Thoracic Aortic Aneurysm Treatment & Management

All aneurysms must be treated with risk-factor reduction. Systemic hypertension probably contributes to the formation of aneurysms and certainly contributes to expansion and rupture. This is especially true of thoracic aneurysms. Strict control of hypertension is implemented in all patients, regardless of aortic aneurysm size.

Tobacco use contributes to aneurysm formation, although the exact pathophysiology is not well understood. Cessation of smoking is recommended. Control of other risk factors for peripheral arterial obstructive disease may be beneficial.

For acute aortic dissections, the first-line treatment of hypertension is with a short-acting beta-blocker (eg, esmolol). Beta blockade decreases the force of contraction, thus decreasing the dP/dt and shear force exerted on the dissection by minimizing the rate of rise of the aortic pressure. It also decreases the heart rate and the inotropic state of the myocardium, and reduces the likelihood of propagation of the dissection. A second-agent added is a vasodilator (eg, nitroprusside), which reduces the systolic blood pressure to, in turn, decrease the aortic wall stress and the possibility of rupture.

Most aneurysm repairs involve aortic replacement with a Dacron tube graft. Dacron grafts allow ingrowth in the interstices to form a pseudoendothelial layer to minimize the risk of embolization. They may be knitted or woven. Knitted grafts are more porous and incorporate tissue well; however, they are prone to more bleeding. Woven grafts are more impervious and therefore are the most commonly used for aortic replacement. Grafts are typically impregnated with collagen to avoid preclotting the graft and to promote optimal healing.

Ascending aortic aneurysms

Surgical treatment of ascending aortic aneurysms depends on the extent of the aneurysm both proximally (eg, involvement of the aortic valve, annulus, sinuses of Valsalva, sinotubular junction, coronary orifices) and distally (eg, involvement to the level of the innominate artery). The choice of operation also depends on the underlying pathology of the disease, the patient's life expectancy, the desired anticoagulation status, and the surgeon's experience and preference.^[20]

Ascending aortic aneurysms with normal aortic valve leaflets, annulus, and sinuses of Valsalva are typically replaced with a simple supracoronary Dacron tube graft from the sinotubular junction to the origin of the innominate artery, with the patient under cardiopulmonary bypass.

If the aortic valve is diseased but the aortic sinuses and annulus are normal, the aortic valve is replaced separately and the ascending aortic aneurysm is replaced with a supracoronary synthetic graft, leaving the coronary arteries intact (ie, Wheat procedure).

Sinus of Valsalva aneurysms with normal aortic valve leaflets and aortic insufficiency due to dilated sinuses may be repaired with a valve-sparing aortic root replacement. Two valve-sparing procedures have been developed: the remodeling method and the reimplantation method. The remodeling method involves resecting the aneurysmal sinus tissue while maintaining the tissue along the valve leaflets and scalloping the Dacron graft to form new sinuses to remodel the root. The reimplantation method involves reimplanting the scalloped native valve into the Dacron graft. Both require reimplantation of the coronary ostia into the Dacron graft.^[21]

Patients with an abnormal aortic valve and aortic root require aortic root replacement (ARR). In nonelderly patients who can undergo anticoagulation with reasonable safety, the aortic root may be replaced with a composite valve-graft consisting of a mechanical valve inserted into a Dacron graft coronary artery reimplantation (eg, classic or modified Bentall procedure, Cabrol procedure).^{[22, 23]}

For elderly patients, young active patients who do not desire anticoagulation, women of childbearing age, and patients with contraindications to warfarin, the options include stentless porcine roots,^[24] aortic homografts, and pulmonary autografts (ie, Ross procedure).^[25] For elderly patients who cannot undergo a complex operation, another option is reduction aortoplasty (ie, wrapping of the ascending aorta with a prosthetic graft).

Patients with Marfan syndrome have abnormal aortas and cannot undergo tube graft replacement alone. They must have either a valve-sparing aortic root replacement or a complete aortic root replacement.

Aortic root replacement with a homograft is ideal in the setting of aortic root abscess from endocarditis.

Aortic arch aneurysms

Arch aneurysms pose a formidable technical challenge. Deep hypothermic circulatory arrest (DHCA) with or without antegrade or retrograde cerebral perfusion is usually used to facilitate reanastomosis of the arch vessels. Aortic arch reconstruction techniques vary depending on the arch pathology.

In patients with proximal arch involvement extending from the ascending aorta, a hemiarch replacement may be performed. The ascending aorta is replaced with a Dacron graft beveled as a tongue along the undersurface of the arch. In patients whose conditions mandate replacement of the entire arch, the distal anastomosis is the Dacron graft to the descending thoracic aorta. The head vessels are reimplanted individually or as an island. Grafts have been developed with a trifurcated head-vessel attachment and with a fourth attachment for the cannula. In this case, the head vessels are attached individually to the trifurcated branches.

For patients in whom the arch replacement is part of a staged procedure, preceding the delayed repair of a concomitant descending thoracic aneurysm, an "elephant trunk" is used. That is, the Dacron graft used to reconstruct the transverse arch ends distally in an extended sleeve that is telescoped into the descending thoracic aorta, facilitating later replacement of the descending thoracic/abdominal aneurysm (2-stage procedure).

The higher morbidity and mortality associated with ascending and arch aortic surgery combined with the increasing experience using thoracic endografts in the descending aorta has evolved into the use of endografts in the ascending and arch aortas. So called "hybrid" procedures represent a combination of both open and endovascular procedures. Although potentially still requiring a median sternotomy and often times revascularization of some or all of the arch vessels, they offer the advantage of potentially less invasiveness through single-staged or single–incision procedures, avoidance of aortic cross-clamping or hypothermic circulatory arrest, or less total revascularization, especially if the ascending or descending aorta is also involved.

Further evolution of the hybrid procedure is demonstrated by the "frozen elephant trunk" technique, which involves standard ascending and arch repair as in the elephant trunk procedure, followed by antegrade reconstruction of the descending thoracic aorta, through the opened transverse arch. These potential advantages theoretically translate into decreased morbidity and mortality. Limited experience with these hybrid procedures are being reported; however, the long-term results and durability have yet to be defined.

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]

Ascending aortic aneurysm

Preoperative assessment of coronary artery disease is essential to determine the need for concomitant coronary artery bypass grafting. Transesophageal echocardiography is crucial preoperatively to examine the need for aortic valve replacement. Patients with aortic stenosis or aortic insufficiency in whom the valve leaflets are anatomically abnormal require replacement, whereas patients with aortic insufficiency and normal aortic valve leaflets may be candidates for valve-sparing procedures. Transesophageal echocardiography is valuable for accurate delineation of the aortic root at the sinuses of Valsalva and sinotubular junction.

Aortic arch aneurysm

The major morbidities from aortic arch aneurysm repair are neurologic, cardiac, and pulmonary in nature. All patients require preoperative assessment of cardiac function and evaluation for coronary artery disease. In the operating room, transesophageal echocardiography is used to monitor ventricular function and to assess for atherosclerosis of the aorta.

A major concern in arch surgery is neurologic injury, both transient neurologic dysfunction and permanent neurologic injury. Patients with a higher risk of stroke undergo preoperative noninvasive carotid ultrasound, and those with a history of stroke undergo a brain CT scan. In the operating room, steroids are often given at the onset of the procedure if hypothermic circulatory arrest is anticipated. Evidence suggests that steroids given preoperatively several hours before the operation may have benefit. Some institutions monitor electroencephalogram silence to assess for adequate duration and temperature of cerebral cooling for hypothermic circulatory arrest.

Descending thoracic aneurysms and thoracoabdominal aneurysms

A devastating complication of descending thoracic aneurysm and thoracoabdominal aneurysm repair is spinal cord injury with paraparesis or paraplegia. Preoperatively, some groups perform spinal arteriograms to attempt to localize the artery of Adamkiewicz for reimplantation during surgery. Neurologic monitoring with somatosensory evoked potentials or motor evoked potentials is used by some to assess spinal cord ischemia and identify critical segmental arteries for spinal cord perfusion. Lastly, preoperative placement of catheters for cerebrospinal fluid drainage is performed to increase spinal cord perfusion pressure during aortic cross-clamping.

Spinal cord injury is less prevalent with endovascular stent grafting than with open repair but exists with both types of surgical treatment.^{[26, 27, 29, 30]} For endovascular stent grafting, cerebrospinal fluid (CSF) drainage and avoidance of hypotension are the primary mechanisms used to prevent paraplegia. The use of CSF drainage is selective among most centers. For some discrete aneurysms, stent graft coverage may allow for preservation of spinal arteries. Others require coverage of the entire descending thoracic aorta. Indications for use of CSF drains include anticipated endograft coverage of T9-T12, coverage of the long segment of the thoracic aorta, compromised collateral pathways from prior infrarenal AAA repair, and symptomatic spinal ischemia.

Although not recommend as primary therapy, a report of an induced endoleak to allow spinal cord perfusion for persistent cord ischemia following endovascular repair, despite CSF drainage, proved successful and may represent a "bail-out" technique to be considered in exceptional circumstances.^[34]

Spinal cord ischemia is an uncommon complication following thoracic endovascular aortic repair, but its development can be identified by a preoperative renal insufficiency. Blood pressure augmentation alone, or in combination with cerebrospinal fluid drainage, serves as an effective early detection process for most patients, the majority of whom enjoy a complete and long-term neurologic recovery.^[35]

Brain protection

Methods used for brain protection during deep hypothermic circulatory arrest (DHCA) include intraoperative EEG monitoring, evoked somatosensory potential monitoring, hypothermia (to temperatures < 20^o C), packing the patient's head in ice, Trendelenburg positioning (ie, head down), mannitol, CO2 flooding, thiopental, steroids, and antegrade and retrograde cerebral perfusion.

General monitoring and anesthesia

Venous access is obtained with 2 large-bore peripheral IVs and a central line. Filling pressures and cardiac output monitoring are performed with a pulmonary artery catheter. Continuous blood pressure monitoring is performed with a radial arterial line. Nasopharyngeal and bladder probes monitor systemic temperature. Intraoperative transesophageal echocardiography is used to assess myocardial and valvular function.

Ascending aortic replacement

Cardiopulmonary bypass is established and the aorta is cross-clamped just below the innominate artery. The heart is arrested with cardioplegia. The aorta is transected at the sinotubular junction and sized for the appropriate Dacron tube graft. The tube graft is sutured to the proximal aorta with running 4-0 Prolene with a strip of felt. The tube graft is measured to length distally and sutured to the distal aorta using running 4-0 Prolene with a strip of felt.

Valve-sparing aortic root replacement

Once the aorta is transected at the sinotubular junction, the valve is inspected for normal anatomy. If sparing is feasible, the appropriate size tube graft is chosen to allow coaptation of the aortic valve leaflets without aortic insufficiency. In the remodeling technique, the tube graft is tailored to form aortic sinuses. The sinuses of Valsalva of the native aorta are removed, and the coronary ostia are mobilized. The neosinuses of the tube graft are sutured to the scalloped aortic valve with running 4-0 Prolene and a strip of felt.

In the reimplantation technique, Tycron sutures are placed along the subannular horizontal plane and passed through the tube graft. The scalloped aortic valve is placed within the tube graft, and the proximal suture line is secured. The scalloped aortic valve is positioned in the graft to achieve valve competence, and the subcoronary suture line along the scalloped valve is performed with running 4-0 Prolene. The valve is examined for competence within the graft. The coronary ostia are reimplanted in the graft. The graft is measured to length distally and sutured to the distal aorta.

In the reimplantation technique, Tycron sutures are placed along the subannular horizontal plane and passed through the tube graft. The scalloped aortic valve is placed within the tube graft, and the proximal suture line is secured. The scalloped aortic valve is positioned in the graft to achieve valve competence, and the subcoronary suture line along the scalloped valve is performed with running 4-0 Prolene. The valve is examined for competence within the graft. The coronary ostia are reimplanted in the graft. The graft is measured to length distally and sutured to the distal aorta.

Aortic root replacement

The aorta is transected, and the aortic valve is removed. The annulus is sized, and the appropriate valved conduit, stentless root, mechanical composite, or homograft is brought to the field. The coronary ostia are mobilized. Annular sutures are placed and are passed through the valve conduit. The proximal suture is thus secured. The coronary ostia are reimplanted. The distal suture line is performed for the mechanical valve composite, but an additional Dacron graft extension may be required for the stentless roots or homografts, depending on their length.

• Modified Bentall procedure ("buttons"): The right and left coronary arteries are dissected as a button, which is then reimplanted into the Dacron composite graft as an aortic button.
• Cabrol procedure: Rarely performed, this technique may be used when the aortic tear or dissection extends into the coronary ostia. It may also be used when adequate mobilization of the coronary ostia is not possible (i.e., from scarring in a reoperation), or when the coronary ostia are too low. The coronary buttons are dissected and anastomosed to a separate 6- or 8-mm Dacron interposition graft; this graft is then anastomosed into the Dacron composite graft. This technique results in a tension-free anastomosis of the coronary buttons and also allows for easier access for hemostasis. However, it is subject to twisting and kinking with resultant myocardial ischemia and, thus, is not as reproducible as the modified Bentall.

Open distal anastomosis

Deep hypothermic circulatory arrest with or without antegrade or retrograde cerebral perfusion is used. When cooled to 18°C (64.4°F), the pump is turned off and the arterial line is clamped. The patient is placed in the Trendelenburg position, and the aortic cross clamp is removed. The distal anastomosis is performed open with running 4-0 Prolene and a strip of felt. The distal anastomosis may be at the level of the innominate artery or, in the case of hemiarch replacement, along the undersurface of the arch to the level of the left subclavian artery. Once the anastomosis has been completed, the pump is restarted with blood flow antegrade into the new graft and open proximal tube graft to flush out air and debris. The graft is then clamped; the proximal aortic reconstruction is performed during rewarming.

Hypothermia decreases oxygen consumption. For each drop in temperature by 1^o C, the oxygen consumption by the tissues is reduced by 10%.

Air (ie, nitrogen) is poorly soluble in blood. The risk of air embolism is reduced by flooding the surgical field with carbon dioxide. Carbon dioxide is denser than air and displaces air. It is rapidly soluble in blood and causes less risk of embolization. Any carbon dioxide absorbed in the blood is removed by increasing the sweep speed of cardiopulmonary bypass.

Aortic arch aneurysm repairs

Cannulation for arch repairs varies among groups. They include the femoral artery, right axillary artery, and ascending aorta. Hypothermic circulatory arrest is required for arch repairs, but the safe period of arrest to avoid neurologic injury is 30-45 minutes at 18°C (64.4°F), but some advocate a shorter period of 25 minutes. Antegrade cerebral perfusion to minimize neurologic injury is thus advocated. Others advocate cooling to 11-14°C (51.8-57.2°F).

Once the patient is cooled to the desired temperature, the circuit is turned off. For retrograde cerebral perfusion, flow is established through the superior vena cava as the arch reconstruction is performed. For antegrade cerebral perfusion, flow is continued through the axillary artery with the innominate artery clamped or individual perfusion catheters are placed into the innominate artery, left carotid artery, and left subclavian arteries. The arch reconstructions are also varied. They basically involve performing the distal anastomosis to the aorta beyond the left subclavian artery as an open distal procedure with or without an elephant trunk. The 3 head vessels may be reanastomosed individually or as an island. They may be reimplanted directly to the graft or anastomosed to a separate graft, which is then attached to arch graft.

Descriptions of different hybrid procedures have been standardized according to the location of the most proximal placement of the endograft in relation to the arch vessels, under the Criado classification: zone 0 extends distally from the ascending aorta to the innominate artery; zone 1 from distal to the innominate artery origin to the left common carotid artery (CCA); zone 2 from distal to the left CCA to the left subclavian artery (LSA); and zone 3 distal to the LSA to the proximal descending thoracic aorta.^[36]

Zone 0 pathology by definition involves all aortic arch vessels and requires revascularization of at least the innominate artery and left CCA and possibly revascularization of the LSA in the case of symptoms of left arm ischemia, functional left internal mammary arterial bypass graft, or dominant left vertebral artery circulation. Revascularization is usually accomplished via a median sternotomy and the use of a bifurcated or trifurcated graft from the ascending aorta to the arch vessels. Following revascularization and during the concomitant operation, a stent-graft is then implanted either in an antegrade or retrograde fashion.

Zone 1 placement, commonly avoids a median sternotomy, via revascularization of the left CCA by a right CCA to left CCA bypass, prior to endograft placement. Depending on the quality of angiographic resources in the operating room, this procedure may be performed in a single or staged procedure to allow use of a dedicated angiographic suite.

A Zone 2 landing requires partial or complete coverage of the LSA. In general, this is well tolerated, however, several reports have detailed higher incidences of neurological complications with LSA coverage and, therefore, a thorough assessment of the carotid, vertebral and circle of Willis circulations should be preoperatively performed.^[37]

Descending thoracic aneurysm and thoracoabdominal aneurysm repairs

Measures to reduce spinal cord injury include cerebrospinal fluid drainage, reimplantation of intercostal arteries, partial bypass, and mild hypothermia. A left thoracotomy or a thoracoabdominal incision is performed. The aorta is cross-clamped either just beyond the left subclavian or between the left carotid and left subclavian for Crawford types I and II. The cross clamp is placed more distally for Crawford types III and IV.

Atrial femoral bypass is established with a Bio-Medicus circuit, and the patient is cooled to 32-34°C (89.6-93.2°F). Distal cross-clamping is performed at T4-T7 to allow continued spinal cord, visceral, and renal perfusion. The proximal anastomosis is performed with running 4-0 Prolene and a strip of felt. When complete, the proximal clamp is released and reapplied more distally on the tube graft. The distal cross clamp is moved sequentially down, if feasible, to allow visceral and renal perfusion. The intercostal arteries may be reimplanted, if desired, or oversewn. If sequential cross-clamping is not feasible, direct catheters may be placed in the visceral and renal vessels to allow continuous perfusion.

If the distal aneurysm extends to the renals, then the distal anastomosis may be beveled to incorporate the visceral and renal vessels and distal aorta. If the distal aneurysm extends to the bifurcation, the visceral and renal vessels are reattached to the tube graft. The left renal artery typically requires a separate anastomosis, but the celiac, superior mesenteric, and right renal arteries are often incorporated as a single island. The patient is rewarmed, and the partial bypass is discontinued as the tube graft perfuses the intercostals and abdominal vessels. The distal anastomosis at the bifurcation is performed as an open distal procedure.

For appropriate descending thoracic aortic aneurysms, endovascular stent grafting is a good alternative. Depending on the size of the patient's femoral or iliac arteries and size of the stent graft required, femoral or iliac artery exposure is performed under general or local anesthesia plus sedation. A sheath is placed and a wire guided under fluoroscopy into the arch. When in proper position, the floppy wire is exchanged with a soft catheter and rewired to a stiffer wire for device placement. The sheath is exchanged for the appropriate device sheath. The contralateral groin is used for angiocatheter placement.

After angiography and determination of stent placement, the device is loaded and, under fluoroscopic guidance, is positioned and deployed. More than one stent may be used, with as much overlap as is feasible, for stability. The proximal and distal landing zones are ballooned to seal the endograft to the aorta. The overlapping stent-graft segments are also ballooned. Angiography is performed to check for endoleaks. Endoleaks may require additional stents.

Thoracoabdominal aortic aneurysms may involve arteries supplying the abdominal viscera. In this case, for a completely endovascular repair, aortic stent grafts with fenestrations or branches oriented towards the intended covered arteries have been devised. These grafts previously have been individualized to the specific anatomy of the patient, although recent data have demonstrated that noncustomized branch grafts may work for most patients.^[33]

Initial placement of the aortic stent graft ensues, carefully aligning the fenestrations or branches to the abdominal viscera. The abdominal visceral arteries are then cannulated with separate guidewires in a retrograde fashion for cranially oriented arteries, or through the brachial artery for in an antegrade fashion for caudally oriented arteries. A bridging covered stent is then deployed to create a visceral seal zone.

Ross procedure (pulmonary autograft)

The aortic root and proximal ascending aorta are replaced with a pulmonary autograft.^[25] The pulmonary valve is then replaced with a pulmonary homograft. Most commonly performed in children with congenital disease, the Ross operation may be used for active young adults with aneurysmal disease (excluding those with connective tissue disorders), women of childbearing age who desire pregnancy, or patients with contraindications to anticoagulation.

Patients who have undergone ascending aneurysm repairs are observed for signs of coronary ischemia, particularly if the coronary ostia were reimplanted, and for signs of aortic insufficiency when the aortic valve is repaired. Following the repair of arch aneurysms, particular attention must be given to neurological status, and patients who have had the elephant trunk repair must be observed for signs of paraplegia because the telescoped sleeve in the descending aorta may obstruct critical spinal vessels.

Paraplegia is the main concern in patients who have had repair of the descending and thoracoabdominal aorta. Cerebrospinal fluid drainage may be continued for up to 72 hours postoperatively if necessary, along with motor evoked potential monitoring. Paraplegia and paraparesis may be acute or delayed postoperatively. If paraparesis or paraplegia is delayed, increased mean arterial pressure with pressors and reinstitution of cerebrospinal fluid drainage may augment spinal cord perfusion to reverse this complication. Paraplegia due to occlusion of critical spinal arteries that were not reimplanted cannot be reversed by these maneuvers. Acute postoperative renal dysfunction may be due to extended periods of ischemic cross-clamping or to hypothermic circulatory arrest.

Patients undergoing endovascular stenting are often extubated early postoperatively with a decreased ICU length of stay.

Development of another aneurysm postoperatively is not uncommon in these patients. For this reason, serial evaluations (ie, CT scans or MRI for ascending, arch, or descending aneurysms; echocardiography for ascending aneurysms) may be performed every 3-6 months during the first postoperative year and every 6 months thereafter.

A recent study evaluated the differences between male and female patients undergoing thoracic endovascular aneurysm repair in a Food and Drug Administration-approved trial. Femake patients had higher rates of periprocedural complications, requiring more blood transfusions, a longer hospital length of stay, and more major adverse events after 30 days. However, female patients also more often had successful aneurysm treatment at 1 year of follow up.^[38]

For patient education resources, see Aortic Aneurysm.

Early morbidity and mortality are related to bleeding, neurologic injury (eg, stroke), cardiac failure, and pulmonary failure (eg, acute respiratory distress syndrome [ARDS]). Risk factors include emergent operation, older age, dissection, congestive heart failure (CHF), prolonged cardiopulmonary bypass time, arch replacement, previous cardiac surgery, need for concomitant coronary revascularization, and reoperation for bleeding. Late mortality is usually related to cardiac disease or distal aortic disease.

Bleeding is a potential complication for all aneurysm repairs. It is minimized by the use of antifibrinolytics, felt strips, and factors, including fresh frozen plasma and platelets. For patients who undergo hypothermic circulatory arrest, the use of aprotinin is controversial, but most groups routinely use aminocaproic acid (Amicar). Coagulopathy and bleeding in severe cases may warrant the use of recombinant factor VII.

Aprotinin (Trasylol), an antifibrinolytic agent used to reduce operative blood loss in patients undergoing open heart surgery, is now only available via a limited-access protocol. Fergusson et al reported an increased risk for death compared with tranexamic acid or aminocaproic acid in high-risk cardiac surgery.^[39]

Stroke is a major cause of morbidity and mortality and typically results from embolization of atherosclerotic debris or clot. Transesophageal echocardiography and epiaortic ultrasound may be beneficial in localizing appropriate areas to clamp. Patients undergoing arch repairs are at the highest risk of permanent and transient neurologic injury. Retrograde cerebral perfusion is beneficial for flushing out embolic debris, but it may be detrimental, with increased intracranial pressure and cerebral edema. Antegrade cerebral perfusion is beneficial for reducing neurologic injury during hypothermic circulatory arrest. Stroke incidence for open surgical repair versus endovascular repair of descending thoracic aneurysms is equivalent.

Myocardial infarction may occur with technical problems with coronary ostia implantation during root replacement for ascending aortic aneurysms and may require reoperation. Pulmonary dysfunction and renal dysfunction are other potentially morbid complications.

Paraparesis and paraplegia, either acute or delayed, are the most devastating complications of descending thoracic aneurysm and thoracoabdominal aneurysm repairs. Despite cerebrospinal drainage, reimplantation of intercostal arteries, evoked potential monitoring, mild hypothermia, and atrial femoral bypass, spinal cord injury still occurs. Endovascular stent grafting has not eliminated spinal cord paraplegia; the incidence varies widely, with an overall incidence of 2.7%.^{[26, 27, 29, 30]}

Complications specific to endovascular stenting include endoleaks, stent fractures, stent graft migration or thrombosis, iliac artery rupture, retrograde dissection, microembolization, aortoesophageal fistula, and complications at the site of delivery (eg, groin infection, lymphocele, seroma).

According to Culliford et al from 1982,^[40] Cabrol et al from 1988,^[41] and Donaldson and Ross from 1982,^[42] the early hospital mortality rate following repair of ascending aneurysms is 4-10%. Contemporary surgical series demonstrated a continued wide range in operative mortality (2-17%). Stroke occurs in 2-5% of patients.

As would be expected, the early mortality rate after repair of arch aneurysms is considerably higher, approaching 25% in series by Crawford and Saleh from 1981,^[43] by Crawford et al from 1979,^[44] by Columbi et al from 1983,^[45] by Ergin et al from 1982,^[46] and by Galloway et al from 1989.^[47] More contemporary results from Coselli and Ueda demonstrate operative mortality of 6-12%. Stroke rate varied from 3-22%. Renal failure that required dialysis occurred in 7% of patients.

The mortality rate after repair of descending thoracic aneurysms is lower, approximately 5-15% according to Crawford et al from 1981,^[43] to Donahoo et al from 1977,^[48] to Livesay et al from 1985,^[49] and to Pressler and McNamara from 1985.^[2] Contemporary results are unchanged, with 12-15% mortality.

As a group, including all repairs, according to Crawford et al from 1978,^[50] Crawford et al from 1981,^[43] and Kitamura et al from 1983,^[51] survival rates after surgery for chronic aortic aneurysms are approximately 60% at 5 years and 30-40% at 10 years.

The longest follow-up data for a multicenter trial comparing endovascular and open techniques for management of thoracic aortic aneurysms are the results of a phase II multicenter trial for the GORE-TAG thoracic endovascular stent. A 1.5% 30-day mortality for endovascular repairs was demonstrated, temporary or permanent spinal cord paraplegia occurred in 3% of patients and stroke in 4% of patients.^[52] At 2 years, aneurysm survival was 97% and overall survival 75%.^[52] For the Medtronic Talent device, the incidence of paraplegia in the stent group was 0-9%, stroke 3.7-8.1%, 30-day mortality 2.9-9.7%, and procedural success of more than 95%.^[28]

When endovascular stent grafting was compared with open surgery for the GORE-TAG device, the rate of paraplegia was 3% in the stent group vs 14% in the open group;^[26] operative mortality was 1% vs 6%, and early death was 2% vs 10%.^[53] The patients in the stent group had a shorter ICU and hospital stay, a quicker recovery time, and a lower incidence of major adverse events (except for vascular complications). Complications at 2 years included 4% proximal stent migration, 6% migration of the graft components, and 15% of patients had an endoleak.

Overall, survival rates were equivalent between the endovascular and open groups at both 2-years and 5-years, 80% and 70% respectively, but aneurysm-related survival significantly favored endovascular repairs at 5 years (97% vs 88%).^[54] However, more contemporary "real world" experienced application has not been as supportive of this discrepancy as noted by Greenberg et al where no significant difference between mortality or paraplegia was discerned in their population at 30 days (5.7 vs 8.3%) nor at one year (15.6% vs 15.9%).^[55]

Midterm results comparing open descending thoracic aneurysm repair with endovascular stent grafting demonstrate less early operative mortality with endovascular repair (10% for stent grafting vs 15% for open repair) but similar late survival (actuarial survival rate at 48 months of 54% for stent grafting vs 64% for open repair).

Success with the results of endovascular repair of contained, degenerative thoracic aortic aneurysms of the descending aorta have created an environment to use endografts for treatment of arch aneurysms as well as acute catastrophes of both the arch and descending aortas.

Recently, data from a multi-center, nonrandomized, prospective study of the use of endografts in emergent pathologies of the descending aorta was published.^[56] In situations that have reported mortality rates as high as 90%, the authors found that in the management of acute type B dissections, traumatic aortic tears, or ruptured aortic aneurysms, endovascular management compared to open resulted in a 14% vs 30% 30-day composite mortality/paraplegia rate.

Although, freedom from aortic related events was 84.5% at one-year for the endovascular cohort, survival was only 66% with the subset of ruptured aneurysms have the worst survival (37%). Another multicenter trial evaluating use in ruptured aneurysms confirmed the perioperative mortality rate, but also noted considerable neurological complications (8%), procedure-related complications such as endoleak (18%) and ongoing aneurysm related death, 25% at 4 years.^[57]

Others have used endografts for arch pathologies, which usually necessitates a "hybrid" approach, a combination of endovascular and open techniques. Small (< 30 patients), single institution series, with limited followup have reported perioperative mortality, stroke and paraplegia rates 0-25%, 0-25%, and 0-4% respectively, questioning the durability and futility of the repairs.^{[58, 59]} However, a series from a single, tertiary care medical center highlighted the results of 400 consecutive patients, demonstrating a 6.5% and 53% 30day and 4-year mortality, respectively, and a paraplegia and stroke rate of 4.5% and 3%, respectively.^[60]

Ascending aortic aneurysm repair has been well established and is performed safely with low morbidity and mortality. The controversies lie in the use of valve-sparing root replacements in patients with Marfan syndrome with regard to the durability of the repair. However, because most patients with Marfan syndrome undergo the operation while they are young, they likely require reoperation eventually and the additional years of sparing their native aortic valve and living without anticoagulation are valuable.

Arch aneurysms still carry the most morbidity and mortality because neurologic injury is a great risk. Most controversies involve the methods of cerebral protection. More and more evidence suggests that antegrade cerebral perfusion is an optimal choice to reduce both temporary and permanent neurologic injury.

Recent advances in the treatment of descending thoracic aneurysms and thoracoabdominal aneurysms have used endovascular stent grafting, which offers a less invasive alternative to open surgical repair. The first FDA-approved device for descending thoracic aneurysm repair was approved in March 2005. The nonrandomized prospective comparison of open surgical versus endovascular stenting demonstrated a reduced incidence of operative mortality and reductions in paraplegia, blood loss, operative time, and length of ICU stay. The incidence of stroke between the two groups was similar.

Long-term results suggest that, although early operative mortality rates are lower with endovascular repair than with open surgical repair, late survival rates are equivalent. Paraplegia rates in the real world (as opposed to in carefully selected patient populations of clinical trials) suggest an increased incidence of paraplegia with endovascular stent grafting but range from 0-12% (average 2.7%).

As greater off-label use of endografts demonstrates excellent perioperative results, the equivalent long-term results between open and endovascular techniques suggests that we have not really addressed the underlying disease. Future studies will continue to examine comparisons of open versus endovascular repair of thoracoabdominal aneurysms and aortic arch aneurysms, and begin to elucidate which subset of pathologies, might actually benefit from these therapies.

Aneurysms are the most commonly diagnosed conditions of the thoracic aorta that require surgery. Recently, many advances in aortic substitutes, cerebral protection, and perioperative care have led to improved survival rates and outcomes.