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Thread: Rapid Assessment and Treatment of Aortic Dissection

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    Arrow Rapid Assessment and Treatment of Aortic Dissection

    Rapid Assessment and Treatment of Aortic Dissection


    TWO THEORIES ON ETIOLOGY

    There are two major theories on the etiology of an aortic dissection. The first postulates that the intimal layer of the aorta has been damaged, exposing the medial layer to high blood pressure forces. A jet of blood dissects this layer, causing the medial and intimal layers to separate. A dissection flap forms at the site, creating a false lumen channel.

    This process presumes a medial layer that is weakened to begin with. Marfan syndrome is an autosomal dominant genetic disorder that weakens connective tissue by altering elastin and fibrillin synthesis. Patients with Marfan syndrome account for 5% to 9% of all aortic dissections, usually presenting at an early age and with proximal involvement. Ehlers-Danlos syndrome is another inherited connective tissue disorder that has been associated with aortic dissection. There is also an increased incidence of aortic dissection in patients with Noonan's and Turner's syndromes.

    There are also less well-defined familial syndromes involving fibrillin-1 gene mutations. Recent gene mapping techniques have led to the identification of certain alleles that may allow for screening in asymptomatic individuals at risk for aortic dissection. Additionally, nonclassic medial degeneration occurs with longstanding hypertension, which is seen in the majority of patients with aortic dissection.

    The second etiology of aortic dissection stems from a spontaneous rupture of the vasa vasorum in the medial layer of the aorta. This creates a localized hematoma that is contained within the medial layer. No dissection flap forms, and the false lumen does not communicate with the true lumen.

    Trauma is an uncommon cause of aortic dissection; blunt forces typically result in a hematoma or transsection rather than dissection. Iatrogenic causes are infrequent but may result from endovascular procedures such as cardiac catheterization.



    PATIENT CHARACTERISTICS


    The peak incidence of aortic dissection occurs in the sixth and seventh decades of life. It is more common in males by a 2:1 ratio. The box lists common risk factors and predisposing traits for aortic dissection. About 80% of patients have pre-existing hypertension. An association with a bicuspid aortic valve has been noted; about 7% to 14% of patients with aortic dissection have this abnormality. Vasculitis, especially of the giant cell type, has also been implicated in aortic dissection. Cocaine has been cited as a cause of dissection, especially in young men without other risk factors. Patients who have undergone cardiac surgery, especially aortic valve replacement, have an increased risk of dissection.


    Pregnancy has been implicated as a risk factor for aortic dissection. In women who are younger than 40 years of age, about 50% of cases of aortic dissection will occur during pregnancy or the postpartum period. The highest incidence is in the third trimester. Women with Marfan syndrome carry the highest risk in this population. Although the association with pregnancy has been noted, the cause is not well defined. The normal increases in blood pressure and cardiac output during pregnancy are not dramatic enough to explain the increased risk of dissection. It has been postulated that the association may simply represent reporting bias.



    CLASSIFICATION OF AORTIC DISSECTION

    Several classification systems are used in describing aortic dissections. The simplest scheme differentiates only proximal from distal anatomic involvement. Proximal dissections involve any portion of the aorta proximal to or involving the origin of the left subclavian artery. Distal dissections involve only that portion distal to the left subclavian artery. This so-called descriptive classification system is easy to use and helps guide treatment.

    The Stanford classification is similar to the descriptive system. It divides aortic dissections into types A and B. Type A dissections involve the ascending aorta; type B dissections involve the aorta distal to the left subclavian artery.

    The DeBakey system describes three types of dissections. Type I dissections involve both the ascending and descending aorta. Type II involves only the ascending aorta. Type III involves only the descending aorta and is the most common type of aortic dissection.


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    Last edited by trimurtulu; 12-21-2008 at 10:40 PM.

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