Since the introduction of thoracic endovascular aortic repair (TEVAR) for the treatment of aortic aneurysms more than 20 years ago, its indications have expanded, and it is now extensively applied to successfully treat a variety of conditions involving the thoracic aorta. Current use of a total endovascular approach, however, is limited to pathologies that are confined to the descending aorta, due to the presence in the aortic arch of critical branch vessels.

Unfortunately, up to 40% of thoracic aortic aneurysms extend into the aortic arch, meaning that a significant number of patients may not benefit from a completely endovascular repair. In the past, coverage of the left subclavian artery (LSA) with a stent-graft was a common practice to manage lesions that involve the aortic arch and/or the proximal descending aorta, however, there is now sufficient evidence that this exposes patients to increased risks of neurological complications. Consequently, this practice should be avoided whenever possible. Now, surgical revascularization of the LSA via a bypass graft from the left common carotid artery (LCCA) or its transposition to the LCCA followed by TEVAR placement across the LSA into Ishimaru zone 2 is a frequent treatment modality.

The Gore Thoracic Branch Endoprothesis (TBE) (W.L. Gore & Associates, Inc.) is a novel, single-branch stent-graft designed and initially studied for the treatment of thoracic aortic aneurysms with an intended proximal landing in zone 2. The applications of the device have then been expanded and it has been studied (with some modifications in terms of the size of the components) to target pathologies involving zones 0 and 1, based on promising preliminary results observed in the zone 2 study.¹

Device

The Gore TBE is a modular system consisting of two key components intended for “off-the-shelf” use: a main aortic component and a side-branch stent-graft. The system also includes an optional aortic extender cuff and an additional DrySeal Side Branch Introducer Sheath (SBIS). The components are made of a nitinol-based stent-frame with an expanded polytetrafluoroethylene graft. The main aortic component is 10 cm to 15 cm long and features sealing cuffs on both ends and a proximal bare apex that aid in generating a circumferential seal. The key characteristic of the main aortic component is the integrated inner portal that allows insertion, seal, and anchoring of the modular side-branch component. The portal is oriented in a retrograde fashion, so that delivery of the side branch is performed through the same femoral artery access used for the main component. The distal edge of the portal (where the side-branch component exits the main aortic component) is located 20 mm to 40 mm distal to the proximal bare apex of the main component. The side branch is a tapered nitinol-based expanded polytetrafluoroethylene stent-graft with a covalently bound heparin coating (CBAS Heparin Surface, Carmeda) which allows for long-term local inhibition of thrombosis. There are three distinct sections in the side-branch component: the branch vessel segment, the tapered flex segment and the internal portal segment. The leading 15 mm branch vessel segment is designed to provide a circumferential seal in the branch vessel. The middle tapered segment is 20 mm long and is designed for optimal flexibility, to accommodate arch movements. The trailing 25 mm constitute the internal portal segment, which provides a seal at the main aortic component portal and features three anchoring apices to prevent any slippage or migration. The optional aortic extender cuff is similar to the main aortic component without the portal and includes bare apices on the distal end. Each of the components is available in various sizes, with a variety of possible combinations that allow for treatment of a wide spectrum of anatomies.

The main benefit of using the Gore TBE for the treatment of zone 2 aneurysms is that it enables total endovascular repair, while maintaining perfusion of the LSA. As for its application to treat pathologies in zone 0, it allows for a relatively low-risk hybrid repair, in conjunction with a revascularization procedure of the LCCA and LSA. Currently available alternative hybrid approaches in this setting would involve a surgical debranching of the innominate artery (IA) with a graft from the ascending aorta, a more invasive and complex procedure that requires a median sternotomy approach, with associated additional operative risks.

Outcomes

Currently, the device has been investigated in two studies that have evaluated the feasibility and early feasibility of the TBE for the treatment of aortic aneurysms in zone 2 and zone 0/1, respectively. Short-term results from the zone 2 trial have been recently published.1 In total, 40 patients have been treated with the device: 9 patients with a proximal landing zone in Ishimaru zone 0, 1 patient in zone 1 (Figure 1) and 31 patients zone 2. 

The primary endpoints of successful access and deployment of the device and primary patency of the side-branch stent-graft (assessed by angiography at the conclusion of the procedure) were achieved in all patients (100%). Additionally, primary patency of the side branch at 1 and 6 months has also been evaluated, and only one case of side-branch thrombosis with loss of patency at 6 months has been observed in the zone 2 study.

Further trials with larger patient cohorts are anticipated. These will include the study of additional pathologies (e.g., dissection, trauma with involvement of zones 0, 1, and 2) and will help clarify the remaining questions regarding the long-term durability of the device.

MICHAEL D. DAKE, MD, is the Thelma and Henry Doelger Professor (III) in the Department of Cardiothoracic Surgery at Stanford University School of Medicine, Falk Cardiovascular Research Center, 300 Pasteur Drive, Stanford, CA 94305-5407. Email:mddake@stanford.edu

References

1. Patel HJ, Dake MD, Bavaria JE, et al. Branched endovascular therapy of the distal aortic arch: preliminary results of the feasibility multicenter trial of the gore thoracic branch endoprosthesis. Ann Thorac Surg. 2016;102:1190-1198.