Endovascular stent grafting has emerged as a therapeutic option for thoracic aortic aneurysms (TAAs), dissections, and trauma.1 Despite expanding indications for treating proximal lesions in the aortic arch with stent grafts, technical and anatomic difficulties persist caused by the inflexible structure of most tubular stent grafts and their inability to conform to the curvature of the aortic arch.

In an earlier effort to address this technical challenge, the Malmö Group2 chose to use the existing Zenith TX2 TAA Endovascular Graft (Cook Medical, Bloomington, IN) and modify it to permit in situ bending. The Zenith TX2 already features a trifold configuration of its proximal end that allows continuous blood flow around the graft during deployment, preventing the windsock effect (Figure 1). It was modified by affixing an additional slipknot and trigger wire to the proximal end, which caused controlled shortening of the inner curvature of the TX2 after deployment (Figure 2). As with the TX2's successor, the Zenith TX2 TAA Endovascular Graft with Pro-Form, this controlled shortening caused the first two proximal stents to overlap, resulting in greater conformability and improved wall apposition without the gap at the inner curvature of the aortic arch (bird's beak effect) (Figures 3 and 4).

EXPERIENCE WITH MODIFIED TX2
The following summarizes cases in which we used the new TX2 with Pro-Form graft (modified TX2) in increasingly difficult anatomy with favorable results. Thoracic endovascular aortic repair (TEVAR) within the aortic arch zones 0 through 2 is especially demanding due to the supra-aortic vessels and the Gothic (angular) arch configuration common to the zone. In such cases, open surgery to treat aneurysms and dissections is still associated with considerable morbidity, with a mortality rate up to 17% and a neurologic complication rate up to 12%. These percentages are partly related to the necessity of cardiopulmonary bypass. If this necessity exists, TEVAR can be performed in combination with debranching or even less invasively with branched grafts (parallel grafts if branch devices are not available) (Figure 5).

To increase prevention of type I endoleaks in aortic arch zone 0-2, a proximal landing zone of at least 2 cm is required for ideal conformability to the inner curvature. The more proximally the graft is deployed, the larger the diameter of the graft required. Additionally, diameter alterations must be taken into account due to the cardiac cycle and changes during systole and diastole. Deployment of the stent graft in the ascending aorta often requires a transvalvular wire and graft manipulations (in cooperation with cardiologists), plus intraoperative transesophageal ultrasounds and inflow occlusions (Figure 6).

We have performed 26 endovascular procedures within the proximal aortic landing zone of areas 0 through 2 during the last 2 years. In 12 cases, stent grafts were deployed in the ascending aorta, with pathologies treated involving true and false aneurysms, as well as type A and type B dissections. The majority of patients were unfit for open surgery. Cases of ascending aneurysms were discussed with cardiac surgeons before stenting. Figure 7 shows a 42-mm TX2 with Pro-Form stent graft in an emergency case with pending rupture, after aortocoronary bypass and aortic valve replacement. Total supra-aortic debranching was performed in combination with a retrograde parallel graft and placement of an occluder device into the innominate artery.3

We had one type I endoleak in an aneurysm involving zone 1. Treatment required an extension of the proximal landing zone with a Pro-Form graft to the ascending aorta. Chimney grafts were deployed if necessary in the left common carotid artery, as well as the innominate trunk, with good midterm results and patency. The Pro-Form graft permitted excellent adaptation to the inner curvature in all cases. It was particularly important in ascending cases because of the regularly curved configuration of the ascending aorta distal to the sinotubular junction.

TYPE A AND B DISSECTIONS
Type A and type B dissections are a completely separate disease entity. Stent grafting with the Pro-Form graft was offered in cases in which the aortic sinus and the aortic valve were not included in the dissection; patients requiring open surgery with a valve-bearing conduit were excluded. In cases with massive thrombus material or severe calcification of the aortic arch, extracorporeal bypass and clamping of the carotid arteries was performed to prevent dislodgment during wire and graft manipulations. In some patients with type B dissections, in addition to sealing the proximal entry tear, the Zenith Dissection Endovascular Stent (Cook Medical) was added to the deployment of the Pro-Form graft, which permitted remodeling of the dissected descending aorta.

The Pro-Form graft has barbs at its proximal end, yet intimal damage from the barbs has never been shown in any of our cases (Figures 7 and 8). The barbs are always positioned in a normal landing zone of a nondissected aorta. We believe this is one reason why graft migration has not been observed in these cases, although all grafts were deployed in an area where high velocity with significant turbulence could easily cause forward movement of the stent graft.

CONCLUSION
Our current series shows the clinical feasibility and safety of in situ bending of thoracic stent grafts. A better proximal apposition of the device at the inner curvature of the aortic arch was achieved in all cases, possibly preventing early and late stent graft complications. In the future, off-the-shelf solutions will be required to meet challenges in the ascending aorta and the aortic arch, including devices with larger diameters, as well as branched grafts and/or premanufactured fenestrations to treat a larger variety of patients.4

Prof. Ralf Kolvenbach, MD, PhD, FEVS, is from the Vascular Center Catholic Clinics Düsseldorf, Augusta Hospital in Düsseldorf, Germany. He has disclosed that he is a paid consultant to Cook Medical. Dr. Kolvenbach may be reached at 0049 2119043301; kolvenbach@ vkkd-kliniken.de.

  1. Thompson M, Loftus I, Morgan R. Endografts and the aortic arch: Zenith TX2 with Pro-Form. Endovascular Today. 2009;8:32-34.
  2. Kölbel T, Dias N, Resch T, et al. In situ bending of thoracic stent grafts: clinical application of a novel technique to improve conformance to the aortic arch. J Vasc Surg. 2009;49:1613-1616.
  3. Criado FJ. A percutaneous technique for preservation of arch branch patency during thoracic endovascular aortic repair (TEVAR): retrograde catheterization and stenting. J Endovasc Ther. 2007;14:54-58.
  4. Lee A. A clinical look at EVAR. Endovascular Today. 2010;1:35-36.