominal aortic aneurysms has been extended for use in the ascending aorta and aortic arch. In 1995, Inoue colleagues9 reported the first successful use of a single-branched endovascular nickel-titanium wire-supported Dacron stent graft in a patient with type B dissection who had a tear near the arch. Chuter and colleagues10 advocated an approach involving carotid-carotid-subclavian hybrid bypass followed by introduction of a stent graft via the right carotid or innominate artery. The bifurcated stent graft has a proximal trunk for implantation into the ascending thoracic aorta, a short wide limb for attachment to the distal tubular component, and a long narrow limb for implantation into the brachiocephalic artery. Other grafts such as double-barrel or chimney stent grafts are also available, but worldwide experience is scarce.11
A prerequisite to complex endovascular treatment of ascending and arch dissection is detailed pre-procedural knowledge of the aortic valve and aortic root morphology, including the longitudinal distance from the aortic annulus to the coronary arteries and annular diameters.12 The stent grafts should be flexible and short-tipped, and the stiff wire has to pass through the aortic valve to park in the right ventricle. Coronary arteries have to be assessed or stented prior to deployment of the stent graft, and the ventricle rapidly paced to decrease the cardiac output and maximize the accuracy of deployment. These bifurcated stent grafts require multiple bypass grafts in the neck, but avoid a median sternotomy and partial aortic clamping. Some reports noted that the primary limitation was the anatomy of the ascending thoracic aorta, which may be too short or too wide.13
Endovascular treatment of type A aortic dissection is evolving. It is a technically challenging procedure that involves expert multidisciplinary efforts from experienced cardiologists, cardiothoracic surgeons, and endovascular surgeons. In conjunction with advances in aortic stent graft design and technology, coronary stenting, and percutaneous aortic valve implantation, it is anticipated that pure endovascular management may one day replace conventional open surgery for the treatment of type A aortic dissection.
REFERENCES
Asian Cardiovasc Thorac Ann 2009;
17:566-567
© 2009 by SAGE Publications
DOI: 10.1177/0218492309348803
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