Descending thoracic aortic aneurysms and thoracoabdominal aneurysms

Descending thoracic aneurysms may be repaired with open surgery or, if appropriate, with endovascular stent grafting techniques.^{[26, 27, 28, 29, 17, 30]}Stent graft repair of descending thoracic aortic aneurysms should be performed if the predicted operative risk is lower than that of an open repair. Patient age, comorbidities, symptoms, life expectancy, aortic diameter, characteristics and extent of the aneurysm, and landing zones, should also be taken into consideration.

Surgically, descending thoracic aneurysms may be repaired with or without the use of a bypass circuit from the left atrium to the femoral artery or femoral vein–femoral artery cardiopulmonary bypass, depending on the length of the anticipated ischemic cross-clamping and the experience of the surgeon. Discrete aneurysms with an anticipated clamp time of less than 30 minutes may be repaired without left heart or cardiopulmonary bypass (ie, "clamp and go" technique). More complex or larger aneurysms are probably safer to repair with the aid of either left heart, partial, or full cardiopulmonary bypass with hypothermic circulatory arrest. The use of left heart or cardiopulmonary bypass is favored to reduce hemodynamic instability and the risk of spinal cord paraplegia.

Descending thoracic aneurysms with the appropriate anatomy may now be repaired by endovascular stent grafts. The GORE TAG is an FDA-approved nitinol-based stent graft designed for descending thoracic aneurysm repair. An appropriate proximal neck of 2 cm prior to the aneurysm is required. Ideally, the proximal landing zone is beyond the left subclavian artery, though, in some circumstances, the stent may be placed proximal to the left subclavian artery. Distally, a sufficient landing zone of 2 cm prior to the celiac artery is required. The aortic inner neck diameters in the proximal and distal landing zones must fall within 23-37 mm. In addition, appropriately sized femoral and iliac arteries (typically >8 mm in diameter) that lack tortuosity and calcium are required for implantation.

The GORE TAG graft has been FDA-approved since March 2005.^[12] More recently, the Zenith TX2 endovascular graft (Cook Medical Inc.; Bloomington, Ind) was approved in March 2008, followed by the Talent Thoracic Stent Graft (Medtronic Inc.; Minneapolis, Minn) in June 2008.^{[31, 32]} The Valiant Thoracic Stent Graft (Medtronic Inc.; Minneapolis, Minn) is approved for use outside the United States.

Thoracoabdominal aneurysms, comprising approximately 10% of thoracic aneurysms, may be repaired with the use of a partial bypass of the left atrium to the femoral artery. Crawford type I thoracoabdominal aneurysms involve Dacron graft replacement of the aorta from the left subclavian artery to the visceral and renal arteries as a beveled distal anastomosis, using sequential cross-clamping of the aorta. Crawford type II thoracoabdominal aneurysm repair requires a Dacron graft from the left subclavian to the aortic bifurcation with reattachment of the intercostal arteries, visceral arteries, and renal arteries. Crawford type III or IV thoracoabdominal aneurysm repairs, which begin lower along the thoracic aorta or upper abdominal aorta, may use either the partial bypass of the left atrial artery to the femoral artery or a modified atrio-visceral and/or renal bypass. Prevention of paraplegia is one of the principal concerns in the repair of descending and thoracoabdominal aneurysms.

Previous investigational trials by Dr. Timothy Chuter at the University of California at San Francisco Medical Center and Dr. Roy Greenberg at the Cleveland Clinic treated thoracoabdominal aneurysms using custom-built fenestrated and branched stent grafts. Such devices required precise anatomic tailoring of the grafts to the specific patient's anatomy for placement of the scallops (for visceral flow) or branches (for direct stenting into the visceral vessels) and resulted in prolonged operative delays. Recent data and improvement in devices demonstrate that standardized multi-branched endografts were applicable to approximately 90% of the patient population, thereby eliminating manufacturing delays and expanding the applicability of these devices in thoracoabdominal aneurysms.^[33]

Date: 2015-12-11; view: 738