Aortic dissection
DEFINITION
A condition where a tear in the aortic intima allows blood to surge into the aortic wall, causing a split between the inner and outer tunica media, and creating a false lumen.
AETIOLOGY
Degenerative changes in the smooth muscle of the aortic media are the predisposing event. Common causes and predisposing factors are:
- hypertension;
- aortic atherosclerosis;
- connective tissue disease (e.g. SLE, Marfan’s, Ehlers–Danlos);
- congenital cardiac abnormalities (e.g. aortic coarctation);
- aortitis (e.g. Takayasu’s aortitis, tertiary syphilis);
- iatrogenic (e.g. during angiography or angioplasty);
- trauma;
- crack cocaine.
Stanford classification divides dissection into
- type A with ascending aorta tear (most common);
- type B with descending aorta tear distal to the left subclavian artery.
Expansion of the false aneurysm may obstruct the subclavian, carotid, coeliac and renal
arteries.
EPIDEMIOLOGY
Most common in < between 40 and 60 years.
HISTORY
Sudden central ‘tearing’ pain, may radiate to the back (may mimic an MI).Aortic dissection can lead to occlusion of the aorta and its branches:
Carotid obstruction: Hemiparesis, dysphasia, blackout.
Coronary artery obstruction: Chest pain (angina or MI).
Subclavian obstruction: Ataxia, loss of consciousness.
Anterior spinal artery: Paraplegia.
Coeliac obstruction: Severe abdominal pain (ischaemic bowel).
Renal artery obstruction: Anuria, renal failure.
EXAMINATION
Murmur on the back below left scapula, descending to abdomen.
Blood pressure (BP):
Hypertension (BP discrepancy between arms of >20 mmHg), wide pulse pressure. If hypotensive may signify tamponade, check for pulsus paradoxus.
Aortic insufficiency:
Collapsing pulse, early diastolic murmur over aortic area.Unequal arm pulses.
There may be a palpable abdominal mass.
INVESTIGATIONS
Bloods: FBC, cross-match 10 units of blood, U&E (renal function), clotting.
CXR: Widened mediastinum, localized bulge in the aortic arch.
ECG: Often normal. Signs of left ventricular hypertrophy or inferior MI if dissection compromises the ostia of the right coronary artery.
CT-thorax: False lumen of dissection can be visualized.
Echocardiography: Transoesophageal is highly specific.
Cardiac catheterization and aortography.
MANAGEMENT
Acute: If suspected, CT-thorax should be performed urgently concurrent to resuscitation.
Resuscitate and restore blood volume with blood products. Monitor pulse and BP in both arms, central venous pressure monitoring, urinary catheter. Best managed in ITU setting.
Type A dissection:
Treated surgically. Emergency surgery because of the risk of cardiac tamponade. Affected aorta is replaced by a tube graft. Aortic valve may also be replaced.
Type B dissection:
Can be treated medically, surgically or by endovascular stenting. Control BP and prevent further dissection with IV nitroprusside and/or IV labetalol (use calcium channel blocker if b-blocker contraindicated). Surgical repair may be appropriate for patients with intractable or recurrent pain, aortic expansion, end-organ ischemia or progression of dissection, and has similar outcome rates. Endovascular repair is a newer technique using endovascular stents and is available in some centres, although evidence of benefit is still lacking (ADSORB trial results pending).
COMPLICATIONS
Aortic rupture, cardiac tamponade, pulmonary oedema, MI, syncope, cerebrovascular, renal, mesenteric or spinal ischaemia.
PROGNOSIS
Untreated mortality: 30% at 24 h, 75% at 2 weeks.
Operative mortality of 5–10%. A further 10% have neurological sequelae.
Prognosis for type B better than type A.
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