What is An Aortic Dissection?
What is An Aortic Dissection?
By Vincent S. DeGeare, M.D., F.A.C.C., F.A.C.P.
The recent deaths of actor John Ritter and quarterback Otto Graham have resulted in renewed interest in aortic dissection. This condition occurs at an incidence of five to 30 cases per million people per year in the United States. Aortic dissection starts as a small tear in the inner lining of the aorta, which then propagates along this vessel and impairs blood flow to whatever structures are supplied by the blood vessels arising from the involved segment of the aorta.
Aortic dissection occurs more frequently in men than in women with various series reporting ratios from 2:1 to 5:1. Most victims are between 50 and 70 years old. Chronic hypertension is the most common predisposing factor. Diseases, which directly affect the wall of the aorta, such as Marfan syndrome, are well-established risk factors, especially in patients less than 40 years old. Pregnancy (especially during the third trimester) is associated with at least half of all aortic dissections reported among women under 40 years old and may be due, in part, to undiagnosed Marfan syndrome. Aortic aneurysms and dilatation, coarctation of the aorta, bicuspid aortic valves and atherosclerosis of the aorta have also been found to increase the risk of aortic dissection.
Direct aortic trauma accounts for approximately five percent of aortic dissections. This may be the result of external trauma such as a motor vehicle accident or internal trauma that occurs in association with cardiac surgery or cardiac catheterization. Cocaine use has been recognized as a cause of aortic dissection in otherwise healthy patients, probably due to rapid, severe elevations in blood pressure.
Symptoms and signs can range from pain without systemic involvement to rapid death if the heart or the arteries to the brain are involved. The most common initial symptom is the sudden onset of excruciating pain that is sharp, ripping, tearing or "knife-like." The pain usually begins in the chest but extends into the back in the majority of cases. In some cases, the pain is migratory, following the anatomic path of the dissection. Less common initial symptoms include acute congestive heart failure, passing out, stroke or sudden death.
Signs of aortic dissection reflect the segment of the vessel involved. Dissections involving the first segment of the ascending aorta and the aortic arch usually cause anterior chest pain. Leakage of the aortic valve may occur and result in congestive heart failure. Bleeding around the heart can result in immediate compression of the heart and sudden death. If the origin of a coronary artery is compromised, signs and symptoms of a myocardial infarction (heart attack) may be present. If the dissection involves the artery leading to one of the arms, the pulse in that limb will be reduced. Neurologic deficits have been reported in 18-30 percent of cases of aortic dissection and may be due to involvement of the major brain arteries (aortic arch), the spinal arteries (descending thoracic aorta) or the arteries leading to the legs (abdominal aorta). Damage to many abdominal organs and the kidneys can occur when their blood supply is compromised by a propagating aortic dissection.
The most important step in diagnosing aortic dissection is to be suspicious of the condition when any of the above signs and symptoms is present. Death rates may reach one percent per hour early in the course of this disorder. The initial evaluation involves an electrocardiogram (to rule out the more common myocardial infarction) and a chest x-ray to exclude other common causes of chest pain. However, neither of these tests is sensitive for the diagnosis of aortic dissection. If aortic dissection remains a concern, the next step is to image the aorta. Computed tomography (CT) scanning is the most commonly used modality given its rapid availability in most centers. Magnetic resonance imaging (MRI) provides even more details about the origin and extent of aortic dissection but is limited by its longer examination time and the inability to closely monitor patients during the scan. Transesophageal echocardiography (TEE) is especially useful to evaluate the involvement of the aortic valve and other cardiac structures but may miss some areas of the aortic arch and is more dependent on the skill of the performing physician than the other methods.
Once the diagnosis of aortic dissection is established, treatment depends on the location of the dissection and the accompanying signs and symptoms. Initially all patients (except those with low blood pressure) are treated with intravenous antihypertensive medications in order to stop propagation of the dissection and lower the risk of aortic rupture. Later, oral medications can be substituted. Patients that have uncomplicated descending thoracic or abdominal aortic dissections may not require further therapy as surgical repair has not been shown to improve survival. Surgery in these patients is reserved for intractable pain or ongoing evidence of organ damage.
Conversely, early surgery is the preferred therapy for most patients with dissections of the ascending aorta or aortic arch in order to limit the compromise of crucial vascular and cardiac structures. This is very major surgery often involving replacement of the dissected aorta and reattachment of the involved blood vessels. Aortic valve repair/replacement and coronary artery bypass may also be required. The initial operative mortality is five to 10 percent and may reach 70 percent in patients with major complicating factors. More recently, the development of less invasive catheter-delivered endovascular stents has proved promising in treating high-risk patients with distal aortic dissections.
Long term, all survivors of aortic dissection require antihypertensive therapy, usually with beta-blocking drugs, and regular imaging studies to detect progressive dissections and the formation of aortic aneurysms which may require surgical intervention. Despite all of these advances, in-hospital mortality rates remain 30 percent for those with proximal aortic dissections and 10 percent for those with distal dissections. After ten years, only 50 percent of those with proximal aortic dissection are alive.
Vincent S. DeGeare, M.D., F.A.C.C., F.A.C.P. is an interventional cardiologist with CardioVascular Associates, PSC in Louisville, KY. For more information, he can be reached at 891-8300.
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