Overview of open surgical repair of the thoracic aorta

INTRODUCTION — Open surgical repair of the thoracic aorta has been the standard for managing a variety of thoracic aortic pathologies but is associated with significant morbidity and mortality. Although minimally invasive approaches have lessened the need, particularly for descending aortic disease, open repair of the thoracic aorta remains necessary for primary disease management as well as for managing complications of thoracic aortic stent-graft placement.

Open repair of the thoracic aorta will be reviewed predominantly as it pertains to the repair of thoracic aortic aneurysm and aortic dissection (TAAD), but variations of surgical techniques required to manage other thoracic aortic pathologies are included, when applicable. Endovascular devices and techniques for repairing the thoracic aorta are discussed elsewhere. (See "Endovascular devices for thoracic aortic repair" and "Endovascular repair of the thoracic aorta".)

INDICATIONS FOR OPEN REPAIR — Open repair of the thoracic aorta is the standard of care for the management of a variety of ascending thoracic aortic pathologies, including ascending thoracic aortic aneurysm and acute ascending thoracic aortic dissection. For descending thoracic aortic pathologies (aneurysm dissection, aortic injury), endovascular repair is emerging as a preferred initial approach, given the lower rates of perioperative morbidity and mortality. For patients with indications for thoracic aortic repair who are not suitable candidates for an endovascular approach, open repair of thoracic aortic aneurysm is still reasonable.

Thoracic aortic pathologies repaired using an open surgical approach include [1] :

●Type A acute aortic syndromes – Type A (ascending) acute aortic dissection or intramural hematoma in the ascending/aortic arch [2,3]. (See "Management of acute type A aortic dissection" and "Overview of acute aortic dissection and other acute aortic syndromes".)

●Bicuspid aortic valve – The bicuspid valve usually becomes sclerotic, with progressive aortic stenosis and/or regurgitation that ultimately requires valve replacement in over 75 percent of patients. In addition, bicuspid aortic valves (BAVs) are often associated with ascending aortic aneurysms even in the absence of significant valve disease (criteria given below). (See "Bicuspid aortic valve: General management in adults" and "Indications for valve replacement for high gradient aortic stenosis in adults".)

●Ascending aortic aneurysm meeting criteria for repair – Aneurysm of the ascending aorta meeting diameter or expansion criteria for repair [1] (See "Management of thoracic aortic aneurysm in adults".).

•Ascending aortic diameter exceeding threshold

->5.5 cm for patients without additional risk factors (ie, degenerative thoracic aortic aneurysm [TAA]) [4-9].

->5.0 cm for patients with TAA associated with genetic predispositions including syndromic conditions such as Marfan syndrome (in the absence of high-risk features) and Ehlers-Danlos syndrome, as well as nonsyndromic conditions such as a familial thoracic aortic aneurysm/dissection (TAAD) or BAV [6-11]. Patients with Marfan syndrome with high-risk features (family history of aortic dissection, rapid aortic expansion [>0.3 cm per year] or marked vertebral arterial tortuosity) should be considered for prophylactic surgery at a lower threshold (4.5 cm).

-Greater than 5 cm aortic root/ascending aortic diameter is recommended when BAV is present if surgery can be performed at a high-volume center with demonstrated low complication rates; otherwise, surgery can be deferred until ascending aortic diameter is >5.5 cm. For patients with BAV who have another indication for cardiac surgery, ascending aortic diameter >4.5 cm warrants repair. (See "Bicuspid aortic valve: Intervention for valve disease or aortopathy in adults", section on 'Approach to identifying candidates for aortic surgery'.)

-The ascending aortic diameter threshold for Turner syndrome may be better described using the Aortic Size Index (ASI) with surgery recommended at ASI >2.5 [12]. (See "Management of Turner syndrome in adults", section on 'Aortic dilatation'.)

-For patients with Loeys-Dietz syndrome, a diameter >4.2 cm by transesophageal echocardiography or 4.4 to 4.6 cm by computed tomography (CT)/magnetic resonance imaging (MRI) [13].

-It may be reasonable to offer TAA repair at smaller aortic diameters for patients with small stature, such as an aortic size index >2.75 [14,15].

•Ascending aortic aneurysm with rapid expansion – Rapid expansion is defined as >0.5 cm per year in an aorta <5.5 cm in diameter.

●Genetically mediated aortic syndromes meeting criteria for repair – Patients with genetically mediated syndromes (syndromic TAAD) and indications for repair should undergo open surgical repair rather than endovascular repair. For patients with nonsyndromic conditions, there is no consensus as to whether an open or endovascular approach should be used. (See "Management of thoracic aortic aneurysm in adults", section on 'Degenerative versus genetically mediated aneurysm' and "Surgical and endovascular management of acute type B aortic dissection", section on 'Genetic predisposition'.)

●Descending aortic pathology meeting criteria for repair and not amenable to an endovascular approach – Although descending thoracic aortic pathology that is not genetically mediated is largely repaired using an endovascular approach, an open approach is necessary for patients with indications for repair but who are not amenable to endovascular repair (ie, unsuitable vascular access, lack of appropriate landing zone) [16,17].

•Thoracic aortic aneurysm – The main indications for repair of descending TAA include:

-Symptomatic aneurysm of any diameter (eg, chest or back pain, frank rupture, dissection)

-Asymptomatic TAA (5 to 6 cm descending TAA), rapid expansion (≥1.0 cm/year)

-Complications following endovascular repair necessitating early or late conversion to an open TAA repair

-Aneurysmal dilation related to prior descending aortic dissection >5.5 cm, or aortic expansion >0.4 cm per year

•Traumatic aortic injury – The preponderance of data suggest that endovascular repair is also the preferred technique for patients with other thoracic pathologies such as blunt thoracic aortic injury and complicated acute type B aortic dissection. (See "Surgical and endovascular repair of blunt thoracic aortic injury" and "Surgical and endovascular management of acute type B aortic dissection".)

•Aortic dissection – Patients with complicated acute type B dissection and chronic type B aortic dissection with progressive aortic dilation may require open replacement of the aorta due to anatomic constraints. (See "Management of acute type B aortic dissection" and "Management of chronic type B aortic dissection".)

Contraindications — Open repair of the thoracic aorta is contraindicated in patients with a prohibitive risk for perioperative mortality and morbidity. An endovascular approach can be tried, but among those with severe medical comorbidities and acute aortic pathologies, palliative care may be more reasonable.

Open repair of the thoracic aorta is less preferred compared with endovascular repair for most descending thoracic aortic pathologies that are not genetically mediated.

ANATOMIC CONSIDERATIONS — Ascending aortic aneurysms and dissections are described relative to key anatomic structures, the aortic root, sinuses, ascending aorta, and arch. Involvement of these structures determines the extent of replacement needed, using various techniques and combinations.

●The ascending aorta (figure 1) originates immediately beyond the aortic valve and ascends initially, then curves to form the aortic arch, and descends caudally adjacent to the spine. The ascending thoracic aorta gives off the coronary arteries, and the aortic arch branches are typically the brachiocephalic trunk (branches to the right carotid and right subclavian arteries) and left carotid and left subclavian arteries; however, aortic arch anatomy can vary (figure 2).

●The descending thoracic aorta (figure 1) provides paired thoracic arteries (T1 to T12) and continues through the hiatus of the diaphragm to become the abdominal aorta, which extends retroperitoneally to its bifurcation into the common iliac arteries at the level of the fourth lumbar vertebra.

●The abdominal aorta is a retroperitoneal structure that begins at the hiatus of the diaphragm and extends to its bifurcation into the common iliac arteries at the level of the fourth lumbar vertebra (figure 3). It lies slightly left of the midline to accommodate the inferior vena cava, which is in close apposition.

Descending thoracic aortic aneurysms are described by the Crawford classification [18], with its modification by Safi [19] (figure 4), while descending thoracic aortic dissections (type B) are described by the Stanford and DeBakey classification system (figure 5). The extent of aortic involvement is the strongest risk factor for paresis and paraplegia. The spinal cord receives its blood supply from three major sources (figure 6), and although it has physiologic reserves via the spinal cord collateral network, the risk for clinically significant spinal cord ischemia increases as more arterial feeders are disrupted. Crawford Extent II aneurysms, which extend from the left subclavian to the aortic bifurcation, have the highest rates of paraplegia related to spinal ischemia [19]. Sacrifice of eight or fewer segmental arteries (figure 1) is well tolerated and has a very low risk of paraplegia [20]. (See 'Descending aorta' below.)

PREOPERATIVE EVALUATION AND PREPARATION — Prior to elective open surgical intervention, additional testing is reasonable to identify and evaluate any comorbidities and develop a risk profile. Detailed aortic imaging is necessary to guide treatment of thoracic aortic pathology.

Risk assessment — Preoperative assessment should include evaluation of left ventricular function and for possible concomitant coronary artery disease. The evaluation may include cardiac catheterization, echocardiography, and pulmonary function tests. These issues are discussed in detail separately. (See "Evaluation of cardiac risk prior to noncardiac surgery" and "Evaluation of perioperative pulmonary risk".)

The patient should also undergo evaluation to identify the presence of atherosclerotic disease.

●For patients identified to have significant coronary artery disease, whether concomitant coronary artery bypass graft surgery is needed is discussed separately. (See "Evaluation of cardiac risk prior to noncardiac surgery" and "Management of cardiac risk for noncardiac surgery", section on 'Revascularization before surgery'.)

●Patients with ascending aortic and particularly arch disease should undergo carotid artery duplex ultrasound examination. (See "Evaluation of carotid artery stenosis".)

●Patients with thoracoabdominal aneurysm require evaluation for any symptoms or signs of peripheral artery disease (PAD). If findings are positive (eg, reduced pulses, claudication), noninvasive lower extremity vascular studies will determine the level and severity of disease. (See "Examination of the arterial pulse" and "Noninvasive diagnosis of upper and lower extremity arterial disease".)

Patients undergoing descending thoracic aortic repair have the greatest risk for postoperative paraplegia. The risk of paraplegia and a strategy for preventing spinal cord ischemia should be discussed with these patients prior to operation [20]. Depending on the planned extent of aortic coverage and perceived risk of spinal cord ischemia, cerebrospinal fluid drainage with a lumbar drain can be considered. Preoperative imaging with careful evaluation of feeding lumbar arteries should be performed to determine which segmental arteries can or should be sacrificed [21]. (See 'Aortic imaging' below.)

Aortic imaging — Detailed aortic images are necessary prior to open surgical repair of the thoracic aorta [1]. First-line imaging modalities are CT and magnetic resonance (MR) angiography. Our preference is for contrast-gated CT angiography as it provides the best evaluation of the ascending aorta and eliminates motion artifact. Images of the entire aorta should be obtained and be detailed enough to evaluate the extent of disease and plan intervention. We use a 128-slice scanner at our institution, but a lesser number of slices may be adequate to view aortic anatomy. Intravenous contrast should be used to optimally differentiate intraluminal and extraluminal structures. MR angiography is an alternative, though cardiac motion may make evaluation difficult.

Anesthesia, monitoring, and organ protection — The choice of anesthesia and patient monitoring should be tailored to individual patient needs to facilitate the selected surgical and perfusion techniques and for monitoring of hemodynamics and organ function [22-24]. Intraoperative transesophageal echocardiography is routinely used in all open surgical repairs of the thoracic aorta, unless there are specific contraindications to its use [25,26]. (See "Intraoperative transesophageal echocardiography for noncardiac surgery" and "Anesthesia for open descending thoracic aortic surgery".)

Open surgical repair of the thoracic aorta often requires cardiopulmonary bypass with a cardioplegia-arrested heart, and specific circulatory measures to protect the brain, spinal cord, kidneys, viscera, and lower extremities [27]. (See 'Surgery' below.)

For patients at high risk for spinal cord ischemia (ie, extent I and II disease, eg, descending thoracic aortic aneurysm and thoracoabdominal aortic aneurysm repair), cerebrospinal fluid drainage and perioperative monitoring of spinal perfusion pressure (mean arterial pressure - spinal pressure of greater than 80 mmHg) and spinal cord function are recommended. In our protocol, we maintain intrathecal pressure ≤10 mmHg. Intraoperative motor or somatosensory evoked potential monitoring can also be used to detect early spinal cord ischemia, which may help guide therapy [28-31]. (See "Anesthesia for open descending thoracic aortic surgery", section on 'Cerebrospinal fluid (CSF) pressure monitoring' and "Anesthesia for open descending thoracic aortic surgery", section on 'Neuromonitoring for spinal cord ischemia'.)

It is reasonable to base the decision to use neurophysiologic monitoring on individual patient needs, institutional resources, the urgency of the procedure, and the surgical and perfusion techniques to be used during open thoracic aortic repair. Intraoperative techniques that maintain proximal aortic pressure and perfuse the distal aorta reduce the incidence of spinal cord injury following open thoracic aortic repair. Intrathecal papaverine also enhances spinal cord perfusion and provides additional protection [32]. Moderate systemic hypothermia is also reasonable. Other adjunctive techniques, including epidural irrigation with hypothermic solutions, high-dose systemic glucocorticoids, osmotic diuresis with mannitol, intrathecal papaverine, and cellular metabolic suppression with anesthetic agents, may also improve the tolerance of the spinal cord to reduced perfusion, when it occurs [33].

In addition to spinal cord ischemia, patients with descending TAA are at risk of renal failure. Preoperative hydration and intraoperative mannitol administration may be reasonable strategies to preserve renal function. Furosemide, mannitol, or dopamine should not be given solely for the purpose of renal protection in descending aortic repairs. We use hypothermia in selected cases [34]. During thoracoabdominal or descending aortic repairs that provide surgical exposure of the renal arteries, renal protection using either cold crystalloid or blood perfusion are options.

The complexity of open thoracic aortic surgery dictates long operative times with large volume blood loss; intractable hemorrhage is a dreaded complication. An algorithmic approach to transfusion, antifibrinolytic, and anticoagulation management is reasonable to use in open thoracic aortic repairs. Institutional variations in coagulation testing capability and availability of transfusion products and other prothrombotic and antithrombotic agents are important considerations in defining such an approach. Massive transfusion protocols are usually in place for these procedures [26], but if after all product has been replaced the patient continues to be coagulopathic and hemorrhage, other anticoagulants like recombinant Factor VII, factor eight inhibitor bypass activity (FEIBA) [31], and tranexamic acid [35] have been used with good results [36,37].

SURGERY — The surgical approach to repair of the thoracic aorta depends on the location and extent of diseased aorta. Involvement of the aortic root, sinuses, ascending aorta, arch, and descending aorta determines the nature of the repair.

Basic principles — Surgical repair of the proximal thoracic aorta requires cardiopulmonary bypass often with a cardioplegia-arrested heart, and additional measures to limit end-organ ischemia, which is a major source of morbidity. During ascending aortic and arch repairs, deep hypothermic circulatory arrest, retrograde cerebral perfusion, and selective antegrade cerebral perfusion techniques are used alone, or in combination, to minimize brain injury [38-42]. Distal aortic perfusion with or without selective perfusion of the renal or visceral vessels can be used during thoracoabdominal repairs. (See 'Ascending aorta' below and 'Aortic arch' below and 'Descending aorta' below.)

Hypothermic circulatory arrest involves the use of cardiopulmonary bypass with the establishment of deep systemic hypothermia (18 to 20°C), followed by controlled exsanguination and total body circulatory standstill [43-45]. Hypothermic circulatory arrest provides the best operative field; however, the duration of deep hypothermic circulatory arrest is an independent predictor of transient and permanent neurologic injury. Stroke rates increase significantly after 45 minutes of arrest [18,46,47]. However, using cerebral perfusion techniques, circulatory arrest times can be extended. Perioperative brain hyperthermia is not recommended in repairs of the ascending aortic and transverse aortic arch, as it is probably injurious to the brain [43].

Basic principles that are followed during thoracic aortic repair/replacement include:

●Sewing to healthy tissue; avoiding anastomotic suture lines in thin aneurysmal tissue

●Replacing the aortic valve if there is leaflet pathology (ie, aortic root replacement)

●Sparing of the aortic valve if there is no pathology (ie, valve-sparing technique)

●Extended hemi-arch replacement if only the proximal arch is involved

●Total arch or elephant trunk replacement if the entire arch is aneurysmal

For patients with genetically mediated syndromes (ie, Marfan syndrome, Ehlers-Danlos syndrome, Turner syndrome, Loeys-Dietz syndrome), or if a bicuspid aortic valve (BAV) is present, strong consideration should be given to replacing the entire ascending aorta from the aortic sinuses to arch vessels during the initial repair. Because their tissue is abnormal and more fragile, these patients have an increased risk for disease progression at the aortic cross-clamp or cannulation site.

Aortic grafts — Graft materials used in aortic reconstruction include polyethylene terephthalate (PET; eg, Dacron) and expanded polytetrafluoroethylene (ePTFE). PET, which is a polyester woven graft, has good tensile strength, is compliant, and promotes tissue ingrowth. PET is the most commonly used graft for aortic replacement though ePTFE grafts are occasionally used in infrarenal aortic repairs [48,49].

Hybrid open/endovascular options — For the ascending aorta and arch, significant progress has been made using a combination of open and endovascular techniques (ie, hybrid repair) to accomplish repair of predominantly aneurysmal disease. Since the introduction of the endovascular aortic stent-graft to treat abdominal aortic pathology, technological improvements extended their use to the treatment of thoracic aortic disease [50-54]. Type B aortic dissection and descending thoracic aneurysms are largely managed using a totally endovascular approach.

Hybrid aortic repair is performed in stages. The goal of the first stage, which uses an open approach, is to bypass critical vessels supplying the brain and/or viscera. This is referred to as a "debranching" procedure (figure 7 and figure 8 and figure 9). In the second stage, the stent-graft is deployed in the diseased aorta to exclude the aneurysm. Although originally described as two separate procedures, with the advent of hybrid operating rooms, hybrid repair can be performed in a single operative setting [51,55-63].

Ascending aorta — Repair of the ascending aorta, whether for acute type A dissection, aortic aneurysm, or aortic intramural hematoma, is approached in a similar manner, with cardiopulmonary bypass including cardioplegia. Aortic root replacement is sometimes required.

With the patient positioned supine, operative exposure is obtained via median sternotomy. The ascending aorta is exposed and cardiopulmonary bypass is established. Arterial cannulation for ascending aortic pathology can be performed centrally or via the femoral or axillary artery. Whenever possible, the author uses a central arterial cannulation directly into the true lumen of the ascending aorta via the Seldinger technique with an 18-Fr cannula [64]. It is important to note, for this technique, transesophageal echocardiography (TEE) must be used to confirm wire placement in the true lumen. For venous cannulation, we use dual-stage inferior vena cava cannulation via a right atriotomy, and superior vena cava cannulation via a right-angled 24-Fr cannula (figure 10). An 18-Fr left ventricular vent is placed in the superior pulmonary vein to decompress the heart. A retrograde 14-Fr cannula is placed via a right atriotomy into the coronary sinus and confirmed by TEE.

Other cannulation sites can be used; however, with femoral cannulation in patients with aortic dissection, the false lumen of a dissected aorta can be inadvertently cannulated, and fenestrations in the descending aorta can prevent central perfusion. With axillary and innominate artery placement, an additional time-consuming anastomosis in a difficult location is required for cannulation. A 2014 meta-analysis of 14 trials that included 4476 patients undergoing aortic surgery compared central aortic cannulation sites (including the axillary artery) with a femoral arterial site [65]. The risk of permanent neurologic deficit was significantly lower for central cannulation (risk ratio [RR] 0.71, 95% CI 0.55-0.90), as was mortality (RR 0.59, 95% CI 0.48-0.70). The advantages seen for central cannulation in this study were attributed to decreased risk of retrograde cerebral embolization or iatrogenic aortic dissection caused by reversed blood flow in the descending thoracic aorta, as well as to facilitate selective antegrade cerebral perfusion (ACP) techniques.

Once cannulation is completed, cardiopulmonary bypass is initiated and the patient is cooled. The aorta is cross-clamped proximal to the cannulation site, and retrograde cardioplegia is administered while the aorta is opened. The aneurysmal aorta or proximal extent of the aortic dissection is resected. Once the root is exposed, antegrade cardioplegia is given directly into the coronary arteries. The aortic root and aortic valve are carefully inspected. If there is extensive dissection of the aortic root, aortic root dilatation, or aortic insufficiency, then aortic root replacement with a composite graft, or a valve-sparing aortic root replacement should be performed. (See 'Involvement of the aortic root' below.)

Once the patient has profound hypothermia (18 to 20°C) and the electroencephalogram is silent, the patient is placed in the head down (ie, Trendelenburg) position and hypothermic circulatory arrest is begun. Speed is of the utmost importance at this time, as length of circulatory arrest is directly related to cerebral morbidity and mortality. Antegrade cardiopulmonary bypass is terminated, the cross-clamp is removed, and retrograde cardiopulmonary bypass is begun via the superior vena cava cannula. For patients with aortic dissection, the distal ascending aorta is resected until the primary tear is excised; it is critical that the site of primary tear is resected. When managing ascending aortic dissection, the proximal extent of dissection should be obliterated with felt and fibrin glue (figure 11). Depending upon the extent of the pathology (aneurysm, dissection), the aortic arch may need to be repaired as well. (See 'Aortic arch' below.)

After the aortic pathology is excised, the distal graft anastomosis is fashioned. For patients with underlying genetic conditions like Marfan syndrome, Ehlers-Danlos syndrome, Turner syndrome, Loeys-Dietz syndrome, or a BAV, replacement of the aorta from the aortic sinuses to arch vessels should be strongly considered during the initial repair, as they are at high risk for progressive disease when using a composite valve graft (modified Bentall procedure) [66], or valve-sparing aortic root replacement. (See 'Involvement of the aortic root' below.)

After completion of the repair, the graft is de-aired, decannulated, and the patient is rewarmed and reperfused. Atrial and ventricular wires are placed, and the patient is optimized then weaned from bypass. Thoracostomy tubes are placed, and the chest is closed in the standard fashion.

Involvement of the aortic root — Aortic root involvement generally necessitates coronary artery re-implantation and may or may not require aortic valve replacement or repair [1,67-71]. In either situation, protection against end-organ damage is accomplished with cardiopulmonary bypass and antegrade aortic perfusion distal to the aneurysm.

Valve-sparing aortic root replacement is recommended for patients without significant aortic valvular disease (figure 12). The nondiseased aortic valve is preserved, but the remainder of the ascending aorta is replaced. The two most common valve-sparing approaches are [67,72,73]:

●Reimplantation (David procedure) – The ascending aorta is replaced with a tube graft that sits below the annulus, thereby protecting the leaflets and annulus from future dilation [74].

●Remodeling (Yacoub procedure) – The ascending aorta is replaced with a polyester tube graft. The aortic root is reduced, and neo-sinuses of Valsalva are created while the annulus is preserved. The downside of this approach is that the annulus may subsequently dilate [75]. In contemporary practice, an internal or external annuloplasty ring is often added to prevent future annular dilation and recurrent aortic insufficiency [76].

In a meta-analysis comparing these valve-sparing techniques in 4777 patients' survival and durability of the repair were similar; however, a lack of standardization limited this study [72].

If both the ascending aorta and valve are diseased, aortic root replacement is necessary (figure 13), most commonly using a modified Bentall procedure [66]. In this procedure, the entire ascending aorta and the valve are excised and replaced with a composite valve (tissue or mechanical)/polyester aortic graft. The coronary arteries are preserved and sewed on as coronary buttons. If a mechanical valve is placed, chronic lifelong anticoagulation with warfarin is necessary. If a tissue valve is placed, anticoagulation is usually not necessary beyond the first several months. Patients with Marfan, Loeys-Dietz, and Ehlers-Danlos syndromes and other patients with dilation of the aortic root and sinuses of Valsalva may need aortic root replacement with valved graft conduit but, if technically feasible, should undergo valve sparing surgery (David repair). (See "Antithrombotic therapy for mechanical heart valves".)

Aortic arch — The operative exposure and general technique for aortic arch repair are the same as for the ascending aorta. (See 'Ascending aorta' above.)

With aortic arch repair, the need for access to the arch vessels mandates interruption of cerebral blood flow and the need for cerebral protection [77,78]. Cerebral protection can be accomplished using retrograde cerebral perfusion or selective antegrade cerebral perfusion.

●Retrograde cerebral perfusion involves perfusing the superior vena cava with cold oxygenated blood in a retrograde manner in conjunction with cardiopulmonary bypass [79-82]. Deoxygenated blood containing cellular metabolic byproducts returns via the carotid orifices. The mechanism of retrograde cerebral perfusion is controversial; it is purported to provide neuronal metabolic support, preserve cerebral autoregulation, and enhance cerebral cooling [83-89]. The risk of stroke is significantly reduced with retrograde cerebral perfusion compared with hypothermic circulatory arrest alone.

●With selective antegrade cerebral perfusion, blood flow is established antegrade via grafts that are anastomosed to the right axillary or innominate artery, or selective cannulation of the cerebral vessels with balloon-tip catheters [90,91]. In the Aortic Surgery Cerebral Protection Evaluation CardioLink-3 Trial, which randomly assigned patients to innominate or axillary artery cannulation, outcomes were comparable [92-94]. New severe ischemic brain lesions seen on diffusion-weighted MRI were similar between groups (axillary: 38.8 percent; innominate: 34.0 percent) as was the rate of clinical stroke/transient ischemic attack (axillary: 7.1 percent; innominate: 3.6 percent). Advantages of selective antegrade cerebral perfusion include the ability to control flow, perfusion pressure, and perfusate temperature to the brain. Although selective antegrade cerebral perfusion is metabolically optimal, it can be technically cumbersome and is associated with risks of cerebral embolism and carotid dissection. A variation of selective antegrade cerebral perfusion using a trifurcated graft (ie, grafts to the brachiocephalic, left carotid, and right carotid arteries) has also been described [95,96]. The trifurcated graft approach may reduce embolic complications.

Excellent results can be achieved with either retrograde cerebral perfusion or selective antegrade cerebral perfusion. There are no good direct comparisons to establish superiority of one technique, although there are numerous publications favoring one strategy over another [97]. A systematic review identified 15 studies comparing selective antegrade cerebral perfusion with retrograde cerebral perfusion in 5060 patients undergoing deep hypothermic circulatory arrest with temperatures ranging from 16 to 26°C for aortic arch surgery [98]. In pooled analyses, perioperative (30-day) mortality, permanent neurologic dysfunction, and transient neurologic dysfunction were similar between the groups.

In the author's preferred technique, once hypothermic circulatory arrest has been established, retrograde cerebral perfusion is initiated and the pathology is excised, often involving the origin of one or more of the arch vessels (innominate, left common carotid, and left subclavian arteries). Any diseased vascular segments are excised and replaced with a graft. Balloon occlusion catheters are placed into the exposed arch vessels for antegrade cerebral perfusion. Once antegrade perfusion to the brain is established, retrograde perfusion is terminated.

Aortic reconstruction is performed with a polyester tube graft starting with the distal anastomosis. Once the distal anastomosis is completed, the graft is cannulated through a side branch and clamped proximally, thus reestablishing perfusion to the body. The patient is then slowly rewarmed. Next, depending upon the extent of arch involvement, a total arch (figure 14) or hemiarch repair (figure 15) can be performed.

●Total arch repair – Replacement of the entire aortic arch is indicated for aneurysms of the entire arch (figure 14); acute dissections where the arch is aneurysmal or if there is extensive destruction and leakage; chronic dissection when the arch is enlarged; and for distal arch aneurysms that also involve the proximal descending thoracic aorta. The entire arch is excised, and the arch vessels are individually re-anastomosed to the replaced arch. After the anastomoses are completed, each of these grafts is cannulated and selective antegrade perfusion is given. Total arch repair typically mandates adjunctive antegrade cerebral perfusion techniques given that circulatory arrest times can be extensive.

The elephant trunk technique is often used in total arch replacement. The elephant trunk technique leaves a graft inside the distal aorta (trunk) (figure 9), which can then be used for a proximal anastomosis in future operations. It was originally described as a two-stage operation but can be performed in one stage [99-103]. With a frozen elephant trunk procedure, the arch is replaced in the manner of a traditional elephant trunk, but instead of performing a second open operation to replace the descending aorta, a thoracic aortic stent-graft is placed into the graft either at the initial operation or at a later date. This allows for a one-stage repair [104-106]. Frozen elephant techniques have essentially replaced the traditional elephant trunk technique in contemporary practice. (See 'Hybrid open/endovascular options' above.)

●Hemiarch repair – With a hemiarch repair, the arch vessels (brachiocephalic, left carotid, left subclavian artery) that are not involved in the disease process can be preserved and excised as a patch. The patch is anastomosed to a polyethylene tube graft that spans the entire arch (figure 15). Given a single distal aortic anastomosis, circulatory arrest times are significantly shorter than extensive arch reconstructions. Therefore, this technique lends itself well to adjunctive retrograde cerebral perfusion techniques.

Once the distal aortic anastomosis is completed, antegrade (anatomical) circulation to the body and brain are restored, the patient is rewarmed, and attention is turned back to the proximal aortic reconstruction. An aortic root graft, if needed (see 'Involvement of the aortic root' above), or native aorta is anastomosed to the aortic arch graft in a beveled end-to-end fashion while the system is de-aired. Once this anastomosis is complete, the cross clamp is removed and the heart is re-perfused. Atrial and ventricular wires are placed. The patient is optimized, surgical results are assessed, and then the patient is weaned from the bypass machine. Thoracostomy tubes are placed and the chest is closed in the standard fashion.

Descending aorta — Open repair for descending thoracic aortic pathology is via a left thoracotomy that may be extended to the abdomen, and although less extensive repairs limited to the thoracic aorta may not require full cardiopulmonary bypass or cardioplegia, measures to protect the spinal cord from ischemia, which can result in paraplegia, are usually important. Those procedures that replace the aorta from the distal left subclavian artery to below the renal arteries, Crawford extent II, are associated with the highest risk for spinal cord ischemia [99,107,108]. (See 'Anesthesia, monitoring, and organ protection' above.)

Although early studies reported that a quick operation (clamp and sew) without adjunctive measures was sufficient for thoracic aortic repair [109-114], later studies suggested that end-organ protection measures, such as cerebrospinal fluid drainage combined with intrathecal papaverine in high-risk patients [29,115]; intercostal re-implantation [116]; distal aortic perfusion using bypass circuitry [29,117-121]; selective perfusion of renal, segmental, and visceral arteries [27,122]; and profound hypothermia [123,124], can markedly decrease the likelihood of spinal, mesenteric, and renal ischemia [125,126]. Patients who benefit most from these protective strategies are higher risk patients, including those with renal dysfunction, peripheral artery disease (PAD), long aortic segment surgery, and prior abdominal aortic aneurysm repair [127].

Exposure for repair of the descending thoracic aorta is obtained with a left-sided posterolateral thoracotomy with the patient in the right semi-lateral decubitus position (shoulders positioned posteriorly 10 to 20°; pelvis is rotated 50 to 60° posteriorly), and the table is flexed at the patient's waist. For access to the distal arch and descending aorta, the incision is made at the fifth or sixth intercostal space. If the left subclavian and distal arch need to be accessed, then an incision in the fifth interspace is appropriate. For thoracoabdominal aneurysms, the left thoracotomy incision is extended across the costal margin to continue midline for a retroperitoneal approach.

Many strategies for cardiopulmonary bypass are described for managing descending aortic dissection and aneurysms. Our preferred method is partial left heart bypass with venous drainage from the left femoral vein using an elongated venous cannula advanced to the level of the right atrium. Arterial cannulation is established via the internal iliac system for thoracoabdominal aneurysm or via the descending aorta for aneurysm limited to the thoracic aorta. Left atrial cannulation in conjunction with femoral artery or descending aorta cannulation has been described, as has femoral-femoral bypass.

Once cardiopulmonary bypass has been established, the proximal aneurysm is carefully exposed, avoiding injury to the nearby phrenic, vagus, and recurrent laryngeal nerves. An aortic cross clamp placed between the left subclavian and left common carotid artery provides proximal aortic control.

●For replacement of the descending thoracic aorta, distal control of the thoracic aorta is obtained. Aortotomy is performed and patent intercostal arteries are oversewn. Re-implantation of patent lower intercostal arteries (T8 through T12) is encouraged since sacrifice of these arteries is more frequently associated with neurologic deficits [128-130]. The risk of paraplegia is significantly increased when eight or more segmental arteries are sacrificed during repair [20]. Somatosensory or motor-evoked potential monitoring to detect spinal cord ischemia is used by some surgeons to guide reimplantation of intercostal arteries. In one retrospective study of 132 patients, re-implantation of the vessels between T8 intercostal and L2 lumbar arteries significantly reduced operative mortality (4.9 versus 13.2 percent for no re-implantation), the incidence of postoperative paraplegia (0 versus 8.8 percent), and the overall rate of spinal cord dysfunction (2.4 versus 9.9 percent) [131].

The diseased aorta is excised from all surrounding tissue including the esophagus. An interposition polyester tube graft is sewn to the distal and proximal aorta while de-airing. The proximal aortic cross clamp is kept in place for the entire aortic repair procedure to avoid retrograde embolism to the brain.

●For patients who also require replacement of abdominal aorta (eg, thoracoabdominal aortic aneurysms (figure 16 and figure 17 and figure 18 and figure 19 and figure 20), the proximal anastomosis is performed at the required level. The distal cross clamp is positioned 2 to 3 cm distal to the site of the proposed distal anastomosis. The aorta is opened posterior to the origin of the left renal artery, and selective perfusion of the viscera is performed with oxygenated cold blood or cold crystalloid solution [120]. Next, island patches of large segmental arteries, visceral vessels (celiac, superior mesenteric, right renal), and the left renal artery are created and anastomosed to the polyester tube graft depending on the extent of affected aorta (figure 21). However, for patients who have genetically mediated syndromes (eg, Marfan, Loeys-Dietz), island patches should not be performed as there is a risk of future aneurysmal dilatation of the patch. Instead, each of the distal vessels should be individually anastomosed to a polyethylene terephthalate (eg, Dacron) interposition graft. With the completion of each of the anastomoses, the cross clamp can be sequentially replaced more distally to reestablish flow to the aortic branch vessels. Once the island patches are completed, the distal aortic anastomosis is performed (figure 22).

For patients with severe aneurysmal disease of the arch, aortic rupture, or calcification necessitating circulatory arrest, the patient is cooled to permissive hypothermia (32°C) and circulatory arrest is established to complete the proximal anastomosis. After de-airing the arch, antegrade flow to the brain is re-established prior to performing the distal anastomosis. Once all anastomoses are complete, hemostasis is meticulously obtained; after patient optimization, the patient is weaned from cardiopulmonary bypass. Thoracostomy tubes are placed and the chest and chest/abdomen are closed in the standard fashion.

POSTOPERATIVE COURSE AND FOLLOW-UP — The postoperative course depends upon the extent of the surgery and the comorbidities of the patient. In general, for elective patients undergoing thoracic aortic replacement, the period of hospitalization is 5 to 6 days, whereas for thoracoabdominal replacement, the postoperative course is longer at 7 to 10 days, provided there are no complications.

Follow-up imaging — There is no formal guidance for determining the interval of follow-up. We typically obtain follow-up vascular imaging using CT or magnetic resonance prior to discharge, then at 1, and 6 months and then annually if residual aneurysmal disease, aortic dissection, or genetic aortopathy is present [1].

Patients with Marfan syndrome who present with aortic dissection requiring emergency surgery require more subsequent interventions than patients who are repaired electively, necessitating more vigilant postoperative surveillance [132].

MORBIDITY AND MORTALITY — Given the operative complexity, it is not surprising that perioperative morbidity and mortality following thoracic aortic repair is high compared with most elective surgical procedures. Factors associated with an adverse 30-day outcome (death, paraplegia, paraparesis, stroke, or acute renal failure) after open surgery for thoracoabdominal aneurysm include preoperative renal insufficiency, advanced age, symptomatic aneurysm, and Crawford type II aneurysm (proximal descending to infrarenal aorta).

The subsets of aortic arch and Crawford type II aneurysms (proximal descending to infrarenal aorta) have the highest morbidity and mortality rates [133-141]. Even higher rates are associated with emergency surgery for thoracoabdominal aneurysm that has ruptured or dissected. In one series, perioperative mortality among 19 patients undergoing emergency thoracoabdominal repair was 42 percent [142]. The incidences of prolonged intubation with controlled ventilation >48 hours, renal failure, and in-hospital mortality more than double after urgent or emergency surgery [1,143-145].

Age is an independent risk factor for death, and older age is often a prohibitive risk for repair of extent II aneurysms. In a single-institution study, operative mortality for thoracic aortic repair was significantly higher for patients >80 years of age compared with ≤80 years of age (26 versus 7 percent) [146]. Chronic renal insufficiency, defined as a Cr >1.8 mg/dL, is also an independent predictor of death (odds ratio [OR], 3.4, 95% CI 1.4-1.8) [136,147,148].

Long-term mortality is related to other cardiovascular events, such as aneurysm in other areas, myocardial infarction, and stroke [149,150]. A population-based study of 1960 patients showed long-term survival at 5, 10, and 15 years to be 78, 59, and 45 percent, respectively [149].

Trends — In studies documenting outcomes in procedures performed through the mid-1990s, it was not unusual to see overall perioperative (30-day) mortality rates exceeding 10 percent [18,82,151]. Mortality rates have decreased significantly in later series, perhaps attributable to improving technology and increased use of the end-organ protective adjuncts described above [27,115,116,123,125,126,152].

●In a review of 108 patients, the use of noninvasive diagnostic studies and newer surgical techniques, including retrograde cerebral perfusion, significantly reduced operative mortality for a later (1994 to 1997) compared with earlier cohort (1987 to 1993; 3 versus 26 percent) [152]. The 10-year actuarial survival was 57 percent; 93 percent of survivors were in New York Heart Association functional class I or II.

●In a review of 360 patients with repair of the ascending aorta and arch, 95 patients with repair of the descending aorta, and 35 patients with thoracoabdominal aorta repair, operative mortalities for these predominantly elective procedures, which were performed between 1995 and 2004, were 2.9, 3.0, and 11.9 percent, respectively [144]. The 10-year survival for the combined group was 73 percent.

Complications — Significant postoperative bleeding requiring urgent or emergency surgical re-exploration occurs in approximately 3 percent of patients after elective aortic surgery and approximately 10 percent after urgent or emergency surgery (table 1) [144]. Postoperative bleeding can lead to cardiac tamponade and hemothorax, as well as shock, dilutional coagulopathy, and transfusion-related complications. Prevention of postoperative bleeding involves correction of coagulation defects and obtaining hemostasis in the postbypass period [1]. The use of antifibrinolytic agents and surgical technical advances have reduced the risk [144,152].

Ischemic complications are related to inadequate perfusion of the brain (stroke), spine (paraplegia, paraparesis), viscera (intestinal infarction, renal failure), and extremity (critical limb ischemia). In one review of 1108 patients, the main predictors associated with an adverse perioperative (30-day) outcome included preoperative renal insufficiency, increasing age, symptomatic aneurysm, and Crawford type II aneurysms (proximal descending to infrarenal aorta) [153].

●In studies documenting outcomes through the mid-1990s, overall 30-day stroke rates were 20 percent with ascending and arch aneurysm repair, and spinal and renal injury rates were 15 percent with repair of a descending aneurysm [18,82,151], but they have decreased to approximately 3 to 6 percent after elective surgery and 11 percent after urgent or emergency surgery [1,143-145]. This improvement is attributed, in part, to the use of current cerebral protection strategies.

●The risk of spinal cord ischemia and consequential paraparesis/paraplegia is between 8 and 30 percent. Spinal cord injury is also associated with increased long-term morbidity and mortality. In a series of 1509 patients who underwent descending aneurysm repair, paraparesis or paraplegia developed in 16 percent [151]. In another report from the same group, the incidence of postoperative acute renal failure severe enough to require dialysis was 7 percent [110].

●In a series of 19 patients undergoing thoracic aortic repair for ruptured thoracic aortic aneurysm (TAA), serious postoperative complications occurring in survivors included renal failure (36 percent), respiratory failure (36 percent), and paraplegia or paraparesis (27 percent) [142].

Peripheral nerve injuries can also occur as a consequence of surgical traction at vascular access sites, but this typically improves with conservative management. Operations involving the distal aortic arch are associated with a risk of injury to the recurrent laryngeal nerve that may cause hoarseness or vocal cord paralysis [1]. Injuries to the phrenic nerve may contribute to postoperative respiratory failure caused by diaphragmatic paralysis.

A small number of patients may require late reoperation following repair of an ascending aorta or aortic root aneurysm because of insufficiency or stenosis of an aortic valve substitute, true or false aneurysm formation, acute dissection, or prosthetic valve endocarditis. Paraanastomotic pseudoaneurysm is one potential late complication following open thoracic aortic repair and usually occurs in the setting of graft infection. Conventional treatment required re-do open surgical repair, which is associated with significant morbidity and mortality. Endovascular repair with stent-graft placement is a reasonable option for patients with suitable anatomy to avoid the reoperative complications but may be only a temporizing measure, as graft reinfection commonly occurs [154,155]. (See "Overview of infected (mycotic) arterial aneurysm".)

In a study of 134 patients who required reoperation, hospital mortality was 6.6 percent [156]. Predictors of death were an interval of less than six months between the first and second surgeries, elevated preoperative creatinine level and need for postoperative dialysis, and acute aortic dissection as the indication for repeat surgery.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Aortic and other peripheral aneurysms" and "Society guideline links: Aortic dissection and other acute aortic syndromes".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topics (see "Patient education: Thoracic aortic aneurysm (The Basics)")

SUMMARY AND RECOMMENDATIONS

●Open thoracic aortic repair – Involvement of the aortic root, sinuses, ascending aorta, arch, and descending aorta determines the nature of the repair. Repair of the thoracic aorta uses open, endovascular, and hybrid surgical techniques. For patients with descending thoracic aortic disease, endovascular treatment is emerging as the treatment of choice. Open or hybrid repair is required to manage ascending aortic, arch, and most thoracoabdominal aortic pathologies. (See 'Indications for open repair' above.)

●Ascending aorta or arch repair – During ascending aortic and arch repairs, deep hypothermic circulatory arrest, retrograde cerebral perfusion, and selective antegrade cerebral perfusion techniques are used alone, or in combination, to minimize brain injury. Repair of pathologies affecting the ascending aorta or aortic arch may involve the aortic root, which necessitates coronary artery reimplantation and may or may not require aortic valve replacement or repair. For patients without significant aortic root dilation, valve-sparing aortic root replacement is recommended. (See 'Surgery' above and 'Ascending aorta' above.)

●Descending aorta – Open repair of the descending thoracic aorta is usually via a thoracotomy, but may require extension into the abdomen, but often does not require full cardiopulmonary bypass or cardioplegia. Distal aortic perfusion with or without selective perfusion of the renal or visceral vessels can be used during thoracoabdominal repairs. Measures to protect the spinal cord are important. Reimplantation of patent lower intercostal arteries (T8 through T12) is encouraged since sacrifice of these arteries is more frequently associated with neurologic deficits. (See 'Surgery' above and 'Descending aorta' above.)

●Complications – Perioperative morbidity is due to cardiovascular (eg, myocardial infarction), pulmonary events, and ischemic complications related to inadequate perfusion of the brain (stroke), spine (paraplegia, paraparesis), viscera (intestinal infarction, acute kidney injury, renal failure requiring dialysis), and extremity (critical limb ischemia). Long-term morbidity and mortality are related to cardiovascular events and large vessel aneurysm in other locations. (See 'Complications' above.)

●Mortality – Mortality following open thoracic aortic aneurysm repair remains high; however, mortality rates have decreased, perhaps attributable to earlier diagnosis, improving technology, and increased use of the end-organ protective adjuncts. Aortic arch and Crawford type II (proximal descending to infrarenal aorta) aneurysms have the highest morbidity and mortality rates. Emergency surgery for thoracoabdominal aneurysm that has ruptured or dissected is associated with a mortality rate of at least 40 percent with serious postoperative complications occurring in approximately 30 percent of patients. (See 'Morbidity and mortality' above.)

ACKNOWLEDGMENTS — The UpToDate editorial staff acknowledges Y Joseph Woo, MD and Christina L Greene, MD, who contributed to an earlier version of this topic review.