Aortic Dissection

An aortic dissection refers to a tear inside the walls of the aorta. Blood can enter and further force layers of the aorta apart.

From inner to outer, the aorta consists of three layers: the intima, media and adventitia. During a dissection, a small tear in the intima allows the high pressure arterial blood to rip through the intimal layer and penetrate into the media. Interestingly, the blood splits the media layer in such a way that it separates the inner two thirds and outer third of the layer. It does not typically penetrate into the adventitia layer. At this point, the blood can dissect along the course of the aorta either in an anterograde fashion (toward the iliac bifurcartion) or retrograde (toward the aortic root).

Most dissections originate in the ascending aorta (65-70%). This is called a Type A dissection. Type B dissections refer to those that originate in the descending aorta (25-30%).  

Some dissections may even penetrate the media layer, dissect for a certain length and then reenter the intravascular lumen. This is referred to as a double-barrel aorta.

Causes are varied and can include hypertension, vasculitis, connective tissue disorders and a congenital condition called bicuspid aortic valve.

Rare. The estimated rate is 3 persons per 100,000 per year. 65% are male. The mean age is 63 years old.

The classic presentation is a male patient with a history of hypertension who presents with acute onset chest pain with a tearing sensation radiating to the back. The area of the dissection correlates with the location of pain. Ascending dissections tend to present with anterior chest pain while descending dissections, back pain.

Other signs and symptoms to raise the suspicion of aortic dissection include new diastolic murmur of aortic insufficiency (if the dissection involves the aortic root), decreased pulsation in peripheral arteries, hypotension (poor prognosis), hypertension, tachycardia, and neurologic sequelae.

You will need radiographic evidence to confirm the diagnosis.

CXR - some studies estimate that 80% of patients with aortic dissection will have an abnormal CXR. There may be evidence of a widened mediastinum or the ‘calcium sign’ : intimal calcium deposits that are distant from the outer contour of the aorta indicating a false lumen.

Most commonly, CT with contrast will be used. It is 83% to 100% sensitive and 87% to 100% specific.

Other modalities, but less likely to be used in an emergency department, include transesophageal echocardiogram and aortogram.

Management depends on the type of dissection.

1. Type A dissection: Prompt surgical intervention. Consult thoracic surgery. Ensure patient connected to monitor, two large bore IVs, fluids for hypotension, cross matched blood. Disposition: admit.

2. Type B dissection: Blood pressure control. Rapidly titratable medications such as esmolol or labetalol are preferred. Disposition: admit.

3. Prognosis: the risk of death is 25% within 24 hours for an untreated dissection.