Aortic dissection: Prompt diagnosis and emergency treatment are critical
ABSTRACTDiagnosing aortic dissection requires a high index of suspicion, as it may mimic other more common conditions that cause chest pain. Prompt diagnosis is key, as it requires emergency evaluation and treatment for optimal chances of survival. This paper reviews key clinical features as well as laboratory and imaging tests.
KEY POINTS
- Aortic surgery is the treatment of choice for dissection of the ascending aorta, whereas dissection of the descending aorta is initially managed medically.
- Look for an underlying genetic predisposition to aortic disease and, in many instances, screen first-degree relatives for aortic disease.
- Long-term management requires serial imaging of the aorta, blood pressure control, and, for many, future aortic procedures.
- Measuring the D-dimer levels may help in decision-making for appropriate imaging in patients presenting with chest pain, as an elevated level raises the suspicion of dissection. However, more study of this and other biomarkers is needed.
- Advances in molecular genetics and the biology of the aortic wall promise to improve the diagnosis and prognosis of aortic disease.
PHYSICAL FINDINGS CAN VARY WIDELY
Findings on physical examination in acute aortic dissection vary widely depending on underlying conditions and on the specific complications of the dissection.
Although the classic presentation is acute, severe pain in the chest or back in a severely hypertensive patient with aortic regurgitation and pulse deficits, most patients do not have all these characteristics.4 Most patients with type B dissection are hypertensive on presentation, but many with type A dissection present with normal blood pressure or hypotension.1 Pulse deficits (unequal or absent pulses) are reported in 10% to 30% of acute dissections and may be intermittent as the dynamic movement of the dissection flap interferes with branch vessel perfusion.1–3
- Aortic leaflet prolapse or distortion of the leaflet alignment
- Malcoaptation of the aortic leaflets from dilation of the aortic root and annulus
- Prolapse of the intimal flap across the aortic valve, interfering with valve function
- Preexisting aortic regurgitation from underlying aortic root aneurysm or primary aortic valve disease (such as a bicuspid aortic valve).
Neurologic manifestations are most common in dissection of the ascending aorta and are particularly important to recognize, as they may dominate the clinical presentation and lead to delay in the diagnosis of dissection.2,3 Neurologic syndromes include:
- Persistent or transient ischemic stroke
- Spinal cord ischemia
- Ischemic neuropathy
- Hypoxic encephalopathy.
These manifestations are related to malperfusion to branches supplying the brain, spinal cord, or peripheral nerves.9
Syncope is relatively common in aortic dissection and may be related to acute hypotension caused by cardiac tamponade or aortic rupture, cerebral vessel obstruction, or activation of cerebral baroreceptors.2,9 It is important to consider aortic dissection in the differential diagnosis in cases of unexplained syncope.3
Aortic dissections may extend into the abdominal aorta, leading to vascular complications involving one or more branch vessels.10 The renal artery is involved in at least 5% to 10% of cases and may lead to renal ischemia, infarction, renal insufficiency, or refractory hypertension.2Mesenteric ischemia or infarction occurs in about 5% of dissections, may be difficult to diagnose, and is particularly dangerous.2,8 Aortic dissection may extend into the iliac arteries and may cause acute lower extremity ischemia.
Acute myocardial infarction due to involvement of the dissection flap causing malperfusion of a coronary artery occurs in 1% to 7% of acute type A aortic dissections.1–3 The right coronary artery (Figure 2) is most commonly involved, leading to acute inferior myocardial infarction. Acute myocardial ischemia and infarction in the setting of dissection may lead to a delay in the diagnosis of dissection and to bleeding complications from antiplatelet and anticoagulant drugs given to treat the acute coronary syndrome.
Cardiac tamponade, occurring in about 10% of acute type A dissections, portends a higher risk of death.2,3
Additional clinical features of aortic dissection include a left-sided pleural effusion, usually related to an inflammatory response. An acute hemothorax may occur from rupture or leaking of a descending aortic dissection.
FINDINGS ON RADIOGRAPHY AND ELECTROCARDIOGRAPHY
Electrocardiography usually has normal or nonspecific findings, unless acute myocardial infarction complicates the dissection.
D-DIMER LEVELS
Biomarkers for the diagnosis of acute aortic dissection are of great interest.
D-dimer levels rise in acute aortic dissection as they do in pulmonary embolism.11 A D-dimer level greater than 1,600 ng/mL within the first 6 hours has a very high positive likelihood ratio for dissection, so this test may be useful in identifying patients with a high probability for dissection. In the first 24 hours after symptom onset, a D-dimer level of less than 500 ng/mL has a negative predictive value of 95%. Thus, elevations in D-dimer may help decide which imaging to perform in a patient presenting with chest pain or suspicion of dissection.11
However, D-dimer levels may not be elevated in dissection variants, such as aortic intramural hematoma or penetrating aortic ulcer. Additionally, once 24 hours have elapsed since the dissection started, D-dimer levels may no longer be elevated. The current ACC/AHA guidelines on thoracic aortic disease concluded that the D-dimer level cannot be used to rule out aortic dissection in high-risk individuals.3
Additional studies may clarify the appropriate role of the D-dimer assay in diagnosing aortic dissection.
