Investigations

No single investigation is entirely suitable.

• ECG & chest x-ray -
  • although chest radiography and electrocardiography are carried out in the emergency care settings in patients with chest pain, these tests cannot establish or exclude aortic dissection:
  • ECG
    • is useful to exclude myocardial infarction (infarction may also be excluded by the absence of changes in cardiac enzymes)
    • in about 20% of type A dissections, ischemic changes on the ECG may be present due to extension of the dissection into a coronary ostium (2)
  • chest x-ray -
    • abnormalities in >80% of cases - the most significant being abnormal aortic contour or widening of the aortic silhouette
    • normal x-ray does not exclude the presence of dissection (1).
• D-dimer levels
  • are elevated in acute aortic dissection and levels below 500 ng/ml within the first 24 hours of symptom onset can exclude acute dissection (negative likelihood ratio of 0.07)
  • further studies are necessary to determine the role of D-dimer assays in acute aortic syndromes (1,2)
• echocardiography
  • is valuable for making rapid diagnosis at the bedside.
  • a meta-analysis of cohort studies found that transoesophageal echocardiography has a high degree of sensitivity and specificity (1)
  • dissection is confirmed by the demonstration of two channels with differential flow between them, and an intimal flap
  • abnormal doppler flow patterns in the left ventricular outflow tract during diastole or diastolic fluttering of the anterior mitral valve leaflet support the diagnosis.
• CT
  • contrast CT is the most commonly used modality
  • may provide information about the location, size and the extent of the disease and demonstrate the intimal flap
  • not appropriate in haemodynamically unstable patients
  • European Society of Cardiology recommends Multidetector computed tomography angiography as the first line of investigation in suspected acute dissection
• MRI
  • may be used in a stable patient
  • useful for long term surveillance of treated dissection and for the assessment of stable patients presenting with chronic dissection
• retrograde aortography - historically considered as the gold standard for diagnosis, nowadays rarely performed (1,2)

Note:

• majority of patients require more than one non-invasive imaging test
• a cross sectional study (carried out in in 464 patients) reported the following as the initial investigation:
  • CT angigrapgy - in 61% of cases
  • echocardiography - in 33% cases
  • aortography - in 4% cases
  • magnetic resonance angiography - in 2% cases (1)

.Reference:

• (1) Thrumurthy SG et al. The diagnosis and management of aortic dissection. BMJ. 2011;344:d8290.
• (2) Braverman AC. Acute aortic dissection: clinician update. Circulation. 2010;122(2):184-8.