Combined Endovascular and Surgical (Hybrid) Approach to Aortic Arch and Thoracoabdominal Aortic Pathology

A hybrid aortic repair consists of an open surgical bypass to perfuse a single or multiple vessels so that a stent-graft can be deployed across their origin(s) to treat aortic pathology. This combined approach was first used at the University of California, Los Angeles to treat a type IV thoracoabdominal aneurysm in 1999 to minimize the morbidity and mortality of a complete open repair in a high-risk patient. Because this technique has evolved, it is now used to treat more extensive pathology of the aortic arch and thoracoabdominal aorta ( Fig. 38.1 ).

A hybrid repair of thoracoabdominal aneurysms avoids proximal aortic cross clamping, thoracotomy, and minimizes the visceral ischemia time. For the aortic arch, avoidance of hypothermic circulatory arrest makes a hybrid approach appealing. Use of thoracic stent-grafts in association with open surgical debranching is considered an “off-label” application of the device.

This chapter focuses on patient selection for hybrid repairs and discusses the techniques of debranching and stent grafting for both the aortic arch and thoracoabdominal aortic pathology. Additional considerations such as use of spinal protection and postoperative management are discussed. The literature and outcomes from case series are also reviewed.

Patient Selection

Indications

The indications to treat an aortic aneurysm with a hybrid approach are no different than those used for open aneurysm repair. They include aneurysm diameter greater than 6 cm, growth greater than 0.5 cm/year, unusual aneurysm morphology suggesting a higher risk of rupture (pseudoaneurysm), or symptomatic aneurysm. The hybrid approach should be reserved for patients who are considered at high risk due to comorbidities and/or prior aortic or abdominal surgery.

Anatomy Considerations

Patients are considered for a hybrid repair if an appropriate proximal and distal landing zone is present, or can be created, allowing for exclusion of the aneurysm by a stent-graft. Partial or complete debranching of the aortic arch is performed to create additional proximal landing zones. For pathology involving the visceral aorta, critical vessels, such as the celiac artery, superior mesenteric artery (SMA), and renal arteries, can be covered by aortic stent grafts after a surgical bypass has been established. Distal landing zone must be present in the native aorta or a preexisting aortic graft. Open infrarenal aortic replacement may be necessary to create a distal landing zone in patients with an infrarenal aneurysm and a short segment of nonaneurysmal aorta.

In any hybrid repair case, planning is of utmost importance to assure that an adequate endograft seal will be obtained by an existing length of normal aorta or as a consequence of the open surgical intervention.

Open Versus Hybrid Approach

The choice of an open or hybrid approach is dependent on a combination of the patient's history, comorbidities, and overall condition. Patients considered high risk include those who cannot tolerate a thoracotomy given severe chronic obstructive pulmonary disease or previous left chest operations. Patients with severe renal insufficiency with an increased risk of renal failure after open repair are also candidates for a hybrid approach. Patients with significant cardiac conditions or an inability to tolerate proximal aortic clamping with increased afterload, should also be considered. Nonoperative, conservative management should be offered to patients with shortened life expectancies or those who are debilitated due to coexisting medical conditions.

Open aortic repair has been shown to be a durable procedure with acceptable results and is the treatment of choice in young patients and those with acceptable operative risk. The hybrid repair is currently reserved for high-risk patients who are considered poor candidates for an open repair.

Aortic Arch Aneurysm

Open repair of aortic arch aneurysms require a sternotomy, extracorporeal circulatory support often with deep hypothermic circulatory arrest, and hemiarch or total arch replacement. In cases of concomitant descending thoracic aorta involvement, an “elephant trunk” technique can be utilized where a second intervention addresses the descending thoracic aorta component. In high-risk patients, a hybrid approach is attractive because it avoids the need for hypothermic arrest, and in cases of descending thoracic involvement, the procedure can be done in one stage.

Safi and colleagues published one of the largest case series of open aortic arch aneurysm repair with thoracic or thoracoabdominal aortic involvement in 2004. They replaced the ascending aorta and aortic arch, leaving an elephant trunk in the descending thoracic aorta in 218 patients. Strokes occurred in 2.7%, and 30-day mortality was 8.7%. Of the surviving 199 patients, 2% expired before returning for the second-stage thoracic or thoracoabdominal aortic repair completion. Of those completing the second surgery, 9.7% expired within 30 days of the second surgery. Smaller case series of open arch repair in association with ascending or thoracoabdominal aortic aneurysms (TAA) involve heterogeneous populations, and report a wide range of perioperative mortality from 5.3% to 30.8%.

There have been no randomized trials of hybrid versus open repair, but institutions have compared cohorts of open and hybrid repairs. The University of Florida in Gainesville identified 58 patients with aortic arch aneurysms and descending thoracic aortic involvement. An open cohort using a two-staged approach with aortic arch replacement and elephant trunk repair ( n = 21) was compared to a cohort using a hybrid approach ( n = 37). Rates of spinal cord ischemia (0% vs. 0%), stroke (10% vs. 11%), 30-day mortality (19% vs. 16%), and survival at 12 months (73% vs. 72%) were similar between the open and hybrid cases. These comparable results were present even though 68% of the hybrid cases still utilized cardiopulmonary bypass.

In 2010, a more recent, single-institution study compared 27 hybrid arch procedures with a contemporary series of 45 cases of open arch repairs. The incidence of permanent cerebral neurologic deficit (4% vs. 9%) and in-hospital mortality (11% vs. 16%) were similar for the hybrid versus open cohort. In the open arch group, it was noted that patients older than 75 years of age had significantly higher mortality than those younger than 75 years of age (36% vs. 9%; P = .05).

Two meta-analyses of hybrid case series have been published. Antoniou and colleagues reviewed 18 studies with a total of 195 patients. Complete arch debranching was performed in 122 patients (63%). The overall technical success rate was 86%. Overall perioperative morbidity and mortality rates were 21% and 9%, respectively. The stroke rate was 7%, and four aneurysm-related deaths were reported during follow-up (2%). No long-term data was reported. The second meta-analysis identified 15 studies with 463 patients in studies published up to May 2008. Overall 30-day mortality was 8.3%, the stroke rate was 4.4%, the paraplegia rate was 3.9%, and the endoleak rate was 9.2%. Treatment on-pump or off-pump did not affect any of the endpoints.

As increasing data on the hybrid approach emerge, the morbidity and mortality rates are comparable to open repair. Considering that hybrid series most often include higher-risk patients, a benefit of the hybrid approach may be implied.

Thoracoabdominal Aneurysm

Open repair of thoracoabdominal aneurysms involve a laparotomy, thoracotomy, proximal aortic cross clamp, and global visceral ischemia. Techniques to optimize open repairs have included left heart bypass and retrograde perfusion of the renal and mesenteric vessels. In high-volume centers, case series of open thoracoabdominal aneurysm repair demonstrate reasonable mortality of 5% to 8.3% with rates of spinal cord ischemia from 3.8% to 16%. Late survival at 5, 10, and 15 years were 54% to 67%, 29%, and 21%, respectively.

In a contemporary series of open thoracoabdominal aneurysm repair published in 2011, 305 patients were reviewed. Twenty percent underwent an urgent or emergent repair, and 57% were Crawford extents type I or II. The majority had cerebrospinal fluid drainage (97%) and left heart bypass (89%). Operative mortality was 8%, renal failure necessitating hemodialysis at discharge was 6%, and permanent paraplegia was 3%. Actuarial survival at 2 years was 79%.

Despite these single-center outcomes, database outcomes find mortalities to be more dismal. In California, after open repair, patient mortality was 19% at 30 days and 31% at 1 year. Nationwide, in-hospital mortality was found to be 22.3%. Higher mortality was seen when comparing low- versus high-volume hospitals (27.4% vs. 15.0%; P < .001) and low- versus high-volume surgeons (25.6% vs. 11.0%; P < .001). Using NSQIP data from 2005 to 2010, Bensley and colleagues identified 450 patients (418 elective, 32 emergent) undergoing open surgical repair of TAA. Thirty-day mortality was better than the previous database studies at 10.0%. Complications included failure to wean from the ventilator (39.1%), pneumonia (23.1%), reintubation (13.8%), and acute renal failure requiring dialysis (10.7%). Multivariate analysis showed emergent repair, age over 70 years, preoperative dialysis, cardiac complication, and renal complications were predictive of mortality.

There have been no randomized comparisons of open versus hybrid thoracoabdominal aneurysm repair. The Massachusetts General Hospital compared a contemporary cohort of open ( n = 77) versus hybrid ( n = 23) thoracoabdominal repairs. Of note, the hybrid patients were not open surgical candidates. Although not significant, the hybrid groups had a higher 30-day mortality (17.4% vs. 7.8%; P = .23), in-hospital mortality (26.1% vs. 10.4%; P = .27), and reoperation rates (39.1% vs. 20.8%; P = .03). However paraplegia rates (hybrid, 4.3% vs. open, 3.9%; P = .98) and 1-year survival (hybrid, 68% vs. open, 73%) were similar for both groups. Additional series of hybrid repairs are limited to small heterogeneous patient populations, with varying extents of type II and III thoracoabdominal aneurysms.

Thus far, the outcomes from hybrid thoracoabdominal and aortic arch aneurysm repair have not exceeded that of open surgery. It should be acknowledged that patients in hybrid case series are often high risk and do not qualify as candidates for open surgical repair. As experience and indications with the hybrid technique continue to grow, it may eventually prove to be an acceptable option for more than just high-risk patients.

Contraindications

An absolute contraindication to a hybrid aortic aneurysm repair is the lack of, or inability to create, a proximal and distal seal zone. Relative contraindications include the inability to safely perform debranching at the aortic arch and/or abdomen. The left carotid and left subclavian arteries require extraanatomic bypass for debranching. In hostile necks from previous surgery or radiation, exposure of the vessels and tunneling of grafts may not be feasible. The same applies in the abdomen. Exposure of the renal or visceral arteries may be difficult in a reoperative abdomen.

Debranching the Aortic Arch

The surgical component of a hybrid repair to the aortic arch is used to create at least a 2-cm proximal seal zone for an endograft. A longer segment is preferred, particularly in an area of curvature or tortuosity. This is done to treat the proximal extent of thoracic or TAA or to treat isolated aortic arch aneurysms. The anatomy of the aneurysm will determine which vessels need to be addressed. A classification scheme separates the aortic arch into proximal seal zones and identifies which vessels will be affected ( Fig. 38.2 ). Zone 0 involves the origin of the innominate artery and a stent-graft landing here compromises blood flow to the left subclavian, left common carotid, and innominate arteries. Zone 1 involves the orifice of the left common carotid artery, and a stent-graft landing here compromises the left subclavian and left common carotid circulation. Zone 2 involves the origin of the left subclavian artery, and a stent-graft landing here affects only the left subclavian artery. Zones 3 and 4 are both distal to the left subclavian artery, within the descending thoracic aorta, leaving the arch vessels unaffected.

FIG 38.2, Thoracic landing zone diagram and aortic arch aneurysm configurations.

Left Subclavian Artery

Early in the endovascular treatment of thoracic aneurysms, coverage of the left subclavian artery (zone 2) was routinely done and appeared safe. It was assumed that a patent right vertebral artery would provide enough collateral circulation to both the basilar system and the left subclavian artery via retrograde flow from the left vertebral artery. More recent data conflicts with this assumption. Meta-analysis suggests no neurological benefit from subclavian revascularization, but in a registry from Europe, multivariate regression analysis found the risk of spinal cord ischemia to increase with left subclavian artery coverage. Late development of subclavian steal and arm claudication was seen in 15% of patients in one series requiring further intervention. We recommend revascularization of the left subclavian artery in all elective cases. In unstable patients, coverage of the left subclavian artery may be reasonable.

A left supraclavicular incision is used to perform either a left subclavian to carotid artery transposition or left common carotid to subclavian artery bypass. A left supraclavicular incision is made and platysmal flaps raised. The heads of the sternocleidomastoid are identified and the lateral head can be divided if needed. The internal jugular vein and common carotid artery are identified lateral to the sternocleidomastoid. The scalene fat pad is retracted laterally, taking care to ligate all lymphatic channels. The phrenic nerve and anterior scalene are identified. If needed, the anterior scalene can be divided for more lateral subclavian artery exposure. Exposure of the left subclavian artery proximal to the left vertebral artery will take the dissection into the mediastinum and the lymphatic duct will need to be ligated.

In a transposition, the subclavian artery is divided proximal to the left vertebral, the stump is ligated, and the subclavian artery sewn end to side onto the common carotid artery. In a bypass, the subclavian artery proximal to the left vertebral needs to be ligated surgically, or can be occluded by endovascular means to avoid a type II endoleak. Endovascular occlusion does not require the more proximal subclavian artery be exposed and can be performed with coils or an Amplatzer plug (ADA Medical Corporation, Plymouth, MN) deployed in a retrograde fashion though the distal anastomosis of the carotid–subclavian artery bypass or from a brachial approach ( Fig. 38.3 ). This should be done after the aortic stent-graft is deployed to prevent developing thrombus on the Amplatzer plug from embolization while there is still antegrade flow through the subclavian artery. Alternatively, the patient can be maintained heparinized until the thoracic endograft covering the origin of the left subclavian artery is deployed.

FIG 38.3, Left carotid–to–subclavian artery bypass. (A) Angiogram and (B) schematic of left carotid–to–subclavian artery bypass (black arrow) completed with Amplatzer plug placed at the left subclavian origin (box) . The left vertebral artery is preserved (white arrow) .

In cases where a left internal mammary artery has been used for a coronary bypass graft, a transposition cannot be performed. In constructing the carotid–subclavian artery bypass, the subclavian anastomosis should be distal to the origin of the internal mammary artery, thereby maintaining native flow during sewing of the anastomosis. After the anastomosis and bypass are complete, the origin of the left subclavian artery is ligated and retrograde flow will fill the internal mammary artery.

Partial Arch Debranching

Partial arch debranching involves revascularization of the left common carotid and left subclavian arteries using the right common carotid artery as inflow. This is in preparation for deploying an endograft just distal to the innominate artery origin (zone 1). This can be done with extraanatomic bypasses, without the need for a sternotomy or thoracotomy ( Fig. 38.4 ).

The carotid bifurcation should be identified by ultrasound so that the incision is placed to expose the common carotid artery proximal and away from the bulb, thus avoiding the most common location of carotid plaque. The right common carotid artery is exposed anterior to the sternocleidomastoid muscle. The left common carotid can be exposed through a matching incision and exposure, or it can be exposed posterior to the sternocleidomastoid through the same incision used to expose the left subclavian artery.

A retropharyngeal tunnel is created between the two common carotid arteries staying just anterior to the anterior spinous ligament of the cervical spine. A bypass is performed with a 6-mm Dacron graft in an end side fashion. The tunnel is made with a gentle downward curve. Alternatively, the tunnel can be placed subcutaneously behind the manubrium for a better cosmetic result. Damage to this bypass can occur if a sternotomy is ever needed and patients should be so informed.

The more proximal left common carotid artery is used to create the left subclavian artery transposition or bypass. The left common carotid artery is ligated proximally at the base of the neck.

Care is taken to avoid bilateral recurrent laryngeal or vagus nerve injury. The carotid arteries should be investigated preoperatively for stenosis. Intraoperative brain monitoring is usually not necessary when clamping is limited to the common carotid artery as external-to-internal carotid artery collaterals will maintain adequate flow to the affected internal system. Similarly, common carotid artery shunting has not been necessary.

You're Reading a Preview

Become a Clinical Tree membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here