Investigations

1st investigations to order

ECG

Test
Result
Test

Always perform an ECG in any patient with acute chest pain to rule out ST-elevation myocardial infarction.[2]​​[6][18]​​​ See ST-elevation myocardial infarction.

However, be aware that myocardial ischaemia or infarction may be present in 10% to 15% of patients with aortic dissection, which can mask the diagnosis of dissection.[2] This may be due to:

  • Aortic false lumen expansion causing compression or obliteration of the coronary ostia

  • Propagation of the dissection into the coronary arteries.

Result

ST segment depression may occur with acute dissection; ST elevation occurs rarely

echocardiography

Test
Result
Test

Organise transthoracic echocardiography (TTE) for all patients with suspected acute aortic dissection, depending on local availability and expertise.[2][18] If the patient is haemodynamically unstable, get help from a senior colleague and organise immediate TTE.[2][32]

  • In the UK, TTE may not be available in some emergency departments and may give poor quality images.[18] In practice, organise CT if TTE is unavailable or inconclusive and the patient is haemodynamically stable

Consider trans-oesophageal echocardiography (TOE) for definitive diagnosis of acute aortic dissection in addition to TTE, depending on local expertise and availability.[2]

  • For type A dissections (ascending), TOE may be performed in the ICU or operating theatre to confirm the diagnosis and better evaluate the aortic valve.

  • Sensitivity and specificity for TOE are higher than for TTE.

  • CT and MRI are alternatives, depending on local availability and the patient’s haemodynamic status.[2]

TOE can also be used to confirm the diagnosis of chronic dissection.[2][Figure caption and citation for the preceding image starts]: Trans-oesophageal echocardiography (transverse aortic section) showing a circumferential dissection of the ascending aorta in a 30-year-old patient with features of Marfan's syndromeBouzas-Mosquera A, Solla-Buceta M, Fojón-Polanco S. Circumferential aortic dissection. BMJ Case Reports 2009; doi:10.1136/bcr.2007.049908 [Citation ends].Trans-oesophageal echocardiography (transverse aortic section) showing a circumferential dissection of the ascending aorta in a 30-year-old patient with features of Marfan's syndrome

Result

intimal flap in acute or chronic dissection; two lumens may be seen in chronic dissection

chest x-ray

Test
Result
Test

Order a chest x-ray for all patients, if the clinical situation allows.[6]​​

If chest x-ray shows widening of the mediastinum or pleural effusion, this can indicate aortic dissection; organise further definitive imaging with CT.[14] TOE and MRI are alternatives.​[2][33]​ However, if you have a high suspicion of aortic dissection, do not delay definitive imaging for aortic dissection, even if the chest x-ray is normal.[6]​​

  • Chest x-ray is of limited value for diagnosis of aortic dissection, particularly if the dissection is confined to the ascending aorta; it is normal in up to 40% of patients with aortic dissection.[2]​​[18][34]

  • Chest x-ray may also show other causes of acute chest pain.[2]

Result

contour of the aortic knob; 'calcium sign', which appears as a separation of the intimal calcification from the aortic wall of >5 mm; tracheal deviation to the right; mediastinal widening; double density appearance within the aorta; deviation of the nasogastric tube to the right

CT (chest, abdomen, and pelvis)

Test
Result
Test

Use urgent CT as first-line imaging for definitive diagnosis of aortic dissection.[14] TOE and MRI are alternatives, depending on local expertise and availability and the patient’s haemodynamic status.[2][18] In practice, CT may also be used as initial imaging for suspected aortic dissection instead of TTE if this is unavailable or inconclusive, and the patient is haemodynamically stable. 

A protocol of non-enhanced CT, followed by contrast-enhanced CT angiography is recommended.[2] This should include CT of the chest, abdomen, and pelvis to visualise the extent of the dissection. [Figure caption and citation for the preceding image starts]: CT scan showing dissecting aneurysm in a 45-year-old patient with Marfan syndrome experiencing chest pain [Citation ends].CT scan showing dissecting aneurysm in a 45-year-old patient with Marfan syndrome experiencing chest pain[Figure caption and citation for the preceding image starts]: CT of a 71-year-old man showing type II dissecting aneurysm of the ascending aorta. Haematoma around the proximal segment of the ascending aorta (panels A-D) compressed the right pulmonary artery, almost occluding its patency and limiting the perfusion of the reciprocal lung [Citation ends].CT of a 71-year-old man showing type II dissecting aneurysm of the ascending aorta. Haematoma around the proximal segment of the ascending aorta (panels A-D) compressed the right pulmonary artery, almost occluding its patency and limiting the perfusion of the reciprocal lung

Result

intimal flap in acute and chronic dissection; in chronic dissection the flap may be thickened and there may be evidence of calcification and fewer periaortic reactive changes

high-sensitivity troponin

Test
Result
Test

Important to exclude myocardial infarction. However, be aware that myocardial ischaemia or infarction may be present in 10% to 15% of patients with aortic dissection, which can mask the diagnosis of dissection.[2] This may be due to: 

  • Aortic false lumen expansion causing compression or obliteration of the coronary ostia

  • Propagation of the dissection into the coronary arteries.

  • See ST-elevation myocardial infarction.

Result

usually negative

.renal function tests

Test
Result
Test

May show renal failure; either pre-existing, or developing if renal perfusion is compromised.[2]

Result

elevated creatinine and urea

liver function tests

Test
Result
Test

May be elevated if hepatic perfusion is compromised.

Result

elevated aspartate transaminase and alanine transaminase

lactate

Test
Result
Test

Indicative of bowel ischaemia or metabolic acidosis due to ischaemia caused by aortic dissection.

Result

elevated or normal

full blood count

Test
Result
Test

Anaemia may be present in the case of haemorrhage.

May show signs of inflammation due to an inflammatory response (such as systemic inflammatory response syndrome [SIRS]) as a consequence of aortic dissection.[2][40]

Result

reduced or normal red blood cell count; evidence of inflammation

C-reactive protein

Test
Result
Test

May be elevated due to an inflammatory response (such as systemic inflammatory response syndrome [SIRS]) as a consequence of aortic dissection.[2][40]

Result

may be elevated

group and save/cross match

Test
Result
Test

Surgical intervention/transfusion may be necessary in some cases.

Result

preparation for surgery

blood gas

Test
Result
Test

Perform a blood gas in all patients.

Result

may show metabolic acidosis

creatine kinase

Test
Result
Test

May be elevated due to reperfusion injury or rhabdomyolysis.[2]

Result

may be elevated

procalcitonin

Test
Result
Test

Can differentiate between systemic inflammatory response syndrome (SIRS), which may be present as a consequence of aortic dissection, and sepsis.[2][40] In practice, the utility of procalcitonin is debatable.

Result

may be raised with infection

Investigations to consider

D-dimer

Test
Result
Test

Order a D-dimer (preferably point-of-care) if you have a low clinical suspicion of aortic dissection.[2]

  • Despite a high sensitivity, D-dimer is not recommended as the sole screening tool for acute aortic dissection; while negative D-dimer may be helpful to rule out aortic dissection in a patient with a low clinical suspicion of dissection, a positive D-dimer lacks specificity when used in isolation.[35][36]

  • However, D-dimer is useful when considering the differential diagnosis (e.g., pulmonary embolism).[18][37]​​

Result

positive

magnetic resonance angiography

Test
Result
Test

Magnetic resonance angiogram is the most accurate, sensitive, and specific test for aortic dissection, but is rarely used in the acute setting because it is more difficult to obtain than CT.[2]​​[14][18]​ It should only be used if the patient is haemodynamically stable; CT and TOE are alternatives depending on local expertise and availability.[2]​​[14][18]

Result

intimal flap in acute or chronic dissection; in chronic dissection the flap may be thickened and there may be evidence of calcification and fewer periaortic reactive changes; two lumens may be seen in chronic dissection

intravascular ultrasound

Test
Result
Test

If the patient has a type B dissection (descending) and surgery is required, intra-operative intravascular ultrasound helps define the morphology of the dissection and assists in the treatment plan, particularly during endovascular treatment.[2]​​[14][18]

Result

intimal flap

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