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Aortic Dissection

Aortic dissection is the most common acute aortic syndrome, and it is an important differential of chest pain. It is three times more common than AAA rupture and associated with a high mortality. 20% of patients die before reaching hospital and 30% die during hospital admission.

Aortic dissection occurs when blood enters the medial layer of the aortic wall, creating a false lumen. Other “acute aortic syndromes” (AAS) include intramural hematoma and penetrating atherosclerotic ulcer.

The following history, examination findings and risk factors are taken from the aortic dissection detection risk score:

History

  • Sudden onset of severe chest, abdominal or back pain described as:
  • Abrupt in onset/severe in intensity AND Ripping/tearing/sharp or stabbing quality

Examination

  • Pulse deficit
  • Systolic BP differential
  • Focal neurological deficit (in conjunction with pain)
  • Murmur of aortic insufficiency (new or not known to be old and in conjunction with pain)
  • Hypotension or shock state

Risk factors

  • Cocaine use
  • Marfan syndrome
  • Connective tissue disease
  • Family history of aortic disease
  • Recent aortic manipulation
  • Known thoracic aortic aneurysm
  • Known aortic valve disease

Investigations

  • ECG: normal sinus rhythm, Ischemia (esp inferior) - 15%, Nonspec ST-T changes - 40%, LVH may be present.
  • Troponin (may be elevated if dissection causes myocardial ischaemia)
  • U/E (Cr elevation if renal artery involvement)
  • Coagulation studies
  • D Dimer (-LR 0.05 consider as a rule out aortic dissection in low risk patients
  • CXR: Mediastinal widening > 8cm at aortic arch (present in 60%). Abnormal aortic contour > 0.5 cm from edge of calcification to edge of contour (present in 45-50%)
  • Limited ECHO: Rule in if aortic outflow tract > 4 cm, detection of pericardial effusion/tamponade or intimal flap
  • Transoesophageal echo: +ve LR 6 -ve LR 0.11
  • CT Angiogram: +ve LR 38 -ve LR 0.05 (intimal flap separating a false lumen from a true lumen)

Management

Immediate cardiothoracic referral on strong suspicion.

  • Large bore IV access
  • Cross match 6 units of packed cells and consider alerting blood bank (to activate massive transfusion protocol).
  • Fluid resuscitation with blood products if required (no more than MAP 65).
  • Fentanyl PCA to control pain (decreases sympathetic output)
  • Target HR 60-80. Esmolol may be given as an initial bolus of 40 mg IV & infusion 20mg/min OR Labetalol to 20 mg IV with repeat doses of 20-40 mg every 10 minutes to effect or a total dose of 300 mg OR Metoprolol may be given in 5mg repeated 5 minutely to a 15mg initial bolus & infusion 5mg/hr.
  • Target right arm BP 100-120 systolic: Right arm likely most accurate, or use higher number
  • Place art line
  • BP control after Beta blocking: Sodium Nitroprusside 0.3 microgram/kg/min IV titrated to effect
  • Correct coagulopathy.
  • Stanford Type A - Surgical repair represents the mainstay of treatment.
  • Stanford Type B - Medical management is the gold standard although endovascular surgery sealing of the intimal entry tear offers potential management in the complicated tears.

Immediate risks to the patient

  • Haemodynamic collapse (Aortic rupture)
  • Aortic regurgitation
  • AMI
  • Tamponade
  • Haemothorax
  • End organ ischemia (further progression of dissection)
  • Altered consciousness or neurologic compromise (carotid involvement)
  • Associated complications of Branch vessel involvement (renal, mesentery)

Evaluation

If an aortic dissection is strongly suspected a CT aortogram is the investigation of choice to exclude this possibility.

For lower risk patients recent evidence suggests a D-dimer may be sufficient to exclude dissection in conjunction with an Aortic Dissection Detection Risk Score of 0 or 1. The ECI supports its use for patients with ADD scores of 0.

Discussion

The D-dimer is a fibrin degradation product (or FDP), a small protein fragment present in the blood after a blood clot is degraded by fibrinolysis. This is elevated when clot is present in the lumen of a blood vessel. D-dimer will be elevated in nearly all aortic dissection, the only exception is when the dissection starts as an intra-mural haematoma. Although rare (1/300 dissections) this poses a problem for the D-dimer as clot may not be present in the lumen and the D-dimer may not be relied upon to exclude dissection.

Multiple meta-analysis have demonstrated the sensitivity of the D-dimer in aortic dissection and evaluated its role in conjunction the American Heart Association Aortic Dissection Detection Risk Score. Recently a large well run study (the ADvISED study) validated these meta-analyses and suggested that a negative d-dimer in conjunction with an ADD score of 0 or 1 can be used in the ED to exclude aortic dissection.

The bottom line in aortic dissection rule out

If you strongly suspect dissection you need to organise a urgent CT aortogram to exclude this serious pathology.

If you do not strongly suspect aortic dissection but have considered it as part of your differential you can exclude the possibility of aortic dissection with a negative D-dimer if they do not have any of the typical history, exam or risk factors listed above. This approach should always be discussed with a senior emergency doctor before being applied.

As with pulmonary embolus exclusion a d-dimer should only be considered if you have already decided the patient requires aortic dissection rule out. Screening patients with D-dimer is not recommended due to the high false positive rate.

Example:

A young healthy patient with no significant medical history presents to the ED with central chest pain which radiates to the back. The onset was not abrupt or severe and the pain is not described as ripping or tearing. He was no risk factors or exam findings suggestive of dissection. You can find no explanation for his pain and feel aortic dissection needs to be excluded. For this patient ADD score is 0 and exclusion of a dissection with a D-dimer is appropriate.

References

Circulation. 2018 Jan 16;137(3):250-258. doi: 10.1161/CIRCULATIONAHA.117.029457. Epub 2017 Oct 13. Nazerian, et al. Diagnostic Accuracy of the Aortic Dissection Detection Risk Score Plus D-Dimer for Acute Aortic Syndromes: The ADvISED Prospective Multicenter Study.

Asha SE et al. "A systematic review and meta-analysis of D-dimer as a rule out test for suspected acute aortic dissection." Annals of EM. 66;4;368-377Ocotber 2015.

Original: Dr John Mackenzie

Update: Dr James Miers

Reviewer: Dr Stephen Asha

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