Thoracic Endovascular Aortic Repair for Descending Thoracic Aortic and Aortic Arch Aneurysms




Abstract


Thoracic endovascular aortic repair (TEVAR) has become an effective treatment for various descending thoracic aortic pathologic processes, including aortic aneurysm and dissection. Although long-term outcome data for this therapy are not available, the short-term and intermediate results have been promising. Long-term data is accumulating and appears to be comparable to open surgery.




Keywords

aortic surgery, TEVAR, aorta, endovascular repair of the aorta

 




Summary





  • Thoracic endovascular aortic repair (TEVAR) has become an effective treatment for various descending thoracic aortic pathologic processes, including aortic aneurysm and dissection. Although long-term outcome data for this therapy are not available, the short-term and intermediate results have been promising. Long-term data is accumulating and appears to be comparable to open surgery.



  • Multiple devices have been investigated and approved in multicenter trials. Multiple iterations and advance in endograft design have helped navigate anatomic limitations. With ongoing improvements in imaging and with the development of branched endografts in particular, surgeons will be able to offer endovascular therapy for the aortic arch and thoracoabdominal aorta to an increased population of patients when appropriate.






Surgical Anatomy





  • Beginning distal to the left subclavian artery, the descending thoracic aorta is the continuation of the aortic arch. As it descends through the posterior mediastinum, the descending thoracic aorta lies to the left of the vertebral bodies and gradually approaches the midline. At the level of the 12th vertebra, it passes through the aortic hiatus in the diaphragm and becomes the abdominal aorta ( Fig. 27.1 ).




    Figure 27.1



  • Anterior branches of the descending thoracic aorta include bronchial and esophageal arteries. These branches continue as the segmental arterial supply to their respective structures. Intercostal arteries are posterior branches along the length of the descending thoracic aorta and provide segmental arterial blood supply to the spinal cord.



  • In most patients, a dominant anterior medullary artery, the artery of Adamkiewicz, arises between levels T7 and L1 and provides most of the blood supply to the anterior spinal artery, perfusing the anterior two-thirds of the spinal cord. Anteriorly, the intercostal arteries continue along the inferior margins of the ribs and form collaterals with the internal thoracic arteries located at the anterior chest wall.



  • There are no major arterial branches in the descending thoracic aorta, enabling the treatment of the entire descending thoracic aorta with TEVAR. The first major branch is the celiac artery, which arises in the abdominal aorta to supply the upper gastrointestinal tract. However, complete coverage of the entire descending thoracic aorta, including the left subclavian artery, is associated with an increased risk of stroke and spinal cord ischemia.






Preoperative Considerations





  • Careful preoperative planning with appropriate imaging is essential for TEVAR. Preoperative assessment must address two important issues: anatomic requirements and vascular access. The gold standard is computed tomography (CT) angiography of the thorax, abdomen, and pelvis, with distal arterial runoffs. Thin-slice helical CT scanning with 2-mm slices is ideal to create three-dimensional reconstructions of the aorta. In patients with contraindications to intravenous contrast, magnetic resonance angiography is an acceptable alternative.




Anatomic Requirements





  • Anatomic requirements center on the suitability of the proximal and distal landing zones. TEVAR involves the deployment of an intraluminal endoprosthesis resulting in the exclusion of the thoracic aneurysm. Therefore, the essential requirement is suitable proximal and distal landing zones to achieve an adequate seal and prevent endoleaks.



  • The evaluation for the suitability of the landing zones involves two major criteria, the length of the zone and the aortic diameter. Although device-specific, the length of the landing zone must be sufficient to achieve adequate exclusion. For most devices, the requirement is 2 cm of aorta without significant tapering. The aortic diameter must safely accommodate a self-expanding endovascular device. For aneurysmal disease, the device should be upsized (compared with the diameter of the landing zone) by 10% to 20% to achieve adequate exclusion. Current devices allow safe treatment for aortic diameters between 18 and 43 mm.



  • For nonaneurysmal disease, such as dissection or traumatic transection, less aggressive upsizing (< 10%) is generally recommended.



  • Additional factors to consider in the evaluation of the landing zones include the presence of thrombus, rapid tapering, calcification, tortuosity, and angulation ( Fig. 27.2 )




    Figure 27.2



  • Circumferential thrombus and extensive calcification at a landing zone may not allow adequate seal, resulting in endoleaks.



  • Minimal tapering of the aortic diameter over the length of the landing zone (< 15%), with minimal tortuosity and angulation, are also desirable to ensure adequate exclusion.



  • Angulation is often a proximal landing zone issue at the level of the distal arch. Severe angulation may result in so-called bird-beaking of the endograft. These and other factors may require extension of the proximal and distal landing zones. If coverage of the branch vessels is necessary at the proximal or distal landing zone, an extraanatomic bypass such as a carotid artery–subclavian artery bypass or mesenteric artery–visceral artery bypass, respectively, may be necessary. However, branched endografts that are currently undergoing feasibility trials may be appropriate in these settings in the future.




Vascular Access





  • A vascular complication is a major component of the morbidity and mortality rates associated with TEVAR. Current devices require a large-caliber delivery system, typically ranging from 18 to 24 F outer diameter. Several device manufacturers are investigating low-profile devices that would potentially decrease vascular complications.



  • Preoperative imaging must include assessment of the iliofemoral vasculature. In addition to diameter, factors such as excessive calcification, tortuosity, history of peripheral vascular disease, and previous aortoiliac surgery may prevent safe delivery of the endograft.



  • If severe peripheral occlusive disease is prohibitive to the safe delivery of the endograft, endovascular balloon angioplasty may be performed preoperatively or concomitantly during TEVAR before the introduction of the delivery devices.



  • If femoral arterial access is inadequate, aortoiliac exposure through a retroperitoneal approach may be required. Other access alternatives include the subclavian artery, carotid artery, direct aortic approach, and transapical




Intraoperative Monitoring





  • Patients undergoing TEVAR are at risk for neurologic complications, including stroke and spinal cord ischemia. Intraoperative neuromonitoring using electroencephalography (EEG), motor-evoked potentials (MEPs), and somatosensory-evoked potentials (SSEPs) should be routinely used for patients undergoing TEVAR. Stroke is associated with wire manipulation in the severely atherosclerotic aortic arch, and systemic heparinization should be attempted before any wire manipulation in the arch.



  • Spinal cord ischemia may result in temporary or permanent lower extremity paraplegia. Factors such as the length of aortic coverage, previous abdominal aortic aneurysm repair, occlusive aortoiliac disease, and coverage of the left subclavian artery may affect the collateral arterial supply to the spinal cord and increase the risk of paraplegia.



  • Intraoperative neuromonitoring may detect early evidence of spinal cord ischemia before a reliable neurologic examination can be performed. Maneuvers such as volume expansion and lumbar drainage should be used to prevent permanent paraplegia if intraoperative neuromonitoring suggests spinal cord ischemia.



  • In patients with preoperative risk factors for spinal cord ischemia (i.e., previous abdominal aortic aneurysm repair, occlusive aortoiliac disease, or total coverage of the descending thoracic aorta), preemptive lumbar drainage should be considered.






Operative Steps



Imaging





  • The primary modality of intraoperative imaging for TEVAR is fluoroscopy. Using a fixed or portable C-arm, fluoroscopy provides real-time imaging. Additional helpful features include digital subtraction angiography (DSA) and road mapping.



  • DSA allows subtraction and removal of background images such as bony structures to enhance visualization of the object injected with contrast (e.g., descending thoracic aorta).



  • Road mapping involves the transfer of a reference image superimposed onto a live image for guidance during deployment of the device ( Fig. 27.3A ).






    Figure 27.3



  • Intravascular ultrasonography (IVUS) is an option for patients with renal insufficiency or any other contraindication to intravenous contrast. Introduced from the femoral artery, IVUS provides the advantage of direct intraluminal imaging, particularly in cases of dissection, where the true and false lumens must be identified. Furthermore, intraoperative evaluation of the aorta, particularly the landing zones, can be performed.



  • Information regarding the characteristics of the landing zones, such as diameter and the presence of thrombus, may be obtained and verified with preoperative imaging (see Fig. 27.3B ).




Access





  • For most patients, the common femoral artery provides adequate vascular access for deployment of the endograft ( Fig. 27.4A and B ). A transverse incision is made at the level of the inguinal ligament. The femoral artery is exposed, and proximal and distal control are obtained. An 18-G needle is used for direct puncture of the femoral artery, and a flexible guidewire (0.035-inch Bentson wire; Boston Scientific, Natick, MA) is introduced retrograde to the aortic arch using the Seldinger technique under fluoroscopy. Alternatively, percutaneous access of the femoral artery can be used with percutaneous closure devices, which are becoming increasingly popular among surgeons.




    Figure 27.4



  • Because of the angulation and tortuosity of the aortic arch, it is often difficult to deliver the endograft with a flexible guidewire, and an extra-stiff guidewire (0.035-inch Lunderquist wire; Cook Medical, Bloomington, IN) is often required. An extra-stiff guidewire should never be introduced into the arch without a guide catheter because of the risk of rupture or dissection. Therefore, a wire exchange maneuver is needed.



  • Under fluoroscopy, a long guide catheter (100-cm MPA [multipurpose angle]; Cordis, Milpitas, CA) is advanced to the arch over the flexible guidewire. Once in position, the MPA is secured, and the flexible guidewire is removed. The Lunderquist wire is then advanced within the MPA to the level of the aortic arch under fluoroscopy. The MPA is removed and the extra-stiff guidewire is in position for deployment of the endograft.



  • If the femoral artery is suboptimal for access, the iliac artery may be exposed with a retroperitoneal approach (see Fig. 27.4C ). The iliac artery can be directly accessed using a technique similar to that described for the femoral artery. A double purse string of 4-0 polypropylene sutures is used to secure the vessel and provide hemostasis with the application of two sets of tourniquets. Alternatively, a 10-mm Dacron graft can be sewn to the iliac artery as a conduit for delivery of the endograft. The conduit may be brought through a separate counterincision in the groin to allow for better angulation of the relatively long and stiff deployment device.



  • A diagnostic catheter (5 F pigtail; Cordis) with multiple side holes is placed percutaneously in the contralateral femoral artery. Standard percutaneous puncture with the Seldinger technique is used, and a 5 F or 7 F introducer sheath (Cordis) may be placed for access. The pigtail catheter is advanced to the aortic arch under fluoroscopy.



  • Occasionally, brachial access is needed for coil embolization of the left subclavian artery to create an adequate proximal landing zone if a carotid artery–subclavian artery bypass was performed. Brachial access is also necessary for patients undergoing branched endograft deployment. This is because precise deployment of the endograft at the left subclavian artery or left common carotid artery can be facilitated with placement of the pigtail catheter through a left brachial artery access.



  • Brachial access can often be achieved percutaneously using the Seldinger technique with placement of a 5 F introducer sheath. Systemic heparinization is recommended before any wire manipulation in the arch.




Deployment of Endograft for Aneurysmal Disease





  • Preoperative planning will have determined the number, size, and sequence of deployment of the endografts. The total treatment length (coverage length) of the descending thoracic aorta determines the length and number of endografts.



  • The diameter of the endografts is determined by the diameter of the aortic landing zones. Although there are device-specific variabilities, the endografts are generally deployed in a proximal to distal sequence. However, if the proximal endograft is larger than the distal device, or precise deployment is required at the celiac artery, it may be preferable to deploy the endografts in a distal to proximal sequence.



  • Under fluoroscopic guidance, the endograft is delivered to the proximal landing zone using a stiff guidewire ( Figs. 27.5 and 27.6 )


Jan 26, 2019 | Posted by in CARDIAC SURGERY | Comments Off on Thoracic Endovascular Aortic Repair for Descending Thoracic Aortic and Aortic Arch Aneurysms
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