AUTHOR INFORMATION

Section 1 of 12

Authored by John Wiesenfarth, MD, MS, FACEP, FAAEM, Assistant Chief, Department of Emergency Medicine, Kaiser-Permanente Hospital Sacramento/Roseville; Assistant Professor, Division of Emergency Medicine, University of California at Davis

John Wiesenfarth, MD, MS, FACEP, FAAEM, is a member of the following medical societies: American Medical Association, and Wilderness Medical Society

Edited by Joseph J Sachter, MD, FACEP, Consulting Staff, Department of Emergency Medicine, Muhlenberg Regional Medical Center; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Gary Setnik, MD, Chair, Department of Emergency Medicine, Mount Auburn Hospital; Assistant Professor, Division of Emergency Medicine, Harvard Medical School; John Halamka, MD, Chief Information Officer, CareGroup Healthcare System, Assistant Professor of Medicine, Department of Emergency Medicine, Beth Israel Deaconess Medical Center; Assistant Professor of Medicine, Harvard Medical School; and Barry Brenner, MD, PhD, FACEP, Professor of Emergency Medicine, Professor of Internal Medicine, and Professor of Anatomy and Neurobiology, Research Director, Department of Emergency Medicine, University of Arkansas for Medical Sciences

Author's Email:	John Wiesenfarth, MD, MS, FACEP, FAAEM
Editor's Email:	Joseph J Sachter, MD, FACEP

eMedicine Journal, October 4 2005, VOLUME 6, Number 10

INTRODUCTION

Section 2 of 12

Background: Much has been written on the subject of aortic dissections, from the first well-documented case of aortic dissection, when King George II of England died while straining on the commode, to the first successful operative repairs by DeBakey in 1955, to modern techniques of diagnosing and repairing thoracic aortic dissections.

Aortic dissection is the most common catastrophe of the aorta, 2-3 times more common than rupture of the abdominal aorta. When left untreated, about 33% of patients die within the first 24 hours, and 50% die within 48 hours. The 2-week mortality rate approaches 75% in patients with undiagnosed ascending aortic dissection.

Dissections of the thoracic aorta have been classified anatomically by 2 different methods. The more commonly used system is the Stanford classification, which is based on involvement of the ascending aorta and simplifies the DeBakey classification.

The Stanford classification divides dissections into 2 types, type A and type B.

• Type A involves the ascending aorta (DeBakey types I and II); type B does not (DeBakey type III).

• This system also helps delineate treatment. Usually, type A dissections require surgery, while type B dissections may be managed medically under most conditions.

The DeBakey classification divides dissections into 3 types.

• Type I involves the ascending aorta, aortic arch, and descending aorta.

• Type II is confined to the ascending aorta.

• Type III is confined to the descending aorta distal to the left subclavian artery.
  • Type III dissections are further divided into IIIa and IIIb.

  • Type IIIa refers to dissections that originate distal to the left subclavian artery but extend both proximally and distally, mostly above the diaphragm.

  • Type IIIb refers to dissections that originate distal to the left subclavian artery, extend only distally and may extend below the diaphragm.

Thoracic aortic dissections should be distinguished from aneurysms (ie, localized abnormal dilation of the aorta) and transections, which are caused most commonly by high-energy trauma.

Pathophysiology: The essential feature of aortic dissection is a tear in the intimal layer, followed by formation and propagation of a subintimal hematoma. The dissecting hematoma commonly occupies about half and occasionally the entire circumference of the aorta. This produces a false lumen or double-barreled aorta, which can reduce blood flow to the major arteries arising from the aorta. If the dissection involves the pericardial space, cardiac tamponade may result.

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.

Dissection sites

The most common site of dissection is the first few centimeters of the ascending aorta, with 90% occurring within 10 centimeters 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.

Diseases leading to aortic dissection

Certain diseases, such as Marfan, Ehlers-Danlos, and other connective tissue diseases, affect the media of the aorta and make it prone to dissection. Pulsatile flow and high blood pressure contribute to propagation of the dissection.

Diseases that weaken the aortic wall predispose the patient to aortic dissection. Shearing forces separate the layers in the media of the aorta. Intimal rupture occurs at points of fixation along the aorta where hydraulic stress is maximal.

Frequency:

• In the US: The true incidence of dissection is difficult to estimate. Most estimates are based on autopsy studies. One population-based study estimated the incidence at roughly 6 new aneurysms per 100,000 person-years. Evidence of dissection is found in 1-3% of all autopsies.

Mortality/Morbidity:

• From 1-2% of patients with aortic dissection die per hour for the first 24-48 hours.

• Aortopathy may be present in heritable diseases such as 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, and connective tissue disorders. It is also seen in heritable metabolic disorders such as homocystinuria and familial hypercholesterolemia.

• Incidence is increased in pregnancy and syphilis. Thoracic aortic dissection also is associated with crack cocaine use and iatrogenic causes, such as cardiac catheterization.

Race: Aortic dissection is more common in blacks than in whites and less common in Asians than in whites.

Sex: The male-to-female ratio is 3:1.

Age: Approximately 75% of dissections occur in those aged 40-70 years, with a peak in the range of 50-65 years.

CLINICAL

Section 3 of 12

History: ". . . spontaneous tear of the arterial coats is associated with atrocious pain, with symptoms, indeed, in the case of the aorta of angina pectoris and many instances have been mistaken for it" William Osler, 1910.

• Chest pain is the most common presenting symptom in patients with an aortic dissection. Consider thoracic aortic dissection in the differential diagnosis of all patients presenting with chest pain.

• The pain usually is described as ripping or tearing. The description of ripping or tearing has been shown to have a likelihood ratio for aortic dissection of 1.2 and 10.8.

• The sudden onset of chest pain has been shown to have a sensitivity of 84%.

• This description is not universal, and some patients present with only mild pain, often mistaken for musculoskeletal conditions, located in the thorax, groin, or back.

• The pain of aortic dissection typically is distinguished from the pain of acute myocardial infarction (AMI) by its abrupt onset.

• Aortic dissection should be considered strongly in all patients reporting acute, sudden, and severe chest pain that is maximal at onset.

• The truly sudden onset of chest pain is seen in few other conditions. In 1926, Spiegel and Wassermann found that acute stretching of the aortic wall produces pain.

• The nervi vascularis, bundles of nerve fibers found in the aortic adventitia, are involved in the production of pain.

• 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 (pain, quality, radiation, severity, and timing) of pain in all able patients. Assess the following characteristics of pain:

• Severity

• Character

• Timing, including rate of onset, duration, and frequency of episodes

• Migration, including aggravating or alleviating factors and associated symptoms

• The description of the pain may indicate where the dissection arises.

• Anterior chest pain and chest pain that mimics AMI 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 that is described in the neck or jaw indicates that the dissection involves the aortic arch and extends into the great vessels of the arch.

• Tearing or ripping pain that is felt in the intrascapular area may indicate that the dissection involves the descending aorta. The pain typically changes as the dissection evolves.

• Aortic dissection is painless in about 10% of patients. Painless dissection is more common in those with neurologic complications from the dissection and those with Marfan syndrome.

• Presenting signs and symptoms in acute thoracic aortic dissection include the following:

• Anterior chest pain - Ascending aortic dissection

• Neck or jaw pain - Aortic arch dissection

• Interscapular tearing or ripping pain - Descending aortic dissection

• Chest pain

• Myocardial infarction

• Neurologic symptoms

• Syncope

• Stroke symptoms

• Altered mental status

• Limb paresthesias, pain, or weakness

• Hemiparesis or hemiplegia

• Horner syndrome

• Dyspnea

• Dysphagia

• Orthopnea

• Anxiety and premonitions of death

• Flank pain if renal artery is involved

• Dyspnea and hemoptysis if dissection ruptures into the pleura

Physical:

• Blood pressure may increase or decrease.

• Hypertension may result from a catecholamine surge or underlying essential hypertension.

• Hypotension is an ominous finding and may be the result of excessive vagal tone, cardiac tamponade, or hypovolemia from rupture of the dissection.

• A blood pressure differential of greater than 20 mm Hg was an independent predictor of aortic dissection. A pressure differential of 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.

• 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 with 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.

• Superior vena cava syndrome, caused by compression of the superior vena cava from a large distorted aorta, may occur.

• Dyspnea may be caused by congestive heart failure or tracheal or bronchial compression.

• Dysphagia from compression of the esophagus may be present.

• Findings suggestive of cardiac tamponade, such as muffled heart sounds, hypotension, pulsus paradoxus, jugular venous distension, and Kussmaul sign, must be recognized quickly.

• Other diagnostic clues include a new diastolic murmur, asymmetrical pulses, and asymmetrical blood pressure measurements. 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.

Causes: Aortic dissection is more common in patients with hypertension, connective tissue disorders, congenital aortic stenosis or bicuspid aortic valve, and in those with first-degree relatives with history of thoracic dissections. These diseases affect the media of the aorta and predispose it to dissection.

• 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)

• Hypertension or pulsatile blood flow can propagate the dissection.

• An estimated 50% of all cases of aortic dissection that occur in women younger than 40 years are associated with pregnancy.

• Syphilis may cause aortic dissection.

• Crack cocaine use may precipitate aortic dissection.

• Iatrogenic causes of aortic dissection include cardiac catheterization.

DIFFERENTIALS

Section 4 of 12

Aortic Regurgitation
Aortic Stenosis
Back Pain, Mechanical
Gastroenteritis
Hernias
Hypertensive Emergencies
Myocardial Infarction
Myocarditis
Myopathies
Pancreatitis
Pericarditis and Cardiac Tamponade
Peripheral Vascular Injuries
Pleural Effusion
Pulmonary Embolism
Shock, Cardiogenic
Shock, Hemorrhagic
Shock, Hypovolemic
Thoracic Outlet Syndrome

Other Problems to be Considered:

Musculoskeletal chest pain

WORKUP

Section 5 of 12

Lab Studies:

• Blood studies

• Usually, the diagnosis is made before the blood work is returned; however, leukocytosis may be present.

• BUN and creatinine are elevated if the dissection involves the renal arteries.

• Troponin and creatine kinase (CK) can be elevated if the dissection has caused myocardial ischemia.

• Decreases in the hemoglobin and hematocrit are ominous findings suggesting the dissection either is leaking or has ruptured.

• Some studies suggest that D-dimer should be a part of the initial workup if aortic dissection is suspected. A negative result makes the presence of the disease unlikely.

• Hematuria, oliguria, and even anuria ( <50 mL/d) may occur if the dissection involves the renal arteries.

Imaging Studies:

• Chest radiography: Findings are abnormal in 80% of patients and are more commonly abnormal in ascending aortic dissections (see Image 1).

• Findings suggesting hemothorax may be found if the dissection ruptures into the pleura (see Image 2).

• Radiographic findings in acute thoracic dissection include a widened mediastinum in many cases (see Image 3).
  • In 2000, the International Registry of Acute Aortic Dissection published data on 464 patients that showed only 25% presenting with this finding.

  • A widened mediastinum is sometimes difficult to identify on a portable anteroposterior (AP) radiograph. If the patient is hemodynamically stable and cooperative, an AP radiograph can be obtained at bedside.

  • Look for a mediastinal width greater than 8 cm on AP chest radiograph.

  • 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.

• 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:
  • Left apical cap

  • Tracheal deviation

  • Depression of left main stem bronchus

  • Esophageal deviation

  • Loss of the paratracheal stripe

• The International Registry for Aortic Dissection revealed that over 12% of the chest radiographs of patients with aortic dissection were read as normal. 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.

• Angiography: Still considered by some as the diagnostic criterion standard test for aortic dissection, it is being replaced by newer imaging modalities.

• Angiography leads to accurate diagnosis of aortic dissection in over 95% of patients (see Image 4) and aids the surgeon in planning the repair operation because blood vessels of the arch can be assessed easily. 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.

  • Misdiagnoses can occur if the false channel is thrombosed. In this instance, the false lumen and intimal flap may not be visualized. Possible simultaneous opacification of the true and false lumens may make discerning the presence of a dissection difficult.

• Computed tomography (CT) scanning: The accepted diagnostic criterion standard, angiography, is being challenged by state-of-the-art CT angiography. With the advent of helical CT with multiplanar and 3D reconstruction and CT angiography, CT scanning is quickly replacing angiography as the diagnostic test of choice in many institutions.

• Prospective studies have shown a sensitivity of 83-94% with a specificity of 87-100%.

• Spiral CT scanning is associated with a higher rate of detection and better resolution than incremental CT scanning. High-quality 2D and 3D reconstructions are possible with spiral CT scanning, which greatly adds to the usefulness of this imaging modality.

• More importantly, 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.

• Faster scanners have decreased the acquisition time to the range of a breath hold, resulting in less motion artifact from breathing.

• 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.

  • CT angiography requires the injection of iodinated contrast.

  • The use of contrast material may harm a patient who has impaired renal function or an allergy to contrast media.

  • CT scanning provides no information on aortic regurgitation.

• Echocardiography

• With its increasing acceptance and use in the ED, ultrasonography is becoming a valuable diagnostic aid, although transthoracic echocardiography (TTE) has a much lower sensitivity (80%) and lower specificity (90%) than angiography.

• 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.

• Echocardiography also is useful in diagnosing cardiac tamponade and aortic regurgitation.

• Benefits include its rapid simple bedside use in the ED and its noninvasive nature.

• Drawbacks include the lack of sensitivity and specificity, especially with arch and descending aortic dissections, and dependence on operator experience.

• Transesophageal echocardiography (TEE) has greater sensitivity and specificity than TTE (in the range of 97-99% and 97-100%, respectively).
  • Advantages include its quick and easy bedside use in the ED, which makes it ideal for patients in unstable condition.

  • TEE detects involvement of the coronary arteries, aortic insufficiency, and cardiac tamponade.

  • It is a relatively quick study to perform and relatively noninvasive.

  • 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)

• MRI has over 90% sensitivity and greater than 95% specificity. It is the most sensitive method for diagnosing aortic dissection and has similar specificity to CT scanning.

• 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.

• Contrast-enhanced magnetic resonance angiography (CE-MRA) is a principle technique for evaluating the thoracic aorta.

• MRI is the preferred tool for imaging chronic dissections and postsurgical follow-up.

• Contrast 3D MRA is an accurate noninvasive imaging modality. It has the advantage of being able to evaluate the aortic valve more effectively than CT angiography.

• 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 scanning.

  • Patients with permanent pacemakers cannot undergo MRI. Most patients with prosthetic heart valves or coronary stents can safely have an MRI.

Other Tests:

• ECG: All patients with suspected thoracic aortic dissection should have an ECG.

• In acute thoracic dissection, ECG can mimic the changes seen in acute cardiac ischemia. In the presence of chest pain, these signs can make distinguishing dissection from AMI very difficult (see Image 5). Keep this in mind when administering thrombolytics to patients with chest pain.

• ST elevation can be seen in Stanford type A dissections because the dissection interrupts blood flow to the coronary arteries.
  • The incidence of abnormal ECG findings is greater in Stanford type A dissections than in other types of dissections.

  • In one study, 8% of patients with type A dissections had ST elevation, while no patients with type B dissections had ST elevation.

  • More commonly, the ECG abnormality is ST depression.

  • If the dissection involves the coronary ostia, it is the right coronary artery that is most commonly involved, leading to inferior ST segment elevation pattern.

TREATMENT

Section 6 of 12

Prehospital Care:

• Assure adequate breathing, maintain oxygenation, treat shock, and obtain useful historic information.

• Establishing the diagnosis in the field is usually difficult or impossible, but certain salient features of aortic dissection may be observed. It is life threatening if not quickly recognized and treated.

• Radio communication with the receiving hospital permits the medical control physician to direct care and select a capable destination hospital while permitting the ED to mobilize appropriate resources.

• In the rare event that the diagnosis can be made based on prehospital information, the physician directing prehospital care should request transport to a facility capable of operative treatment of an aortic dissection.

Emergency Department Care:

• The mortality rate of patients with aortic dissection is 1-2% per hour for the first 24-48 hours. Initial therapy should begin when the diagnosis is suspected. This includes 2 large-bore intravenous lines (IVs), oxygen, respiratory monitoring, and monitoring of cardiac rhythm, blood pressure, and urine output.

• Clinically, the physician should reassess the patient frequently for hemodynamic compromise, mental status changes, neurologic or peripheral vascular changes, and development or progression of carotid, brachial, and femoral bruits.

• Aggressive management of heart rate and blood pressure should be initiated.

• Beta-blockers should be given initially to reduce the rate of change of blood pressure (dP/dt) and the shear forces on the aortic wall.

• The target heart rate should be 60-80 beats per minute.

• The target systolic blood pressure should be 100-120 mm Hg.

• End organ perfusion should be evaluated. Balancing the risks of dP/dt on the aortic wall versus the benefits of acceptable end organ perfusion may be a difficult clinical decision.

• Urgent surgical intervention is required in type A dissections.

• The area of the aorta with the intimal tear usually is resected and replaced with a Dacron graft.

• The operative mortality rate is usually less than 10%, and serious complications are rare with ascending aortic dissections.

• The development of more impermeable grafts, such as woven Dacron, collagen-impregnated Hemashield (Meadox Medicals, Oakland, NJ), aortic grafts, and gel-coated Carbo-Seal Ascending Aortic Prothesis (Sulzer CarboMedics, Austin, TX) has greatly enhanced the surgical repair of thoracic aortic dissections.

• With the introduction of profound hypothermic circulatory arrest and retrograde cerebral perfusion, the morbidity and mortality rates associated with this highly invasive surgery have decreased.

• Dissections involving the arch are more complicated that those involving only the ascending aorta because the innominate, carotid, and subclavian vessels branch from the arch. Deep hypothermic arrest usually is required. If the arrest time is less than 45 minutes, the incidence of central nervous system complications is less than 10%.

• Aortic stent grafting is a challenging technique. It may prove feasible and has offered good results in a small series of patients. It may be a reasonable alternative in high-risk patients in the near future.

• Retrograde cerebral perfusion may increase the protection of the central nervous system during the arrest period.

• The mortality rate of aortic arch dissections is about 10-15%, with significant neurologic complications occurring in another 10%.

• The mortality rate is influenced by the patient's clinical condition.

• The definitive treatment for type B dissections is less clear.

• Uncomplicated distal dissections may be treated medically to control blood pressure.

• Distal dissections treated medically have the same or a lower mortality rate as those treated surgically.

• Surgery is reserved for distal dissections that are leaking, ruptured, or compromising blood flow to a vital organ.

• Acute distal dissections in patients with Marfan syndrome usually are treated surgically.

• Inability to control hypertension with medication is also an indication for surgery in those with a distal thoracic aortic dissection.

• Patients with a distal dissection are usually hypertensive, emphysematous, or older.

• Long-term medical therapy involves a beta-adrenergic blocker combined with other antihypertensive medications. Avoid antihypertensives (eg, hydralazine, minoxidil) that produce a hyperdynamic response that would increase dP/dt (ie, alter the duration of P or T waves).

• Survivors of surgical therapy also should receive beta-adrenergic blockers.

• A recent series of patients with type B dissections demonstrates that aggressive use of distal perfusion, CSF drainage, and hypothermia with circulatory arrest improves early mortality and long-term survival rates.

• Aortic stent grafting may play a role in how type B dissections are treated in the near future.

• Definitive treatment involves segmental resection of the dissection with interposition of a synthetic graft.

• When thoracic dissections are associated with aortic valvular disease, replace the defective valve.

• With combined reconstruction–valve replacement, the operative mortality rate is approximately 5% with a late mortality rate of less than 10%.

• Operative repair of the transverse aortic arch is technically difficult, with an operative mortality rate of 10% despite induction of hypothermic cardiocirculatory arrest.

• Repair of the descending aorta is associated with a higher incidence of paraplegia than repair of other types of dissections because of interruption of segmental blood supply to the spinal cord.

• The operative mortality rate is approximately 5%.

Consultations:

• Once a thoracic dissection is suspected, consult a thoracic surgeon.

• Because many patients with this disorder have concomitant medical illness, consult the patient's primary care physician to expedite preoperative preparation.

• Early consultation is encouraged when ordering further imaging studies if the patient requires rapid operative intervention.

• Consult a radiologist prior to obtaining aortography.

MEDICATION

Section 7 of 12

Initial therapeutic goals include elimination of pain and 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 dP/dt.

To prevent exacerbations of tachycardia and hypertension, treat patients with IV morphine sulfate. This reduces the force of cardiac contraction and the rate of rise of the aortic pressure (dP/dt). It then retards the propagation of the dissection and delays rupture.

Drug Category: Antihypertensives -- 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.

Drug Name	Esmolol (Brevibloc) -- Ultra–short-acting beta2-blocker, particularly useful in patients with labile arterial pressure, especially if surgery is planned, because it can be discontinued abruptly if necessary. Normally used in conjunction with nitroprusside. May be useful as a means to test beta-blocker safety and tolerance in patients with history of obstructive pulmonary disease who are at uncertain risk of bronchospasm from beta-blockade. Elimination half-life is 9 min.
Adult Dose	250-500 mcg/kg/min for 1 min as loading dose, followed by a 4-min maintenance infusion of 50 mcg/kg/min; repeat loading dose and follow with maintenance infusion using increments of 50 mcg/kg/min for 4 min; if therapeutic effects not observed in 5 min, repeat sequence up to 4 times prn As desired BP is approached, omit loading infusion and reduce incremental dose of maintenance infusion from 50 mcg/kg/min to 25 mcg/kg/min or lower; may increase interval between titration steps to 5-10 min if desired
Pediatric Dose	Not established
Contraindications	Documented hypersensitivity; uncompensated CHF; bradycardia; cardiogenic shock; AV conduction abnormalities
Interactions	Aluminum salts, barbiturates, NSAIDs, penicillins, calcium salts, cholestyramine, and rifampin may decrease bioavailability and plasma levels, possibly resulting in decreased pharmacologic effect; sparfloxacin, astemizole (recalled from US market), calcium channel blockers, quinidine, flecainide, and contraceptives may increase cardiotoxicity; digoxin, flecainide, acetaminophen, clonidine, epinephrine, nifedipine, prazosin, haloperidol, phenothiazines, and catecholamine-depleting agents may increase toxicity
Pregnancy	C - Safety for use during pregnancy has not been established.
Precautions	Beta-adrenergic blockers may mask signs and symptoms of acute hypoglycemia and clinical signs of hyperthyroidism; symptoms of hyperthyroidism, including thyroid storm, may worsen when medication is withdrawn abruptly; withdraw drug slowly and monitor patient closely

Drug Name	Labetalol (Normodyne, Trandate) -- Blocks alpha-, beta1-, and beta2-adrenergic receptor sites, decreasing BP.
Adult Dose	Initial dose: 20 mg (0.25 mg/kg for 80-kg patient) IV over 2 min; follow with 20-80 mg q10-15min until BP controlled Maintenance dose: 2 mg/min continuous IV infusion; titrate up to 5-20 mg/min; not to exceed a total dose of 300 mg
Pediatric Dose	Not established
Contraindications	Documented hypersensitivity; cardiogenic shock; AV block; uncompensated CHF; pulmonary edema; bradycardia; reactive airway disease
Interactions	Decreases effects of diuretics and increases toxicity of methotrexate, lithium, and salicylates; may diminish reflex tachycardia associated with nitroglycerin use without interfering with hypotensive effects; cimetidine may increase blood levels; glutethimide may decrease effects by inducing microsomal enzymes
Pregnancy	C - Safety for use during pregnancy has not been established.
Precautions	Caution in impaired hepatic function; discontinue therapy with signs of liver dysfunction; in elderly patients, lower response rate and higher incidence of toxicity may be observed

Drug Name	Propranolol (Inderal, Betachron E-R) -- Class II antiarrhythmic nonselective beta-adrenergic receptor blocker. Has membrane-stabilizing activity and decreases automaticity of contractions. Not suitable for emergency treatment of hypertension. Do not administer IV in hypertensive emergencies.
Adult Dose	40-80 mg PO bid initially; increase to usual range of 160-320 mg/d prn; up to 640 mg/d may be required
Pediatric Dose	0.5 mg/kg/d PO divided bid/qid; increase gradually q3-7d; usual dosage range is 2-4 mg/kg/d divided bid; not to exceed 16 mg/kg/d
Contraindications	Documented hypersensitivity; uncompensated CHF; bradycardia; cardiogenic shock; AV conduction abnormalities
Interactions	Aluminum salts, barbiturates, NSAIDs, penicillins, calcium salts, cholestyramine, and rifampin may decrease effects; calcium channel blockers, cimetidine, loop diuretics, and MAOIs may increase toxicity; may increase toxicity of hydralazine, haloperidol, benzodiazepines, and phenothiazines
Pregnancy	B - Usually safe but benefits must outweigh the risks.
Precautions	Beta-adrenergic blockade may decrease signs of acute hypoglycemia and hyperthyroidism; abrupt withdrawal may exacerbate symptoms of hyperthyroidism, including thyroid storm; withdraw drug slowly and monitor closely

Drug Name	Metoprolol (Lopressor) -- Selective beta1-adrenergic receptor blocker that decreases automaticity of contractions. During IV administration, carefully monitor BP, heart rate, and ECG. When considering conversion from IV to PO dosage forms, use ratio of 2.5 mg PO to 1 mg IV metoprolol.
Adult Dose	100 mg/d PO qd or divided bid/tid initially; increase at 1-wk intervals prn; not to exceed 450 mg/d prn
Pediatric Dose	Not established
Contraindications	Documented hypersensitivity; uncompensated CHF; cardiogenic shock; bradycardia; AV conduction abnormalities
Interactions	Aluminum salts, barbiturates, NSAIDs, penicillins, calcium salts, cholestyramine, and rifampin may decrease bioavailability and plasma levels, possibly resulting in decreased pharmacologic effects; sparfloxacin, phenothiazines, astemizole (recalled from US market), calcium channel blockers, quinidine, flecainide, and contraceptives may increase toxicity; may increase toxicity of digoxin, flecainide, clonidine, epinephrine, nifedipine, prazosin, verapamil, and lidocaine
Pregnancy	B - Usually safe but benefits must outweigh the risks.
Precautions	Beta-adrenergic blockade may reduce signs and symptoms of acute hypoglycemia and may decrease clinical signs of hyperthyroidism; abrupt withdrawal may exacerbate symptoms of hyperthyroidism, including thyroid storm; monitor patient closely and withdraw drug slowly; during IV administration, carefully monitor BP, heart rate, and ECG

Drug Name	Nitroprusside (Nitropress) -- Causes peripheral vasodilation by direct action on venous and arteriolar smooth muscle, thus reducing peripheral resistance. Commonly used IV because of rapid onset and short duration of action. Easily titratable to reach desired effect. Light sensitive; both bottle and tubing should be wrapped in aluminum foil. Prior to initiating nitroprusside, administer beta-blocker to counteract physiologic response of reflex tachycardia that occurs when nitroprusside used alone. This physiologic response increases shear forces against aortic wall, thus increasing dP/dt. Objective is to keep heart rate at 60-80 bpm.
Adult Dose	0.5-3 mcg/kg/min IV; rates > 4 mcg/kg/min may lead to cyanide toxicity
Pediatric Dose	Administer as in adults
Contraindications	Documented hypersensitivity; subaortic stenosis; idiopathic hypertrophic subaortic stenosis; atrial fibrillation or flutter
Interactions	None reported
Pregnancy	C - Safety for use during pregnancy has not been established.
Precautions	Caution in increased intracranial pressure, hepatic failure, severe renal impairment, and hypothyroidism; in renal or hepatic insufficiency, levels may increase and can cause cyanide toxicity; sodium nitroprusside has ability to lower BP and thus should be used only in patients with mean arterial pressures >70 mm Hg

Drug Category: Analgesics -- Pain control is essential to quality patient care. It ensures patient comfort, promotes pulmonary toilet, and prevent exacerbations of tachycardia and hypertension.

Drug Name	Morphine sulfate (Astramorph, Infumorph) -- DOC for narcotic analgesia because of reliable and predictable effects, safety profile, and ease of reversibility with naloxone. Similar to fentanyl, morphine sulfate easily titrated to desired level of pain control. If administered IV, may be dosed in a number of ways; commonly titrated until desired effect obtained.
Adult Dose	Initial dose: 0.1 mg/kg IV/IM/SC Maintenance dose: 5-20 mg/70 kg q4h IV/IM/SC
Pediatric Dose	0.1-0.2 mg/kg IV/IM/SC q2-4h prn
Contraindications	Documented hypersensitivity; hypotension; potentially compromised airway in which establishing rapid airway control would be difficult
Interactions	Phenothiazines may antagonize analgesic effects; tricyclic antidepressants, MAOIs, and other CNS depressants may potentiate adverse effects
Pregnancy	C - Safety for use during pregnancy has not been established.
Precautions	Avoid in hypotension, respiratory depression, nausea, emesis, constipation, and urinary retention; caution in atrial flutter and other supraventricular tachycardias; has vagolytic action and may increase ventricular response rate

FOLLOW-UP

Section 8 of 12

Further Inpatient Care:

• Patients with symptomatic dissection should undergo immediate repair, especially if it is leaking or expanding.

• Symptomatic patients require admission to a center experienced in cardiopulmonary bypass and operative care.

• Completely asymptomatic patients may have their repair performed electively but may require admission to expedite their evaluation or for preoperative stabilization of their condition.

• Patients with chest pain should undergo serial ECGs and CK determinations if AMI is indicated.

Further Outpatient Care:

• Follow-up examinations with radiologic studies are recommended at 3-month intervals for the first year and every 6 months for the next 2 years.

• After this, follow up annually.

Transfer:

• Symptomatic patients require care at a facility equipped to perform cardiopulmonary bypass with aortic and/or valvular repair.

• Contact the receiving physician as soon as possible to transfer patients before their condition deteriorates.

• Early airway management is indicated in the presence of hemoptysis or stridor.

• If coronary insufficiency is suspected, nitrates may be used, but therapy with thrombolytic agents and aspirin should be avoided.

• Patients should be monitored and accompanied by personnel capable of resuscitation.

• If a prolonged ground transport time is anticipated, consider air transport.

Prognosis:

• On the basis of his experience, Crawford has stated that "no patient should be considered cured of the disease."

• The 5-year survival rate is about 75% whether the patient is treated medically or surgically.

• The 10-year survival rate is between 40% and 69% for both surgically and medically treated dissections.

• In the pretreatment era, the 1-year survival rate was 5-10%.

• Reoperation may be necessary for late complications.

Patient Education:

• For excellent patient education resources, see eMedicine's Heart and Blood Vessels Center, Circulatory Problems Center, and Heart Center and the patient education article Chest Pain.

MISCELLANEOUS

Section 9 of 12

Medical/Legal Pitfalls:

• Failure to diagnose (especially in patients presenting with chest pain)

• Use of thrombolytics in the patient presenting with chest pain and ECG changes

• Multiple case reports describe patients who received thrombolytics and were found later to have a dissection. The diagnosis of aortic dissection can be subtle.

• The diagnosis depends on clinical suspicion, with contributory findings on history, physical examination, and imaging studies.

• Obtaining a chest radiograph prior to administering thrombolytics is considered prudent.

• Checking blood pressures in both arms and listening for carotid bruits also can help diagnose aortic dissection prior to administering thrombolytics. The entire clinical picture must be taken into account.

TEST QUESTIONS

Section 10 of 12

CME Question 1: ECG findings consistent with acute thoracic aortic dissection can include which of the following?

A: ST segment elevation
B: ST segment depression
C: No change
D: All of the above
E: None of the above

The correct answer is D: All of these ECG finding may be present in the patient with a dissecting thoracic aorta. In one study, up to 8% of patients with type A dissection had ST segment elevation.

CME Question 2: Which of the following is the test of choice for a patient in unstable condition in whom acute thoracic aortic dissection is suspected?

A: MRI
B: Angiography
C: Spiral CT scanning
D: Transesophageal echocardiography (TEE)
E: None of the above

The correct answer is D: In the unstable patient, TEE is the best choice because it can be performed at bedside in the ED. Many studies have shown the sensitivity and specificity to be 97-100%. Each of the other choices requires transporting the patient out of the ED.

Pearl Question 1 (T/F): A widened mediastinum on chest radiography is one finding consistent with thoracic aortic dissection.

The correct answer is True: A widened mediastinum greater than 8 cm, left apical cap, tracheal deviation, depression of left main stem bronchus, esophageal deviation, ring sign (ie, extension of the aorta more than 5 mm past the calcified intima), blunting of the aortic knob, and loss of the paratracheal stripe are all possible findings on the chest radiograph of a patient with a thoracic aortic dissection.

Pearl Question 2 (T/F): Two methods are used for classification of thoracic aortic dissections.

The correct answer is True: The more commonly used system is the Stanford classification, which is based upon involvement of the ascending aorta. The Stanford classification divides dissections into 2 types, type A and type B. Type A dissections involve the ascending aorta (DeBakey type I and II), and type B do not (DeBakey type III). Usually, type A dissections require surgery, while type B dissections require medical management.

The DeBakey classification divides the dissections into 3 types. Type I dissections involve the ascending aorta, aortic arch, and descending aorta. Type II dissections are confined to the ascending aorta. Type III dissections are confined to the descending aorta distal to the left subclavian artery. Type IIIa refers to dissections that originate distal to the left subclavian artery but extend both proximally and distally, the majority of which are above the diaphragm. Type IIIb refers to dissections that originate distal to the left subclavian artery, extend only distally, and can extend below the diaphragm.

Pearl Question 3 (T/F): Thoracic dissections are clinically the same as thoracic aneurysms and thoracic transections.

The correct answer is False: Thoracic dissections are a completely different and distinct disease, separate from thoracic aneurysms and traumatic transections. Thoracic aneurysms usually do not dissect.

Pearl Question 4 (T/F): A herniated thoracic disk is the suspected diagnosis in the patient with Marfan syndrome who has interscapular back pain described as ripping and tearing.

The correct answer is False: Thoracic aortic dissection is the suspected diagnosis.

PICTURES

Section 11 of 12

Caption: Picture 1. Chest radiograph of a patient with aortic dissection. Image courtesy of Dr. K. London, University of California at Davis Medical Center.
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Caption: Picture 2. Chest radiograph of a patient with aortic dissection presenting with hemothorax.
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Caption: Picture 3. Chest radiograph demonstrating widened mediastinum in a patient with aortic dissection.
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Caption: Picture 4. Angiogram demonstrating dissection of the aorta (same patient as in Image 3).
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Caption: Picture 5. Electrocardiogram of a patient presenting to the ED with chest pain; this patient was diagnosed with aortic dissection.
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Caption: Picture 6. Patient with an ascending type A aortic dissection showing the intimal flap. Image courtesy of Kaiser-Permanente.
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Caption: Picture 7. Patient with an ascending type A aortic dissection showing the intimal flap (same patient as in Images 6-9). Image courtesy of Kaiser-Permanente.
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Caption: Picture 8. Patient with an ascending type A aortic dissection showing the intimal flap (same patient as in Images 6-9). Image courtesy of Kaiser-Permanente.
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Caption: Picture 9. Patient with an ascending type A aortic dissection showing the intimal flap (same patient as in Images 6-9). Image courtesy of Kaiser-Permanente.
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Caption: Picture 10. Patient with a type A aortic dissection involving the ascending and descending aorta. Image courtesy of Kaiser-Permanente.
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Caption: Picture 11. Patient with a type A aortic dissection involving the ascending and descending aorta (same patient as in Images 10-13). Image courtesy of Kaiser-Permanente.
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Caption: Picture 12. Patient with a type A aortic dissection involving the ascending and descending aorta (same patient as in Images 10-13). Image courtesy of Kaiser-Permanente.
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Caption: Picture 13. Patient with a type A aortic dissection involving the ascending and descending aorta (same patient as in Images 10-13). Image courtesy of Kaiser-Permanente.
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Caption: Picture 14. Patient showing a type B aortic dissection with extravasation of blood into the pleural cavity. Image courtesy of Kaiser-Permanente.
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Caption: Picture 15. Patient showing a type B aortic dissection with extravasation of blood into the pleural cavity (same patient as in Images 14-17). Image courtesy of Kaiser-Permanente.
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Caption: Picture 16. Patient showing a type B aortic dissection with extravasation of blood into the pleural cavity (same patient as in Images 14-17). Image courtesy of Kaiser-Permanente.
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Caption: Picture 17. Patient showing a type B aortic dissection with extravasation of blood into the pleural cavity (same patient as in Images 14-17). Image courtesy of Kaiser-Permanente.
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BIBLIOGRAPHY

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