Cath Lab Digest

Author:

Mustafa Halawa, MD, Benjamin Patterson, MD, Peter Holt, MD, Matt Thompson, MD, Ian M. Loftus, MD

Author Affiliations:

From St. George’s Vascular Institute, London, England.

Correspondence: Ian Loftus, MD, St. George’s Vascular Institute, St. George’s Hospital, Blackshaw Road, London, England SW170QT
Manuscript submitted September 12, 2008, provisional acceptance given October 15, 2008, and accepted November 6, 2008.

Disclosure: The authors report no financial relationships or conflicts of interest regarding the content herein.

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Abstract

Thoracic aortic pathology confers specific challenges to stent graft design and performance. The indications for endovascular intervention are expanding, and the complexity of cases is increasing. Graft design has evolved, and several new iterations of endografts have been introduced into clinical practice. While most devices are probably suitable for straightforward cases, extra care should be exercised in device selection for complex pathology. The assessment of these new grafts is difficult, due to the changing indications for their use and a lack of large-scale clinical trials. Although clinical trials provide the highest level of evidence, they often utilize strict anatomical criteria for inclusion and may not be representative of clinical practice. Despite their inherent shortcomings, multicenter registry data offer a good opportunity for evaluating new endovascular grafts and techniques, as large numbers of cases can be collected in relatively short periods of time.

Introduction

Endovascular repair of thoracic aortic pathology has gained support due to evidence from registries demonstrating acceptable operative mortality and paraplegia rates.1,2 The United States Food and Drug Administration (FDA) approved the commercial use of thoracic endografts in the treatment of thoracic aortic aneurysms (TAA) in 2005.3 Since then, several trials have shown endovascular repair to be a safe and effective alternative to open surgery, with clear outcome benefits.4–6

In comparison with earlier devices, the latest generation of stent grafts have improved the ease of use and reliability, but the question of the long-term durability of endografts remains unanswered. This may be addressed by the analysis of registries that have been created at the request of advisory bodies such as the National Institute for Health and Clinical Excellence in the United Kingdom. Organizations such as these have had particular interest in this technology, as the cost of development has been significant and the current market cost of the devices remains a major consideration in a healthcare system with limited resources.

The demands of vascular specialists have outstripped the provision of endograft design and manufacture, as the indications for stent grafting have expanded and the complexity of cases undertaken has increased.7–10 This has exposed some of the technical limitations of the early endograft designs. The thoracic aorta poses specific difficulties in endograft delivery, deployment, and fixation.11 Procedures such as hybrid endovascular repair of the thoraco-abdominal aorta with visceral and supra-aortic trunk debranching and repair of the disease of the aortic arch typify these challenges (Figure 1). It is difficult to determine if the choice of device significantly impacts a patient’s outcome, due to a lack of studies that examine graft choice. This could be explained, to a degree, by the fact that a combination of patient factors, different aortic morphologies, and anatomical factors may lend themselves to a particular device.

What Particular Problems Does Thoracic Endografting Pose?

During deployment, a long length of devices must often negotiate heavily diseased arteries. This can cause trauma to the aortic wall and increases the risk of embolization of atheromatous debris into the brain or distally to the limbs. Once the device has been manipulated into place, endografts can fail to conform to the curved shaped of the aortic arch, due to their relatively inflexible configuration (Figure 2). If this happens, grafts can be subject to migration, collapse, and pseudo-coarctation.

If a device is not fixed securely, long-term durability may be jeopardized, and although data are not comprehensive, some recent studies have suggested there may be an incidence of late aortic-related deaths following thoracic endografting.18 Methods such as hooks and radial force have been used to facilitate fixation of the devices, and this produces a certain amount of stress within the wall of the aorta. Damage to the intima-provoking aortic dissection and erosion through the aortic wall are possible consequences. These factors should be considered when using certain devices for specific indications, although, as yet, there is no definite evidence to support this practice. Another difficulty faced when placing a graft in the thoracic aorta is the accuracy of deployment, particularly in the aortic arch. Torque placed on the delivery system by the operator outside the patient may not be translated to device movement in the proximal aorta. This may result in forceful manipulation of the device before deployment. If the device is not deployed accurately, proximal endoleaks or occlusion of proximal aortic branches may occur.

Selection of Endograft

There are a number of devices currently available with variable amounts of clinical data to support their use. Some devices have relatively unique features that differentiate them from others.

Gore TAG Endoprosthesis