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Sunday, May 04, 2008

thoracic aorta disection



Aortic dissection is the most common catastrophe affecting the aorta. The aorta is the largest artery of the body through which blood leaves the heart to deliver oxygenated blood to the rest of the body. It occurs in about 24 people per million each year in the U.S. It is caused when the inner layer of the aortic wall tears and then peels or separates away from the next layer of the aorta. This creates two channels; the original aortic channel for blood flow (the true lumen) is still present while the peeling away of the outer layer in the dissection creates a new additional flow channel (the false lumen).






Symptoms of Aortic Dissection
Location of Pain:
Chest pain
Back pain
Flank pain
Abdominal pain
Leg pain

Quality of Pain
Pain that is tearing or sharp
Abrupt onset of pain
Pain that migrates or radiates
Neurological Deficits
Coma/Altered consciousness
Paralysis
Extremity numbness
Difficulty with speaking or slurred speech
Light-headedness/Fainting
Difficulty breathing/shortness of breath


There are three primary tests used to diagnose aortic dissection. Aortic dissection can be diagnosed with a CAT scan of the aorta or an MRI scan. A transesophageal echo (TEE) may also be performed. A TEE is a special type of ultrasound test during which a small ultrasound probe is passed through the mouth and into the stomach and esophagus to take very detailed pictures of the heart and aorta. Currently there are no blood tests that can accurately diagnose aortic dissection.




In all cases, the first treatment for patients with aortic dissection is aggressive control of blood pressure with medications, usually given through an intravenous line (IV). Patients with aortic dissection are generally monitored in the intensive care unit. A team of experts cares for patients with aortic dissection, including emergency medicine physicians, cardiac and vascular surgeons, cardiologists, radiologists, and internal medicine specialists. The treatment of aortic dissection depends upon a number of factors, including the location of the tear in the aortic wall, how much of the aorta is involved, the effects of the dissection on the branch vessels of the aorta and the perfusion of the organs, and the patient’s symptoms. For patients with aortic dissection who require invasive treatment, surgery to repair the dissected portio of the aorta is generally the recommended treatment. In some cases, minimally invasive stenting procedures can be used to treat aortic dissection.
For all patients who have an aortic dissection long-term follow-up with a physician is a very important part of treatment. Blood pressure and heart rate need to be carefully monitored and controlled with medications. For many patients, CAT scans or MRI scans will be repeated at regular intervals (such as every 6 months or every year) to monitor the size of the aorta and the status of the dissection.

Magnetic resonance imaging (MRI) is currently the gold standard test for the detection and assessment of aortic dissection, with a sensitivity of 98% and a specificity of 98%. An MRI examination of the aorta will produce a three-dimensional reconstruction of the aorta, allowing the physician to determine the location of the intimal tear, the involvement of branch vessels, and locate any secondary tears. It is a non-invasive test, does not require the use of iodinated contrast material, and can detect and quantitate the degree of aortic insufficiency.
The disadvantage of the MRI scan in the face of aortic dissection is that it has limited availability and is often located only in the larger hospitals, and the scan is relatively time consuming. Due to the high intensity of the magnetic waves used during MRI, an MRI scan is contraindicated in individuals with metallic implants. In addition, many individuals experience claustrophobia while in the MRI scanning tube.

Aortic dissection is associated with hypertension (high blood pressure) and many connective tissue disorders. Vasculitis (inflammation of an artery) is rarely associated with aortic dissection. It can also be the result of chest trauma. 72 to 80% of individuals who present with an aortic dissection have a previous history of hypertension.
The highest incidence of aortic dissection is in individuals who are 50 to 70 years old. The incidence is twice as high in males as in females (male-to-female ratio is 2:1). Half of dissections in females before age 40 occur during pregnancy (typically in the 3rd trimester or early postpartum period).
A bicuspid aortic valve (a type of congenital heart disease involving the aortic valve) is found in 7-14% of individuals who have an aortic dissection. These individuals are prone to dissection in the ascending aorta. The risk of dissection in individuals with bicuspid aortic valve is not associated with the degree of stenosis of the valve.
Marfan syndrome is noted in 5-9% of individuals who suffer from aortic dissection. In this subset, there is an increased incidence in young individuals. Individuals with Marfan syndrome tend to have aneurysms of the aorta and are more prone to proximal dissections of the aorta.
Turner syndrome also increases the risk of aortic dissection, by aortic root dilatation[4].
Chest trauma leading to aortic dissection can be divided into two groups based on etiology: blunt chest trauma (commonly seen in car accidents) and iatrogenic. Iatrogenic causes include trauma during cardiac catheterization or due to an intra-aortic balloon pump.
Aortic dissection may be a late sequalae of cardiac surgery. 18% of individuals who present with an acute aortic dissection have a history of open heart surgery. Individuals who have undergone aortic valve replacement for aortic insufficiency are at particularly high risk. This is because aortic insufficiency causes increased blood flow in the ascending aorta. This can cause dilatation and weakening of the walls of the ascending aorta.

The long term follow-up in individuals who survive aortic dissection involves strict blood pressure control. The relative risk of late rupture of an aortic aneurysm is 10 times higher in individuals who have uncontrolled hypertension, compared to individuals with a systolic pressure below 130 mmHg.
The risk of death is highest in the first two years after the acute event, and individuals should be followed closely during this time period. 29% of late deaths following surgery are due to rupture of either the dissecting aneurysm or another aneurysm. In addition, there is a 17% to 25% incidence of new aneurysm formation. This is typically due to dilatation of the residual false lumen. These new aneurysms are more likely to rupture, due to their thinner walls.
Serial imaging of the aorta is suggested, with MRI being the preferred imaging technique.

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