Aortic dissection (AD) is a lethal, treatable disruption of the aortic vessel wall. It often presents without classic features, mimicking symptoms of other conditions, and diagnosis is often delayed. Established high-risk markers of AD should be sought and indicate advanced aortic imaging with CT, MRI, or TEE. Treatment is immediate surgical evaluation, aggressive symptom relief, and reduction of the force of blood against the aortic wall by control of heart rate, followed by blood pressure.
Key points
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Aortic dissection is an uncommon disease that often presents with varied and atypical findings suggestive of more frequently encountered conditions; therefore, it poses an exceptional diagnostic challenge to emergency providers.
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Mortality associated with aortic dissection is significant at presentation and advances with every hour the lesion is left untreated.
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Although almost all patients who have symptoms possibly caused by aortic dissection will not have aortic dissection, key features of the disease, including risk factors, pain characteristics, physical examination findings, and routine ancillary studies, allow clinicians to develop a rational approach to diagnostic testing.
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When the diagnosis is sufficiently likely to indicate definitive testing, computed tomography angiography is the advanced imaging test of choice in most centers, but transesophageal echocardiography and MRI may be appropriate alternatives in certain circumstances.
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Patients with diagnosed or strongly suspected aortic dissection require expeditious surgical evaluation, aggressive analgesia and anxiolysis, and treatment with rapid-acting, titratable agents to first lower heart rate, and then blood pressure, to specific targets.
Introduction
Aortic dissection (AD) is among the most immediately lethal diseases in medicine, with a mortality of 1% per hour, and has effective temporizing medical therapies and a surgical cure. AD is, therefore, among the disorders of greatest interest to emergency physicians, yet is not diagnosed on its initial presentation in up to half of cases. In fact, 1 expert asserts that “difficulty in diagnosis, delayed diagnosis or failure to diagnose are so common as to approach the norm for this disease, even in the best hands…” This article explains why AD poses a diagnostic dilemma, proposes a strategy for its rational evaluation, and describes the principles of treatment.
Introduction
Aortic dissection (AD) is among the most immediately lethal diseases in medicine, with a mortality of 1% per hour, and has effective temporizing medical therapies and a surgical cure. AD is, therefore, among the disorders of greatest interest to emergency physicians, yet is not diagnosed on its initial presentation in up to half of cases. In fact, 1 expert asserts that “difficulty in diagnosis, delayed diagnosis or failure to diagnose are so common as to approach the norm for this disease, even in the best hands…” This article explains why AD poses a diagnostic dilemma, proposes a strategy for its rational evaluation, and describes the principles of treatment.
Pathophysiology
AD occurs when the innermost layer of the aortic vessel wall is torn, creating a false lumen that transmits a longitudinal column of blood. It is sometimes referred to as a dissecting aortic aneurysm; however, this term is discouraged because it is both inaccurate and conflates AD with aortic aneurysm, a distinct clinical entity. AD is thought to result from the hydrostatic pressure accumulated as blood is pumped through the aorta, as well as movement of the aorta itself, with every cardiac cycle. Histologically, AD is associated with characteristic changes in the vessel wall known as medial degeneration. The former term, cystic medial necrosis, has fallen out of favor because the observed lesion demonstrates neither cysts nor necrosis.
Conditions that increase the pressure exerted by blood on the vessel wall predispose patients to AD. These include hypertension, pregnancy, stimulant use (eg, cocaine), weight-lifting, and pheochromocytoma. AD is more likely in conditions that weaken the vessel and accelerate medial degeneration, such as large-vessel vasculitides and congenital connective tissue disorders, including Marfan, Loeys-Dietz, Ehlers-Danlos, and Turner syndromes. Finally, AD may be caused by lesions of the aortic valve itself, such as bicuspid aortic valve, aortic valve instrumentation or aortic surgery, and syphilitic aortitis.
The Stanford classification designates type A dissections as lesions involving the ascending aorta, whereas type B dissections are confined to the descending aorta. Type A dissections are more common and much more dangerous, which drives differences in the therapeutic approach. Variants of AD include aortic intramural hemorrhage, which is a hematoma completely contained within the vessel wall, and penetrating aortic ulcer, which is a disruption in the vessel wall that usually leads not to dissection but to aneurysm. These lesions are both treated similarly to AD.
AD causes morbidity and mortality by several mechanisms. Type A dissections can progress proximally to cause pericardial effusion with tamponade, as well as acute aortic valve insufficiency. Both types of dissections can breach the outer adventitial layer of the vessel, leading to free rupture and exsanguination into the chest or abdomen. Most sequelae of AD, however, result from the false lumen extending across ostia of branch arteries, leading to acute ischemia of potentially any organ in the body.
Clinical features and epidemiology
AD is an uncommon disease, with prevalence estimates ranging from 3.5 to 6.0 per 100,000 patient-years in the general population. Untreated, AD carries a devastating mortality of 40% on presentation and an additional 1% rate of death per hour, to a 1-year mortality of 90%. In a center where postmortem CT is routinely performed on patients with out-of-hospital cardiac arrest of uncertain cause, AD was determined to be the cause in 7% of cases.
Approximately 1 in 10,000 emergency department (ED) patients will have AD, a number so small that emergency providers may only see several cases in their career. Only one-quarter of patients with AD present with a combination of classic features (pain of sudden onset or ripping or tearing quality, blood pressure differential, and widened mediastinum on chest xray [CXR]); 1 in 25 patients diagnosed with AD has none of the classic features. Furthermore, AD can cause myriad symptoms localizing to any organ system or body part, and each of these symptoms can be explained by more common conditions, often by more common dangerous conditions that quite reasonably establish the focus of care but ultimately turn out to be distractors.
Emergency clinicians are thus confronted with innumerable patients whose symptoms could be caused by AD but almost certainly are not. AD could, therefore, be said to represent not just a needle in a haystack but a needle in a haystack that is disguised as a blade of hay. Consequently, physicians evaluating patients whose symptoms may be caused by AD must understand the clinically relevant risk factors and clinical manifestations of this condition and develop a risk stratification strategy that identifies as many patients with the disease as possible without overusing advanced imaging studies that subject patients to important harms.
Despite the rarity of the disease, good data are available on clinical features of AD, owing to the International Registry of Acute Aortic Dissection (IRAD) and a variety of other longitudinal studies. Pain is more likely to be abrupt and most severe at onset than to be tearing or ripping. Pain location is a reflection of the site of the lesion and includes chest pain radiating to the neck, jaw, or classically, the back; thoracic or lumbar back pain; and abdominal pain. Although chest pain is the most common presenting symptom, 1 study found that of ED subjects diagnosed with AD, more than 40% did not have chest pain on presentation. Another study found 1 subject diagnosed with AD for every 980 subjects presenting with atraumatic chest pain. Seventeen percent of subjects in 1 series had painless AD. These subjects presented predominantly with transient or persistent disturbance of consciousness or focal neurologic deficits.
Constitutional symptoms are often marked and include nausea, diaphoresis, and (classically) extreme apprehension with a (justified) sense of impending doom. Patients with AD present with focal neurologic symptoms in 17% and syncope in 9% of cases. Though scenarios classically associated with AD, such as migratory pain, chest pain with neurologic deficits, and chest pain of sudden onset or with pulse deficit, occur in only a minority of cases, their presence strongly suggests the disease. It is commonly believed that patients with AD must be very ill or distressed with abnormal vitals, but ambulatory mode of arrival is an important risk factor for missing the disease at initial presentation.
Many patients with AD will present with acute on chronic hypertension and AD is a cardinal hypertensive emergency. Hypotension is ominous in the setting of AD because it often indicates either proximal extension with cardiac tamponade or free or contained rupture. Pseudohypotension, peripheral hypotension with central normotension, may be caused by dissection across the subclavian arteries. Subclavian or iliac artery embarrassment may also lead to a pulse deficit or blood pressure differential across limbs; this classic finding is present in only 20% to 30% of cases; its absence should not be reassuring. The murmur of aortic regurgitation, or signs of cardiac tamponade, may be present. If the dissection involves the left or (more commonly) right coronary artery, acute myocardial infarction (AMI) and its attendant signs and symptoms can result. A variety of neurologic deficits, including weakness or even coma, may be caused by AD, depending on the cerebral or spinal branch arteries affected. Distal AD can cause ischemia to either kidney, lower extremity ischemia, mesenteric ischemia, and resulting abdominal pain, back pain, or diarrhea.
Diagnosis
Routine laboratory testing is not helpful for ruling in or ruling out AD. Troponin positivity is much more likely to represent primary cardiac pathology condition but is common in AD. Therefore, when clinical features suggest dissection, a positive troponin should not dissuade the practitioner from ruling out the diagnosis of AD.
The use of serum quantitative D-dimer testing has been proposed as a strategy to rule out AD because blood in the false lumen activates the clotting cascade, generating fibrin degradation products detected by modern D-dimer assays with high sensitivity. Unfortunately, further work has demonstrated an unacceptably high false-negative rate, and the ACEP clinical policy recommends that clinicians “not rely on D-dimer alone to exclude the diagnosis of aortic dissection.” In 1 study, D-dimer was falsely negative in 9 of 113 confirmed AD cases, perhaps due to an AD variant in which the thrombosed lumen does not communicate with circulating blood, isolating the clot from detection by serum testing. Furthermore, although a decision analysis of D-dimer and computed tomography (CT) angiography testing thresholds has been performed, there is no evidence that D-dimer testing can be incorporated into a larger risk stratification strategy that would allow clinicians to sensitively exclude AD without greatly expanding the number of patients who receive advanced imaging studies. Given the experience with D-dimer testing to rule out pulmonary embolism, which has increased the number of advanced imaging studies ordered without increasing the number of pulmonary embolism diagnoses, a comprehensive approach that accounts for false negatives and false positives should be validated before D-dimer testing is used routinely in the diagnosis of AD.
Plain CXR is indicated in patients with chest pain of uncertain cause and whenever AD is considered. The CXR is most useful when it provides an alternative explanation for the patient’s symptoms. A variety of CXR abnormalities are associated with AD ( Box 1 ), the most important being mediastinal widening, which is present in more than half of cases but is nonspecific. The absence of suggestive CXR findings makes AD less likely. However, 10% to 20% of patients with AD have a normal CXR; therefore, a negative study cannot exclude the disease and should not play a decisive role in the decision to pursue advanced imaging.
Mediastinal widening
Disruption of normally distinct contour of aortic knob
Calcium sign: separation of intimal calcification from the vessel wall greater than 5 mm
Double-density appearance within aorta
Tracheal deviation to the right
Deviation of nasogastric tube to the right
The electrocardiogram in AD is used to evaluate the differential diagnosis and usually demonstrates nonspecific findings but may also indicate acute myocardial ischemia. This presents a clinical challenge because not only do the symptoms of AD overlap with the symptoms of myocardial ischemia, AD can cause myocardial ischemia when the dissection flap involves the ostium of the left or right coronary artery. When myocardial infarction complicates AD, treatment is directed at AD. Furthermore, usual therapies for AMI may directly worsen outcomes of patients with AD. The clinician caring for a patient whose symptoms may be caused by either diagnosis must, therefore, have a strategy for managing their possible convergence (see later discussion).
Transthoracic echocardiography (TTE) poorly visualizes much of the aorta and is limited by patient, operator, and machine characteristics. AD cannot be excluded by TTE. However, point-of-care ultrasound by emergency physicians is recommended for all patients with suspected AD and should be considered for all patients with chest or abdominal pain of uncertain cause. In addition to evaluating alternative diagnoses, an intimal flap at either the aortic root or descending aorta may be distinguished by TTE, especially when augmented by suprasternal notch views, and is diagnostic. TTE also reliably identifies complications of AD such as pericardial effusion and aortic regurgitation.
Transesophageal echocardiography (TEE) is very accurate in both ruling in and ruling out AD and can be performed in a critical care area as resuscitative efforts are ongoing, which is a distinct advantage compared with CT and MRI, the 2 other definitive imaging modalities. However, TEE is uncommonly performed by emergency clinicians and not widely available on a consultative basis in many EDs. Invasive echocardiography may play a more prominent role in the emergency evaluation of AD as the technique sees broader application by emergency providers.
Intravenous (IV) contrast-enhanced CT reliably confirms and excludes AD and may elucidate alternative diagnoses, including pulmonary embolism and obstructive coronary artery disease. Contemporary CT scanning is rapid and widely available. Therefore, CT is the most common definitive imaging study used in patients with suspected AD. Beyond the concerns raised by moving a potentially critically ill patient to the radiology suite, drawbacks of CT include the risks of IV contrast and ionizing radiation, as well several diagnostic pitfalls ( Box 2 ). Though CT angiography is an excellent test for AD, these harms are underappreciated by both physicians and patients.
Radiation or oncogenesis
Contrast harms (kidney injury, allergy, extravasation, volume overload)
False negatives, false positives
Incidental findings (may lead to further testing and therapies)
Overdiagnosis (true positives that would not have harmed patient)
Resource utilization (time, monetary cost, opportunity cost)
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