81. Complex Aortic Interventions- Review of CT Surgery

Juan B Umana-Pizano, Patrick R. Vargo, and Eric E. Roselli

Background

Since the first report of thoracic endovascular aortic repair (TEVAR) in 1994 by Dake et al. and the later FDA approval of the first commercially available device, the Gore TAG, in 2005, other endovascular devices have continued to be developed for the treatment of thoracic aortic disease. The advent of TEVAR has allowed for the treatment of thoracic aortic pathology with the use of hybrid and totally endovascular techniques, such that it is the preferred approach for suitable descending thoracic aortic aneurysms and complicated type B aortic dissections. The treatment algorithms and evidence regarding the management of thoracic aortic diseases is discussed elsewhere in this text. Instead, this chapter will focus on hybrid and endovascular interventions.

Ascending Aorta and Arch (Aortic Zones 0–2):

Currently there are no commercially approved devices in the United States for the endovascular management of ascending aortic or arch pathology, but there are several devices in development and trials. Zone 0 deployment is challenging due to the short length between the coronary ostia and the innominate artery origin, the anatomical variation, the hemodynamics and the curvature of the ascending aorta. Zone 0 contains three different sub classifications that confer different risks during an endovascular intervention: Zone 0A annulus to the distal margin of the highest coronary, Zone 0B from above the coronaries to the distal margin of the right pulmonary artery and Zone 0C from above the right pulmonary artery to the innominate artery. After multivariable adjustment, Zone 0A involvement had significantly higher mortality than pathology limited to Zone 0C. Complications of TEVAR of the ascending aorta include death, stroke, device malfunctioning and migration, aortic valve insufficiency, endoleak, myocardial infarction, and renal failure. 

Hybrid procedures involving the ascending aorta for extensive aortic pathology have been described involving debranching of the arch vessels to the innominate artery or to the mid ascending aorta followed by a staged Zone 1 or 0 TEVAR deployment. Treatment of aortic arch pathology that extends into the descending aorta can be managed with the “Elephant Trunk” procedure. The technique originated with aortic arch reconstruction via sternotomy and circulatory arrest, at which time a dacron graft was secured in the arch and allowed to float freely into the descending aorta. At a later stage, it was then sewn to in a completion open descending aorta replacement or extended with stent-grafting via TEVAR. This has now evolved into the “frozen” elephant trunk, which employs the use of an endovascular stentgraft rather than the traditional dacron tube, for ease of facilitating subsequent TEVAR. The stentgraft can be deployed in an antegrade manner during circulatory arrest, and its more proximal end secured to the aortic arch.

Variations of hybrid arch repair with frozen elephant trunk have been described, and dacron-stent combination devices are in development and trial – though not commercially available in the United States. Arch branch vessels can be debranched individually, taken as an island, or bypassed. One such modification is the Branched Stented Anastomoses Frozen Elephant trunk Repair (BSAFER) technique. This strategy employs a Zone 1 or 2 frozen elephant trunk deployment with on-table fenestration and stenting of the left subclavian artery.

The Descending Thoracic Aorta (Aortic Zones 3–5)

There are currently four covered endografts commercially available in the US for the management of descending thoracic aortic pathology: the Bolton RelayPlus (Terumo Aortic, Sunrise, FL, USA), the Cook Medical Zenith Alpha Thoracic (Cook Inc., Bloomington, Indiana), the Gore Conformable TAG Thoracic Endoprosthesis (W.L. Gore, Flagstaff, Arizona), the Medtronic Valiant Thoracic Stent Graft (Medtronic, Santa Rosa, California).

Principles of sizing endografts for the descending thoracic aorta includes the assessment of suitable proximal and distal landing zones. Devices require a landing zone of 20mm of “normal” aorta that is free of pathology allowing for parallel device alignment to achieve seal. Sizing diameter and length of the endografts is done using measurements of the aorta from multi-planar computed tomography reconstructions. The diameter of the endograft is chosen by oversizing the proximal and distal landing zones by 10-20% for aneurysmal disease. In the case of dissection, it is important not to oversize more than 10% due to the increased risk for retrograde type A dissection.

In an emergency, if there is insufficient landing zone proximally, the left subclavian artery can be covered with a Zone 2 deployment often without major complications. Common complications of occlusion include left upper extremity ischemia, vertebral artery steal syndrome, endoleak, and spinal cord ischemia. In an elective setting, the left subclavian artery can be transposed to or bypassed from the left common carotid artery. Additionally, a proximal landing zone can be created through a hybrid approach during an arch repair by debranching the head vessels to the ascending aorta or performing an “elephant trunk procedure” (discussed previously). Similarly, a distal landing zone can be created by visceral debranching, or a staged open thoracoabdominal completion repair.

In the case of aortic dissection, there are endovascular adjuncts to promote true lumen flow, false lumen thrombosis, and reverse remodeling. It should be noted that intravascular ultrasound (IVUS) is crucial to guide wires and devices through the desired lumen. To improve true lumen expansion through the reno-visceral aorta, an uncovered bare metal stent, the Cook Medical Zenith Dissection Stent (Cook Inc., Bloomington, Indiana) has been approved for both use in acute and chronic dissections. For chronic dissection, following the deployment of a covered device in the descending thoracic aorta, a compliant balloon can be used to “Balloon Fracture Fenestrate” the dissection flap and promote full expansion of the stent and decrease retrograde false lumen perfusion. Likewise, the false lumen can be intentionally entered to deliver coils or plugs and embolize the false lumen.

Though minimally invasive and generally well-tolerated, TEVAR can have serious complications. One such complication is the development of a retrograde type A aortic dissection. This has been reported to happen in 1.7% of patients and mortality after its occurrence is calculated at 33.6% and is most common after TEVAR for acute type B dissection. Oversizing of the graft has been shown to be the greatest risk factor, increasing the risk of occurrence by 14% for each percent point of oversizing greater than 9% (19). Due to the coverage of segmental arteries originating from the descending aorta and their contribution to the collateral network of spinal cord blood flow, spinal cord ischemia and paraplegia has been reported to occur at 1-10% and is most closely associated with the extent of aortic coverage. To mitigate this, it is important to consider prophylactic placement of a cerebrospinal fluid drain, maintain higher postoperative blood pressure goals, ensure left subclavian artery patency, avoid anemia, and limit the amount of aorta covered during one intervention to permit time for compensatory collateralization.                                                                                                                                                                                

Abdominal Aorta (Zones 6–9)

There are no devices currently approved in the US for the management of thoracoabdominal aortic aneurysms with a zone 6 through 9 landing zone. Hybrid management with total abdominal visceral debranching and subsequent landing of an endovascular grafts has been previously described for the management of complex thoracoabdominal aortic disease. There are currently several branched and fenestrated devices under investigation for the management of these challenging group of patients with encouraging results.

Suggested Readings

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