Endovascular Management of the Ascending Aorta and the Aortic Arch
Camilo A. Velasquez, MD
Young Erben, MD
Mohammad A. Zafar, MD
Chandni Patel, MD
Ayman Saeyeldin, MD
Anton A. Gryaznov, MD, PhD
Bulat Ziganshin, MD, PhD
John A. Elefteriades, MD, PhD (hon)
Key Points
Thoracic aortic aneurysms are usually asymptomatic and not easily detectable until an acute and often catastrophic complication occurs.
Diameters greater than 6 cm increase the risk of death and complication threatening to produce death. Recently, evidence has shown hinge points at 5.25 cm and 5.75 cm, suggesting a leftward shift in the aortic diameter at which intervention should be recommended.
The imaging modalities used for diagnosing pathology of the ascending aorta are computed tomography, magnetic resonance imaging, and echocardiography.
Type A acute aortic dissection is a surgical emergency requiring immediate consultation and intervention.
Open surgical intervention with the replacement of the ascending aorta or the aortic arch with a graft is the gold standard for the treatment of thoracic aortic pathology.
High-risk patients who are unable to undergo open surgical repair may fairly be managed with medical therapy with adequate outcomes.
Endovascular management of aortic pathology is an alternative for high-risk patients in whom the open approach is prohibited.
There are no specific approved devices for the endovascular management of the ascending aorta and the aortic arch.
I. Introduction
A. Thoracic aortic diseases are virulent, often capable of leading to death of the patient.1,2 Generally, the thoracic aorta is a silent organ that only becomes symptomatic when a catastrophic event such as death or a major complication that threatens to produce death occurs.1 According to data from the Centers for Disease Control and Prevention, from the years 1999 to 2015, aortic aneurysm was the 19th leading cause of death in all ages and the 16th cause of death in patients older than 65 years.3 Approximately, 10,000 aortic deaths per year have been reported, with a decrease in incidence from 15,807 deaths in 1999 to 9988 deaths by 2015.1,3
B. The aorta itself is considered an active organ with mechanical properties and an intrinsic and complex biology. Diseases of the aorta are categorized based on location: aortic root, ascending aorta, aortic arch, and descending aorta. The diseases affecting the aorta are separated in two distinct entities at the level of the ligamentum arteriosum: above the ligament (ascending aorta and aortic arch), the disease is nonarteriosclerotic in nature, whereas below the ligament (descending aorta and abdominal aorta), arteriosclerosis is abundant.1
C. Thoracic endovascular aortic repair (TEVAR) has been shown to reduce perioperative mortality and morbidity with a sustained benefit during follow-up. However, recent studies of endovascular approaches to aneurysms in the abdominal and thoracic aorta show a seriously disturbing tendency to endoleak by 5 years.4,5,6 In recent years, TEVAR has become an accepted treatment for patients with suitable anatomy in the descending thoracic aorta.7,8
However, an endovascular approach for repair of the ascending aorta and aortic arch pathology is troublesome. Anatomic and physiologic challenges are formidable for the adequate deployment of endovascular systems. Fundamental problems abound. Proximal graft fixation close to both the aortic valve and the coronary ostia is difficult and dangerous. Distal landing zones may impinge on the innominate artery. These are examples of the complexity of endovascular techniques applied in the “high-rent” region proximal to the ligamentum arteriosum.1 Additionally, the hemodynamic forces experienced in the ascending aorta can be an obstacle for accurate graft deployment.
D. There are no current societal guidelines for endovascular management of ascending aortic aneurysm. In fact, several case reports constitute the bulk of the current literature.9 Therefore, this chapter aims to provide the reader with the current state of the art in the emerging endovascular treatment of the ascending aorta and the aortic arch. The pathologies amenable to intervention will be discussed, and the current devices and techniques available for the ascending and arch segments will be described.
II. Aortic Pathology for the Endovascular Treatment of the Ascending Aorta
A. Current Management and Treatments
In recent years, interest in the management of aortic diseases with endovascular devices has seen an expansion beyond the treatment of the abdominal aorta to an increased attention to more proximal segments of the thoracic aorta. The ascending aorta and the aortic arch became the ultimate frontiers for utilization of endovascular techniques.8,10 Additionally, with the increased safety of open aortic surgery,11,12 the endovascular approach has been reserved for patients who pose a prohibitive risk for an open procedure, or as a last resort in emergent conditions in which an open surgical approach is not feasible and sole medical management can be expected to lead to decreased survival.10 Endovascular management of the ascending aorta and aortic arch can be applied in high-risk patients with the following conditions: type A aortic dissection, aortic pseudoaneurysm, penetrating aortic ulcer (PAU), intramural hematoma (IMH), ascending aortic aneurysm, and ascending aortic rupture.8,10
B. Thoracic Aortic Dissection
1. Comorbidities that are associated with an increase in the wall stress (hypertension, weightlifting, coarctation, cocaine use) or aortic media abnormalities (Marfan disease, Loeys-Dietz, Ehlers-Danlos, bicuspid aortic valve, familial aortic aneurysm, steroid treatment) can predispose to the development of aortic dissection (Table 5B.1).13
TABLE 5B.1. Risk Factors Associated With the Development of Aortic Dissection13
Conditions Associated With Increased Aortic Wall Stress
Uncontrolled hypertension
Pheochromocytoma
Cocaine and other stimulants
Weightlifting and Valsalva maneuvers
Trauma
Deceleration or torsional injury
Coarctation of the aorta
Conditions Associated With Aortic Media Abnormalities
Genetic
Marfan syndrome
Ehlers-Danlos syndrome, vascular form (type IV)
Bicuspid aortic valve
Turner syndrome
Loeys-Dietz syndrome
Familial thoracic aortic aneurysm and dissection syndrome
Inflammatory Vasculitis
Takayasu arteritis
Giant cell arteritis
Bechet arteritis
Others
Pregnancy
Polycystic kidney disease
Chronic corticosteroid and immunosuppression agent administration
Infections involving the aortic wall
2. Depending on the severity and degree of dissection, multiple organ systems can be affected, including cardiovascular, pulmonary, renal, neurologic, gastrointestinal, and peripheral vascular (Table 5B.2).14
3. Overall, type A dissections are treated emergently with operative repair. This is in contrast to patients with type B dissections, who are initially treated conservatively with anti-impulse therapy, with surgery being reserved for patients with complications.15,16 The indications for surgical, endovascular, and medical therapy are as follows (Table 5B.3):
Acute type A aortic dissections pose substantial risk of aortic rupture, aortic regurgitation with heart failure, stroke, cardiac tamponade, and visceral ischemia.
In the IRAD registry, patients with type A aortic dissection who were medically managed had a mortality rate of 58% compared with 26% in those who underwent surgery.17
TABLE 5B.2. Complication by Organ System in Patients With Aortic Dissection14
Cardiovascular
Cardiac arrest
Syncope
Aortic regurgitation
Congestive heart failure
Coronary ischemia
Myocardial infarction
Cardiac tamponade
Pericarditis
Pulmonary
Pleural effusion
Hemothorax
Hemoptysis (aortotracheal or bronchial fistula)
Renal
Acute renal failure
Renovascular hypertension
Renal ischemia or infarction
Neurologic
Stroke
Transient ischemic attack
Paraparesis or paraplegia
Encephalopathy
Coma
Spinal cord syndrome
Ischemic neuropathy
Gastrointestinal
Mesenteric ischemia or infarction
Pancreatitis
Hemorrhage (aortoenteric fistula)
Peripheral vascular
Upper or lower extremity ischemia
Systemic
Fever
Surgical Therapy
Acute type A dissection
Retrograde dissection into the ascending aorta
Endovascular and/or Surgical Therapy
Endovascular therapy in acute type A dissection for patients with prohibitive risk for surgical therapy
Acute type B dissection complicated by
Visceral ischemia
Limb ischemia
Rupture or impending rupture
Aneurysmal dilatation
Refractory pain
Medical Therapy
Uncomplicated type B aortic dissection
Uncomplicated isolated arch dissection
The goal of repair is to excise/obliterate the proximal entry tear, prevent pericardial rupture, prevent or treat coronary ostial dissection, correct aortic valve regurgitation, restore flow into the true lumen, correct malperfusion, and, if possible, obliterate the distal false channel.14
4. If the aortic valve is unable to be repaired, aortic valve replacement is often required. Therefore, the emergent treatment of type A dissection consists in the replacement of the ascending aorta, often together with replacement of the aortic valve and the dissected aortic arch.1 In patients in whom open repair is not feasible, endovascular techniques have been applied. These involve placement of an endograft in the ascending aorta and the aortic arch. However, such applications are investigational in nature and often carried out on a compassionate use basis.
C. Thoracic Aortic Aneurysm
1. Thoracic aortic aneurysms (TAAs) are defined as enlargements of the aorta greater than 1.5 times its normal size.1 We often use a diameter greater than 4 cm as the definition for TAA. True aneurysms involve the three layers of the aortic wall without losing continuity; however, inherent weakness of the aortic wall predisposes to diameter expansion and rupture.13,14,18 On the other hand, false aneurysms, or pseudoaneurysms, occur when there is a loss of continuity in the aortic wall itself, with bleeding that is contained by the adventitia or the surrounding perivascular tissues. Pseudoaneurysms generally pose an increased risk of rupture compared with true aneurysms.14
2. The pathophysiology of aortic dilatation is generally attributed to cystic medial degeneration and inflammatory changes within the aortic wall. In cystic medial degeneration, there is a disruption and loss of elastic fibers with increased deposition of proteoglycans in the medial layers. During inflammatory changes, there is a shift toward excessive degradation of the extracellular matrix, overriding its synthesis, thus adversely affecting the delicate homeostasis that normally exists between the vascular smooth muscle cells and the extracellular proteins in the medial layer of the aorta.1,19,20 The activity of the proteolytic enzymes such as matrix metalloproteinases (MMPs) plays a major pathophysiologic role in aortic aneurysm formation. MMPs, especially the MMP-2 and MMP-9 subtypes, degrade the elastin, fibrillin, and collagen in the medial layer of the aortic wall. Normally, MMPs are regulated by the presence of tissue inhibitors of metalloproteinases (TIMPs), but in aneurysmal patients, the balance between MMPs and TIMPs is shifted toward an increase in proteolysis, correlating with the observed degradation and thinning seen in the aortic wall.1,21 Additionally, inflammatory conditions such as Takayasu arteritis, rheumatoid arthritis, and giant cell arteritis, among others, can lead to the development of TAAs, further exemplifying the inflammatory role in aneurysm formation.1
3. Anatomical Categorization of Ascending Thoracic Aortic Aneurysms: TAAs can be categorized in three general classes according to the pattern of aortic root involvement (see Fig. 5B.1).1
FIGURE 5B.1: Three common patterns of ascending aortic aneurysm disease: supracoronary, annulo-aortic ectasia, and tubular (see text for discussion). Reproduced with permission from Elefteriades JA. Thoracic aortic aneurysm: reading the enemy’s playbook. Curr Probl Cardiol. 2008;33(5):203-277.
Supracoronary aneurysm: The aortic annulus and the short segment of aorta between the annulus and the coronary orifices are of normal size, with supracoronary dilatation of the ascending aorta.
Marfanoid aneurysm: Also termed annuloaortic ectasia, this type of aneurysm involves a dilatation of the aortic annulus and the proximal portion of the aorta.
Tubular aneurysm: In this category, the aortic annulus and the proximal aorta are somewhat but not markedly dilated, with a uniform caliber throughout the ascending aorta conferring a “tubular” appearance.
On rare occasions, one may also see a saccular aneurysm, which protrudes like a sack from the aortic lumen, involving only a small portion of the aortic wall length and circumference.
These patterns of anatomic enlargement are important because surgical therapy is predicated on the precise pattern of enlargement.
4. Long-term Complications of Thoracic Aortic Aneurysms
Growth of TAAs predisposes the patient in the long term to suffer aortic dissection or rupture.
Work done to unveil the natural history of ascending aortic aneurysms has revealed diameter “hinge points” at which risk of rupture and dissection increases dramatically.1
FIGURE 5B.2: Note the “hinge point” at 6 cm diameter, at which the natural risk of an ascending aneurysm increases dramatically. Reproduced with permission from Elefteriades JA. Natural history of thoracic aortic aneurysms: indications for surgery, and surgical versus nonsurgical risks. Ann Thorac Surg. 2002;74(5):S1877-S1880; discussion S1892-S1898.
Traditionally, in the case of ascending aortic aneurysms, the hinge point has been 6 cm, where 31% of the patients will have suffered a dissection or rupture by the time the aneurysm reaches this point1,22,23,24 (see Fig. 5B.2).
Current data, more granular as the number of studied patients has grown, have shown hinge points at 5.75 cm and again at 5.25 cm suggesting that criteria for intervention should be moved leftward to smaller sizes.25
Clinical features of an acute aortic event (rupture or dissection) depend on the location of the pathology. Generally, ascending aortic dissections produce tearing, severe, substernal pain. Generally, descending aortic aneurysms produce severe interscapular pain, which often radiates and progresses caudally down the body.
5. Criteria for Surgical Intervention
The generally accepted criterion for intervention in patients with chronic ascending thoracic aneurysms is a diameter of the ascending aorta greater than 5.5 cm. For institutions with large experience, which can deliver operation at low risk, 5.0 cm is an accepted criterion. However, a critical point for emphasis is that dimensional criteria apply for asymptomatic aneurysms only.
Symptomatic aneurysms require operation regardless of size, as pain in an aneurysm portends rupture. It is said that rapid growth of the thoracic aorta, at or above 0.5 cm/y, requires operation. In matter of fact, such rapid growth is extremely rare in the thoracic aorta.
Putative growth at this rate is usually due to measurement error (oblique measurements or comparison on noncorresponding aortic segments). Furthermore, connective tissue diseases and familial TAAs may require a more aggressive surgical approach, because dissections can occur at quite small sizes.
We often operate even before 5 cm for patients with Marfan syndrome, Loeys-Dietz, Ehlers-Danlos, and other inherited aortopathies (see Fig. 5B.3).26 In Turner syndrome, where dissection can occur suddenly at small sizes, surgery can be considered when the ascending aorta reaches 3.5 cm or greater1,13 (Table 5B.4).
6. Surgical Procedures
Surgical treatment for ascending aortic aneurysms usually involves resection and grafting +/− aortic valve replacement. Generally, surgery of the ascending aorta requires arresting of the heart during the aortic reconstruction and institution of artificial blood circulation via the use of cardiopulmonary bypass. One of the biggest challenges in the surgical approach to ascending aortic aneurysms is intervention on the aortic arch. When the aortic arch is intervened upon, blood flow to the head vessels generally must be interrupted (requiring methods for cerebral protection, such as deep hypothermic circulatory arrest [DHCA]) or substituted artificially. Currently, three methods for cerebral protection are used independently or concurrently: DHCA, antegrade cerebral perfusion (ACP),
and retrograde cerebral perfusion (RCP). Furthermore, three approaches for the aortic arch replacement are generally applied according to anatomic indications.14
FIGURE 5B.3: Simplified schematic illustration of ascending aorta dimensions for prophylactic surgical intervention divided by gene category: ECM genes, SMC contractile unit and metabolism genes, and TGF-β signaling pathway genes. ECM, extracellular matrix; LDS, Loeys-Dietz syndrome; MFS, Marfan syndrome; SMC, smooth muscle cell; EDS, Ehlers-Danlos syndrome. Reproduced with permission from Brownstein AJ, Ziganshin BA, Kuivaniemi H, Body SC, Bale AE, Elefteriades JA. Genes associated with thoracic aortic aneurysm and dissection: an update and clinical implications. Aorta (Stamford). 2017;5(1):11-20.
TABLE 5B.4. Indications for Surgery According to Ascending Aortic Diameter
Ascending aortic diameter at which surgery is recommended
TAA (no other coexisting conditions)
5.5 cm
BAV, Marfan, familial TAA
5 cm
Loeys-Dietz
4.4-4.6 cm by CT or MRI; 4.2 cm by TEE
Turner syndrome
>3.5 cm
Proximal hemiarch resection: In this procedure, the arch vessels are left intact while just the undersurface of the aortic arch is replaced. This suffices for many ascending aneurysms that taper gradually as they reach the arch zone.
Complete arch resection: In these procedures, the entire aortic arch is replaced. Cerebral blood flow is reconstituted either by reattaching an “island” of aortic wall carrying the great vessels (Carrel patch) or by grafts to the head vessels themselves.
Elephant trunk procedure: This procedure is used if the aneurysm extends into the descending aorta, requiring a two-stage approach. During the first stage one accomplishes placement of an “elephant trunk” sewn to the end of the aortic arch with the distal end of the graft hanging freely in the descending aorta. During the second stage, about 4 weeks later, the descending aneurysm is resected and the distal end of the elephant trunk is attached to the normal aorta below.
Currently, open surgery of the ascending aorta and aortic arch has proven to be exceptionally safe, with a mortality of 2.1% at 30 days; including a 1.5% mortality for elective cases and a 6.3% mortality for emergent cases.12 Therefore, open surgical repair is the current standard of treatment for patients with ascending aortic pathology. Furthermore, several other pathologies such as aortic pseudoaneurysm, PAU, IMH, and a rupture of the ascending aorta can be effectively approached with an open surgical repair, thus eliminating their inherent risk of catastrophic events. Endovascular repair is reported in the literature less frequently for these pathologies than for aortic dissection; however, the focal localization of these lesions in the aorta makes them amenable to the placement of an endograft.8,10
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