Study objectives: To compare diagnostic strategies for the emergency assessment of patients with suspected acute thoracic aortic dissection and to measure the effect of delays related to the availability of these tests on the selection of the most appropriate one.
Methods: We carried out a decision analysis representing the risks of performing one or two sequential tests, the tests' accuracy, the risks and benefits of treatment, and the time-dependent mortality rate in untreated patients with dissection (1%/hour). Data were drawn from a Medline search. Our subjects were patients who presented to the emergency department with chest pain in whom acute thoracic aortic dissection was suspected. For different clinical probabilities of aortic dissection, we compared the risks and benefits of testing using the following procedures (alone and in combinations): aortography, computed tomography (CT), magnetic resonance imaging (MRI), and both transesophageal (TEE) and transthoracic echocardiography (TTE). We then measured the effect of delays in these tests on the selection of the appropriate procedure. The outcome studied was 30-day survival.
Results: We determined that the "threshold" clinical probability of aortic dissection above which the benefits of testing outweigh its risks is low. It ranges from 2% with the most reliable procedure (MRI) to 9% with the least (TTE). At low probability of dissection (< 15%), the accuracy of all tests except TTE is sufficient to rule out dissection. Delays have negligible effect on these results. When the likelihood of dissection is higher, the preferred option is to order a second diagnostic test if the results of the first are negative. The threshold probabilities above which to order a second test range from 15% (CT, then aortography) to 35% (MRI, then aortography). Excessive delays may affect the selection of tests when the likelihood of dissection is high (eg, 50%). Thus, although it is less accurate, a CT scan obtained within 2 hours or a TEE obtained within 6 hours of presentation to the ED yields a higher survival rate than an MRI obtained within 9 hours. Similarly, the benefits of ordering a second test, if the result of the first are negative, outweigh the risks only if the delay in obtaining the test does not exceed 10 hours.
Conclusion: All patients in whom aortic dissection is suspected, even if the index of suspicion is very low, should undergo one of the available diagnostic procedures (except TTE). A patient with a moderate to high probability of disease should undergo a second investigation if the findings of the first are negative. When the probability of dissection is high, the physician must consider delays in obtaining specific diagnostic tests and order those that will be the most quickly available.