Aortic Dissection

Summary

Aortic dissection (see the image below) is defined as separation of the layers within the aortic wall. Tears in the intimal layer result in the propagation of dissection (proximally or distally) secondary to blood entering the intima-media space. Mortality is still high despite advances in diagnostic and therapeutic modalities.

Aortic dissection

Signs and symptoms Aortic dissection can be rapidly fatal, with many patients dying before presentation to the emergency department (ED) or before diagnosis is made in the ED. No one sign or symptom can positively identify acute aortic dissection. Clinical manifestations include the following:

• Sudden onset of severe chest pain that often has a tearing or ripping quality (classic symptom)

• Chest pain may be mild

• Anterior chest pain: Usually associated with anterior arch or aortic root dissection

• Neck or jaw pain: With aortic arch involvement and extension into the great vessels

• Tearing or ripping intrascapular pain: May indicate dissection involving the descending aorta

• No pain in about 10% of patients

• Syncope

• Cerebrovascular accident (CVA) symptoms (eg, hemianesthesia, and hemiparesis, hemiplegia) [1]

• Altered mental status

• Numbness and tingling, pain, or weakness in the extremities

• Horner syndrome (ie, ptosis, miosis, anhidrosis)

• Dyspnea

• Hemoptysis

• Dysphagia

• Flank pain (with renal artery involvement

• Abdominal pain (with abdominal aorta involvement)

• Fever

• Anxiety and premonitions of death

Diagnosis The diagnosis of acute aortic dissection requires a high index of suspicion and involves the following:

• History and physical examination

• Imaging studies

• Electrocardiography

• Complete blood count, serum chemistry studies, cardiac marker assays

Possible physical examination findings include the following:

• Hypertension

• Hypotension

• Interarm blood pressure differential greater than 20 mm Hg

• Signs of aortic regurgitation (eg, bounding pulses, wide pulse pressure, diastolic murmurs)

• Findings suggestive of cardiac tamponade (eg, muffled heart sounds, hypotension, pulsus paradoxus, jugular venous distention, Kussmaul sign)

• Neurologic deficits (eg, syncope, altered mental status)

• Peripheral paresthesias

• Horner syndrome

• New diastolic murmur

• Asymmetrical pulses (eg, carotid, brachial, femoral)

• Progression or development of bruits

Possible laboratory study findings include the following:

• Leukocytosis: Stress state

• Decreases in hemoglobin and hematocrit values: Leaking or rupture of the dissection

• Elevation of the blood urea nitrogen and creatinine levels: Renal artery involvement or prerenal azotemia

• Elevation of the myocardial muscle creatine kinase isoenzyme, myoglobin, and troponin I and T levels: Myocardial ischemia from coronary artery involvement

• Lactate dehydrogenase elevation: Hemolysis in the false lumen

• Smooth muscle myosin heavy-chain assay: Increased levels in the first 24 hours are 90% sensitive and 97% specific for aortic dissection

• Fibrin degradation product (FDP) elevation: In symptomatic patients, a plasma FDP of 12.6 μg/mL or higher suggests possible aortic dissection with a patent false lumen; an FDP level of 5.6 μg/mL or higher suggests the possibility of dissection with complete thrombosis of the false lumen [2]

Imaging studies Chest radiography:

• Initial imaging technique if it is readily available at the bedside

• Widening of the mediastinum is the classic finding

• Hemothorax may be evident if the dissection has ruptured

Computed tomography (CT) with contrast:

• The definitive test in most patients with suspicion of aortic dissection [3]

• Useful only in hemodynamically stable patients

• Findings help determine whether hypothermic circulatory arrest is necessary for surgery

Echocardiography:

• Transesophageal echocardiography (TEE) is more accurate than transthoracic echocardiography (TTE) [4]

• TTE is most useful in ascending aortic dissections

• TEE is as sensitive and specific as CT and magnetic resonance imaging (MRI)

• TEE is strongly dependent on operator experience

MRI:

• The most sensitive method for diagnosing aortic dissection

• Specificity is similar to that of CT

Aortography:

• Has been the diagnostic criterion standard study for aortic dissection

• Is being replaced by newer, safer imaging modalities

Management Acute aortic dissection can be treated surgically or medically. In surgical treatment, the area of the aorta with the intimal tear is usually resected and replaced with a Dacron graft. Endovascular repair is emerging as the preferred treatment for descending aortic dissection. Medical management includes the following:

• Decreasing the blood pressure and the shearing forces of myocardial contractility

• Antihypertensive therapy, including beta blockers, is the treatment of choice for all stable chronic aortic dissections

• Pain management: Narcotics and opiates are the preferred agents

Emergency surgical correction is the preferred treatment for the following:

• Stanford type A (DeBakey type I and II) ascending aortic dissection

• Complicated Stanford type B (DeBakey type III) aortic dissections with specific clinical or radiologic evidence

Background

Aortic dissection is defined as separation of the layers within the aortic wall. Tears in the intimal layer result in the propagation of dissection (proximally or distally) secondary to blood entering the intima-media space. An acute aortic dissection (< 2 weeks) is associated with high morbidity and mortality rates. Mortality is highest in the first 7 days; indeed, many patients die before presentation to the emergency department (ED) or before diagnosis is made in the ED. Patients with chronic aortic dissection (>2 weeks) have a better prognosis. The mortality associated with aortic dissection is still high despite advancements in diagnostic and therapeutic modalities. [5, 6] Although acute aortic dissection classically produces sudden onset of severe chest pain that often has a tearing or ripping quality, no one sign or symptom can positively identify acute aortic dissection. The clinical manifestations are diverse, making the diagnosis difficult and necessitating a high index of suspicion. [5, 7, 6] (See Presentation.) An estimated 38% of acute aortic dissections are missed on initial evaluation. [8, 1, 9] There are no validated clinical decision rules to help identify acute aortic dissection. The diagnosis is best made when there is high clinical suspicion. A good patient history and physical examination are essential, along with imaging studies, electrocardiography, and laboratory studies (see Workup). Acute aortic dissection can be treated surgically or medically. In surgical treatment, the area of the aorta with the intimal tear is usually resected and replaced with a Dacron graft. (See Treatment and Medication.) For patient education information, see the Heart and Blood Vessels Center, the Circulatory Problems Center, and the Heart Center, as well as Chest Pain. History of aortic dissection and its repair The first well-documented case of aortic dissection occurred in 1760, when King George II of England died while straining on the commode. In 1761, the celebrated Italian anatomist Giovanni Battista Morgagni provided the first detailed pathologic description of aortic dissection. Aortic dissection was associated with a high mortality rate before the introduction of the cardiopulmonary bypass in the 1950s, which led to aortic arch repair and construction. DeBakey performed the first successful operative repair in 1955. Modern techniques of diagnosing and repairing thoracic aortic dissections transformed the condition from a death sentence to a treatable disorder—as shown by the experience of Dr DeBakey himself, who developed aortic dissection at age 97, and at age 98 became the oldest patient to survive the surgical procedure he pioneered. [10] Later advances in the field of stent placement and percutaneous aortic fenestrations have further lowered mortality. However, despite these advances, the mortality associated with aortic dissection remains high, as illustrated by the deaths of Princess Diana, actor John Ritter, and diplomat Richard Holbrooke. [5, 6]

Anatomy The aorta is composed of the intima, media, and adventitia. The intima, the innermost layer, is thin, delicate, lined by endothelium, and easily traumatized. The media is responsible for imparting strength to the aorta and consists of laminated but intertwining sheets of elastic tissue. The arrangement of these sheets in a spiral provides the aorta with its maximum allowable tensile strength. The aortic media contains very little smooth muscle and collagen between the elastic layers and thus has increased distensibility, elasticity, and tensile strength. This contrasts with peripheral arteries, which, in comparison, have more smooth muscle and collagen between the elastic layers. The outermost layer of the aorta is adventitia. This largely consists of collagen. The vasa vasorum, which supplies blood to the outer half of the aortic wall, lies within the adventitia. The nervi vascularis, bundles of nerve fibers found in the aortic adventitia, are involved in the production of pain, which occurs with acute stretching of the aortic wall from a dissection. [11] The aorta does not have a serosal layer. The aorta plays an integral role in the forward circulation of the blood in diastole. During left ventricular contraction, the aorta is distended by blood flowing from the left ventricle, and kinetic energy from the ventricle is transformed into potential energy stored in the aortic wall. During recoil of the aortic wall, this potential energy is converted to kinetic energy, propelling the blood within the aorta to the peripheral vasculature. The volume of blood ejected into the aorta, the compliance of the aorta, and resistance to blood flow are responsible for the systolic pressures within the aorta. Resistance is mainly due to the tone of the peripheral vessels, although the inertia exerted by the column of blood during ventricular systole also plays a small part. The aorta has thoracic and abdominal regions. The thoracic aorta is divided into the ascending, arch, and descending segments; the abdominal aorta is divided into suprarenal and infrarenal segments. The ascending aorta is the anterior tubular portion of the thoracic aorta from the aortic root proximally to the innominate artery distally. The ascending aorta is 5 cm long and is made up of the aortic root and an upper tubular segment. The aortic root consists of the aortic valve, sinuses of Valsalva, and left and right coronary arteries. It extends from the aortic valve to the sinotubular junction and supports the base of the aortic leaflets. The aortic root allows the three sinuses of Valsalva to bulge outward, facilitating the full excursion of the leaflets in systole. The left and right coronary arteries arise from these sinuses. The upper tubular segment of the ascending aorta starts at the sinotubular junction and ends at the beginning of the aortic arch. The ascending aorta lies slightly to the right of the midline, with its proximal portion in the pericardial cavity. Structures around the aorta include the pulmonary artery anteriorly; the left atrium, right pulmonary artery, and right mainstem bronchus posteriorly; and the right atrium and superior vena cava to the right. The arch of the aorta curves upward between the ascending aorta and descending aorta. The brachiocephalic arteries originate from the aortic arch. Arteries that arise from the aortic arch carry blood to the brain via the left common carotid, innominate, and left subclavian arteries. The initial part of the aortic arch lies slightly left and in front of the trachea; the arch ends posteriorly to the left of the trachea and esophagus. Inferior to the arch is the pulmonary artery bifurcation, the right pulmonary artery, and the left lung. The recurrent laryngeal nerve passes beneath the distal arch, and the phrenic and vagus nerves lie to the left. The junction between the aortic arch and the descending aorta is called the aortic isthmus. The isthmus is a common site for coarctations and trauma. The descending aorta extends from the area distal to the left subclavian artery to the 12th intercostal space. Initially, the descending aorta lies in the posterior mediastinum to the left of the course of the vertebral column. It passes in front of the vertebral column in its descent and ends behind the esophagus before passing through the diaphragm at the level of the 12th thoracic vertebra. The abdominal aorta extends from the descending aorta at the level of the 12th thoracic vertebra to the level of bifurcation at the fourth lumbar vertebra. The splanchnic arteries branch from the abdominal aorta. The thoracoabdominal aorta is the combination of the descending thoracic and abdominal aorta. With increasing age, the elasticity and distensibility of the aorta decline, thus inducing the increase in pulse pressure observed in elderly individuals. The progression of this process is exacerbated by hypertension, coronary artery disease, or hypercholesterolemia. Histologically, the loss of distensibility is marked by fragmentation of elastin and the resultant increase in collagen and, thus, a higher collagen-to-elastin ratio. This, along with impairment in flow in the vasa vasorum, may be responsible for the age-related changes. These factors cumulatively lead to increased left ventricular systolic pressure and wall tension with associated increases in end-diastolic pressure and volume.

Pathophysiology

The aortic wall is exposed to high pulsatile pressure and shear stress (the steep slope of the pressure curve; ie, the water hammer effect), making the aorta particularly prone to injury and disease from mechanical trauma. The aorta is more prone to rupture than any other vessel, especially with the development of aneurysmal dilatation, because its wall tension, as governed by the Laplace law (proportional to the product of pressure and radius), is intrinsically high. An aortic dissection is a split or partition in the media of the aorta; this split is frequently horizontal or diagonal. An intimal tear connects the media with the aortic lumen, and an exit tear creates a true lumen and a false lumen, resulting in a double-barreled aorta (see the image below).

Aortic dissection. True lumen and false lumen separated by an intimal flap. The true lumen is lined by intima, and the false lumen is within the media. Although the false lumen is within the media, suggesting that it is "lined" with media is misleading; if the aortic dissection becomes chronic, the lining becomes a serosal pseudointima. The true lumen is frequently smaller than the false lumen, but not invariably. Typically, flow in the false lumen is slower than in the true lumen, and the false lumen often becomes aneurysmal when subjected to systemic pressure. The dissection usually stops at an aortic branch vessel or at the level of an atherosclerotic plaque. Most classic aortic dissections begin at one of the following three distinct anatomic locations:

• Approximately 2.2 cm above the aortic root

• Distal to the left subclavian artery

• The aortic arch

The most common site of dissection is the first few centimeters of the ascending aorta, with 90% occurring within 10 cm of the aortic valve. The second most common site is just distal to the left subclavian artery. Between 5% and 10% of dissections do not have an obvious intimal tear. These often are attributed to rupture of the aortic vasa vasorum as first described by Krukenberg in 1920. Keeping the descending aorta in mind is important. The descending aorta is the location of most late clinical events after any dissection of the aorta. [12] Ascending aortic involvement may result in death from wall rupture, hemopericardium and tamponade, occlusion of the coronary ostia with myocardial infarction, or severe aortic insufficiency. The nervi vascularis (ie, bundles of nerve fibers found in the aortic adventitia) are involved in the production of pain. Classification

Two major anatomic classification schemes for aortic dissection are the DeBakey and the Stanford systems (see the image below).

Image A represents a Stanford A or a DeBakey type 1 dissection. Image B represents a Stanford A or DeBakey type II dissection. Image C represents a Stanford type B or a DeBakey type III dissection. Image D is classified in a manner similar to A but contains an additional entry tear in the descending thoracic aorta. Note that a primary arch dissection does not fit neatly into either classification. DeBakey et al classified aortic dissection into three types, as follows:

• Type I - The intimal tear occurs in the ascending aorta, but the descending aorta is also involved

• Type II - Only the ascending aorta is involved

• Type III - Only the descending aorta is involved; type IIIA originates distal to the left subclavian artery and extends as far as the diaphragm, whereas type IIIB involves the descending aorta below the diaphragm

The Stanford classification specified two types, as follows:

• Type A - The ascending aorta is involved (DeBakey types I and II)

• Type B - The descending aorta is involved (DeBakey type III)

This system also helps delineate treatment. Type A dissections usually must be treated surgically, whereas type B dissections are managed medically under most conditions. [13]

Etiology

Congenital and acquired factors, alone or in combination, can lead to aortic dissection. Aortic dissection is more common in patients with hypertension, connective tissue disorders, congenital aortic stenosis, or a bicuspid aortic valve, [14] as well as in those with first-degree relatives with a history of thoracic dissection. These diseases affect the media of the aorta and predispose it to dissection. Congenital causes Aortopathy may be due to the following heritable diseases:

• Marfan syndrome

• Ehlers-Danlos syndrome

• Annuloaortic ectasia

• Familial aortic dissections

• Adult polycystic kidney disease

• Turner syndrome

• Noonan syndrome

• Osteogenesis imperfecta

• Bicuspid aortic valve

• Coarctation of the aorta

• Connective tissue disorders

• Metabolic disorders (eg, homocystinuria, familial hypercholesterolemia)

Acquired conditions Arterial hypertension is an important predisposing factor for aortic dissection. [6] Of patients with aortic dissection, 70% have elevated blood pressure. Hypertension or pulsatile blood flow can propagate the dissection. Pregnancy can be a risk factor for aortic dissection, particularly in patients with an underlying anomaly such as Marfan syndrome. An estimated 50% of all cases of aortic dissection that occur in women younger than 40 years are associated with pregnancy. Most cases occur in the third trimester or early postpartum period. Other acquired causes of aortic dissection include the following:

• Syphilitic aortitis

• Deceleration injury possibly with related chest trauma

• Cocaine use

Cystic medial necrosis The normal aorta contains collagen, elastin, and smooth muscle cells that contribute the intima, media, and adventitia, which are the layers of the aorta. With aging, degenerative changes lead to breakdown of the collagen, elastin, and smooth muscle and an increase in basophilic ground substance. This condition is termed cystic medial necrosis. Atherosclerosis that causes occlusion of the vasa vasorum also produces this disorder. Cystic medial necrosis is the hallmark histologic change associated with dissection in those with Marfan syndrome. Cystic medial necrosis was first described by Erdheim in 1929. Sources disagree over the accuracy of this term in elderly patients because the true histopathologic changes are neither cystic nor necrotic. Researchers have used the term cystic medial degeneration. Early on, cystic medial necrosis described an accumulation of basophilic ground substance in the media with the formation of cystlike pools. The media in these focal areas may show loss of cells (ie, necrosis). This term still is used commonly to describe the histopathologic changes that occur. Iatrogenic causes Iatrogenic aortic dissection can result from cardiologic procedures such as the following:

• Aortic and mitral valve replacements

• Coronary artery bypass graft surgery

• Percutaneous catheter placement (eg, cardiac catheterization, percutaneous transluminal coronary angioplasty)

Aortic dissection occurs when the layers are split in the process of cannulation or aortotomy. In late 2018, the US Food and Drug Administration (FDA) issued a warning that fluoroquinolone antibiotics can increase the occurrence of aortic dissections and suggested that unless other treatment options are unavailable, these agents should not be used in patients at increased risk, including those with a history of blockages or aneurysms of the aorta or other blood vessels, those with high blood pressure, those with certain genetic disorders that involve blood vessel changes, and the elderly. [15]

Prognosis

Hospital-based mortality for aortic dissection is approximately 30%. Patients with type A aortic dissection who undergo surgical treatment have a 30% mortality; patients who receive medical treatment have a 60% mortality. Comorbidities and advanced age can pose a contraindication to surgery in selected patients. Medically treated patients with type B dissection have a 10% mortality; surgically treated patients with type B dissection have a 30% mortality. An acute aortic dissection (< 2 weeks) is associated with high morbidity and mortality (highest mortality in the first 7 days). From 1% to 2% of patients with aortic dissection die per hour for the first 24-48 hours. Patients with chronic aortic dissection (>2 weeks) have a better prognosis.

Clinical Presentation

History Patients with acute aortic dissection typically present with the sudden onset of severe chest pain, although this description is not universal. Some patients present with only mild pain, often mistaken for a symptom of musculoskeletal conditions in the thorax, groin, or back. Consider thoracic aortic dissection in the differential diagnosis of all patients presenting with chest pain. The location of the pain may indicate where the dissection arises. Anterior chest pain and chest pain that mimics acute myocardial infarction usually are associated with anterior arch or aortic root dissection. This is caused by the dissection interrupting flow to the coronary arteries, resulting in myocardial ischemia. Pain in the neck or jaw indicates that the dissection involves the aortic arch and extends into the great vessels. Tearing or ripping pain in the intrascapular area may indicate that the dissection involves the descending aorta. The pain typically changes as the dissection evolves. The pain of aortic dissection is typically distinguished from the pain of acute myocardial infarction by its abrupt onset and maximal severity at onset, though the presentations of the two conditions overlap to some degree and are easily confused. Aortic dissection can be presumed in patients with symptoms and signs suggestive of myocardial infarction but without classic electrocardiographic (ECG) findings. Aortic dissection is painless in about 10% of patients. [1] Painless dissection is more common in those with neurologic complications from the dissection and those with Marfan syndrome. Neurologic deficits are a presenting sign in as many as 20% of cases. Syncope is part of the early course of aortic dissection in approximately 5% of patients and may be the result of increased vagal tone, hypovolemia, or dysrhythmia. [1] Cerebrovascular accident (CVA) symptoms include hemianesthesia and hemiparesis or hemiplegia. [1] Altered mental status is also reported. Patients with peripheral nerve ischemia can present with numbness and tingling, pain, or weakness in the extremities. Horner syndrome is caused by interruption in the cervical sympathetic ganglia and manifests as ptosis, miosis, and anhidrosis. Hoarseness from recurrent laryngeal nerve compression has also been described. Cardiovascular manifestations involve symptoms suggestive of congestive heart failure [1] secondary to acute severe aortic regurgitation. These include dyspnea and orthopnea. Respiratory symptoms can include dyspnea and hemoptysis if dissection ruptures into the pleura or if tracheal or bronchial obstruction has occurred. Physical findings of a hemothorax may be found if the dissection ruptures into the pleura. Other manifestations include the following [17] :

• Dysphagia from compression of the esophagus

• Flank pain if the renal artery is involved

• Abdominal pain if the dissection involves the abdominal aorta

• Fever

• Anxiety and premonitions of death

A retrospective chart review of 83 patients with a thoracic aortic dissection revealed that only 40% of alert patients were asked the basic questions about their pain. Remember to cover the P, Q, R, S, and T (position, quality, radiation, severity, and timing) of pain in all able patients. Timing includes the rate of onset, duration, and frequency of episodes. Also ask about migration of pain, aggravating or alleviating factors, and associated symptoms.

Physical Examination Hypertension may result from a catecholamine surge or underlying essential hypertension. [1, 18] Hypotension is an ominous finding and may be the result of excessive vagal tone, cardiac tamponade, or hypovolemia from rupture of the dissection. An interarm blood pressure differential greater than 20 mm Hg should increase the suspicion of aortic dissection, but it does not rule it in. Significant interarm blood pressure differentials may be found in 20% of people without aortic dissection. Signs of aortic regurgitation include bounding pulses, wide pulse pressure, and diastolic murmurs. Acute, severe aortic regurgitation may result in signs suggestive of congestive heart failure [1] : dyspnea, orthopnea, bibasilar crackles, or elevated jugular venous pressure. Other cardiovascular manifestations include findings suggestive of cardiac tamponade (eg, muffled heart sounds, hypotension, pulsus paradoxus, jugular venous distention, Kussmaul sign). Tamponade must be recognized promptly. Superior vena cava syndrome can result from compression of the superior vena cava from a large, distorted aorta. Wide pulse pressure and pulse deficit or asymmetry of peripheral pulses are reported. Patients with right coronary artery ostial dissection may present with acute myocardial infarction, commonly inferior myocardial infarction. Pericardial friction rub may occur secondary to pericarditis. Neurologic deficits are a presenting sign in up to 20% of cases. The most common neurologic findings are syncope and altered mental status. Syncope is part of the early course of aortic dissection in about 5% of patients and may be the result of increased vagal tone, hypovolemia, or dysrhythmia. Other causes of syncope or altered mental status include strokes from compromised blood flow to the brain or spinal cord and ischemia from interruption of blood flow to the spinal arteries. Peripheral nerve ischemia can manifest as numbness and tingling in the extremities. Hoarseness from recurrent laryngeal nerve compression also has been described. Horner syndrome is caused by interruption in the cervical sympathetic ganglia and presents with ptosis, miosis, and anhidrosis. Other diagnostic clues include a new diastolic murmur or asymmetrical pulses. Pay careful attention to carotid, brachial, and femoral pulses on initial examination and look for progression of bruits or development of bruits on reexamination. Physical findings of a hemothorax may be found if the dissection ruptures into the pleura.

Complications

Complications are diverse and numerous; anatomic-related complications are deducible and include the following:

• Hypotension and shock as a result of aortic rupture, with eventual death from exsanguination

• Pericardial tamponade secondary to hemopericardium; this complicates type A aortic dissection

• Acute aortic regurgitation as a complication of proximal aortic dissection propagating into a sinus of Valsalva with resultant aortic valve insufficiency

• Pulmonary edema secondary to acute aortic valve regurgitation

• Rare occurrence of right or left coronary ostium involvement leading to myocardial ischemia

• Neurologic findings due to carotid artery obstruction - Ischemic CVA, hemiplegia, hemianesthesia (aortic branch involvement can lead to spinal cord ischemia, ischemic paraparesis, and paraplegia)

• Mesenteric and renal ischemia - Can lead to bowel or visceral ischemia, renal infarction, hematuria, or acute renal failure (ARF)

• Compressive symptoms, such as superior vena cava syndrome, Horner syndrome (when it affects the superior cervical ganglia), dysphagia (when it involves the esophagus), airway compromise, and hemoptysis (when it compresses the bronchus)

• Other compressive symptoms - Can be associated with vocal cord paralysis and hoarseness

• Claudication - Can develop from extension of the dissection into the iliac arteries

• Redissection and progressive aortic diameter enlargement

• Aneurysmal dilatation and saccular aneurysm

Diagnostic Considerations

Consider thoracic aortic dissection in the differential diagnosis of all patients presenting with chest pain. The pain is usually localized to the front or back of the chest, often the interscapular region, and typically migrates with propagation of the dissection.

The pain of aortic dissection is typically distinguished from the pain of acute myocardial infarction by its abrupt onset, though the presentations of the two conditions overlap to some degree and are easily confused. Aortic dissection can be presumed in patients with symptoms and signs suggestive of myocardial infarction but without classic electrocardiographic findings.

Differential Diagnoses

• Aortic Regurgitation Imaging

• Aortic Stenosis Imaging

• Cardiogenic Shock

• Emergent Management of Pleural Effusion

• Mechanical Back Pain

• Myocardial Infarction

• Myocarditis

• Pleural Effusion

• Pulmonary Embolism (PE)

• Thoracic Outlet Syndrome Imaging

Workup

Approach Considerations Aortic dissection is usually diagnosed by using imaging techniques before the result of blood work is interpreted. The choice of imaging techniques depends in part on whether or not the patient is hemodynamically stable. Chest radiography is the initial imaging technique and may or may not reveal any abnormality. Computed tomography (CT) is useful in hemodynamically stable patients; emergency CT angiography (CTA) with three-dimensional (3D) reconstruction is rapidly becoming the diagnostic test of choice. Magnetic resonance imaging (MRI) is as accurate as CT and may benefit patients who have adverse reactions to the use of intravenous (IV) contrast agents. For hemodynamically unstable patients, echocardiography is ideal. Aortography is still considered by some as the diagnostic criterion standard test for aortic dissection. However, it is being replaced by newer imaging modalities. For more information on imaging in this disorder, see Aortic Dissection Imaging. All patients with suspected thoracic aortic dissection should undergo 12-lead electrocardiography (ECG). However, ECG often demonstrates a nonspecific abnormality or normal results.

Blood Studies A complete blood count (CBC), serum chemistry studies, and cardiac marker assays should be performed. On the CBC, leukocytosis may be present, which usually represents a stress state. Decreases in hemoglobin and hematocrit values are ominous findings suggesting that the dissection is leaking or has ruptured. Elevation of the blood urea nitrogen (BUN) and creatinine levels may indicate involvement of the renal arteries or prerenal azotemia resulting from blood loss or associated dehydration (mainly when the BUN-to-creatinine ratio exceeds 20). Patients with dissection involving the renal arteries may also exhibit hematuria, oliguria, or even anuria (< 50 mL/day). Myocardial muscle creatine kinase isoenzyme, myoglobin, and troponin I and T levels are elevated if the dissection has involved the coronary arteries and caused myocardial ischemia. The lactate dehydrogenase level may be elevated because of hemolysis in the false lumen. Measurement of the degradation products of plasma fibrin and fibrinogen can facilitate the diagnosis of acute aortic dissection. In symptomatic patients, aortic dissection with a patent false lumen should be considered if the plasma fibrin degradation product (FDP) level is 12.6 μg/mL or higher; the possibility of dissection with complete thrombosis of the false lumen should be considered if the FDP level is 5.6 μg/mL or higher. [2] Some authors suggest that a D-dimer assay should be a part of the initial workup if aortic dissection is suspected. [19] A negative result makes the presence of the disease less likely.

Smooth-Muscle Myosin Heavy-Chain Assay A smooth-muscle myosin heavy-chain assay is performed in the first 24 hours. Increased levels in the first 24 hours are 90% sensitive and 97% specific for aortic dissection. levels are highest in the first 3 hours. A cutoff of 2.5 has a sensitivity of 91%, a specificity of 98%, and an accuracy rate of 96%, respectively. The smooth muscle myosin heavy-chain assay has greater sensitivity and specificity than transthoracic echocardiography (TTE), CT, and aortography, but it has less sensitivity and specificity than transesophageal echocardiography (TEE), MRI, and helical CT.

Chest Radiography Although chest radiography is not the definitive imaging study for aortic dissection, it should be performed as the initial imaging technique if it is readily available at the bedside and does not cause delay in obtaining CT or MRI. [3] Chest radiography (see the images below) may or may not reveal any abnormality. Widening of the mediastinum is the classic finding.

Chest radiograph demonstrating widened mediastinum in a patient with aortic dissection

Aortic dissection. Mediastinal widening.

Aortic dissection. Mediastinal widening. In 2000, the International Registry of Acute Aortic Dissection published data on 464 patients. Chest radiography showed a widened mediastinum in approximately 62% of patients. [5] If the patient is hemodynamically stable and cooperative, an anteroposterior (AP) radiograph can be obtained at bedside. A widened mediastinum is sometimes difficult to identify on a portable AP radiograph. Look for a mediastinal width greater than 8 cm on the AP view. A tortuous aorta, common in hypertensive patients, may be hard to distinguish from a widened mediastinum. If in doubt, a good posterior-anterior radiograph is recommended. The differential diagnosis of a widened mediastinum includes tumor, adenopathy, lymphoma, and enlarged thyroid. If an aortic dissection ruptures, blood can extravasate into the ipsilateral pleural space, causing a hemothorax (see the image below).

Chest radiograph of a patient with aortic dissection presenting with hemothorax. With type A dissection, an abnormal aortic contour is observed in a minority of patients. An abnormal (ie, blunted) aortic knob was observed in 66% of patients in one study. Ring sign (displacement of the aorta >5 mm past the calcified aortic intima) is considered a specific radiographic sign. Other radiologic abnormalities seen on chest radiography include the following:

• Pleural effusion

• Left apical cap

• Tracheal deviation to the right

• Depression of left mainstem bronchus

• Esophageal deviation

• Loss of the paratracheal stripe

The International Registry for Aortic Dissection revealed that more than 12% of the chest radiographs of patients with aortic dissection were read as normal. [5] Several studies concluded that the overall diagnosis of aortic dissection is not determined by any one sign; rather, a combination of all findings leads to suspicion of dissection.

Computed Tomography CT with contrast is used more frequently in emergency department (ED) settings. CT is useful only in hemodynamically stable patients, because of its lack of portability and its potential limitations in patients with contraindications to intravenous contrast agents. A 2014 guideline from the American College of Radiology recommended CTA as the definitive test in most patients with suspicion of aortic dissection. [3] CTA provides detailed anatomic definition of the dissection as well as information on plaque formation. Prospective studies have shown a sensitivity of 83-94% and a specificity of 87-100%. However, 3D reconstruction may not be available in smaller centers. [20] Spiral (helical) CT is associated with a higher rate of detection and better resolution than incremental CT scanning. Faster scanners have decreased the acquisition time to the range of a breath hold, resulting in less motion artifact from breathing. High-quality two-dimensional (2D) and 3D reconstructions are possible with spiral CT, greatly adding to the usefulness of this imaging modality. More important, imaging information, including the type of lesion, location of the pathologic lesion, extent of the disease, and evaluation of the true and false lumen can be assessed quickly and help the surgeon plan the operation. This information helps determine if hypothermic circulatory arrest is necessary for surgery; this procedure increases the complexity, length, morbidity, and mortality associated with surgery. One study reported that extended hypothermic circulatory arrest times, as a consequence of disease severity, contribute to a higher mortality rate, as do redo surgery and the overall extent of disease. Emergency surgery and extracardiac arteriopathy are associated with increased risk of neurological injury. Age, however, was not associated with increased risk for neurologic injury or mortality. [21] Drawbacks include the following:

• Transportation of a patient in potentially unstable condition from the ED, even for the relatively short time needed for this procedure, places the patient at risk

• CTA requires the injection of iodinated contrast, which may harm a patient who has impaired renal function or an allergy to contrast media

• CT provides no information on aortic regurgitation

See the images below for CT scans showing aortic dissection.

Aortic dissection. CT scan showing a flap (right side of image)

Aortic dissection. True lumen versus false lumen in an intimal flap.

Aortic dissection. Left subsegmental atelectasis and left pleural effusion. Flap at lower right of image

Aortic dissection. Significant left pleural effusion

Aortic dissection. CT scan showing a flap (center of image)

Aortic dissection. CT scan showing a flap (center of image)

Aortic dissection. CT scan showing a flap

Aortic dissection. CT scan showing a flap.

Aortic dissection. CT scan showing a flap.

Aortic dissection. CT scan showing a flap

Aortic dissection. CT scan showing a flap.

Aortic dissection. Thrombus and a patent lumen.

Aortic dissection. Thrombus.

Aortic dissection. True lumen and false lumen separated by an intimal flap.

Aortic dissection. CT scan showing a flap

Aortic dissection. Intimal flap and left pleural effusion.

Aortic dissection

Patient with an ascending type A aortic dissection showing the intimal flap. Image courtesy of Kaiser-Permanente

Patient with an ascending type A aortic dissection showing the intimal flap. Image courtesy of Kaiser-Permanente

Patient with an ascending type A aortic dissection showing the intimal flap. Image courtesy of Kaiser-Permanente

Patient with an ascending type A aortic dissection showing the intimal flap. Image courtesy of Kaiser-Permanente

Patient with a type A aortic dissection involving the ascending and descending aorta. Image courtesy of Kaiser-Permanente.

Patient with a type A aortic dissection involving the ascending and descending aorta. Image courtesy of Kaiser-Permanente.

Patient with a type A aortic dissection involving the ascending and descending aorta. Image courtesy of Kaiser-Permanente.

Patient with a type A aortic dissection involving the ascending and descending aorta. Image courtesy of Kaiser-Permanente.

Patient showing a type B aortic dissection with extravasation of blood into the pleural cavity. Image courtesy of Kaiser-Permanente.

Panitnen with aortic dissection with a colection of blood into the pleural cavity. Image courtesy of Kaiser-Permanente.

Patient showing a type B aortic dissection with extravasation of blood into the pleural cavity. Image courtesy of Kaiser-Permanente

Patient showing a type B aortic dissection with extravasation of blood into the pleural cavity. Image courtesy of Kaiser-Permanente

Echocardiography Echocardiography is an important imaging modality for detecting aortic dissection. [22, 4] It also is useful in diagnosing cardiac tamponade and aortic regurgitation. TEE has greater sensitivity (97-99% vs 80%) and specificity (97-100% vs 90%) than TTE. [4] TTE is most useful in ascending aortic dissections, especially those closest to the aortic root and within a few centimeters of the aortic valve. Sensitivity is highest in this location. TTE is much less accurate for arch and descending aortic dissections. TEE is as accurate as CT and MRI in terms of sensitivity and specificity, and it can be used at the bedside, which makes it ideal for hemodynamical

ly unstable patients. It is a relatively quick study to perform and relatively noninvasive. However, obesity, a narrow intercostal space, pulmonary emphysema, and mechanical ventilation decrease the accuracy of TEE. False-positive results with TEE are about 10%. [22, 4] In one study, color Doppler TEE using biplanar views detected intimal flaps in 18 of 18 patients with type A dissections and in 10 of 39 with type B dissections. [23] Intimal tears were detected in 15 (83%) patients with type A and in 35 (90%) patients with type B (both confirmed by surgery or angiography). Intimal entry was detected in 16 of 18 patients using biplanar views and in 34 of 39 patients using single planar views. Using longitudinal views, only two intimal entries were detected in 18 patients. Using biplanar views, the intimal entries in two patients with type B entries wer

e not visualized by TEE because the dissection was in the aortic arch and was obscured by the trachea and the left mainstem bronchus. The intimal entries in two patients with type B entries were in the abdominal aorta. [23] Color Doppler TEE using biplanar views has the advantages of additional acoustic windows, ease of spatial orientation, more accurate visualization of the entry, and ease of application. The main drawback of TEE is its strong dependence on operator experience. Other drawbacks are that false-positive results can occur from reverberations in the ascending aorta and that the upper ascending aorta and arch may not be visualized well, leading to false-negative results. TEE cannot be performed in patients with esophageal varicosities or stenosis. If the findings are negative and clinical suspicion remains high, a second diagnostic test is recommended.

Magnetic Resonance Imaging MRI has approximately 98% sensitivity and specificity for detecting thoracic aortic dissection. It is the most sensitive method for diagnosing aortic dissection and has similar specificity to CT. MRI shows the site of intimal tear, type and extent of dissection, and presence of aortic insufficiency, as well as the surrounding mediastinal structures. Other benefits are that MRI requires no contrast medium and no ionizing radiation. It is the preferred modality for patients with renal failure and those with an allergy to iodine, as well as for imaging chronic diss

ections and postsurgical follow-up. Its use in acute dissection is limited because it is not portable. [24] A study of 53 consecutive patients with clinically suspected aortic dissection found that for type A dissection, MRI was 100% sensitive and specific, while TEE was 100% sensitive and 78% specific. In patients with type B dissection, MRI was 100% sensitive and specific, whereas TEE was 90% sensitive and 97% specific. [25] With regard to epiphenomena, visualization of the site and spatial extent of the intimal flap with TEE was 78% specific in the ascending aorta, 94% in the aortic arch, and 92% in the descending aorta. MRI and TEE were equal in the detection of the site of entry of the aortic dissection. Sensitivity in the detection and localization of intraluminal thrombi was 75% for TEE and 100% for MRI. [25] Contrast-enhanced magnetic resonance angiography (CE-MRA) is an accurate noninvasive imaging modality. It has the advantage of being able to eva

luate the aortic valve more effectively than CTA can. Drawbacks include the following:

• MRI is not readily available at most institutions, requiring transportation of patients in unstable condition away from the ED

• MRI requires much more time to acquire images than CT does

• Patients with permanent pacemakers cannot undergo MRI (however, most patients with prosthetic heart valves or coronary stents can safely undergo MRI)

Aortography Aortography has been the diagnostic criterion standard study for aortic dissection, but it is difficult to perform in patients with hemorrhage, shock, and/or cardiac tamponade. Aortography is being replaced by newer imaging modalities because of risks associated with invasiveness and adverse reactions to intravenous contrast agents. Aortography (see the image below) leads to accurate diagnosis of aortic dissection in over 95% of patients and aids the surgeon in planning the repair operation because blood vessels of the arch can be assessed easily.

Angiogram demonstrating dissection of the aorta in a patient with aortic dissection presenting with hemothorax

Benefits include visualization of the true and false lumens, intimal flap, aortic regurgitation, and coronary arteries. Drawbacks include the following:

• The procedure is invasive

• The patient must be transported to the radiology department, leaving the ED

• The use of contrast media may be harmful to patients who have renal insufficiency or an allergy to iodine

• The false lumen and intimal flap may not be visualized if the false channel is thrombosed, which can lead to misdiagnosis

• Simultaneous opacification of the true and false lumens may make discerning the presence of a dissection difficult

Electrocardiography All patients with suspected thoracic aortic dissection should have a 12-lead ECG. However, the ECG often demonstrates a nonspecific abnormality or normal results (approximately 31% of patients). One study reported normal findings in 63 (90%) of 70 patients. In acute thoracic aortic dissection, the ECG changes can mimic those seen in acute cardiac ischemia. In the presence of chest pain, these signs can make distinguishing dissection from acute myocardial infarction very difficult (see the image below). Keep this in mind when administering thrombolytics to patients with chest pain.

Electrocardiogram of a patient presenting to the ED with chest pain; this patient was diagnosed with aortic dissection. The incidence of abnormal ECG findings is greater in Stanford type A dissections than in other types of dissections. ST-segment elevation can be seen in Stanford type A dissections because the dissection interrupts blood flow to the coronary arteries. In one study, 8% of patients with type A dissections had ST-segment elevation, whereas no patients with type B dissections had ST-segment elevation. More commonly, the ECG abnormality is ST-segment depression. If the dissection involves the coronary ostia, the right coronary artery is most commonly involved. This can result in ST-segment elevation in leads II, III, and aVF, a pattern similar to that seen in inferior wall infarctions.

Treatment & Management

Approach Considerations Acute aortic dissection can be treated surgically or medically. In surgical treatment, the area of the aorta with the intimal tear is usually resected and replaced with a Dacron graft. Emergency surgical correction is the preferred treatment for Stanford type A (DeBakey type I and II) ascending aortic dissection. It is also preferred for complicated Stanford type B (DeBakey type III) aortic dissections with clinical or radiologic evidence of the following conditions:

• Propagation (increasing aortic diameter)

• Increasing size of hematoma

• Compromise of major branches of the aorta

• Impending rupture

• Persistent pain despite adequate pain management

• Bleeding into the pleural cavity

• Development of saccular aneurysm

Cautions and relative contraindications to surgery include the following:

• Cerebrovascular accident (CVA)

• Severe left ventricular dysfunction

• Coagulopathy

• Pregnancy

• Previous myocardial infarction (< 6 months)

• Significant arrhythmias

• Advanced age

• Severe valvular disease

Medical management remains the treatment of choice for descending aortic dissections unless they are leaking or ruptured. With the progress in stenting technology, descending dissections can be approached with this modality in selected cases. [6, 13, 26, 27, 28, 29] Medical therapy is also administered to surgical patients preoperatively, intraoperatively, and postoperatively to prevent progression or recurrence of aortic dissection. Medical management consists of decreasing the blood pressure and the shearing forces of myocardial contractility in order to decrease the intimal tear and propagation of the dissection. Medical management with antihypertensive therapy, including beta blockers, is the treatment of choice for all stable chronic aortic dissections. Pain management is an important but difficult aspect of medical therapy. Narcotics and opiates are the preferred agents.

Pharmacologic Therapy Initiate medical therapy as soon as the diagnosis is considered. To guide medical therapy, admit the patient to the intensive care unit (ICU) or coronary care unit (CCU) for hemodynamic studies, as follows:

• Arterial blood pressure monitoring with an arterial line

• Central venous pressure monitoring with a central catheter

• Cardiac performance and filling pressures with Swan-Ganz catheterization

• Urine output monitoring with a Foley catheter and bag

Initiate therapy to reduce cardiac contractility. Administer drugs with negative inotropic effects, such as beta blockers (the agents of choice); administer calcium-channel blockers if beta blockers are contraindicated. The following beta blockers are commonly administered, intravenously (IV) or orally:

• Labetalol

• Propranolol

• Esmolol

Initiate therapy to reduce systemic arterial pressure and shear stress if the patient's blood pressure allows this type of intervention. The following agents are commonly used:

• IV nitroprusside drip

• IV labetalol: it has a dual effect of decreasing blood pressure and cardiac contractility

• Calcium channel blockers (eg, diltiazem): they lower blood pressure and cardiac contractility

The following conditions contraindicate beta-blocker therapy:

• Hypersensitivity to drug/class

• Severe asthma

• Heart block

• Uncompensated heart failure

• Bradycardia (heart rate < 60 beats/min)

• Severe chronic obstructive pulmonary disease

• Hypotension

The following conditions contraindicate calcium channel blocker therapy:

• Hypersensitivity to drug/class

• Second- or third-degree atrioventricular block

• Sick sinus syndrome

• Hypotension

• Left ventricular dysfunction

• Pulmonary congestion

The following conditions contraindicate nitroprusside infusion:

• Hypersensitivity to drug/class

• Poor cerebral perfusion

• Poor coronary perfusion

Surgical Overview The major objectives of surgery for aortic dissection are to alleviate the symptoms, decrease the frequency of complications, and prevent aortic rupture and death. The affected layers of the aorta are sutured together, and the aorta is reinforced with a Dacron graft. Improved cardiopulmonary bypass circuits have decreased the prevalence of injury to blood elements. Morbidity and mortality associated with this highly invasive surgery have decreased with the introduction of profound hypothermic circulatory arrest and retrograde cerebral perfusion. [30] A number of advances have resulted in a decreased frequency of complications associated with surgery on the aorta. Dacron grafts with impregnated collagen or gelatin have been developed that are impervious to blood. The development of more impermeable grafts has greatly enhanced the surgical repair of thoracic aortic dissections. Such grafts include the following:

• Woven Dacron

• Collagen-impregnated Hemashield (Meadox Medicals) aortic grafts

• Gel-coated Carbo-Seal Ascending Aortic Prosthesis (Sulzer CarboMedics)

The operative mortality with ascending aortic dissection is usually less than 10%. Serious complications are rare. Dissections involving the arch are more complicated than those involving only the ascending aorta because the innominate, carotid, and subclavian vessels branch from the arch. Deep hypothermic arrest is usually required. If the arrest time is less than 45 minutes, the rate of central nervous system (CNS) complications is lower than 10%. Retrograde cerebral perfusion may improve the protection of the CNS during the arrest period. The mortality associated with aortic arch dissections is approximately 10-15%. Significant neurologic complications occur in an additional 10% of patients. Postoperative complications for extensive disease involving the thoracoabdominal aorta include myocardial infarction, respiratory failure, renal failure, stroke, and paraparesis or paraplegia. The use of adjunct procedures has decreased the frequency of procedure-related spinal cord injury during descending aorta and thoracoabdominal surgeries. These include the following:

• Distal aortic perfusion

• Induction of profound hypothermia

• Cerebrospinal fluid (CSF) drainage

• Monitoring of somatosensory and motor evoked potentials in the brain and spinal cord

Endovascular therapy is rapidly emerging as the preferred treatment for descending aortic dissection, provided vascular access is available. This methodology still remains controversial for ascending dissection. [31, 32, 33, 34, 35] A 2011 study that included 28 complicated acute aortic dissection patients treated with endovascular repair suggested that this technique has improved mortality as compared with traditional surgical interventions. [36] Preparation for surgery Numerous factors may increase mortality and morbidity rates for surgical intervention on the aorta, including a history of myocardial infarction, respiratory failure, renal failure, or stroke. Preoperative evaluation is, therefore, essential in patients with these histories. Because aortic dissection is more common in elderly patients (ie, aged 70-80 years), this group of patients has different comorbidities. Patients older than 50 years have a high prevalence of atherosclerotic heart disease and may require a thorough cardiac workup. Symptoms of aortic dissection are always difficult to differentiate from those of myocardial infarction. Patients with electrocardiographic (ECG) changes suggestive of myocardial infarction or ischemia undergo workups with emergency cardiac catheterization and angiography, followed by percutaneous transluminal coronary angioplasty or coronary artery bypass grafting concomitant with aortic repair or construction. Patients with valvular heart disease undergo workups with echocardiography or coronary angiography. If any valvular abnormalities are found, appropriate surgical correction (valve replacement or commissurotomy) is performed prior to or simultaneous with aortic repair. Surgeries involving the descending or thoracoabdominal aorta require a lateral thoracotomy. A history of smoking or chronic obstructive pulmonary disease is of significant concern; perform pulmonary function testing on such patients. Additionally, arterial blood gas testing may be required. In elective cases, treat reversible restrictive diseases and excessive sputum production with antibiotics and bronchodilators. Preoperative renal dysfunction is considered the most important predictor of postoperative acute renal failure (ARF). Preoperative management to decrease the frequency of ARF involves adequate hydration; hypotension, a low cardiac output state, and hypovolemia must be avoided. Perform appropriate workups for patients presenting with any neurologic signs suggestive of central nervous system pathology (eg, stroke). This usually consists of Doppler imaging of the carotid arteries and, if needed, angiography of brachiocephalic and intracranial arteries. If the study findings are positive, perform a carotid endarterectomy before the aortic surgery. Operative goals The objectives of surgical therapy for aortic dissection are to resect the damaged segment, excise the intimal tear, and obliterate the entry into the false lumen. Suturing the edges of the dissected aorta both proximally and distally obliterates the entry into the false lumen. The desirability of obliterating the entrance to the false lumen is controversial because of multiple portals. Aortic continuity after dissection of a diseased segment is reestablished by means of a prosthetic sleeve graft between the two ends of the aorta.

Repair of Type A Dissections Patients with type A dissections are treated with immediate surgical correction. This involves transfer to the operating room, where median sternotomy is performed. Profound hypothermia is initiated after the patient is placed on cardiopulmonary bypass. Cardiopulmonary bypass is performed by femoral-femoral cannulation and through the superior vena cava for retrograde cerebral perfusion. Myocardial temperature is kept below 15°C (59°F) by cardioplegic perfusion via the coronary sinus. This provides myocardial protection throughout the procedure. Ventricular distention is avoided by decompressing the left ventricle by venting through the left superior pulmonary vein or artery. The pump is stopped when the electroencephalogram is isoelectric and the nasopharyngeal temperature reaches 12°C (53.6°F). Retrograde cerebral perfusion is then started via the superior vena cava. The ascending aorta is inspected for the site and extent of the tear and the involvement of the transverse arch and for an assessment of intimal disruption that requires repair. Through a longitudinal approach, the ascending aorta is opened and transected just proximal to the innominate artery. In patients with involvement of the transverse aortic arch, either the proximal arch or the total arch is replaced. If the intima is fragmented or shows evidence of rupture, the whole arch is replaced. If the transverse arch is free of reentry, the intima and adventitia are sutured together with fine 4-0 and 5-0 polypropylene suture. A gelatin- or collagen-woven Dacron graft is sutured to the reinforced proximal aortic arch in end-to-end fashion and reinforced from both inside and outside with 4-0 pledgeted sutures. At the time of completion of the distal anastomosis, retrograde cerebral perfusion is stopped and cardiopulmonary bypass is restarted via the femoral artery. This evacuates all air and debris from the brachiocephalic vessels. The graft is clamped proximal to the origin of the innominate artery. Flow to the cerebral and systemic circulation is restored after clamping the graft proximal to the origin of the innominate artery. Hypothermic circulatory arrest is a valuable tool in aortic dissection repair. Emptying the major vessels allows ingress of air, which causes complications related to air embolism, a major hazard associated with this procedure. Ensure that the patient's head is not elevated; rather, depress it and allow blood to gravitate into the head vessels, thus displacing the air (upward) to the periphery. This is essential. The patient is rewarmed with restoration of anterograde flow through a side arm line inserted in the ascending aorta. The aortic valve is suspended with 4-0 polypropylene pledgeted sutures if it is normal and no evidence of aortic root dilatation is present. The intima and adventitia of the aorta superior to the coronaries are sutured together and reinforced from inside the graft. If the aortic valve or the root is dilatated, a composite valve graft is placed. A button or modified Cabrol technique is used to reattach the coronary arteritis. When aortic regurgitation is present, simple decompression of the false lumen may be all that is required to allow resuspension of the aortic leaflets and restoration of valvular competence. More often, however, the two layers of the dissected aortic wall are approximated, and resuspension of the commissures is accomplished with pledgeted sutures. Prosthetic aortic valve replacement also may be necessary in certain situations. After the procedure is completed, the patient is brought to sinus rhythm by defibrillation. The patient is then weaned from cardiopulmonary bypass.

Repair of Type B Dissections Surgical management of acute type B aortic dissections is undertaken only in the presence of indications such as the following:

• Persistent pain

• Aneurysmal dilatation greater than 5 cm

• End-organ or limb ischemia

• Evidence of retrograde dissection to the ascending aorta

Patients without such indications are treated with intensive medical therapy. [13] The operation involves transection of the proximal descending aorta distal to the left subclavian artery. The proximal and distal intima and adventitia of the transected aorta are reinforced in the same manner as that for the ascending aorta, with a 4-0 polypropylene suture. A gelatin- or collagen-woven Dacron graft is sewn directly to the reinforced acutely dissected proximal thoracic aorta, with the posterior row reinforced using interrupted polypropylene sutures. Blood is rechanneled into the true lumen of the distal aorta by cutting the descending thoracic graft and suturing it to the reinforced distal aorta. Adjunct procedures are used to minimize complications. The entire thoracoabdominal aorta is opened if extensive involvement of the descending and abdominal aorta is present that requires replacement. The septum between the false and true lumen is excised, and the visceral vessels and renal arteries are reattached to the graft directly or via a Dacron graft. In chronic dissections, the intercostal arteries (T9-T12) are reimplanted by side graft or a side hole. This is in contrast to acute dissections, in which the intercostals and lumbar arteries are ligated. Surgical techniques have been developed that use fibrin sealant or gelatin-resorcin-formaldehyde glue. Glue replaces the use of pledgeted sutures to seal the false lumen of the aortic stumps after resection of the diseased aortic segment and before the implantation of the Dacron prosthesis. The glue hardens and reinforces the dissected aortic tissue. Other advantages include simplification of the operation, facilitation of the resuspension of the aortic valve, and, possibly, reduction in the frequency of late aortic root aneurysm formation.

Endovascular Repair Because of the high operative mortality in patients with renal or visceral artery compromise from dissection, endovascular approaches are under investigation. Several endovascular techniques are available. [26, 29, 37, 38] One involves the formation of a site of reentry to allow blood to pass from the false lumen to the true lumen. This requires passing a wire past the intact intimal flap, passing a balloon-tipped catheter over the wire, and tearing a hole in the intimal flap by inflating the balloon. Another technique involves percutaneous stenting to decrease the ischemic complications of aortic dissection. This is performed on arteries that have compromised flow from the dissection. Sutureless intraluminal prostheses placed during cardiopulmonary bypass are also being used. Another technique involves percutaneously placement of intraluminal stent-grafts using a transfemoral catheter technique. This procedure results in the closure of the site of entry into the false lumen and decompresses and promotes thrombosis of the false lumen. It also alleviates obstruction of the branch vessels complicating a dissection. Thoracic endovascular aortic repair (TEVAR) is a minimally invasive approach used to treat patients who cannot tolerate open surgical repair. A study of outcomes after TEVAR in patients with retrograde type A aortic dissection (RAAD) and an entry tear in the descending aorta found it to be safe and effective for these highly selected patients. All repairs were technically successful, and all patients survived through the follow-up period. TEVAR yielded a significant decrease in the diameter and the false lumen of both ascending and descending aortas. [39] Early results from the ADSORB trial suggest that in the treatment of acute type B aortic dissection, TEVAR plus best medical therapy may have an advantage over medical therapy alone with respect to aortic remodeling outcomes 1 year after dissection. [40] For endovascular therapy, the patient is prepared for general anesthesia and open procedure. The patient is then taken to the vascular suite, and after the induction of general anesthesia, bilateral groin cutdowns are performed to gain access to the common femoral artery. Because of the large size of the sheath needed to introduce the stent, a synthetic graft may be sewn to the artery to gain access. Once groin access is obtained, the patient is heparinized and the stent is positioned and deployed using radiographic guidance. [35]

Management of Intramural Hematomas and Penetrating Ulcers

Intramural hematomas and penetrating atherosclerotic ulcers of the aorta are conditions that result in aortic dissection or rupture. Both are more common in the descending aorta; medical therapy is first-line treatment. When the ascending aorta or the arch is affected, the need for surgery is more likely. Intramural hematomas are hemorrhages into the medial layer of the aortic wall without an intimal tear. Because these hematomas have a natural history similar to that of aortic dissection and aneurysm, they are treated similarly. Surgical therapy is initiated for patients with proximal hematomas; medical therapy is reserved for patients with distal hematomas. Medical therapy consists of optimizing blood pressure control, decreasing aortic pulse pressure, controlling risk factors for atherosclerosis, and maintaining close long-term follow-up care. Penetrating atherosclerotic ulcers penetrate the internal elastic lamina, causing hematoma formation within the media of the aortic wall. Almost all are in the descending aorta. Because the natural history of these ulcers is undefined, a definitive treatment strategy has not been formulated. Consider surgery in patients with penetrating atherosclerotic ulcers who are hemodynamically unstable or who have evidence of pseudoaneurysm formation or transmural rupture. Other indications for surgery include recurrent pain, distal embolization, and progressive aneurysmal dilatation from the ulcer. If patients present without these complications, they are treated with antihypertensive medications and close monitoring. [41]

Consultations Once a thoracic dissection is suspected, consult a thoracic surgeon. Because many patients with this disorder have concomitant medical illness, the emergency department physician should consult the patient's primary care provider to expedite preoperative preparation. Early consultation is encouraged when ordering further imaging studies if the patient requires rapid operative intervention. Consult a radiologist before obtaining aortography.

Long-Term Monitoring Provide the following long-term care for patients with aortic dissection, whether treated medically or surgically:

• At 1 month, a follow-up check for any new symptoms, such as chest or back pain, and signs suggestive of progression of the aortic dissection

• Adequate blood pressure control, with systolic blood pressure maintained at 90-120 mm Hg

• Routine chest radiographs, CT with contrast, and MRI at 3-, 6-, and 12-month intervals, respectively, in an outpatient setting to evaluate any progression of the condition

Medication

Medication Summary Initial therapeutic goals include the elimination of pain and the reduction of systolic blood pressure to 100-120 mm Hg or to the lowest level commensurate with adequate vital organ (ie, cardiac, cerebral, renal) perfusion. Whether systolic hypertension or pain is present, beta-blockers are used to reduce arterial delta pressure/delta time (dP/dt). To prevent exacerbations of tachycardia and hypertension, treat patients with intravenous morphine sulfate. This reduces the force of cardiac contraction and the rate of rise of the aortic pressure. It then retards the propagation of the dissection and delays rupture.

Antihypertensives, Other Class Summary These agents are used to reduce arterial dP/dt. For acute reduction of arterial pressure, the potent vasodilator sodium nitroprusside is effective. To reduce dP/dt acutely, administer an IV beta-blocker in incremental doses until a heart rate of 60-80 beats/min is attained. When beta-blockers are contraindicated, such as in second- or third-degree atrioventricular block, consider using calcium channel blockers. Sublingual nifedipine successfully treats refractory hypertension associated with aortic dissection. Esmolol (Brevibloc)

Esmolol is an ultra–short-acting beta1-blocker. It is particularly useful in patients with labile arterial pressure, especially if surgery is planned, because it can be discontinued abruptly if necessary. This agent is normally used in conjunction with nitroprusside. It may be useful as a means to test beta-blocker safety and tolerance in patients with a history of obstructive pulmonary disease who are at possible risk of bronchospasm from beta-blockade. The elimination half-life of esmolol is 9 minutes. Labetalol (Trandate)

Labetalol blocks alpha-, beta1-, and beta2-adrenergic receptor sites, decreasing blood pressure. Propranolol (Inderal LA, InnoPran XL, Inderal XL, Hemangeol)

Propranolol is a class II antiarrhythmic nonselective beta-adrenergic receptor blocker. It has membrane-stabilizing activity and decreases the automaticity of contractions. Propranolol is not suitable for emergency treatment of hypertension. Do not administer propranolol IV in hypertensive emergencies. Metoprolol (Lopressor, Toprol XL)

Metoprolol is a selective beta1-adrenergic receptor blocker that decreases the automaticity of contractions. During IV administration, carefully monitor the blood pressure, heart rate, and electrocardiogram (ECG). When considering conversion from IV to oral (PO) dosage forms, use the ratio of 1 mg IV to 2.5 mg PO metoprolol. Nitroprusside (Nitropress)

Nitroprusside causes peripheral vasodilation by direct action on venous and arteriolar smooth muscle, thus reducing peripheral resistance. It is commonly given intravenously because of its rapid onset and short duration of action. It is easily titratable to reach the desired effect. Nitroprusside is light sensitive; both bottle and tubing should be wrapped in aluminum foil. Before initiating nitroprusside, administer a beta-blocker to counteract the physiologic response of reflex tachycardia that occurs when nitroprusside is used alone. This physiologic response increases shear forces against the aortic wall, thus increasing dP/dt. The objective is to keep the heart rate at 60-80 bpm. Nifecipine

Nifedipine is one of the more common channel blockers used for hypertension.

Analgesics Class Summary Pain control is essential to quality patient care. It ensures patient comfort, promotes pulmonary toilet, and prevents exacerbations of tachycardia and hypertension. Morphine sulfate (Astramorph, Infumorph, MS Contin, Avinza, Kadian)

Morphine is the drug of choice for narcotic analgesia because of its reliable and predictable effects, safety profile, and ease of reversibility with naloxone. Like fentanyl, morphine sulfate is easily titrated to the desired level of pain control. If administered IV, morphine may be dosed in a number of ways; it is commonly titrated until the desired effect is obtained.

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