Volume 12, Issue 3 , Pages 167-177, Autumn 2007
Hybrid Repairs of the Distal Aortic Arch and Proximal Descending Thoracic Aorta
Article Outline
- Preoperative Considerations
- Operative Techniques
- Postoperative Considerations
- Current Role of Hybrid Procedures
- Acknowledgment
- Copyright
Compared with aneurysms that are limited to the mid and distal descending thoracic aorta, those that extend up to or into the transverse aortic arch are more challenging to repair with open techniques. This is due, in part, to the difficulty of exposing the aorta in this region, the attendant risk of injury to adjacent structures during the repair, and, when the arch is involved, the need for a period of hypothermic circulatory arrest. In patients with poor physiologic reserve, these operations carry substantial risk, making endovascular repair an attractive option. The proximity of the aneurysm to the brachiocephalic branches, however, makes it difficult to achieve a satisfactory proximal landing zone for an endograft. In this situation, hybrid procedures that combine open and endovascular techniques can be used to effectively “debranch” the arch and thus allow these vessels to be covered by the stent-graft.
Preoperative Considerations
Endovascular stenting for aneurysmal disease is an especially attractive alternative to open repair in patients with conditions that increase the risk of mortality and morbidity from open repair. These conditions include advanced physiologic age, multi-organ dysfunction, inability to tolerate the single-lung ventilation required for open repair, and prior operative procedures or incision site infections that make exposure difficult.
One group of patients who, in general, should not undergo endovascular stenting is young patients with Marfan syndrome. The aorta in these patients has a greater propensity to dilate with time, even after an aneurysm is excluded from direct exposure to systemic pressures. The landing zone is likely to increase in size, and the seal at these sites is eventually lost, subjecting the patient to complications such as endoleak, device migration, device erosion, and the need for reoperation to remove the device and repair the aneurysm. These reasons for avoiding endovascular stenting in Marfan patients should probably be extended to include patients with other connective tissue disorders, such as the Ehlers–Danlos and Loeys–Dietz syndromes.
Deciding a patient’s candidacy for an endovascular repair requires detailed assessment of the vascular anatomy and the aneurysm’s characteristics. Multiple 5-mm-slice computed tomographic angiography (CTA) of the brain, chest, abdomen, and pelvis is recommended for preoperative evaluation, and three-dimensional vascular reconstructions are highly desirable. Ideally, the patient will have a femoral or iliac artery of sufficient caliber to accommodate the sheath size needed for deployment of the stent. Otherwise, access to the common iliac artery, the distal aorta, or the ascending aorta may be required. In some cases, excessive tortuosity or calcification of the access vessels precludes their use for stent deployment.
Deploying the stent requires proximal and distal aortic landing zones that are at least 2 cm in length; the diameter of these landing zones should not be much smaller than the smallest sized, or any larger than the largest sized, stent-grafts. Additionally, excessive calcification or thrombus at the landing zones can preclude successful creation of seal zones, so these characteristics may exclude patients from candidacy. With aneurysms involving the distal aortic arch, establishing a 2-cm proximal landing zone is not possible without covering one or more of the great vessels. In such instances, arch debranching can make stenting procedures a viable treatment alternative in patients for whom it would otherwise be ruled out. Brain imaging is used to define the status of the cerebral circulation and help determine the safest approach to managing the arch branches. For example, in patients who are dependent on the left vertebral artery because of inadequate collateral vessels in the circle of Willis, left carotid-to-subclavian artery bypass should precede endovascular coverage of the left subclavian artery.
If the patient has previously had his or her abdominal aorta replaced, or if we anticipate that the endograft will cover much of the distal descending thoracic aorta (beyond the 6th thoracic vertebra), we place an intrathecal drainage catheter in the intervertebral disk space between L3 and L4 or between L4 and L5. Cerebrospinal fluid (CSF) is allowed to drain passively from the catheter and is aspirated with a closed collection system as needed to keep the CSF pressure between 8 and 10 mm Hg during the operation.
Operative Techniques
Figure 1.
The distal aortic arch and proximal descending thoracic aorta are aneurysmal. Establishing a 2-cm proximal landing zone will require covering the origins of the arch vessels with the stent-graft; a debranching procedure will allow for device deployment in the arch while preserving blood flow to these vessels. The distal landing zone exceeds the 2 cm requirement and does not involve the celiac trunk. Despite the availability of a long length of aorta distally, one should not cover more aorta than is necessary to effectively seal the device, because this may cover important intercostal arteries supplying the anterior spinal artery, thereby causing spinal cord ischemia that may result in paraplegia or paraparesis. (Color version of figure is available online at http://www.us.elsevierhealth.com/optechstcvs.)
Figure 2.
A “Y” graft is fashioned before any vessels are clamped. Here, an 8-mm graft is sewn to a 10-mm graft with continuous 4-0 polypropylene suture. The end of the 8-mm graft is beveled to create a gently angled branch. (Color version of figure is available online at http://www.us.elsevierhealth.com/optechstcvs.)
Figure 3.
The patient is prepped and draped from the neck to the knees, allowing for access to the chest and both groins. A sternotomy provides exposure of the ascending aorta and brachiocephalic branches. The proximal end of the “Y” graft is beveled to allow a gentle takeoff from the aorta after its attachment. A side-biting clamp is placed on the lateral aspect of the proximal ascending aorta after 100 units/kg (1 mg/kg) heparin is administered intravenously. An aortic punch is used to cut a hole in the ascending aorta in the region excluded by the side-biting clamp. Here, the anastomosis is fashioned between the graft and the aorta with running 4-0 or 5-0 polypropylene suture. (Color version of figure is available online at http://www.us.elsevierhealth.com/optechstcvs.)
Figure 4.
The “Y” graft is clamped proximally, and the side-biting clamp is removed. The left common carotid artery is clamped distally, ligated proximally, and divided. The 8-mm branch of the graft is anastomosed end-to-end to the left common carotid artery with running 5-0 or 6-0 polypropylene suture. We have found that it is generally easier to attach this deeper vessel before attaching the innominate artery. (Color version of figure is available online at http://www.us.elsevierhealth.com/optechstcvs.)
Figure 5.
The clamp on the proximal portion of the “Y” graft is moved distal to the takeoff of the 8-mm side branch after the left carotid branch is appropriately de-aired. The clamp on the left common carotid artery is removed, restoring flow to this vessel. Now the innominate artery is clamped distally, ligated proximally, and divided. An anastomosis between the 10-mm graft and the distal end of the transected innominate artery is fashioned by using running 5-0 or 6-0 polypropylene suture. The graft is de-aired, and the clamp is removed, restoring flow to the innominate artery. The proximal stumps of the innominate and left common carotid arteries are then oversewn with running 4-0 or 5-0 polypropylene sutures. (Color version of figure is available online at http://www.us.elsevierhealth.com/optechstcvs.)
Figure 6.
At this point in the operation, one has the option of arranging for an antegrade deployment of the endovascular stent-graft or using the more common, retrograde approach. Here, the antegrade approach is illustrated. A 10-mm graft is anastomosed to the proximal ascending aorta on the lateral side; a side-biting clamp is used to exclude a portion of the aorta where the graft is attached. After the anastomosis is completed and the clamp is removed, the side of the 10-mm graft is prepared for insertion of the stent delivery system sheath; using this approach instead of advancing the sheath into the free end of the graft results in better hemostatic control. A clamp is placed on the free end of the 10-mm graft, and a guidewire is introduced into the side of the graft through a needle. Throughout the procedure, fluoroscopic guidance is used to directly visualize each intravascular manipulation of a guidewire, catheter, sheath, and device. The guidewire is advanced through the ascending aorta and arch until it reaches the distal descending thoracic aorta. The introducer needle is removed, and a Bern catheter is used to exchange the flexible guidewire for a stiff one that sits in the descending thoracic aorta. This stiff guidewire is needed to advance the stent-graft delivery system. A needle is used to create a second opening in the 10-mm graft, and a guidewire is advanced for a short distance. Over this guidewire, a 5-French sheath is introduced into the ascending aorta. A marked pigtail catheter is advanced over the guidewire, and the wire is removed. This catheter is used to inject dye for fluoroscopic imaging of the aneurysm and then to determine the length of stent that will be required. (The distance between marks represents 1 centimeter.) Although one should have an idea of the necessary treatment length from the results of appropriate preoperative imaging, it is during this stage of the operation that the final decision is made. An appropriately sized stent-graft can now be advanced over the stiff guidewire in the delivery system sheath until the device lies in position at the distal landing zone; this landing zone must be at least 2 cm in length. The marked pigtail catheter is retracted so as to sit proximal to the proximal portion of the stent-graft, and the device is deployed under direct fluoroscopic imaging while the anesthesiologist suspends ventilation. Should the treatment length require it, additional stent-grafts can be deployed to completely exclude the aneurysm. Obviously, the proximal portion of the stent-graft must not cover the origin of the graft to the great vessels, and the delivery system sheath must also be pulled back far enough so as not to hinder opening of the stent-graft. If a second graft needs to be deployed, it is recommended that there be at least 5 cm of overlap between same-diameter grafts and 3 cm overlap between grafts with different diameters. The general rule is that the larger graft should be deployed within the smaller graft to ensure an appropriate seal. The stent delivery system is then withdrawn through its sheath, and a balloon dilator is advanced through the sheath over the stiff guidewire. An endoluminal balloon is used to expand the proximal landing zone first, then the overlap region(s), if any, and finally the distal landing zone. A final pigtail catheter injection during fluoroscopy is used to confirm proper seating of the stent-graft and complete exclusion of the aneurysm. (Color version of figure is available online at http://www.us.elsevierhealth.com/optechstcvs.)
Figure 7.
The endovascular stent-graft can be introduced retrograde through the femoral artery, external iliac artery, common iliac artery, or distal aorta. This figure shows deployment through the left common femoral artery. The right common femoral artery is used to introduce the marked pigtail catheter for measuring treatment lengths and landing zones. Again, fluoroscopic guidance is used whenever intravascular instruments are manipulated. After the arch vessels have been transferred to the graft off the proximal aorta, a small incision is made over the femoral artery. A soft guidewire is advanced through a needle in the femoral artery until it lies in the ascending aorta. A Bern catheter is used to exchange the soft wire for a stiff one. The sheath for the device is then advanced into the artery over the stiff guidewire. An appropriately sized endovascular stent-graft is then introduced through the sheath until it lies within the proximal portion of the arch. Through the contralateral femoral artery, a marked pigtail catheter is advanced over a guidewire into the ascending aorta. This can be done percutaneously or through a small cut-down. Fluoroscopy with contrast is used to position the device for deployment. The proximal portion is positioned to create a landing zone of at least 2 cm in an area of minimal angulation or tapering. It is important to note that, when deployed, the stent will abut the greater curvature of the aorta, and this must be accounted for during positioning. Otherwise, the proximal portion of the stent-graft may land well short of the intended proximal landing zone as it moves to occupy the curvature of the aorta. A good way to avoid this problem is to make certain that the stiff wire follows the aortic wall along its greater curvature so that the stent-graft, when introduced over this wire, will do likewise. Once the guidewire is properly positioned, the stent is deployed, the landing zones are balloon-dilated, and completion angiograms are obtained. If the aneurysm is of sufficient length to require more than one stent-graft, the general rule is to deploy the smaller graft first. Whenever feasible, the distal-most stent-graft is deployed before proximal grafts are placed. Adequate overlap of grafts is necessary to minimize the risk of endoleak. (Color version of figure is available online at http://www.us.elsevierhealth.com/optechstcvs.)
Figure 8.
The deployed and properly seated endovascular stent-graft and debranched aortic arch are pictured in this figure. Here and in the previous figures, the left subclavian artery has been left intact but covered by the stent-graft. In the majority of instances, this can be done without causing postoperative complications. However, this technique has the potential to result in ischemia of the left arm, subclavian steal syndrome, stroke, stent-graft failure due to type II endoleak, and even myocardial ischemia if the patient has a patent left internal thoracic arterial graft supplying a coronary artery. Usually the deployed graft will conform to the greater curvature of the arch and occlude the orifice of the left subclavian artery, thereby preventing back-bleeding and a type II endoleak. If the completion angiogram shows an endoleak in this area despite proper graft deployment and balloon dilation, the left subclavian artery can be ligated and divided (inset) through the sternotomy incision. Covering the left subclavian artery carries a small risk of cerebral ischemia; this risk is increased in patients who are dependent on the left vertebral artery for posterior cerebral perfusion (either because it is the dominant or the sole vertebral artery or because there is concurrent high-grade left common carotid stenosis). The next figures illustrate our approach to maintaining perfusion to the left subclavian artery despite its coverage by the stent-graft. (Color version of figure is available online at http://www.us.elsevierhealth.com/optechstcvs.)
Figure 9.
The aneurysm depicted here involves the aorta immediately distal to the left subclavian artery. Deploying an endovascular stent-graft in this region and allowing for a 2-cm proximal landing zone will require coverage of the left subclavian artery, but not necessarily the other great vessels. Especially in cases in which there is a sufficient distance between the left common carotid and left subclavian arteries, as suggested in this figure, one can plan to deploy a stent-graft without covering the left common carotid and innominate arteries. Because this obviates the need to debranch the proximal arch vessels, a sternotomy incision is not necessary. If there is concern about covering the orifice of the left subclavian artery, we perform a left carotid-to-subclavian artery bypass. (Color version of figure is available online at http://www.us.elsevierhealth.com/optechstcvs.)
Figure 10.
This illustration demonstrates the surgical approach used for left carotid-to-subclavian artery bypass. A 6- to 7-cm incision is made beginning just lateral to midline, 3 to 4 cm superior and parallel to the clavicle. The platysma muscle is divided, and the clavicular head of the sternocleidomastoid is retracted medially or divided to facilitate exposure. The common carotid artery is dissected free from the adjacent jugular vein and vagus nerve. After the omohyoid muscle and scalene fat pad are divided, the phrenic nerve is identified and protected. The anterior scalene muscle is then divided to expose the subclavian artery. The vertebral and internal thoracic arteries are identified and spared. After heparin is administered, the carotid artery is temporarily clamped while an 8-mm graft is anastomosed to the vessel in an end-to-side manner with 6-0 polypropylene suture. The graft is de-aired and clamped; the carotid clamp is removed, and the conduit is cut to appropriate length. The subclavian artery is then clamped, and an end-to-side anastomosis between the graft and artery is fashioned. The clamps are released, restoring subclavian artery circulation, and, finally, the subclavian artery proximal to the anastomosis is ligated with a heavy silk ligature. (Color version of figure is available online at http://www.us.elsevierhealth.com/optechstcvs.)
Figure 11.
The deployed stent-graft is shown in proper position, distal to the left common carotid artery and covering the left subclavian artery origin. The subclavian artery is ligated proximal to the carotid-subclavian bypass conduit, thereby limiting the risk of an endoleak at the seal zone. (Color version of figure is available online at http://www.us.elsevierhealth.com/optechstcvs.)
Postoperative Considerations
After operation, our vigilance for spinal cord ischemia varies according to the length of aorta that was covered by the stent-graft. Although coverage of any portion of the aorta can result in ischemia to the spinal cord, a stent-graft that extends beyond T6 carries a higher risk of paraplegia. Accordingly, in these patients, spinal cord perfusion pressure is managed by keeping mean arterial blood pressure (MAP) high and intrathecal pressure low. Intravenous fluid, vasopressors, and inotropes are used to maintain MAP between 70 and 90 mm Hg. Initially, the intrathecal pressure is kept between 12 and 15 mm Hg by draining no more than 25 mL of CSF every hour. Once the patient is awake and able to demonstrate motor function of the legs, CSF pressure is allowed to rise to between 15 to 18 mm Hg. If motor function of the legs is lost or diminished, we allow MAP to rise above 100 mm Hg and administer steroids and mannitol, although the evidence for these drugs’ benefits is equivocal.
All patients are discharged home with an antiplatelet agent, usually coated acetylsalicylic acid. For those with bypass grafts 10 mm or smaller in diameter, we prescribe daily clopidogrel for 6 months. A follow-up 5-mm-slice CTA scan is performed with and without contrast to assess for endoleak and device migration before the patient is discharged from the hospital. Thereafter, surveillance CTA scans are obtained at 3 months, 6 months, and then yearly, barring any aneurysm expansion, endoleak, or device migration, which warrant more frequent imaging.
Current Role of Hybrid Procedures
Hybrid procedures are not currently considered the treatment of choice for most patients with distal arch or proximal descending thoracic aortic aneurysms, primarily because the long-term durability of these repairs remains uncertain. Regrettably, it is unlikely that randomized controlled trials comparing open replacement to hybrid operations will be performed; therefore, definitive efficacy data will remain scarce. Hybrid procedures are well-suited for patients with discrete saccular aneurysms and pseudoaneurysms, because their repair requires covering only a limited length of aorta and because the landing zones are usually of sufficient length, and are not tapered, angled, or calcified. This is not to say that these procedures should not be considered for patients with more extensive aneurysms; however, at present, hybrid procedures are best used in patients with significant comorbidities who would otherwise not be considered for aortic repair. It is worth reiterating that, in general, patients with Marfan syndrome or other connective tissue disorders are not best served by endovascular procedures.
Acknowledgment
The authors thank Stephen N. Palmer, PhD, ELS, for editorial assistance.
PII: S1522-2942(07)00064-5
doi:10.1053/j.optechstcvs.2007.05.005
© 2007 Elsevier Inc. All rights reserved.
Volume 12, Issue 3 , Pages 167-177, Autumn 2007
