Thoracic and Abdominal Aortic Debranching in the Endovascular Treatment of Thoracoabdominal Aortic Aneurysms

Aortic Arch and Proximal Descending Aortic Aneurysm Debranching

Operative mortality and morbidity of open repair of arch aortic aneurysm, descending aortic aneurysm, and TAAA has improved since the 1990s. The mortality of 3.9% to 9.3% in open arch replacement and 4.6% to 10% in open TAAA repair is achieved in centers of excellence. However, outside of these centers, mortality percentages have been reported in excess of 20% for open TAAA repair.

Commercially available thoracic aortic stent grafts are typically deployed distal to the origin of the left subclavian artery (SCA), with a 2- to 2.5-cm requirement for the proximal landing zone to achieve a proximal seal ( Figure 1 ). Landing zone 0 involves the ascending aorta proximal to the innominate artery, zone 1 involves the aortic arch between the innominate and left common carotid artery (CCA), zone 2 involves the aortic arch between the left CCA and the left SCA, zone 3 involves the proximal descending thoracic aorta distal to the left SCA, and zone 4 involves the mid descending thoracic aorta.

The degree of debranching required for any specific patient is dictated by the location of a suitable proximal landing region. Given the high degree of curvature within the arch, longer landing zones than those defined by the device manufacturer are typically required to ensure adequate exclusion of the aneurysm and durability of the repair.

For zone 2 TEVAR implantations, left SCA revascularization can be accomplished either with transposition of the left SCA and the left CCA ( Figure 2 A) or with left CCA to left SCA bypass, usually with 8-mm ringed polytetrafluoroethylene (PTFE) graft ( Figure 2 B). Potential differences with respect to patency and infection rates between these two interventions have never been definitively established. Initially, the left SCA was considered somewhat superfluous (in the absence of internal mammary–based coronary circulation or dominant vertebral flow), and coverage with the aortic endograft proximally was routinely performed with little perceived risk. Recent research has demonstrated a greater clinical importance of this vessel. When the left SCA is intentionally occluded proximally in the absence of revascularization, vertebral artery blood flow becomes retrograde and provides inflow for the arm. By providing antegrade flow to the left SCA from the carotid, antegrade left vertebral and internal mammary flow is maintained. Controversy still exists regarding routine revascularization and selective revascularization of the left SCA when endografting covers the origin of this artery.

Patients with dominant left vertebral circulation originating directly from the arch require special mention. Consideration must also be given to preserving vertebral arteries arising directly from the arch. In this setting, transposition of the vertebral onto the common carotid can readily be performed simultaneously with a carotid–subclavian bypass through the same incision. Preservation of antegrade vertebral flow can contribute to the spinal cord circulation and diminish the risk for paraplegia in the setting of long descending thoracic grafts that extend into the arch. The risks associated with such a bypass are minimal, particularly when proximal dissection and ligation of the SCA is not performed but the bypass is completed with endovascular coils or plugs.

The choice of a transposition or bypass procedure depends on the surgeon’s experience. In cases of a prior coronary artery bypass graft using the left internal mammary artery, the presence of right vertebral artery occlusion, or posterior inferior cerebellar artery (PICA) syndrome, a bypass is preferentially performed over a transposition. A left SCA transposition or a bypass is typically performed through a supraclavicular transverse incision.

In situations where zone 1 implantation is intended, a left CCA bypass is needed. This can be combined with revascularization of the left SCA as previously described. Typically the left CCA is revascularized through a carotid-to-carotid bypass graft ( Figure 3 ). Tunneling can be accomplished through either a retropharyngeal or subcutaneous route. It has been our preference for the former to avoid potential complications with a median sternotomy if one might be needed in the future. Concomitant left SCA bypass can be performed depending upon the preoperative workup to ensure adequate collateral circulation, especially in the vertebral artery territory. The proximal left SCA in nearly all situations is either embolized through percutaneous techniques or ligated to prevent a type II endoleak ( Figure 4 ). Other techniques have been described and include right CCA to left SCA bypass with implantation of the left CCA to the bypass ( Figure 5 ).

For zone 0 treatments, the patient requires a median sternotomy with ascending aortic side clamping. The bypass graft is constructed from the proximal ascending aorta to the innominate and left CCA arteries. The left SCA is often difficult to revascularize through the median sternotomy incision; the left SCA is typically revascularized through previously described techniques and before median sternotomy. Other methods exist to bypass the innominate and the left CCA including a single, large, 12- to 14-mm Dacron tube graft from ascending aorta to the innominate artery, followed by left CCA transposition onto the graft ( Figure 6 ) or with a jump graft to the left CCA. Anastomotic configurations are typically end to end, with oversewing of the main stump. Trifurcated grafts or new hybrid grafts are available with side arms for reconstructing great vessels. An additional side arm is often incorporated that can be used to deploy the endograft in antegrade fashion without the need to access the femoral arteries ( Figures 7 and 8 ).

Ascending, Arch, and More Extensive Aneurysms

Hybrid procedures exist for treating proximal aortic aneurysms of the ascending aorta and the arch, or extensive aneurysms starting from the ascending aorta all the way to distal descending aorta ( Figure 9 ). In cases where adequate endograft attachment exists in the ascending aorta for landing in zone 0, the supraaortic branches are debranched from the ascending aorta. In general, the aortic diameter in the proximal attachment region must not be larger than 37 to 40 mm in diameter. With this approach, type 1 hybrid repairs do not require cardiopulmonary bypass. In situations where the ascending aortic diameter in zone 0 is greater than 40 mm in diameter, there is an increased risk for endograft migration, endoleak formation, and development of a retrograde ascending aortic dissection. Hybrid treatment can still be accomplished with an ascending aortic interposition graft using a trifurcated Dacron graft configuration for supraaortic debranching and placement of antegrade endograft (see Figure 9 ). This procedure also requires cardiopulmonary bypass. The patients who present with extensive ascending, arch, and descending aneurysmal disease typically require open ascending and arch or hemiarch repair with creation of an elephant trunk followed by antegrade thoracic endograft implantation at the same time or retrograde transfemoral TEVAR usually at a later procedure (see Figure 9 ).

Increased complication rates appear to be associated with proximal landing zones and extent of disease. The reported mortality of 3% to 5% and morbidity rates of up to 20% including stroke, paraplegia, and endoleaks have raised the question of the utility of debranching procedures in comparison to traditional open repairs, which have comparable results in centers of excellence. Direct comparisons between these techniques have not been studied prospectively, and as with all complex procedures, patient selection is critical.

Vallejo and colleagues reported their experience with 38 high-risk patients including aortic dissections with zone 0 and zone 1 endograft placement. They documented a 13% risk of stroke and 23% mortality with the hybrid technique in high-risk patients. Eighteen studies and data from 195 patients were analyzed by Antoniou and colleagues, including complete arch repair performed in 122 patients (63%). The technical success rate was 86%. The most common reason for technical failure was endoleak (9%). Overall perioperative morbidity and mortality rates were 21% and 9%, respectively. The most common perioperative complication was stroke (7%). Four aneurysm-related deaths were reported during follow-up (2%).