Endovascular Therapy for the Treatment of Thoracic Aortic Pathologies

Gore TAG

The Gore TAG thoracic endoprosthesis (W.L. Gore, Inc., Flagstaff, AZ) was approved by the FDA in March 2005 for the treatment of descending thoracic aortic aneurysms. The first device to be approved, the Gore TAG, is a self-expanding polytetrafluoroethylene endograft comprised of nitinol support. Concern over fracture of the longitudinal support wire led to the revision of the original Gore device to its current Gore TAG endoprosthesis. Unique to this device system is the introducer sheath, which enables the delivery of multiple devices and minimizes traumatic injury to the femoral access vessels. The introducer sheath ranges from an inner diameter of 20 Fr to 24 Fr depending on the size of the Gore TAG devices required for treatment. The Gore TAG endoprosthesis ranges from a minimal diameter of 26 mm to a maximum diameter of 40 mm, with lengths ranging from a minimum of 10 cm to a maximum of 20 cm ( Fig. 72-2 ). The mechanism of deployment involves release of the endograft from a center to peripheral fashion. Thus, precise deployment of the proximal and distal landing zones may be difficult.

In August 2011, Gore Conformable-TAG (C-TAG) device received FDA approval. The C-TAG has essentially replaced the older-generation TAG device. It provides greater flexibility and conformability, with a broad, oversizing window (6%-33%), and is available in straight and tapered forms. The C-TAG is available in a smaller-diameter range than the TAG device (21 mm) and can be placed using an 18 Fr (inner diameter) delivery system. C-TAG is now FDA approved for use in thoracic aortic aneurysm disease, PAU, blunt thoracic aortic injury, and complicated type B dissection.

Medtronic Talent and Valiant Thoracic Endoprosthesis

The Talent Device

Recently approved in June 2008 by the FDA for the treatment of descending thoracic aortic aneurysms, the Talent device is a preloaded stent graft incorporated into a CoilTrac delivery system. It is a stent graft composed of a polyester graft (Dacron) sewn to a self-expanding nitinol wireframe skeleton. Radiopaque markers are sewn to the graft material to aid in visualization during fluoroscopy. The CoilTrac delivery system is a sheathless, push-rod–based delivery system. Preloaded onto an inner catheter, the Talent device is deployed by pulling back an outer catheter, allowing the device to self-expand and contour to the aorta. A balloon may be used to ensure proper apposition of the graft to the aneurysmal aorta after deployment.

The Talent device is designed as a modular system. Forty-seven different configurations ranging from a diameter of 22 to 46 mm and cover lengths from 112 to 116 mm are available. To accommodate the size differences often found between the proximal and distal portions of the aorta in thoracic aneurysms, tapered grafts are available for better aneurysmal conformability and prevention of junctional endoleaks. Four configuration categories are available: proximal main, proximal extension, distal main, and distal extension ( Fig. 72-3 ). The proximal configurations and the distal extension are offered with a bare-spring design (Free-Flo design). The bare-spring design allows for placement of the device crossing the arch vessels proximally and the celiac artery distally for suprasubclavian and infraceliac fixation, respectively.

Cook Zenith TX2 Thoracic Endoprosthesis

Recently approved in 2008 by the FDA, the Cook Zenith TX2 thoracic endoprosthesis (Cook, Inc., Bloomington, IN) is designed as a modular system with a specific proximal and distal configuration ( Fig. 72-4 ). The graft consists of stainless steel Z-stents with full-thickness polyester fabric. Similar to the Medtronic delivery system, the Zenith TX2 system does not require a delivery sheath, and it is introduced as a preloaded catheter with triggers. The device sheath has a hydrophilic coating and sizes range from 18 to 22 Fr, depending on the diameter of the endoprosthesis. The diameter of the endoprosthesis ranges from 22 to 42 mm and lengths from 120 mm to 207 mm. The two components are designed to be deployed from a proximal to distal direction, and tapered devices are available.

Deployment of the TX2 is achieved through a trigger system to ensure a controlled deployment. Flushed at the proximal end with barbs to prevent migration and endoleak, the device is deployed by an unsheathing mechanism. To minimize the “wind sock” effect during deployment (thus distal migration), the proximal barb component of the device is not released until the graft is deployed and the trigger released. The distal component is deployed in a similar mechanism. However, in addition to barbs, the distal component also has bare springs at its caudal portion. Proximal and distal extensions are available if additional coverage is necessary.

Access

Safe vascular access for thoracic aortic device deployment is the key to thoracic aortic stent grafting. The majority of the morbidity and mortality is a direct result of arterial access complications. Extensive preoperative planning with appropriate imaging is mandatory. The “gold standard” for preoperative evaluation is a computed tomography (CT) angiogram that includes the thorax, abdomen, pelvis, and femoral arteries. Fine-cut helical CT scanning with at minimum 3-mm slices is ideal ( Fig. 72-5 ). In patients who cannot receive a CT with contrast, magnetic resonance angiography is an acceptable substitution.

All the thoracic endovascular devices take a long time to reach the descending aorta, are of large caliber to contain the thoracic aortic endoluminal graft, and are relatively stiff to allow “pushability” through the iliofemoral access points and through the abdominal aorta. The management of the delivery of the thoracic aortic stent graft is often the most challenging aspect of the case. Delivery systems of the three currently FDA-approved thoracic endoprostheses will require arterial access size of a minimum of 7.5 to 8.0 mm. Creation of a conduit to the femoral or iliac artery may be necessary to achieve adequate access. Not only the size of the arterial vessels, but also the anatomy of the iliofemoral and abdominal aorta, must be considered when planning the access route. Excessive tortuosity and atherosclerosis with occlusive disease may provide barriers to safe delivery of the endograft. In approximately 20% of patients, retroperitoneal access to the common iliac arteries will be required owing to issues of femoral or external iliac artery size and/or tortuosity.

Careful review of preoperative studies will indicate which patients will have difficult access. Patients with atherosclerotic occlusive iliac disease may be treated with standard endovascular techniques of balloon angioplasty to reduce the obstruction. Iliac stents should be avoided because of the potential interference of these stents with the thoracic aortic access devices. These procedures on the access vessels should be carried out at least 6 weeks before thoracic aortic stent grafting to allow healing of the iliac arteries post-angioplasty and manipulation. At the completion of the thoracic aortic endografting, iliac stents may be placed if appropriate.

Access to the retroperitoneum allows several options for safe device deployment. The common iliac artery may be used for device deployment. An open surgical conduit can be constructed to allow an end-to-end anastomosis or a side-to-side anastomosis. A 10-mm conduit of synthetic Dacron is commonly used and allows ample size for insertion of all necessary devices. The conduit may be brought through a separate counterincision in the groin to allow better angulation of the relatively long and stiff deployment devices. At the conclusion of the procedure, these conduits may be used to revascularize distal obstructions if needed.

Alternatively, the retroperitoneal iliac vessels, or even the distal aorta, may be accessed using direct sheath insertion. A double purse string of 4-0 Tycron is used to secure the vessel and provide hemostasis with the application of two sets of tourniquets. Direct needle puncture of the artery is followed by dilation and insertion of the device. At completion, the device is removed and the purse string sutures are tied down. Excessive tortuosity of the iliofemoral arteries requires adaptive strategies. The use of external manual manipulation provides a simple method of straightening some of the tortuosity of the aorta and iliac arteries. During fluoroscopy the operator hand can provide gentle force to the tortuous arterial segment to allow straightening and subsequent endovascular access.

In cases of iliac artery tortuosity, advanced endovascular techniques may aid in straightening these segments. The use of stiff wires or buddy wire techniques can provide some degree of straightening of the diseased arteries. In severe cases of tortuosity, brachiofemoral access may be required to perform “body flossing” with an appropriately stiff wire. Typically, a 5 Fr sheath with a long catheter is placed into the aortic arch and then into the descending aorta. A long, stiff wire, such as a 450-cm SS Guidewire (Boston Scientific, Natick, MA), is guided from the brachial artery and retrieved through the femoral artery. Gentle traction on both the brachial and femoral sites will straighten out the tortuosity. Of note, a long catheter must be placed through the brachial artery into the aorta to prevent excessive trauma by the stiff wire along the arch and innominate vessels.

At the completion of the deployment and ballooning of the thoracic stent graft, the entire route of access must be carefully examined to ensure that there has been no injury. The stiff guidewire that was used to position the thoracic endograft should be left in place as the sheaths and remaining endovascular materials are removed. A smaller sheath should be reinserted and a diagnostic aortoiliac arteriogram should be performed to evaluate for thrombus, dissection, or complete avulsion.

The removal of the large sheath, especially when inserted with some force and manipulation, is a particularly dangerous period when injury may occur. There have been numerous reports of successful thoracic endografting with a sheath removed with a complete iliac artery avulsed and attached ( Fig. 72-6 ). At the time of recognition, a stiff wire through this injured artery may be life-saving and allow insertion of an occluding balloon proximally to allow control of a potentially life-threatening bleed. In addition, both blood pressure and heart rate should be carefully monitored during removal and completion of the endovascular procedure for signs of an occult injury.