Aortic Dissection

There are several conditions that can affect the integrity or elasticity of the aortic wall: aging, atherosclerosis, chronic hypertension, chest injury and genetically inherited conditions. As a result, the aortic wall loses its strength and could potentially leak, or worse, rupture due to the blood pressure.

An Aortic dissection refers to an abnormal separation of the layers of the wall of the aorta. Aortic dissection occurs when blood leaves its "channel" through a small tear in the aortic wall. It then forms a new channel between the inner and outer walls of the aorta.

What will happen as a result of aortic dissection?

Blood will travel through the new channel or lumen in the direction towards the feet. The new lumen can become distended and cause narrowing of the original lumen there by impairing blood flow in it and thus limiting blood flow to body tissues.

Causes of Aortic dissection:

Any factor that weakens the aortic wall put you at risk for developing aortic dissection. Classically seen in Marfan’s syndrome and  Ehlers Danlos syndrome in which the tissue building your aortic wall are degenerated and weakened.

Risk factors:

1. High blood pressure (hypertension)
2. males (2:1 ratio)
3. age 60-70 years.
4. Congenitally deformed aortic valve (bicuspid aortic valve)
5. 3rd trimester of pregnancy
6. Trauma
7. Intra aortic balloon pump placement
8. Heart surgery.

Types:

Aortic dissection is classified into Type A which involve the ascending aorta and  Type B which involves the descending aorta.

Symptoms and signs

Sudden onset of tearing back pain or chest pain. Severity is at its maximum from the beginning of symptoms, unlike heart attack. Pain can travel anywhere in chest or abdomen as the blood flows in the new lumen downwards.

1. Hypertension in 70% of patients.
2. Absent pulses caused by compression of true lumen by the new lumen
3. Murmur of aortic regurgitation is heard in some patients
4. Altered mental status and limb weakness.
5. Stroke
6. Blood in the chest especially on the left side.

Diagnosis

Chest x-ray: widening of the aortic shadow.

Major diagnostic tools are aortography in which a dye is injected and x-rays are taken. chest CT scan, magnetic resonance imaging, and transesophageal echocardiogram (TEE).  Fastest and most portable test is TEE, especially useful in Emergencies. TEE should be the first study if available. MRI is unsuitable for unstable patients but is considered a gold standard, useful for following dissections. Chest CT is readily available but may not be as accurate as TEE.

Management

1. Patient will have immediate two large bore IVs and admission to ICU.
2. Blood pressure reduction to keep your systolic blood pressure 100-120.
3. Intravenous beta blockers with goal of BP reduction until HR 60-80.
4. Nitroprusside is very effective drug which should be used with beta blocker
5. If hypertension is resitant to the above treatment, a dissection flap might be compromising kidney arteries, in which case an ACE inhibitor should be used.

Surgical management

Type A dissections are surgical emergencies given risk of blood collecting around the heart and compressing it as well as heart attack.

Uncomplicated Type B dissections are generally treated medically. Indications for surgery include occlusion of major aortic branch, uncontrolled hypertension, continued expansion of dissection, and aortic rupture.

Recently endovascular stent grafts are used to treat type B dissections. A thoracic stent graft is designed to exclude the diseased portion of the aorta and reinforce the weakened wall. It greatly reduces the rupture risk and restores the blood flow to its normal channel.