Introduction
The Conformable TAG (CTAG) endoprosthesis (WL Gore and Associates, Flagstaff, Arizona) is the third-generation thoracic endograft approved for treatment of aneurysm, traumatic transection, and Type B dissection in the descending thoracic aorta. The second-generation TAG endoprosthesis was the first stent graft approved for thoracic endovascular aortic repair (TEVAR) of descending aortic aneurysm by the US Food and Drug Administration (FDA) in 2005. More than 40,000 TAG devices were distributed worldwide prior to its discontinuation in 2013. These devices have been studied extensively in various clinical trials and real-world use clinical series and are associated with significantly lower short-term mortality and morbidity than open surgery for thoracic aortic aneurysm. The efficacy of the newer CTAG device has been further studied for the treatment of Type B aortic dissection and traumatic aortic transection.
The expansion of the use of the TAG and CTAG devices in treating thoracic pathologies have led to a unique set of device-related complications, which will be summarized in this chapter. The complications can be divided into intraoperative (maldeployment, retrograde dissection, branch occlusion), early events, and late events (stent graft collapse, stent fracture).
TAG Endoprosthesis
The TAG thoracic endoprosthesis is a self-expanding device comprising of an expanded polytetrafluoroethylene (ePTFE) and fluoroethylpropylene (FEP) tube graft, which is supported externally by a nitinol stent. There are flared covered scallops and a radiopaque gold marker at each end of the device ( Fig. 20.1 ). An ePTFE sleeve is used to constrain the stent graft on the delivery catheter and remains in place between the external surface of the device and the aorta after deployment. The TAG endoprosthesis was available in sizes ranging from 26 to 45 mm for use in intended aortic inner diameters of 23–42 mm, with the recommended oversizing window of 8%–17%.
The phase II pivotal study was a prospective, nonrandomized, multicenter study, which enrolled 142 patients who underwent TEVAR of descending thoracic aortic aneurysms with the first generation TAG device. The enrollment was between 1999 and 2001 and a total of 139 patients (98%) underwent successful implantation of the device. Three patients had procedural failure (2%) resulting from access issues secondary to iliac artery size and tortuosity. Two patients had misplacement of the device, resulting in unplanned coverage of subclavian and/or visceral arteries. The patient with coverage of visceral vessels underwent open removal of the displaced device. Major adverse events (MAE) within 30-days occurred in 32% of patients, including bleeding (9%), cardiac event (3%), pulmonary event (10%), and vascular complications (14%). The overall operative mortality was 2% and five patients (3.5%) suffered a perioperative stroke. Four patients developed spinal cord ischemia and the subsequent placement of spinal drain was beneficial in three out of those four patients. Five patients developed early endoleak, including one Type I and four Type II endoleaks. The patient who had early Type I endoleak was treated with placement of an additional proximal endograft.
The all-cause mortality and aneurysm-related mortality for the pivotal trial was 75% and 79% respectively at 2 years. There were three proximal migrations and four component migrations during 2-year follow-up. Three patients underwent endovascular interventions and one had conversion to open surgery. No aneurysm rupture was reported during the follow-up. The cumulative rate of endoleak was 15% (21 patients) during the first 2 years after surgery. There were 20 stent fractures, which were identified in 19 patients. Up to 90% of the stent fractures occurred in the longitudinal spine and two in the apical nitinol support ring. The majority of patients with stent fracture in this cohort were asymptomatic (18 patients) and only one patient developed a Type III endoleak, which was treated successfully with extension of the pre-existing stent graft.
The complication of stent fractures in the initial pivotal trial led to voluntary withdrawal of the device in May 2001 and the development of the second generation TAG device. The first generation TAG device was constructed with two ePTFE layers and was supported by two longitudinal columnar spines ( Fig. 20.1A ). The modified second generation TAG device was constructed with three ePTFE layers and the longitudinal wires, which were susceptible to fracture, were removed ( Fig. 20.1B ). The modified device was evaluated in the confirmatory trial, which enrolled 51 patients from 11 clinical sites. The MAE was 12% at 30-day follow-up and there was no device-related MAE reported.
The intermediate and long-term results for the TAG pivotal trial were published in 2007 and 2008. The rate of aneurysm-related mortality was significantly lower in the TAG group when compared with the open surgical group (2.8% versus 11.7%, P =0.008). Endoleaks developed in 10.6% of TAG patients and the majority were Type Ia endoleak at the attachment site. Five TAG patients required aneurysm-related endovascular and open reinterventions (3.6%): one arch aneurysm repair for Type I endoleak and migration, five endovascular interventions in three patients for endoleaks, and one open conversion for aortoesophageal fistula. There were no additional spine fractures other than the previously reported 20 fractures (19 patients) after 24 months.
Structurally the TAG device was not as flexible as the newer generation CTAG device (described later). In patients with deep arch curves or so-called gothic arches, suboptimal placement resulted in a “bird-beak” appearance as a result of incomplete inner aortic curve apposition to the aortic arch ( Fig. 20.2 ). This theoretically increased the risk of Type Ia endoleak and/or endograft collapse. The less flexible TAG endograft was also found in other off-label use to cause new antegrade intimal tears when it was used to treat aortic dissection ( Fig. 20.3 ). In our practice we recommend the placement of an extension endograft to correct the “bird beak” to eliminate the pressure onto the membrane of dissection. This type of graft-related complications have fortunately been minimized with the more flexible new generation CTAG endoprosthesis ( Fig. 20.4 ).
CTAG Endoprosthesis
Similar to the TAG endoprosthesis, the CTAG device is a self-expanding ePTFE/FEP graft which is supported by a nitinol stent and is constrained on the delivery catheter by a sewn ePTFE sleeve. In the CTAG the flared scallops on the proximal TAG device were eliminated and replaced by uncovered stent apices ( Fig. 20.4A ). The stent apices on the distal device are covered with graft material. The construction of the CTAG device has been optimized to allow for improved comfirmability to accommodate various aortic anatomies better. The structural changes from eight to nine stent apices and the increased wire diameter on the nitinol stent allow for improvement in compression resistance. The CTAG device is available in sizes between 21 and 45 mm and in 10, 15, and 20 cm length. The device is intended to be used in the inner aortic landing zone diameter between 16 and 42 mm, and the oversizing window for the CTAG has been expanded to 6%–33%. Two tapered devices are also available (26×21 and 31×26 mm).
The effectiveness of the CTAG device for the treatment of blunt thoracic aortic injury was evaluated in a company-sponsored trial published in 2013. Fifty-one patients were enrolled between 2009 and 2011 at 21 sites. The majority were victims of motor vehicle collision (84.3%). The mean age for the cohort was 44.1 years, and the mean aortic diameter at the proximal implantation zone was 24.1 mm. Technical success for this cohort was 100%, and the mean time from injury to endovascular repair was 21 hours. Up to 88% of patients received one CTAG device. Six patients (12%) received two devices, including three patients with maldeployment distal to intended location and a patient who required a second implant because of a Type III endoleak. Mortality at 30-days was 7.8%, and the majority was caused by the injury and not procedure- or device-related. Although there was a 39% serious adverse event rate, there were no major device events reported in this trial. There was one reported stent migration of more than 10 mm on repeat imaging, but there were no cases of wire fracture or device collapse in this cohort. The data from this trial led to FDA approval for the use of the CTAG endoprosthesis for the treatment of traumatic aortic transection.
Maldeployment
Endograft maldeployment is one of the operator’s worst nightmares that fortunately happens infrequently. The TAG and CTAG devices have a single-step deployment mechanism that is appealing to operators because of its simplicity. The device is deployed by unlocking and pulling on the deployment knob at the distal end of the delivery catheter. The knob is connected to the deployment sleeve, which is used to constrain the stent graft on the delivery catheter. The pulling of the knob allows delivery of the device with expansion from the middle toward both ends of the stent graft simutaneously ( Fig. 20.5A ). The rapid expansion of the device during deployment minimizes the intraluminal movement related to arterial blow. There is, however, no backup deployment mechanism in the event the primary manoeuvre fails.
