Fenestrated-Branched and Parallel Stent-Grafts for Endovascular Repair of Aortic Arch and Thoracoabdominal Aortic Aneurysms

Introduction

Endovascular repair has become the first treatment option in most patients with abdominal and thoracic aortic aneurysms. Prospective randomized studies have shown that endovascular aortic repair (EVAR) is associated with lower morbidity, mortality, blood loss, and earlier recovery compared with open surgical repair. For thoracic aneurysms and dissections, endovascular repair (TEVAR) has been shown to decrease mortality, morbidity, and risk of paraplegia compared with open surgical repair. Anatomical factors such as short or angulated landing zones, side branch involvement, difficult access, tortuosity, and diffuse aortic disease have limited the widespread use of endovascular techniques to treat patients with more challenging anatomy. For these patients, innovative techniques have been developed to incorporate side branches with fenestrations, directional branches, and parallel stent-grafts. This chapter summarizes the indications, preoperative planning, techniques of implantation, and outcomes of fenestrated, branched, and parallel stent-grafts to treat thoracoabdominal aortic aneurysms (TAAAs) and aortic arch aneurysms.

Historical Perspectives

The first fenestrated endovascular repair was performed by Park and colleagues in 1996. Subsequently, a group led by Michael Lawrence-Brown and David Hartley developed a novel fenestrated platform based on the Cook Zenith abdominal stent-graft (Brisbane, Australia). John Anderson from Adelaide, Australia, performed the first clinical implantation of a Cook Zenith fenestrated stent-graft for a juxta-renal aortic aneurysm in 1998. In 2001, Tim Chuter from the University of California, San Francisco introduced the concept of multibranched endografts to treat TAAAs. Concurrently, improvements in the design and delivery system have widened the applications of fenestrated and branched stent-grafts with significant contributions by Roy Greenberg (Cleveland, OH), Wolf Stelter (Frankfurt, Germany), Eric Verhoeven (Nuremberg, Germany), Stephan Haulon (Lille, France), Krassi Ivancev (Malmo, Sweden), Tim Resch (Malmo, Sweden), and multiple other investigators. These improvements included changes in the modular design, diameter reducing-ties, reinforcement of fenestrations, alignment stents, development of preloaded guidewires and catheters, and lower profile fabric. More than 20,000 patients have been treated worldwide by fenestrated and branched stent-grafts for arch, TAAA, and aortoiliac aneurysms. Other aortic device manufacturers have also embarked on the development of complex platforms to expand indications of EVAR to patients with complex anatomy.

Despite the increasing interest in these techniques, physician access has been limited by regulatory issues, cost, lack of specialized training, and time delay to manufacture devices. Other creative techniques have been introduced as a means to overcome the lack of widespread availability of manufactured devices. Roy Greenberg described the first use of parallel grafts to treat a pararenal aneurysm in 2003. The technique was later disseminated by Criado, Lachat, Lobato, and other pioneers, who coined a variety of terms, including “chimney,” “snorkel,” “periscope,” and “sandwich” grafts. These techniques had in common the use of aortic and bridging stent components deployed in parallel, side by side, to extend landing zones across side branches. Device modifications were first described by Krassi Ivancev and Renan Uflacker in a report of three patients in 2006. Ben Starnes coined the term “physician-modified endovascular graft” (PMEG) to describe modifications of manufactured devices by creation of fenestrations to incorporate branches. Oderich has reported numerous technical refinements, including the addition of diameter-reducing ties, minicuffs, directional branches, and preloaded wire systems to facilitate the technique.

Indications

The indications for endovascular repair using fenestrated, branched, and parallel stent-grafts are the same applied for open surgical or hybrid repair. Because these operations carry higher risks of morbidity and mortality, it is of paramount importance to carry out a balanced risk-benefit analysis, taking into consideration institutional experience and results. The risk of rupture should be analyzed in contrast to the risk of perioperative death or major disability, which should also consider the risks of paraplegia, major stroke, and dialysis. Treatment is recommended in patients with ruptured or symptomatic aneurysms, independent of the size. For elective repair, most patients have maximum aneurysm diameter greater than 6 cm. Analysis of body surface area helps optimize indications of repair based on size criteria. Repair should be also considered in patients with rapid aneurysm enlargement (>5 mm growth in 6 months) and in those who develop dissection, intramural hematoma, or penetrating ulcers within the aneurysm. Saccular aneurysms have a poorly defined natural history, and therefore most experts agree that repair should be considered at smaller size diameter for saccular aneurysms. Finally, elective repair of a TAAA should only be considered when the risk of rupture outweighs the risks of the operation, given the patient's age, comorbidities, and anticipated long-term survival.

Endovascular repair of complex aneurysms is relatively contraindicated in patients with infectious etiology, systemic sepsis, connective tissue disorders (e.g., Marfan, Ehlers-Danlos, Loyes-Dietz syndrome), excessive amount of atherosclerotic debris, inadequate landing zones, unsuitable femoral access, and renal-mesenteric targets. Although endovascular repair can be applied in select patients with infected aneurysms and also for connective tissue disorders, studies are limited by small numbers of patients and short follow-up. Endovascular repair is an alternative in patients with connective tissue disorders who have prior open surgical grafts that serve as landing zone for a new endograft, and in those with ruptured aneurysms as a bridge to definitive open surgical repair.

Definitions

The term fenestrated endovascular repair is applied when a fenestrated stent-graft is used to repair an aneurysm with inadequate or short infrarenal neck, yet the target vessels (e.g., renal arteries) originate from normal aorta. There is no gap between the fenestration and the target vessel. Alignment stents are typically used to prevent vessel occlusion or stenosis from misalignment between the fenestration and the origin of the target vessel. Examples of devices designed for fenestrated repair include the Zenith (ZFEN, Cook Medical Inc., Brisbane, Australia) and Vascutek Anaconda fenestrated stent-grafts.

A branched endovascular repair is indicated for aneurysms involving side branches. In these cases, the target vessel originates from the aneurysm, and there is a space gap between the main aortic stent-graft and the aortic wall. The branches can be constructed using one of two approaches. Fenestrated-branches are based on reinforced fenestrations, which are bridged by balloon-expandable covered stents that connect the fenestration to the target vessel, whereas directional branches are based on pre-sewn cuffs. The most commonly utilized branch configuration is a straight cuff or portal, which is accessed via the brachial approach. However, directional branches can be helical, upgoing (or retrograde), and can be internal or external to the main aortic device. Selection of bridging stent is more variable for directional branches, including self-expandable and balloon-expandable covered stents. Examples of thoracoabdominal multibranched stent-grafts include the Cook t-Branch and patient-specific stent-grafts, the Gore ThoracoAbdominal Multi-Branched Endograft (TAMBE), and recent developments using Bolton, Medtronic, and Jotec stent-grafts.

The term parallel graft technique refers to a wide range of techniques that use stent-grafts deployed alongside each other. The terms “chimney,” “snorkel,” “periscope,” “octopus,” and “sandwich” stent-grafts have all been coined to describe specific configurations of parallel grafts placed from proximal or distal landing zones. “Chimney grafts” consist of parallels grafts coming from the proximal landing zone and placed in parallel between a healthy aortic segment and the aortic stent-graft. These have been used to incorporate the renal-mesenteric arteries in patients with short-neck or pararenal aortic aneurysms. “Periscope grafts” utilize the same concept, but the side stents are placed in retrograde configuration and are based on the distal landing zone. “Sandwich grafts,” a term coined by Armando Lobato from Sao Paulo, Brazil, apply a “graft within graft” concept and can be combined with the previously mentioned techniques to treat more extensive aneurysms such as TAAAs, aortic arch, and aortoiliac aneurysms. The “octopus” technique was described by Kasijaran using abdominal bifurcated stent-grafts deployed in the thoracic aorta, coupled with parallel stent-grafts deployed within the iliac limbs to revascularize the renal-mesenteric arteries.

Preoperative Assessment

Imaging Evaluation

Computed tomography angiography (CTA) of the chest, abdomen, and pelvis is the single most important imaging modality to plan aortic repair ( Fig. 39.1 ). Its utility relies on the accurate assessment of etiology, extent of disease, involvement of side branches ( Fig. 39.2 ), adequacy of access vessels, and presence of extravascular diseases that might affect treatment selection and approach. Imaging requires tailoring of the exam to a specific indication and established preexisting protocols in collaboration with radiologists. Communication among multiple specialties, including the radiologists performing the study, is critical to properly address specific issues.

Sealing Zones

The proximal landing zone should be based on at least 2-cm length of “normal,” noncalcified, parallel aorta to allow circumferential stent-graft apposition to the vessel wall ( Fig. 39.3 ). Analysis of neck morphology determines the selection of “healthy aortic segments” for proximal and distal fixation. Regions that have extreme tortuosity or that appear conical or noncylindrical, and segments that contain atheromatous debris, thrombus, or calcification are not considered safe to fix and seal endovascular devices. Assessment of landing zones is performed using centerline of flow (CLF) projections. A parallel aortic segment with less than 10% variation in diameter is considered normal aorta for placement of endograft. Although the minimum recommended length for proximal landing zone is 20 to 25 mm, longer segments may be needed in patients with ectatic, thrombus-laden, or diseased aortas.

Endovascular Techniques

Basic principles can be used to facilitate endovascular repair of complex aneurysms, independent of which technique is selected to incorporate side branches. Advanced endovascular skills and familiarity with branch vessel stenting and “bail-out” maneuvers are minimum requirements to achieve successful results with these complex procedures. A comprehensive endovascular inventory with a wide range of catheters, balloons, and stents is required to perform these procedures.