Definition, Classification

The emergency physician should not use the antiquated term “dissecting aortic aneurysm,” as more than 80% of dissections have no pre-existing aneurysm. Furthermore, the pathophysiology and resultant treatment of AAD is fundamentally different from that of aortic aneurysms.²

The Stanford system of classification for AAD is the most widely used. Stanford Type A dissections represent 62% of AADs, according to the International Registry of Acute Aortic Dissection (IRAD), and involve the ascending aorta. They are usually managed with emergent surgery. Stanford Type B dissections have lower mortality, do not involve the ascending aorta, and are often managed medically.¹⁰

Signs and Symptoms

The IRAD enrolls patients from 12 large referral centers in six countries with confirmed nontraumatic AAD and collects data regarding demographics, history, physical findings, management, imaging results, and outcomes.¹⁰ The results (see chart) are compiled from two analyses of IRAD data.^9,10

The classic history of pain in AAD is excruciating, abrupt, and most severe at onset. Physical exam should include pulses in bilateral upper and lower extremities, auscultation for diastolic murmur, and assessment for gross motor and sensory deficitis.⁷ In one prospective study with 51% prevalence of AAD, inter-arm systolic blood pressure difference greater than 20 mm Hg was an independent predictor of AAD, with a positive predictive value of 98%.³

Several studies have examined the accuracy of history and physical in detecting AAD. ^3,4,10-23 Most, however, are retrospective and lack a control group. Therefore, inclusion bias and a lack of independence between the confirmatory test and initial history overestimate sensitivity, and no study can accurately assess specificity.⁷ The emergency physician should not rely on any individual sign or symptom to rule out AAD. In four studies that included patients based on an overall clinical picture suggestive of AAD after patient history and physical exam, chest x-ray (CXR), and laboratory studies, the pooled incidence of AAD was 52%, arguing for the role of combinations of signs.^3,11,23,24 None of these studies outlined an explicit algorithm for identifying such patients. A lack of classic pain features (severe, sudden-onset, tearing), inter-arm blood pressure/pulse differential, and wide mediastinum had an LR of 0.1, but decreased incidence only to 4%.³ Therefore, available evidence suggests that no combination of patient history, physical exam, CXR, or laboratory findings can obviate the need for advanced imaging in patients suspected of having AAD.

Imaging in AAD

Sixteen percent of patients with aortic dissection have a normal CXR.10 Even in patients with an abnormal CXR, there are no validated standards for radiographic findings in AAD, leading to low intra-observer and inter-observer agreement.⁷ Every patient with suspected AAD should undergo advanced imaging to confirm the diagnosis, establish Stanford classification, and detect valvular or branch involvement.^2,5 The European Society of Cardiology guidelines recommend CT aortography or transesophageal echocardiogram (TEE) for diagnosis of AAD.⁵