Workup
Laboratory Studies
- Aortic dissection is usually diagnosed using imaging techniques before the result of blood work is interpreted.
- Leukocytosis may be present, which usually represents a stress state.
- BUN and creatinine levels are elevated, possibly indicating involvement of the renal arteries or prerenal azotemia resulting from blood loss or associated dehydration (mainly when the BUN-to-creatinine ratio is >20).
- 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.
- Acute anemic states with a decrease in hemoglobin and hematocrit values are ominous findings suggesting that the dissection is leaking or has ruptured.
- Hematuria, oliguria, and even anuria (<50 mL/d) may occur if the dissection involves the renal arteries.
- 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.
- Levels are highest in the first 3 hours.
- Cutoff of 2.5 has sensitivity, specificity, and accuracy of 91%, 98%, and 96% compared with normal and 88% compared with acute myocardial infarction.
- This assay has greater sensitivity and specificity than transthoracic echocardiography (TTE), CT scanning, and aortography but less sensitivity and specificity than transesophageal echocardiography (TEE), MRI, and helical CT scanning.
- The lactate dehydrogenase level is elevated because of hemolysis in the false lumen.
- D-dimer elevation may is an indicator of dissection
Imaging Studies
- Aortic dissection can be diagnosed with imaging techniques based on whether or not the patient is hemodynamically stable.
- Chest radiography is the initial imaging technique and may or may not reveal any abnormality.
- An absence of mediastinal widening is observed in 40% of patients. With type A, an abnormal aortic contour is observed in a minority of patients. An absence of both is observed in 20% of patients.
- Other chest radiograph findings include deviation of the trachea to the right or pleural effusion. No abnormality is observed in 12% of patients.
- CT scanning with contrast is used more frequently in ED settings.
- CT scanning 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.
- Emergency CT angiography with 3-dimensional reconstruction is rapidly becoming the diagnostic test of choice. It provides detailed anatomical definition of the dissection as well as information on plaque formation. Limited availability of 3-D reconstruction in smaller centers may be a limiting factor in the use of this diagnostic modality.9
- Pleural effusion can be seen on CT scan.
Aortic dissection. Left subsegmental atelectasis and left plural effusion. Flap at lower right of image.
Aortic dissection. Significant left plural effusion.
Aortic dissection. Intimal flap and left plural effusion.
- Echocardiography is an important imaging modality for detecting aortic dissection.10,11
- TEE is preferable to TTE.11 TEE is as accurate as CT scanning and MRI in terms of sensitivity and specificity.
- TEE has more advantages than other imaging techniques because it is portable and can be used in hemodynamically unstable patients; however, obesity, a narrow intercostal space, pulmonary emphysema, and mechanical ventilation decrease the accuracy of TEE.
- In one study, detection of intimal flaps occurred in 100% of type A patients (in 18 of 18 with type A using biplanar views, in 10 of 39 with type B using biplanar views). 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 2 intimal entries were detected in 18 patients. Using biplanar views, the intimal entries in 2 patients with type B entries were not visualized by TEE because the dissection was in the aortic arch and was obscured by the trachea and the left main stem bronchus. The intimal entries in 2 patients with type B entries were in the abdominal aorta.
- 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.
- False positive results with TEE ranges about 10%10,11
- MRI is as accurate as CT scanning in the diagnosis of aortic dissection. Its use is limited because it is not portable.12
- MRI may benefit patients who have adverse reactions to the use of intravenous contrast agents; the use of MRI with gadolinium is an alternative.
- MRI and TEE have 100% sensitivity, and TTE has 82% sensitivity. MRI has 100% specificity and TEE has 68% specificity.
- In patients with type A, MRI is 100% sensitive and specific while TEE is 100% sensitive and 78% specific. In patients with type B, MRI is 100% sensitive and specific, while TEE is 90% sensitive and 97% specific. With regard to epiphenomena, visualization of the site and spatial extent of the intimal flap with TEE is 78%, 94%, and 92% specific in the ascending, arch, and descending aorta, respectively. MRI and TEE are equal in the detection of the site of entry of the aortic dissection. TEE is 75% sensitive and MRI is 100% sensitive in the detection and localization of intraluminal thrombi.13
- Chest radiography is the initial imaging technique and may or may not reveal any abnormality.
Other Tests
- Twelve-lead ECG most frequently demonstrates a nonspecific abnormality and normal results (approximately 31% of patients). One study reported normal findings in 63 (90%) of 70 patients.
Diagnostic Procedures
- Aortography is the criterion standard but is difficult to perform in patients with hemorrhage, shock, and/or cardiac tamponade. Aortography is not performed frequently in current practice because of risks associated with invasiveness and adverse reactions to intravenous contrast agents.
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References
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Kaya A, Heijmen RH, Rousseau H, Nienaber CA, Ehrlich M, Amabile P, et al. Emergency treatment of the thoracic aorta: results in 113 consecutive acute patients (the Talent Thoracic Retrospective Registry). Eur J Cardiothorac Surg. Dec 22 2008;[Medline].
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Keywords
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