Section 3. Heart and Blood Vessel Disorders

Chapter 35. Aneurysms and Aortic Dissection

Topics: Introduction | Aneurysms | Aortic Dissection

Aortic Dissection

An aortic dissection (dissecting aneurysm, dissecting hematoma) is an often fatal disorder in which the inner layer (lining) of the aortic wall tears.

When the lining of the aorta tears, blood can surge through, 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 and less common among Asians. About three fourths of aortic dissections occur in people aged 40 to 70.

See the figure Understanding Aortic Dissection.

Most aortic dissections occur because the artery's wall deteriorates. Most commonly, such deterioration is associated with high blood pressure, which is present in more than two thirds of people who have an aortic dissection. Aortic dissection may be caused by hereditary connective-tissue disorders, especially Marfan syndrome (see Section 23, Chapter 279) and Ehlers-Danlos syndrome (see Section 23, Chapter 279). It may also be caused by birth defects of the heart and blood vessels (see Section 23, Chapter 265), such as coarctation of the aorta, patent ductus arteriosus (a connection between the aorta and the pulmonary artery), and defects of the aortic valve. Other causes include arteriosclerosis and injury. Rarely, a dissection occurs accidentally when doctors are inserting a catheter into an artery (for example, during aortography or angiography) or performing surgery on the heart or blood vessels.

Symptoms

Virtually everyone who has an aortic dissection experiences pain--typically sudden, excruciating pain, often described as tearing or ripping. 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.

As the dissection advances, 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. Consequences 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), sudden abdominal pain (if the mesentery arteries, which supply the intestines, are blocked), lower back pain (if the renal arteries, which supply the kidneys, are blocked) and nerve 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 (see Section 3, Chapter 30).

Diagnosis

The distinctive symptoms of an aortic dissection usually make the diagnosis obvious to doctors, although the disorder produces 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. 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; they show a widened aorta in 90% of people with symptoms. However, this finding may be due to other disorders. Computed tomography (CT) performed after injecting a radiopaque dye can quickly and reliably detect aortic dissection and thus is useful in an emergency. Standard or transesophageal echocardiography (see Section 3, Chapter 21) can also reliably detect aortic dissections, even very small ones.

Treatment and Prognosis

People with an aortic dissection are admitted to intensive care units, 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, usually sodium nitroprusside plus a beta-blocker, 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. 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 closest to the heart, unless complications of the dissection make the risk of surgery too high. For dissections farther from the heart, doctors usually continue drug therapy without surgery. However, surgery is 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. In specialized major medical centers, the risk of death during surgery is about 15% for aortic dissections close to the heart and is somewhat higher for those farther away (because the risk of complications is higher).

During surgery, the surgeon removes the largest possible area of dissected aorta, closes the false channel between the middle and outer layers of the aorta's wall, and rebuilds the aorta with a synthetic graft. If the aortic valve is leaking, the surgeon repairs or replaces it. Removal and repair of a dissected aorta usually takes 3 to 6 hours, and the hospital stay is usually 7 to 10 days.

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 usually consists of a beta-blocker or calcium channel blocker plus another antihypertensive drug such as an angiotensin-converting enzyme (ACE) inhibitor (see Section 3, Chapter 22).

Doctors watch closely for late complications. 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.

Without treatment, about 75% of people who have an aortic dissection die within the first 2 weeks. With treatment, 60% of people who survive the first 2 weeks are still alive 5 years after treatment; 40% live at least 10 years. Of people who die after the first 2 weeks, about one third die of complications of the dissection; the other two thirds die of other disorders.