Building upon the endovascular knowledge gained by stent graft treatment of abdominal aortic aneurysms, and using that same femoral approach to treat thoracic aortic pathology has been successful, except in cases where the larger thoracic stent grafts are difficult to place through many femoral arteries. In the Gore TAG trial, upwards of 15% of the patients required retroperitoneal conduits to implant these devices. The topic of iliac conduits is discussed in a separate section in the Endovascular Technology Portal.
Clearly, as the technology is applied more frequently, more retroperitoneal conduits will be needed to treat a wider range of patients for various thoracic aortic pathologic conditions. Because of this increasing difficulty in access using large thoracic devices, alternative approaches have been tried with some success, deploying the stent graft in an antegrade fashion through various access sites in the ascending aorta. Regarding evaluation for potential access approaches, if it is deemed that retrograde femoral, iliac, or direct abdominal aortic approaches are not possible, then CT angiogram appears to be the modality of choice at most institutions for evaluating ascending aortic access. There is no question that additional modalities like digital subtraction angiography, intravascular ultrasound, and MRI may be used to better select those patients who might benefit from alternative access approaches and also for endograft sizing.
Today’s abdominal stent graft systems range from 21 French outer diameter devices up to 25 French devices, like the Zenith 36 device. Thoracic stent grafts, on the other hand, can be almost as large as 28 French for the Gore thoracic 40 mm device, and requires a sheath with an outer diameter of 27.4 French. These large sizes require good iliofemoral anatomy in order to be placed in a retrograde fashion. Clearly, smaller men and women may have iliac arteries that are too small, even if they have no significant peripheral vascular disease.
Complications have occurred with all of the thoracic stent grafts that are either FDA approved or in trials currently, one of the most frequent being artery access problems. These include the inability to get the device up the iliacs, iliac artery injuries and dissections, and even the “iliac on a stick” problem (of which I have had two), where the external iliac artery comes out with the stent graft deployment system leading to catastrophic bleeding. Rapid balloon occlusion of the proximal aorta along with advanced endovascular skills or experienced surgical skills for thoracic abdominal aortic repair and retroperitoneal cut down are a necessary part of thoracic stent grafting. Alternative antegrade access sites can be both appealing and perhaps safer for a certain subset of patients.
There have been a few reports by May and Estes outlining their use of the common carotid artery as an alternative access site for thoracic and abdominal stent grafts. While May preferred the right common carotid artery and Estes preferred the left, both had acceptable results with their preferred access site. Duplex scanning and CT angiography are necessary preoperative tests for these access sites. Caution is advised, as they may be associated with increased stroke rates.
With regard to ascending aortic access, this route is especially enticing for treatment of type III/type B aortic dissections in order to gain as much arch fixation and seal zone as well as guaranteeing the graft starts in the true lumen. This avoids the difficult, tedious, and sometimes dangerous placement of a thoracic stent graft from the groin up through a complicated aortic dissection with multiple fenestrations (Figure 1). The other purported advantage of using the ascending aorta would be if those patients needed additional surgical procedures such as coronary bypass grafting or valve surgery (Figure 2).
Another potential advantage of a median sternotomy approach is the novel idea of using a proximal Dacron graft banding procedure around the distal ascending or aortic arch. This would facilitate stent graft fixation by acting as proximal landing zone at that fixed diameter area, therefore reducing the incidence of type I endoleaks and stent graft migration in this very complex, high pressure environment. This course requires an arch transposition from the more proximal ascending aorta followed by banding, then stent graft placement through the ascending aorta.
Another antegrade approach to the ascending aorta is right thoracotomy. This gives one access to the ascending aorta in order to perform the proximal anastomosis of the arch transposition bypass graft. You then tunnel the bifurcated graft up to the brachiocephalic/carotid arteries with small incisions, all without a mid-line sternotomy, which to some patients is not cosmetically appealing.
In conclusion, iliac tortuosity, severe calcific and occlusive peripheral vascular disease, and small caliber iliofemoral arteries all may preclude the use of a retrograde approach to place thoracic stent grafts in some patients. With careful preoperative evaluation, many patients can be treated in an antegrade fashion using a less invasive approach when treating arch and descending thoracic aortic pathology, thus allowing the patient to be a candidate for an endovascular stent graft repair. Certainly, these approaches carry with them a defined and different set of risk factors when these alternative sites are used, and these unique risk factors have to be weighed carefully against the risks and benefits of trying to "push the envelope" with the retrograde approach or the known morbidity and mortality of an open repair. As experience increases with these alternative approaches, more data and perhaps newer modifications of techniques and stent graft technology will allow us to offer thoracic stent grafting to a greater subset of patients who, for anatomic reasons, are marginal candidates for the standard retrograde approach.