section name header

Information ⬇

Author: John B. Chambers

Consider acute aortic syndrome in any patient with chest, back or upper abdominal pain of abrupt onset. Aortic dissection is the most common acute aortic syndrome and is classified as proximal (Type A; involving the ascending thoracic aorta) or distal (Type B; only involving the descending thoracic aorta) (Figure 50.1). The risk of death is very high in the first few hours, so immediate discussion with an aortic surgical centre is vital. Management of suspected aortic dissection is summarized in Figure 50.2.

Priorities ⬆ ⬇

  • Put in an IV cannula and relieve pain with morphine 5–10 mg IV (2.5–5 mg in the small or elderly) with further doses every 15 min as required. Obtain an ECG to exclude acute myocardial infarction as an alternative cause for the pain. Very rarely, aortic dissection can involve the right coronary artery, causing inferior infarction (p. 326).

  • Complete your clinical assessment (Table 50.1). Urgent investigations are given in Table 50.2.

    Review the chest X-ray. Abnormalities which may be seen are shown in Table 50.3.

    • A PA film alone is normal in around 50% of cases.
    • AP (anteroposterior) films commonly show apparent widening of the mediastinum in normal subjects and this feature in isolation should not be given undue weight.

If immediately available, transthoracic echocardiography (Table 50.3) should be done, looking for: a diagnostic intimal flap (seen in 80% of proximal and 50% of distal dissections); suggestive signs (dilatation of the ascending aorta, aortic regurgitation not associated with thickening of the aortic valve, pericardial fluid (which is an ominous sign signifying retrograde extension into the pericardial space); evidence of high-risk (impaired LV or RV function).

The working diagnosis is aortic dissection if (Table 50.4):

Further Management ⬆ ⬇

  1. Working diagnosis of aortic dissection
    • Make sure adequate analgesia has been given.
    • Start hypotensive treatment (Table 50.5).
      • Put in a bladder catheter to monitor urine output.
      • Aim to reduce systolic blood pressure to 100–120 mmHg, providing the urine output remains >30 mL/h.
    • Discuss further management with a cardiothoracic surgeon at your regional aortic centre.
    • Patients with clinically definite or a high suspicion of dissection should be transferred immediately for further investigation, unless they would not be candidates for surgery, for example because of advanced age or severe comorbidity.
      • Proximal dissections require urgent repair.
      • The early death rate is very high and time should not be lost arranging investigation locally.
      • Distal dissections will usually be managed medically unless there are complications.
  2. Aortic dissection is likely clinically but there is no dissection flap on transthoracic echocardiography
    • Other causes of an acute aortic syndrome are:
    • Pseudoaneurysms and free or contained rupture should be suspected after deceleration injuries or cardiac catheterization or cardiac surgery
    • The differential diagnosis is made with a CT scan or TOE. A scan without contrast shows an intramural haematoma and with contrast shows a dissection flap or leakage into a pseudoaneurysm or rupture. The CT must be ECG gated and must have sufficiently frequent cuts. A CT pulmonary angiogram may not detect an abnormal aorta.
    • The treatment for all acute aortic syndromes is surgery, except for intramural haematoma of the descending thoracic aorta which is initially treated medically.
  3. The diagnosis is clinically uncertain
    • If the clinical suspicion is low, a normal plasma D-dimer level (within 24h of onset of symptoms) is a good rule-out for aortic dissection as well as pulmonary embolism. It may rarely be normal with intramural haematoma or localized dissections.
    • Very high D-dimer level favours dissection over pulmonary embolism.
    • If the chest X-ray is normal and expert emergency transthoracic echocardiography is not available, and if an acute aortic syndrome remains a clinical possibility with no alternative cause for pain (e.g. pleurisy, vertebral crush fracture), further investigation is needed: either CT or transoesophageal echocardiography as available.
    • Pitfalls of CT to be aware of are:
      • An intimal flap can be missed if the contrast is too dense.
      • Failure to gate to the ECG may cause artefacts resembling a dissection flap.
      • CT scans with a small number of cuts (as performed for detecting pulmonary emboli) may miss a localized dissection.
      • Views without contrast may be needed to show an intramural haematoma.
    • Transoesophageal echocardiography in trained hands detects aortic dissection and intramural haematoma (Table 50.3).
    • If dissection remains highly likely clinically but the initial CT or TOE is normal, consider the alternative test or magnetic resonance imaging.
  4. Confirmed distal aortic dissection
    • If, after discussion, the decision is to manage locally, this means that the patient has a dissection unequivocally involving only the descending thoracic aorta. Emergency endovascular stent implantation for a stable Type B dissection is not routine and not definitely better than medical therapy.
    • Transfer the patient to an ICU or CCU, and continue IV hypotensive therapy. Start oral therapy, which should include a beta blocker (with ACE-inhibitor/angiotensin receptor blocker added later) unless there are major contraindications.
    • Maintain adequate pain relief (initially with a combination of opiate and non-steroidal anti-inflammatory drug).
    • Monitor for evidence of complications (Table 50.6)
    • Discuss with a cardiothoracic surgeon if the dissection becomes complicated as defined by one or more of:
      • Severe pain continues or recurs.
      • Signs of rupture (large pleural effusion, increasing para-aortic or mediastinal haematoma).
      • The urine output falls. If not due to excessive hypotensive therapy or hypovolaemia, this suggests involvement of the renal arteries and is an ominous sign.
      • There is evidence of other branch artery involvement (e.g. abdominal pain with bloody diarrhoea due to ischaemic colitis).
      • Refractory hypertension.
      • Early aortic expansion.
    • The preferred treatment of a complicated Type B dissection is with an endovascular stent, which has better outcomes than surgery (30-day mortality 8%, stroke 8% and spinal cord ischaemia 2%).

Problems

The patient is hypotensive

  • Check for clinical evidence of a large left pleural effusion (as a sign of constrained rupture).
  • Review the CT scan for evidence of a contained rupture or extensive mediastinal or abdominal haematoma.
  • On the transthoracic echo cardiogram look for:
    • Pericardial tamponade
    • Impaired LV function either pre-existing or secondary to acute myocardial ischaemia
    • Severe aortic regurgitation
    • Evidence of hypovolaemia (flat IVC, small RV and LV cavities)
  • If hypovolaemic, give a fluid challenge.
  • If evidence of contained rupture, pericardial tamponade or severe aortic regurgitation discuss immediately with a cardiac surgeon.

Clinically dissection is possible but there is inferior ST elevation on ECG

  • Coronary disease is the overwhelming cause of inferior infarction. Only about 3% of dissections involve the right coronary artery and acute dissection occurs at a frequency about 1% of an ACS.
  • However, if the pain was of instantaneous onset and there are other reasons for concern (e.g. Marfan syndrome, widened mediastinum), investigate further for dissection before starting reperfusion therapy.
  • The troponin level is raised in 25% acute dissections and therefore will not be helpful in distinguishing between dissection and ACS.
  • If a dissection flap is not definitely visible on transthoracic echocardiography arrange an urgent CT scan with contrast.
  • If the diagnosis is confirmed the management is as for dissection. The coronary artery should not be treated as for an ACS.

Further Reading ⬆

Mussa FF, Horton JD, Moridzadeh R, Nicholson J, Trimarchi S, Eagle KA (2016) 2016 Acute aortic dissection and intramural hematoma: a systematic review. JAMA 316, 754–763.

The Task Force for the diagnosis and treatment of aortic diseases of the European Society of Cardiology (ESC) (2014) 2014 ESC Guidelines on the diagnosis and treatment of aortic diseases. European Heart Journal 35, 2873–2926. DOI: 10.1093/eurheartj/ehu281.