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Aortic Dissection

Definition: Classically an intimal tear in the aorta resulting in hematoma formation. Accumulating blood in false lumen of arterial wall leads to propagation of a dissection. Alternatively may begin as an intrawall hematoma without intimal tear.

Classification:
Stanford: (mot commonly used)
Type A: Involves ascending aorta up to the or including the aortic notch
Type B: Involves the descending aorta
Non Type A/Non-type B: isolated involvement of the aortic notch

DeBakey:
Type 1: Ascending Aorta
Type 2: Aortic notch
Type 3: Descending Aorta

Epidemiology:
Type A is most commonly occurs in patients greater than 60 years of age. Type B dissection patients are typically older. Patients with Marfan’s average 36 years of age.

Risk Factors:
Hypertension (70%), old age, atherosclerosis, collagen abnormalities (marfan’s, ehlers-danlos), drug use, inflammatory vasculitis (takayasu, giant cell arteritis), chest trauma, turner syndrome, bicuspid aorta.

Diagnosis:
Maintain a high index of suspicion in a male patient 60-80 years old with a history of hypertension. Patients will oftentimes describe the pain as abrupt onset, sharp and severe, Most often type A affects the patient in the chest/sternal area and type B occurs in the back or abdomen. A positive family history of dissection should also raise suspicion. Physical exam findings include hypotension in Type A, hypertension in Type B, pulse deficit, aortic regurgitation, signs of CHF, limb ischemia or MI.

Diagnostic Tests:
MRI, TEE and CT with IV contrast all have around a 95% sensitivity. MRI however is not indicated for unstable patients and patients with certain pacemakers and devices. It is often used for long-term management and follow-up.

CT with IV contrast may be done as a CT scanner is usually readily available.

A transesophageal echocardiogram may be done bedside in an unstable patient. It takes around 15-20 minutes to perform. If there is a high index of suspicion and the 1st test is negative a 2nd test must be performed.
Contrast angiography may be used specifically as a diagnostic tool especially when visceral perfusion defects are suspected. It may also provide an entry point into endovascular treatment of dissection.

** Of note, 60% of intimal tears occur in the proximal ascending aorta. The rest occur at the origin of the left subclavian artery and the ligamentum arteriosum, the descending aorta, in the aortic notch and in the abdomen.

Treatment:
Aortic Dissection is an acute occurrence. The first priority is to maintain hemodynamic stability. There should be a low threshold for ICU admission. Arterial blood pressures should be monitored in less stable patients.

For uncomplicated Type B dissections, medical management is considered first line treatment. Patients should be started on Beta-Blockers such as Labetalol, Propranolol, Metoprolol or Esmolol. If the patient is unable to handle Beta-Blockers or has severe asthma, calcium channel blockers with negative inotropic and chronotropic effect such as Verapamil or Diltiazem may be used. Surgical intervention is indicated for Type B only if the patient has continued aortic expansion, impending aortic rupture, occlusion of a major arterial vessel, persistent or recurrent chest pain, or a pre-aortic or mediastinal hematoma. Surgical intervention is typically associated with worse outcomes than medical therapy.

On the other hand, the first line treatment for a Type A dissection is surgical intervention. Those patients who are inappropriate candidates for surgery have a mortality rate of 50%. Surgical correction aims to resect the ascending aorta with a conduit graft.

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