In an aortic dissection, a weakened portion of inner wall of the aorta tears causes blood to flow between the layers of the aortic wall, forcing the inner and middle layers apart. Aortic dissection is a medical emergency and can quickly lead to death, should the blood-filled section rupture through the outside aortic wall.
Aortic dissection, though uncommon, when it occurs it is most frequently in me aged 60 to 70. When an aortic dissection is detected early and treated promptly, chance of survival greatly improves.
Aortic dissections are divided into two groups, A and B, depending on whether the ascending aorta is involved.
- Type A - The tear can originate in the aorta where it exits the heart, or as a tear extending from the upper to lower sections of the aorta Type A is the more common and dangerous dissection type.
- Type B - This type involves the lower aorta only, where the tear originates and which may extend into the lower abdomen.
There are several risk factors for developing aortic dissection, including:
- Chronic High Blood Pressure (Hypertension)
- Genetic condition, e.g. Marfan syndrome
- Weakened and enlarged aorta
- Rare: traumatic injury to chest area
The following factors also make one more susceptible to aortic dissection:
- Sex. Men have about double the incidence of aortic dissection.
- Age. The incidence of aortic dissection peaks in the 60s and 70s.
- Cocaine use. This drug may be a risk factor for aortic dissection because it temporarily raises blood pressure.
- Pregnancy. Infrequently, aortic dissections occur in otherwise healthy women during pregnancy.
Signs and Symptoms
Aortic dissection symptoms may be similar to those of other heart problems, and because of this may be confused with the pain of a heart attack. Typical signs and symptoms include:
- Sudden severe chest or upper back pain, often described as a tearing, ripping or shearing sensation, that radiates to the neck or down the back
- Loss of consciousness (fainting)
- Shortness of breath
- Sudden difficulty speaking, loss of vision, weakness, or paralysis of one side of your body, such as having a stroke
- Weak pulse in one arm compared to the other
Because of the varying symptoms and signs of aortic dissection depending on the initial intimal tear and the extent of the dissection, the proper diagnosis is sometimes difficult to identify.
While taking a good medical history from the individual may point to an aortic dissection, the diagnosis cannot always be made by history and physical signs alone. Often the diagnosis is made by looking at the wall defect on a diagnostic imaging test. Common tests used to diagnose an aortic dissection include a CT scan of the chest with a contrast dye and a trans-esophageal echocardiogram. The proximity of the aorta to the esophagus allows the use of higher-frequency ultrasound for better anatomic images. Other tests that may be used include an aortogram or magnetic resonance angiogram (MRA) of the aorta. Each of these tests have varying pros and cons and they do not have equal sensitivities and specificities in the diagnosis of aortic dissection.
In general, the imaging technique chosen is based on the pre-test likelihood of the diagnosis, availability of the testing modality, patient stability, and the sensitivity and specificity of the test.
Magnetic resonance imaging (MRI) is a widely used method for the detection and assessment of aortic dissection. An MRI examination of the aorta will produce a three-dimensional reconstruction of the aorta, allowing the physician to determine the location of the aortal wall 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.
Another method for examining aortic dissection is the transesophageal echocardiogram (TEE). TEE is a comparatively good test in the diagnosis of aortic dissection. It is a relatively non-invasive test, requiring the individual to swallow the echocardiography probe. It is especially good in the evaluation of AI in the setting of ascending aortic dissection, and to determine whether the ostia (origins) of the coronary arteries are involved. While many institutions give sedation during transesophageal echocardiography for added patient comfort, it can be performed in cooperative individuals without the use of sedation. Disadvantages of the TEE include the inability to visualize the distal ascending aorta (the beginning of the aortic arch), and the descending abdominal aorta that lies below the stomach. A TEE may be technically difficult to perform in individuals with esophageal strictures or varices.
An aortogram involves placement of a catheter in the aorta and injection of contrast material while taking x-rays of the aorta. The procedure is known as aortography. Previously thought to be the diagnostic "gold standard", it has been supplanted by other less invasive imaging modalities.
Surgery and Treatments
Because of the potentially fatal nature of aortic dissection, patients are treated immediately. Drugs are administered to reduce the blood pressure and heart rate. If the dissection is small, drug therapy alone may be used. In other cases, surgery is performed. In surgery, damaged sections of the aorta are removed and a synthetic graft is often used to reconstruct the damaged vessel. The objective in the surgical management of aortic dissection is to remove the most severely damaged segments of the aorta, and to eliminate the entry of blood into the tear. While excision of the tear may be performed, it does not significantly change mortality.
Some methods of repair are:
- Replacement of the damaged section with a tube graft when there is no damage to the aortic valve.
- Insertion of a stent graft (covered stent), e.g. in TEVAR (thoracic endovascular aortic repair). It is usually combined with on-going medical management
- Replacement of the damaged section of aorta with a sutureless vascular ring connector-reinforced graft. Vascular ring connector (VRC) is a titanic ring used as a stent in the vascular graft to achieve a quick, blood-sealed, and sutureless connection.
In an acute dissection, treatment choice depends on its location. For Type A dissection, surgery is preferred over medication. For uncomplicated Type B (distal aortic) dissections, medical management is preferred over surgical.
The risk of death due to aortic dissection is highest in the first few hours after the dissection begins, and decreases afterwards. Because of this, the therapeutic strategies differ for treatment of an acute dissection compared to a chronic dissection. An acute dissection is one in which the individual manifests symptoms of dissection within the first two weeks. If the individual has managed to survive this window period, his prognosis is improved. About 66% of all dissections present in the acute phase. Individuals who present two weeks after the onset of the dissection are said to have chronic aortic dissections. These individuals can be treated with medical therapy as long as they are stable.
Aortic dissection generally appears as a hypertensive emergency, and the prime consideration of medical management is strict blood pressure control. Beta blockers are a first line treatment for patients with acute and chronic aortic dissection. Vasodilators such as sodium nitroprusside can be considered for patients with ongoing hypertension, but they should never be used alone, as they generally cause reflex tachycardia.