75. Type A Aortic Dissection- Review of CT Surgery

Habib Jabagi, Alexander A. Brescia, and Bo Yang

This chapter is a revision and expansion of a chapter on all aortic dissection included in the previous editions of the TSRA Review written by Sandeep Sainathan (2^nd edition), J. Chad Johnson (1^st edition), and Jason A. Williams (1^st edition). 

Thoracic aortic disease is one of the most challenging sequelae for the cardiac community. Understanding of the full spectrum of aortic syndromes and their optimal management pathways remains incomplete. In addition, surgical treatments for aortic pathology are technically demanding and high risk. Further complicating things, the incidence of aortic pathologies is increasing, secondary to improved imaging techniques and longer life expectancies with prolonged exposure to high blood pressure. 

Aortic dissection (AD) is one of three clinical entities that make up acute aortic syndromes (AAS), with the other two being intramural hematomas (IMH) and penetrating aortic ulcers (PAU). All three can be acute or chronic, affect any part of the aorta, and are considered to be interrelated conditions with similar characteristics, but varying stability.   

Aortic dissections (classical-communicating AAS) occur through a tear in the aortic intima, resulting in the separation of the layers of the media of the aortic wall, creating a true (TL) and false lumen (FL).  Pulsatile blood flow can enter this false lumen causing dissection propagation (ante- or retrograde), as well as new re-entry tears elsewhere along the aorta. In comparison, rarer non-communicating AAS (IMH and PAH) usually have absent luminal flow.  IMH may arise from either spontaneous rupture of aortic vaso vasorum or thrombosed false lumen, while PAU occurs secondary to atherosclerotic plaque rupture, similar to coronary plaque rupture, resulting in an intimal defect and pseudoaneursym with or without blood flow in it. Clinical presentation of AAS is often indistinguishable between the three entities, requiring computed tomography (CTA) for definitive diagnosis and confirmation.

With the establishment of the International Registry of Acute Aortic Dissection (IRAD) database, our understanding of AAS has greatly increased. Incidence of Acute type A aortic dissection (ATAAD) in the US is approximately 10 per 10,000. With a 1-3% mortality rate/hr without surgical repair, ATAAD is a deadly condition, making prompt diagnosis and treatment of paramount importance. Untreated (medically and surgically), ATAAD mortality rates are over 33% in the first 24 hrs, 50% at 48 hrs, and approach 75-90% at two weeks. In contrast, with aggressive treatment 30-day survival can reach 80-90%.

Classification – Anatomy & Chronicity

Several different classification systems exist; however, the two most commonly used systems are based on anatomical extent:

Stanford classification

• Type A:  requires involvement of the ascending aorta
  • Type B:  all dissections not involving the ascending aorta (usually occur distal to the left subclavian artery, but may involve in the aortic arch)

DeBakey classification

• Type I:  involves the ascending aorta, aortic arch, and descending aorta
  • Type II:  involves the ascending aorta only
  • Type III:  involves the descending aorta only (distal to the left subclavian artery)
    • Type IIIa:  confined to the aorta above the diaphragm
    • Type IIIb:  extends below the diaphragm

Timing of dissection is also important in classifying AAS, as it can grossly change management strategies. The chronicity of aortic dissections is typically classified based on the initial tear or symptom onset, and fall into 3 categories according to the consensus 2010 North American and 2014 European guidelines for thoracic aortic disease:

• Acute: ≤14 days
  • Subacute: 15 to 90 days
  • Chronic: >90 days

Pathophysiology of Aortic Dissections

The normal aortic wall consists of three layers: intima, media (made of smooth muscles and connective tissue proteins), and the adventitia which provides its tensile strength and is the strongest layer. Normal aortic diameters vary depending on patient age, size, and sex. In general, the ascending aorta ranges between 2-3 cm in diameter, the aortic arch between 2.2-3.6 cm, while the descending aorta is usually between 2-3 cm. AD occurs as a consequence of increased wall stress (based on Laplace’s law), where tension (wall stress) is equal to pressure x radius (T = P x R). Therefore, any mechanism that increases wall stress beyond its capacity will predispose the aorta to dissection.

Most dissections occur between the ages of 60 to 70 (mean age at diagnosis of 63 years), and have a 3:1 male predisposition. Chronic hypertension is the most common predisposing risk factor and is present in >75% of cases. Connective tissues diseases (CTD) are also important risk factors and the three most common are Marfan (MFS), Loeys-Dietz (LDS) and Ehlers-Danlos (EDS), syndrome, with MFS being the most common. These CTDs all weaken the elastin or collagen layers within the media of the aortic wall, which could predispose these patients to dissections and aneurysms of the aorta. A wide range of risk factors for AD exist, and are best split into those having a direct mechanical force on the aortic wall and those that affect aortic wall composition:

Direct Mechanical Forces	Aortic Wall Composition
Increasing age	MFS: autosomal dominant (1:5,000), Fibrilin-1 (FBN1) gene defect (Chromosome 15), Ghent criteria for diagnosis
Male	EDS: autosomal dominant, > 13 types, type IV most common, mutation of COL3A1 gene encoding type III collagen
Chronic hypertension (↑ pressure)	LDS: autosomal dominant, 5 types, mutations in TGF-β receptors (TGFBR) 1 & 2
Pre-existing aortic aneurysms (↑ radius)	Familial Thoracic Aortic Aneurysm and Dissection (FTAAD): commonly involved genes include MYH11, ACTA2, and TGFBR1&2
Iatrogenic: cardiac surgery, catheter based therapies	Hereditary: bicuspid aortic valve (BAV) associated with NOTCH-1 gene mutation, aortic coarctation
Pregnancy related: rare, concomitant CTD	Turner Syndrome : 45X, or 45X0
Miscellaneous: drugs, trauma, weight lifting	Inflammatory and autoimmune diseases: Giant cell arteritis, Takayasu, Rheumatoid arthritis, Syphilis

In ATAAD, the intimal tear starts most commonly at the right anterior aspect of the proximal or middle ascending aorta along the great curvature and spirals through the aortic arch down the descending thoracic aorta and abdominal aorta on the left posteriorly. Sometimes, intimal tears can occur at the level of the aortic arch or descending thoracic aorta with retrograde progression. In type B dissections (TBAD), the intimal tear most commonly occurs distal to the left subclavian artery or less frequently from an abdominal intimal tear with retrograde progression (<1% cases). The dissection tends to occur towards the outer layers of the media, making the outer wall of the false lumen thinner than the intimal flap and dependent upon the adventitia for its strength. Vessels arising from the aorta such as the coronary arteries, arch vessels, intercostal arteries, visceral vessels, and iliac arteries may be sheared off the lumen, occluded by the dissecting media, stay in communication with the false lumen or be uninvolved. The false lumen may rupture, re-communicate with the true lumen by re-entry tears, thrombose, or remain intact, leading to future aneurysm formation.

Clinical Presentation

Based on a study in Oxford, about 50% of patients present with sudden death due to rupture, coronary ischemia (especially left main coronary artery involvement), and acute severe aortic insufficiency from commissural detachment of the aortic valve. Heightened suspicion is the key to early diagnosis as 30% of patients with dissection were initially thought to have another diagnosis. Severe pain is the major symptom, being mid-sternal in ascending aortic dissection and inter-scapular in descending aortic dissection. Painless dissection can also occur in aneurysmal aortas. Patients may present with signs of malperfusion of the coronary (myocardial ischemia), cerebral (stroke in 5%, which may not improve), visceral (mesenteric ischemia, renal failure), intercostal (paraplegia), or limb vessels. Absence of abrupt pain, pulse changes, and mediastinal widening makes the diagnosis of acute dissection rare.

With respect to IMH, it most often occurs in the descending aorta and in older patients. Chest or back pain are the main characteristics of IMH, whereas malperfusion and pulse deficits are usually less likely present when compared to classic ADs. PAUs are also most commonly found in the descending aorta or aortic arch, as they develop in aortic segments where atherosclerotic changes are most common (>90% in the descending thoracic aorta). Patients are typically elderly (>65 years of age) with hypertension and diffuse atherosclerosis, who present with chest or back pain, but without signs of aortic insufficiency or malperfusion. Chronic PAU patients are usually asymptomatic and are often incidental diagnoses during imaging for other reasons; or even less commonly, present only with signs of distal embolization.  

Diagnostic Tests

Several tests exist which help diagnose AD. Chest X-ray (CXR), ECG, and bedside markers are usually the first tests done in someone presenting with acute-onset chest pain. In ATAAD, CXRs are usually abnormal (60-90%) and show a widened mediastinum. The presence of a calcium sign (separation between calcifcaiton of the aortic intima and the lateral aortic wall of the aortic knob >10 mm) and right tracheal deviation are also common, while less common signs include obliteration of the aorta knob and left main stem bronchus depression. All CXR findings are nonspecific and can be normal in patients with AD. ECGs are often normal in ATAAD, unless there is coronary involvement, with ST changes reflecting the involved coronary distribution. Other ECG findings may include left ventricular hypertrophy, electrical alternans, and low voltage criteria (seen with concomitant tamponade), and changes associated with pericarditis.

Currently, there are no biomarkers for acute aortic dissection. Cardiac enzymes (Hs-troponins) are frequently mildly elevated and D-dimers are best used to rule out ATAAD in patient with a low likelihood of AD, with a NPV of 95% in the first 24 hrs if <500 µg/L. Various aortic specific biomarkers are under investigation based on studies that have shown increased blood concentrations of certain connective tissues (elastin, smooth muscle myosin heavy chain proteins, and matrix metallopeptidases) hours after aortic surgery, but currently there is no established evidence for their utility.

CT
Positives	Negatives
Fast	Coronary tree or AV not assessed
Spiral CT for 2D/3D images	Motion artifact
Lesion type/location, branch vessel involvement	Streak artifact
Image entire aorta, ddx PAU & IMH	Contrast Load
TL vs FL identification	Transportation
Operative planning	Radiation
Type A & B

 The mainstay for diagnosis of AD is diagnostic imaging. CT, MRI, and TEE are the main diagnostic modalities, with aortography largely fallen out of favor. CT and echocardiography are used most often, with CT being the preferred method for first test (63%) and TEE (32%) for the second. The choice of imaging test is largely dependent on clinician preference and availability in the emergency room, since all 3 imagining modalities have sensitivity and specificity in excess of 95%. Each modality has its own advantages and disadvantages, and are listed in the table below:

TEE
Positives	Negatives
Aortic proximity	Semi-invasive / discomfort
Fast	Blind spot – distal asc/proximal arch interface
Aortic Valve, Coronaries, pericardial views	Operator/interpreter dependent
LVF assessment	Sedation
At the bedside	Contraindications – esophageal surgery, hiatal hernias
	Poor Type B visualization

MRI
Positives	Negatives
No radiation	Limited availability
Type A & B	Contraindications – pacemakers
Features of IMH/PAH	Expensive
Follow up tests	Slow
Gadolinium safer vs contrast
Asses AI & LVEF

CT is the most commonly performed modality and is the method of choice for diagnosing AD according to the American College of Radiology. It is fast and provides valuable information for operative planning, but at a cost of intravenous contrast load and radiation exposure. It also provides no information on aortic valve function. TEE is the second most commonly used tool and has a distinct anatomical advantage over TTE, secondary to its proximity to the aorta. Benefits include full assessment of the heart and function, as well as bedside testing. Drawbacks include a 2–5 cm blind spot at the distal ascending and proximal arch interface, operator and interpreter variability, and its semi-invasive nature may elevate patient blood pressure and precipitate dissection or rupture. MRI seems to rectify many of the shortcomings seen with both CT and TEE, but availability and logistics limit its widespread use. Importantly, several studies have shown that coronary angiography performed prior to Type A repair has no effect on the occurrence of CABG, hospital survival, and result in considerable delays to surgery and therefore should be avoided.

IMH has a variable radiologic appearance according to the area of aorta involved, and CT is often the modality of choice in its diagnosis. Imaging criteria in IMH are based on the presence of fresh thrombus in the aortic wall, with no blood flow in the false lumen. IMHs are distinguished from acute dissections by an absence of either a definable dissection flap or communication between the true and thrombosed false aortic lumen. On TEE, IMH are diagnosed by the presence of a crescentic or circular thickening of the aortic wall with maximal thickness ≥7 mm without intimal flap or longitudinal flow in the FL. While on non-contrast CT, the same findings can be seen with the thickened wall having a higher tissue density than unenhanced blood on CT and is without enhancement after contrast on CT or MRI. Increased risk factors for complications or mortality in IMH patients include involvement of the ascending aorta with a diameter >5 cm or IMG thickness >10 mm. As previously stated, PAUs are often incidental findings on CT, and when viewed tangentially, the classic appearance of this lesion is a mushroom-like outpouching (pseudoaneurysm) of the aortic lumen with overhanging edges, resembling a gastric ulcer.

Treatment

Immediate Surgical Repair

ATAAD a surgical emergency, requiring prompt diagnosis and treatment. Once the diagnosis of ATAAD is made, medical management should begin immediately, with a focus on BP reduction in order to limit FL propagation, aortic rupture, and dynamic malperfusion. Since aortic wall stress is affected by force and rate of contraction (dP/dT), as well as BP, the mainstay of treatment is beta blockers (first line), as they control all 3 parameters. Esmolol is often used in patients without contraindications to beta blockers, owing to its shorter half-life. Second line agents in patients with difficult to control blood pressure include sodium nitroprusside (beware of cyanide toxicity with high doses – antidote sodium thiosulfate), and nicardipine. Whatever the agent used, it is titrated to a goal systolic BP <110 mmHg. Other important things to consider include:

1. Early consult to cardiac surgery
2. Pain control – fentanyl, morphine, hydromorphone
3. Patients often need multiple antihypertensive agents to obtain goal targets
4. In the event of beta-blocker allergy, other vasodilators should be considered to lower the blood pressure to prevent rupture and dynamic malperfusion
5. Blood work – type & cross, CBC, Cr, urea, lytes, lactate, LFTs, myoglobin
6. Foley – monitor urine output for renal dysfunction 

Not all patients with ATAAD present with hypertension. Hypotension in ATAAD patients is an ominous sign, and in these circumstances careful evaluation for loss of blood volume is mandatory before administering fluids. Hypotension should alert the physician to possible rupture and/or tamponade, as well as mesenteric malperfusion. Vasopressors should only be used if end organ perfusion cannot be maintained, since there is risk of end organ ischemia. In the setting of tamponade, pericardiocentesis as a temporizing measure has been reported, and slow release of the tamponade is important to avoid surging of BP causing aortic rupture.

Mortality with medical management is 60-80%; thus, definitive management with surgery is the mainstay of treatment for ATAADs. Since the natural history of IMH and PAU are not fully understood and tend to be unpredictable in nature, consensus in the surgical community is that the same treatment strategy for ATAADs should be followed when acute type A PAUs and IMHs involve the ascending aorta. This recommendation is supported by numerous studies that show improved outcomes with surgery using this methodology.

Traditionally, the major goal of surgery in patients with ATAADs was to resolve malperfusion, acute aortic insufficiency, and prevent aortic rupture. With over 50 years of proof of concept, the basic approach has been excision of the primary entry tear, followed by reconstruction of the aorta with an interposition graft and, depending on associated complications, interventions on the AV to make it competent, reimplantation of coronary arteries to prevent myocardial ischemia, as well as arch vessel reconstitution to maintain cerebral and upper body perfusion. The treatment strategy is ultimately up to the surgeon, but also depends on tear location, cannulation strategy for institution of cardiopulmonary bypass, cerebral and myocardial protection, end-organ perfusion/protection, as well as intraoperative temperature management. 

With advancements in both surgical practice and techniques, more aggressive treatments are being performed, where in addition to removal of the primary entry tear, surgeons will resect re-entry tears at the arch, and place a frozen elephant trunk in the proximal descending thoracic aorta. As such, surgical outcomes have continued to improve over the last two decades.

The simplest and most limited surgical treatment for ATAADs is valve-preserving surgery using a Dacron interposition graft. These procedures are performed when the primary intimal defect is isolated to the ascending aorta and both the aortic root and valve are normal in size and function, with no connective tissue disease. This procedure can be modified with the addition of hemiarch replacement when the distal ascending aorta or proximal arch is involved with the intimal tear. With more extensive involvement of the arch and/or branch vessels, the complexity and risks of the procedure increase. Criteria for repair of a dissected aortic arch with transverse arch (hemiarch) replacement include no intima tear at the arch, arch diameter <4 cm, and no malperfusion of the innominate or left common carotid artery. In the presence of arch branch vessel dissection (ABVD) without cerebral malperfusion, hemiarch replacement has been shown to be an adequate repair but does carry a higher risk of late reoperation. When cerebral malperfusion is present, the affected vessels should be repaired and reimplanted individually into the graft used for arch replacement or with a multibranch Dacron graft. When the aortic arch is >4 cm or there is an intimal tear at the arch, both of which can not be resected by a hemiarch replacement, aggressive arch replacement should be considered. With surgical interventions on the aortic arch and its branches, adjunctive measures must be used including: hypothermic circulatory arrest (HCA), antegrade, and/or retrograde cerebral perfusion.     

In the case of aortic root dilation, aortic valve insufficiency, and/or coronary artery involvement, several different options exist for treatment. Criteria for direct aortic root repair (technique described in proximal reconstruction) include no intimal tear at the root, no CTD, and root diameter <4.5 cm. Patients not meeting criteria for direct aortic root repair are treated with either valve sparing aortic root replacements (VSAR) or total aortic root replacements depending on whether or not the aortic valve can be preserved or repaired. Two main valve sparing techniques for aortic root replacement with or without valve repair are available: David Procedure (re-implantation) and Yacoub procedure (re-modeling). The David procedure is the preferred method for patients with CTDs as it stabilizes the aortic annulus from further dilation, while the Yacoub Procedure is known to provide improved hemodynamics with the creation of three neoaortic sinuses. Up to 75% of ATAADs are complicated by AI due to the dissection involving the commissure posts; however, the valve can usually be preserved by aortic valve resuspension (described later). In the event the AV cannot be preserved, a composite graft could be used to replace the aortic valve and root (total aortic root replacement or Bentall Procedure) with both biologic and mechanical options available. All three of these procedures require coronary re-implantation with the use of coronary buttons and add another level of complexity to the repair.

Operative Techniques for ATAAD Surgical Repair

ATAADs repairs are performed via median sternotomy. Venous cannulation is usually achieved through the right atrium, although femoral vein cannulation can be used in the unstable or ruptured patient. There are many sites for arterial cannulation and they are surgeon/anatomy dependent. Arterial cannulation is often achieved peripherally via the femoral artery, as it is the easiest and fastest. The non-dissected side is chosen based on CT. If a CT is unavailable, then the side with the weaker pulse is chosen, as it is more likely to be the true lumen. The major drawback of femoral artery retrograde perfusion is the risk of atheroembolism and stroke, especially when the descending aorta has extensive atherosclerosis.

Axillo-caval cannulation via the right axillary artery or central innominate or subclavian artery cannulation can also be used and is the preferred method when intervention on the aortic arch is necessary, which is frequently required in ATAAD repair. With interventions on the aortic arch, the addition of hypothermic circulatory arrest with cerebral perfusion are also needed to ensure cerebral protection. Typically, an 8-10 mm Dacron “chimney” graft is sutured to the right axillary artery, intrathoracic right subclavian artery, or innominate artery, which allows for selective antegrade cerebral perfusion (ACP) by clamping the proximal innominate artery during HCA, as well as decreased risk of stroke and incorrect FL cannulation. However, this approach can be time consuming and is contraindicated in patients with right aberrant subclavian artery (absolute contraindication, <2% of population), dissection (rarely involved), severe atherosclerosis or calcification, and morbid obesity (relative contraindication). Direct ascending aortic cannulation of the true lumen is also an option using a modified Seldinger’s technique and elongated one piece aortic cannula (EOPA) with TEE guidance to confirm TL cannulation. Additional means for antegrade cerebral perfusion can be achieved with the insertion of cannulas into individual arch branch vessels. 

Traditionally, cerebral protection has been achieved with the use of deep hypothermic circulatory arrest (DHCA). The patient is cooled to 18°C, as measured by the nasopharyngeal temperature probe for 30 to 45 minutes, which results in EEG quiescence and provides a safe circulatory arrest time of around 30-40 minutes. The concept of deep hypothermia to reduce oxygen and metabolic requirements of hypoxic tissue is well-documented, but it is not achieved without adverse effects on body homeostasis and processes, including: longer cardiopulmonary bypass times increased coagulopathy, multi-organ dysfunction, systemic inflammatory response (SIRS), endothelial dysfunction, and neuronal apoptosis. With the development of ACP, aortic dissection operations are increasingly being performed under warmer circulatory arrest temperatures, with reductions in both mortality and morbidity. Retrograde cerebral perfusion via the SVC can also be employed with DHCA, but has been shown to have no added benefits to DHCA alone.

The distal reconstruction is commonly performed under DHCA; thus as soon as cannulation and perfusion are established, the patient is cooled. During cooling, proximal work and dissection can be performed until the desired target temperature is reached, at which time attention is directed to completing the distal reconstruction as fast as possible to limit hypothermic and circulatory arrest times, mitigating the negative consequences of each. It is at this time, ACP is instituted providing cerebral perfusion with lower body ischemia only. Usually, a hemiarch replacement will suffice and is the preferred method for non-aortic surgeons, as it is simple and will limit HCA times. Total arch repair can be time consuming for surgeons who infrequently perform the procedure, thus adding to operative risk. While replacing the arch decreases the chance of repeat interventions and makes future interventions on a dilated descending thoracic aortic or residual aortic dissection easier, the arch itself rarely dilates except in cases of CTDs such as Loeys-Dietz syndrome. Once distal reconstruction is complete, lower body perfusion is reinstituted and re-warming commences usually with a side branch on the arch graft in the case of total arch replacement, or with unclamping of the innominate artery in the case of hemiarch replacement allowing the axillary artery cannulation to perfuse the whole body once again. 

Proximal reconstruction can be completed before circulatory arrest if completed prior to target temperature ascertainment or returned to and finished once the distal reconstruction is completed during re-warming. Direct aortic root and simple aortic valve repair can be achieved by valve resuspension using single pledgeted commissural sutures and sino-tubular junction reconstruction with 5-0 prolene without felt, both of which can be completed quickly. As mentioned previously, more extensive and complex procedures, such as valve sparing aortic root replacements and Bentall procedures can be performed as indicated, but are beyond the scope of this chapter.

Lastly, surviving the operation does not guarantee freedom from subsequent aortic events.  Despite significant improvements in outcomes and operative techniques, morbidity and mortality remain high, with a 10-year survival rate between 30–60%. Keeping in mind that the primary goal of surgery in ATAADs is patient survival, surgery has traditionally taken a conservative treatment approach to an already deadly disease (i.e., do the least possible to mitigate intra-operative death and postoperative complications by minimizing operative time and extent of surgery). This philosophy often results in residual dissected aorta, distal intimal tears, and patent FLs being left behind at time of index surgery. Consequently, late reoperations are a relatively common occurrence due to continued aneurysmal growth of residual dissected aorta. Known risk factors for downstream aortic reoperation include both pre- (presence of CTDs especially MFS, LDS, aortic isthmus diameter >4 cm) and postoperative factors (persistent hypertension, increased rate of FL growth, presence of intimal tears at the aortic arch). Studies have shown reoperation in aortic dissection patients carry an even higher surgical risk than the primary surgery depending what reoperation is performed.     

With improved control over the operative field and new technologies available to perform more advanced repairs, a divide among surgeons has ensued, with some advocating a conservative tear-orientated approach and others a more aggressive approach with systematic total ascending and arch replacement and liberal use of elephant trunk techniques. There are advantages and disadvantages to both approaches, and both of these approaches can be applied to both proximal and distal repairs. When disease extends into the descending aorta, extended distal repairs require either total or hemiarch replacement with elephant trunk. The choice of approach depends on patient anatomy, condition, and surgeon comfort. Hybrid procedures also exist, and consist of combined open surgical and endovascular repair (at index surgery or at a later time), to completely eliminate residual arch and thoracic aortic disease.  

The conventional elephant trunk approach consisted of two stages, where a graft is left in the distal aorta for future open replacement of the thoracic aorta or endovascular deployment of a thoracic stent graft. With the development of endovascular techniques and stented grafts, single-stage elephant trunk deployment during index surgery (Frozen Elephant Trunk) became possible and is quickly becoming the preferred technique, with the assumption it obviates the risk of having major repeat open surgery on the proximal descending thoracic aorta. Endovascular stent grafts can be deployed in various ways, including during HCA or as a warm stent graft to limit HCA times, as well as both antegrade and retrograde deployment. An added advantage of antegrade deployment is direct visualizing of true and false lumens to ensure correct delivery into the TL as well as reducing the need for advanced endovascular skills, and elimination of contrast and procedural complications seen with retrograde deployment.

Unfortunately, there are no prospective trials on extended distal aortic repair versus the more conservative replacements in TAAD, and available studies have many limitations, such as small sample sizes, surgeon preference guided extents of distal repairs, as well as heterogeneous repair techniques and intraoperative management strategies. The main benefit of extended TAAD repairs with FET are a higher percentage of complete FL obliteration and increased TL expansion, which is believed to translate into less reoperations and decreased occurrence of malperfusion. Conversely, FET significantly increases the post-operative risk of paraplegia from <1% to 5-10%, with the highest being 15%.

Delayed Surgical Repair

Although immediate open repair for ATAADs is recommended to prevent catastrophic rupture and death in the majority of patients, end-organ failure due to malperfusion in a subset of ATAAD patients may actually represent a more imminent life-threatening problem.  Patients with malperfusion have been shown to have operative morality with central aortic repair of up to 60-70%. Malperfusion is inadequate blood flow to the end organs. Malperfusion syndrome (MPS) is the consequence of prolonged malperfusion, including cell, tissue, and organ necrosis, dysfunction and failure. The difference between malperfusion and malperfusion syndrome is similar to the difference between bacteremia and sepsis, or HIV and AIDS. Malperfusion can be diagnosed via clinical exam (absent pulse) and imaging studies (such as CT angiogram or arteriography with manometry). Malperfusion syndrome can be diagnosed by clinical assessment, including symptoms (such as abdominal pain), physical exam (peritoneal signs), and lab tests (serum lactate, LFTs, and arterial blood gas).  

Taking into account the high operative mortalities of ATAAD repairs with untreated malperfusion and the fact that not all untreated ATAADs rupture, hemodynamically stable patients who present with severe MPS (in the absence of aortic rupture or tamponade) make up a specific subset of patients that may benefit from delayed ATAAD repair. The diagnosis of MPS requires both clinical features and laboratory findings, such as severe refractory abdominal pain and tenderness, decreased urine output, elevated lactate, liver or pancreatic enzymes, as well as bilirubin and creatinine, absence of peripheral pulses, motor or sensory deficits of the extremity and neurologic deficits. Radiological findings demonstrating dynamic or static obstruction consistent with low or absent blood flow to damaged end-organs may also be included. In these patients, it has been shown at specialized centers to be beneficial to follow a staged approach, where treatment of the MPS takes precedent over open ATAAD repair. This strategy involves upfront endovascular reperfusion via fenestration and/or stenting of the critically malperfused abdominal organs and/or extremities, followed by open ATAAD repair at resolution of organ failure or shock. This approach yields several advantages for this subset of patients, including: resolution of both dynamic and static arterial obstruction immediately and completely with a percutaneous procedure (whereas immediate open repair would only resolve dynamic but not static obstruction), gives borderline operative candidates with MPS time to recover, avoids futile open aortic repair in those who will not benefit from such an intervention, and provides favorable short- and long-term survival.

Suggested Readings

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3. Norton EL, Wu X, Farhat L, Kim KM, Patel HJ, Deeb GM, et al. Dissection of Arch Branches Alone: An Indication for Aggressive Arch Management in Type A Dissection? Ann Thorac Surg. 2020;109(2):487-94.
4. Yang B, Malik A, Waidley V, Kleeman KC, Wu X, Norton EL, et al. Short-term outcomes of a simple and effective approach to aortic root and arch repair in acute type A aortic dissection. J Thorac Cardiovasc Surg. 2018;155(4):1360-70.e1
5. Yang B, Rosati CM, Norton EL, Kim KM, Khaja MS, Dasika N, et al. Endovascular Fenestration/Stenting First Followed by Delayed Open Aortic Repair for Acute Type A Aortic Dissection With Malperfusion Syndrome. Circulation. 2018;138(19):2091-103.
6. Deeb GM, Williams DM, Bolling SF, Quint LE, Monaghan H, Sievers J, et al. Surgical delay for acute type A dissection with malperfusion. Ann Thorac Surg. 1997;64(6):1669-75; discussion 75-7.