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Aortic Dissection

(Dissecting Aneurysm; Dissecting Hematoma)

By John W. Hallett, Jr., MD, Medical University of South Carolina;Roper St. Francis Heart and Vascular Center

An aortic dissection is an often fatal disorder in which the inner layer (lining) of the aortic wall tears and separates from the middle layer of the aortic wall.

  • Most aortic dissections occur because high blood pressure causes the artery’s wall to deteriorate.

  • People have sudden, excruciating pain, most commonly across the chest but also in the back between the shoulder blades.

  • Doctors usually do x-rays or computed tomography to confirm the diagnosis.

  • People usually take drugs to decrease blood pressure, and doctors do surgery to repair the tear or place stent grafts to cover the tear.

The aorta is the largest artery of the body. It receives oxygen-rich blood from the heart and distributes it to the body through smaller arteries that branch off of it. The thoracic aorta, where most aortic dissection occurs, is the part of the aorta that passes through the chest.

When the lining of the aorta tears, blood can push through the tear, separating (dissecting) the middle layer of the wall from the still intact outer layer. As a result, a new, false channel forms in the wall of the aorta. Aortic dissections are 3 times more common among men and are more common among blacks (specifically African-Americans) and less common among Asians. About three fourths of aortic dissections occur in people aged 40 to 70.

The most common cause of aortic dissection is

More than two thirds of people who have an aortic dissection have high blood pressure.

Less common causes of aortic dissection include

  • Hereditary connective tissue disorders, especially Marfan syndrome and Ehlers-Danlos syndrome

  • Birth defects of the heart and blood vessels, such as coarctation (narrowing) of the aorta, patent ductus arteriosus (a connection between the aorta and the pulmonary artery), and defects of the aortic valve

  • Injury such as a car crash or fall causing a strong blow to the chest

Rarely, a dissection occurs accidentally when doctors are inserting a catheter into an artery (for example, during aortography or angiography) or doing surgery on the heart or blood vessels.

Understanding Aortic Dissection

In an aortic dissection, the inner layer (lining) of the aortic wall tears, and blood surges through the tear, separating (dissecting) the middle layer from the outer layer of the wall. As a result, a new, false channel forms in the wall.

Symptoms

Virtually everyone who has an aortic dissection experiences pain—typically sudden, excruciating pain, often described as tearing or ripping. Some people may faint as a result of the pain. Most commonly, the pain is felt across the chest but is often also felt in the back between the shoulder blades. The pain frequently travels along the path of the dissection as it advances along the aorta. Thus, people may have abdominal pain or lower back pain if the mesenteric arteries, which supply the intestines, are blocked.

As the aortic dissection lengthens along the aorta, it can close off the points at which one or more arteries branch off from the aorta, blocking blood flow. The consequences vary depending on which arteries are blocked.

Complications of aortic dissection

Complications include

  • Stroke (if the cerebral arteries, which supply the brain, are blocked),

  • Heart attack (if the coronary arteries, which supply the heart muscle, are blocked),

  • Kidney failure (if the renal arteries, which supply the kidneys, are blocked)

  • Nerve and/or spinal cord damage that causes tingling or an inability to move a limb (if the spinal arteries are blocked).

Blood may leak from the dissection and accumulate in the chest. Blood leaking from a dissection near the heart may enter the pericardial space (between the two layers of membranes that surround the heart), preventing the heart from filling properly and causing cardiac tamponade—a life-threatening disorder.

A dissection that involves the first few inches of the aorta (ascending aorta) closest to the heart may affect the attachments of the aortic valve, the heart valve that keeps blood from flowing back into the heart. If the aortic valve attachments are weakened, the valve can leak, causing heart failure.

Diagnosis

  • Imaging tests such as CT scan, MRI, or ultrasonography

The distinctive symptoms of an aortic dissection usually make the diagnosis obvious to doctors, although the disorder causes a variety of symptoms that sometimes resemble those of other disorders. In about two thirds of people with aortic dissection, pulses in the arms and legs are diminished or absent. Depending on the location of the dissection along the aorta, there may be a difference in blood pressure between the right and left arm. A dissection that is moving backward toward the heart may cause a murmur that can be heard through a stethoscope.

Chest x-rays are the first step in detecting aortic dissection. X-rays show a widened aorta in 90% of people with symptoms. However, this finding may be due to other disorders. Computed tomography (CT) done after injecting a contrast agent (dye) can quickly and reliably detect aortic dissection and thus is useful in an emergency. Standard or transesophageal echocardiography or magnetic resonance angiography can also reliably detect aortic dissections, even very small ones.

Prognosis

Without treatment, about 80% of people who have an aortic dissection die within the first 2 weeks. With treatment, about 70% who have dissection of the first part of the aorta and about 90% of those who have dissection of the aorta farther from the heart survive to leave the hospital. About 60% of people who survive the first 2 weeks are still alive 5 years after treatment, and 40% live at least 10 years. Of people who die after the first 2 weeks, about one third die of complications of the dissection, and the other two thirds die of other disorders.

Treatment

  • Surgery or sometimes an endovascular stent graft

People with an aortic dissection are admitted to an intensive care unit, where their vital signs (pulse, blood pressure, and rate of breathing) are closely monitored. Death can occur a few hours after an aortic dissection begins. Therefore, as soon as possible, drugs are given intravenously to reduce the heart rate and blood pressure to the lowest level that can maintain a sufficient blood supply to the brain, heart, and kidneys. The lower heart rate and blood pressure help limit the spread of the dissection. Soon after drug therapy begins, doctors must decide whether to recommend surgery or to continue drug therapy without surgery.

Doctors almost always recommend surgery for dissections that involve the first few inches of the aorta (ascending aorta) closest to the heart, unless complications of the dissection make the risk of surgery too high. During surgery, surgeons remove the largest possible area of dissected aorta, close the channel that was torn between the middle and outer layers of the aorta’s wall, and rebuild the aorta with a synthetic graft. If the aortic valve is leaking, surgeons repair or replace it. Removal and repair of a dissected aorta usually takes 3 to 6 hours, and the hospital stay is usually 7 to 10 days.

For dissections in the aorta farther from the heart (descending aorta), doctors usually continue drug therapy without surgery or consider placement of an endovascular stent-graft, To do an endovascular stent-graft, doctors thread a long, thin wire through the large artery in the groin (femoral artery) and up to the dissecting area. Then they slide the stent-graft, which is a hollow tube like a collapsible straw, over the wire and inside the damaged area of the aorta. Then the stent-graft is opened, forming a stable channel for blood flow . This procedure takes 2 to 4 hours, and the hospital stay is usually 1 to 3 days. Stent-grafts, which are less invasive than open surgery, have improved the survival rate and lowered the risk of complications for people with dissections of the descending aorta.

Surgery or a stent-graft repair is always necessary if the dissection causes the artery to leak blood, blocks the blood supply to the legs or to vital organs in the abdomen, causes symptoms, is enlarging, or occurs in a person with Marfan syndrome.

All people who have an aortic dissection, including those treated surgically, have to take drug therapy to keep their blood pressure down, usually for the rest of their lives. Such therapy helps reduce stress on the aorta. Drug therapy to lower blood pressure usually consists of a beta-blocker or calcium channel blocker plus another antihypertensive drug such as an angiotensin-converting enzyme (ACE) inhibitor. Cholesterol-lowering drugs and diet modification are used if the person has atherosclerosis.

Doctors watch closely for complications that can occur in people who have had an aortic dissection. The most important are another dissection, development of aneurysms in the weakened aorta, and increasing leakage backward through the aortic valve. Any of these complications may require surgical repair.

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