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What is aortic dissection?

The aorta is the main blood vessel that arises from the heart and supplies blood flow to the rest of the body. The aorta is divided into sections. The ascending aorta starts at the heart and travels up the chest toward the head. Its main branches are the coronary arteries, which supply blood flow directly to the heart. The aortic arch (Figure 1A) curves over the heart and gives off branches that supply blood flow to the brain and arms. The descending aorta courses through the chest, and after passing the lungs and diaphragm becomes the abdominal aorta. Branches from the abdominal aorta provide the blood supply to the major organs (liver, kidney, stomach and intestines) as well as to the legs (Figure 1B).

Figure 1. (A) Normal aortic arch. (B) The aorta is the main blood vessel that supplies blood to the entire body. Reprinted with permission, Cleveland Clinic Center for Medical Art & Photography © 2014. All Rights Reserved.

The aorta is the largest artery in the body. Its wall has several layers (Figure 2). The innermost layer is called the intima. This layer is made up mainly of cells called endothelial cells and is in direct contact with the blood. The middle layer of the wall of the aorta is called the media. This layer contains smooth muscle cells and elastic fibers, which allow the aorta to contract and expand during the cardiac cycle. The outermost layer is the adventitia. This layer consists of connective tissue that gives additional support to the aorta.

Figure 2. The wall of the aorta has three layers. The inner layer tears in an aortic dissection. Reprinted with permission, Cleveland Clinic Center for Medical Art & Photography © 2014. All Rights Reserved.

Aortic dissection is a serious and potentially life-threatening medical condition that occurs when the inner layer (intima) tears, causing it to separate from the middle layer (media). Blood then flows between the layers, creating a channel called a dissection. You may hear your doctor discuss this channel as the ‘false lumen’, implying that the blood should not be there, versus the ‘true lumen’ whose layers have not been violated. Reduced blood flow in the dissected aorta can lead to major organ damage, or the channel may rupture or burst open through the outer layer (adventitia), which can be fatal.

Aortic dissection usually develops in the chest (thoracic) part of the aorta. It can involve the ascending aorta, descending aorta, or both. Dissections can also occur in the abdominal aorta, although this is less common. Two different classification systems are used by physicians to describe the location and extent of an aortic dissection.

The Stanford classification refers to dissections as Type A or Type BType A means the dissection involves the ascending aorta, and Type B means it involves the descending aorta and/or abdominal aorta, without affecting the ascending aorta. The DeBakey classification system distinguishes between Type IType II, and Type III dissections. Type I involves the entire aorta, Type II involves the ascending aorta only, and Type III excludes the ascending aorta and aortic arch (Figure 3).

Figure 3. Dissection classification. Based on the Stanford classification, Type A aortic dissections involve only the ascending aorta and Type B dissections involve the descending aorta. Based on the DeBakey classification, Type I dissections involve the whole aorta, Type II only the ascending aorta, and Type III only the descending aorta. Reprinted with permission, Cleveland Clinic Center for Medical Art & Photography © 2014. All Rights Reserved.

Acute Type A dissection (involving the ascending aorta) is a surgical emergency. It is often fatal if not detected quickly, with a mortality rate of 1–2% per hour within the first day1 and up to 50% within the first 48 hours if left untreated. Acute Type B dissection (involving the descending aorta) is not as threatening as Type A dissection, but the mortality rate can be as high as 10% in the first month. Prompt medical treatment is critical in both types of dissection.

Many people may not be familiar with aortic dissection because it is relatively uncommon. Awareness is important since complications occur quickly and the outcome is often fatal. Survival rates are much better if aortic dissection is recognized early and treated with proper medical and surgical care.

Aortic dissection was propelled into the spotlight in 2003, when 54-year-old actor John Ritter developed sudden chest pain on the set of his TV show. He was taken to a California hospital where he was initially misdiagnosed as having a heart attack. A few hours later as his condition worsened, he was diagnosed with an aortic dissection and unfortunately died during surgery. The John Ritter Foundation (http://johnritterfoundation.org/) focuses on promoting awareness of aortic disease.

In 2010, the US Special Envoy to Pakistan and Afghanistan, Richard Holbrooke, suffered a fatal aortic dissection at the age of 69 while in a meeting at the State Department – he was unable to recover despite undergoing over 20 hours of emergency surgery.

Dr Michael DeBakey (1908–2008) was a world-renowned heart surgeon who pioneered the surgical procedure used to treat acute Type A aortic dissection, known as the DeBakey procedure. Ironically, at the age of 97, he survived an aortic dissection after undergoing several hours of surgery followed by a prolonged recovery. At age 98, he became the oldest survivor of his own operation.2

Who is at risk and what causes aortic dissection?

Aortic dissection occurs in 5 to 30 out of every 1 million people.3 It can affect men and women of all ages but is most commonly seen in men between 60 and 80 years of age.4 The most important risk factors for aortic dissection are uncontrolled high blood pressure and atherosclerosis (hardening of the arteries). Younger patients may have other predisposing factors such as a pre-existing aortic aneurysm (a bulge or ballooning in the aorta due to a weakened wall), a bicuspid aortic valve (two leaflets instead of three leaflets of the aortic valve of the heart), or inflammatory diseases with vasculitis (inflammation of the blood vessels).

Importantly, certain genetic conditions increase the risk of aortic dissection. These disorders of the connective tissue, called collagen, include Marfan’s syndrome, Ehlers–Danlos syndrome, and Loeys–Dietz syndrome. Other genetic mutations associated with aortic dissection have also been identified. In most (but not all) of these cases, multiple family members have had an aortic dissection or have an aortic aneurysm. Other less common causes of aortic dissection include high-intensity weight lifting and the use of cocaine.

What are the signs and symptoms of aortic dissection?

Most patients with an aortic dissection typically experience severe and sudden chest pain that is usually sharp or tearing, particularly in dissections involving the ascending aorta (Type A). With dissections in the descending aorta (Type B), the pain may be more in the upper back or in the abdomen. In both types, the pain is usually terrible and often described as the worst pain a patient has ever experienced. Other symptoms caused by a decrease in blood flow to the body include fainting, nausea/vomiting, sweating, shortness of breath, or leg pain. Uncontrolled high blood pressure is common.

Aortic dissection can also cause a heart attack, acute heart failure, or stroke due to lack of blood flow to the heart or brain. Unfortunately, the diagnosis of aortic dissection may then be delayed in such cases when patients do not have typical symptoms of severe chest pain. Other signs of aortic dissection include a new heart murmur, weak pulses in the feet or wrists, or a significant difference in the blood pressure measurement between the right and left arms.5

How is aortic dissection diagnosed?

When the diagnosis of aortic dissection is suspected, accurate imaging studies must be performed immediately. The imaging studies must determine whether a dissection is present and, if so, how extensive it is and which parts of the aorta are involved. The location of the dissection determines the urgency of the situation and whether emergency surgery is necessary.

Computed tomography (CT scan) is the most widely available test and can be done in most emergency rooms. CT scans are accurate in diagnosing aortic dissection, including the location and extent. An additional advantage of CT is that branches of the aorta can also be seen well to determine if they are involved in the dissection. Some disadvantages include the radiation exposure and the need for using intravenous (IV) contrast dye, which some patients cannot receive due to allergy or kidney problems.

Echocardiography (an ‘echo’) may help in the diagnosis of aortic dissection. An echo is an ultrasound of the heart and aorta. The simpler type of echo uses an ultrasound probe with gel over the chest, referred to as transthoracic echocardiography (TTE). In some cases, a camera probe can be inserted into the esophagus for more detailed ultrasound imaging, referred to as transesophageal echocardiography (TEE). The advantages of echocardiography are that it can be done at the bedside and results are immediately available. Aortic dissection is diagnosed if two channels of blood flow are seen, separated by a dissection flap. TTE looks at the part of the aorta near the heart (for Type A), while TEE looks at the entire thoracic aorta (for Type A and Type B) and has the additional advantage of imaging the aortic valve in the heart to see if it is affected by the dissection.

Magnetic resonance imaging (MRI) is also accurate at imaging the aorta, but it is not usually available in emergency rooms and thus unlikely to be used in an emergency situation. MRI exams also take much longer than CT scans.

How is aortic dissection treated initially?

Type A or ascending aortic dissections are considered surgical emergencies because patients have a high mortality rate: about 1–2% per hour once symptoms begin. ‘Open heart’ surgery for Type A dissection typically involves replacing the affected part of the aorta with a graft (a synthetic tube). The mortality from the surgery itself for repair of Type A dissection can be high, but without surgery the rate is much higher. Sometimes the aortic valve needs to be repaired or replaced when the aorta is replaced.

Type B or descending aortic dissections are often treated with medical therapy and observation, without the need for surgery. Patients are typically monitored closely in an intensive care unit (ICU) setting. Medical therapy consists mainly of aggressive control of heart rate and blood pressure, usually with medications administered through an intravenous (IV) line. Medications used may include blood pressure medicines such as beta-blockers and nitroprusside, along with medications to control the pain.

If a Type B (descending) aortic dissection is complicated by a reduction in blood flow to a vital organ, such as the kidney or legs, then surgery or endovascular repair (insertion of a stent graft through an artery in the groin) is recommended. In rare cases, a Type B dissection may lead to growth of the aorta (aneurysm) and threat of rupture, and an endovascular stent graft may be lifesaving.

What about life after an aortic dissection? How is aortic dissection treated and monitored over the long-term?

After an aortic dissection, lifelong medical follow-up is critical to prevent problems with the aorta down the road (Table 1). Several different specialists may be involved in the medical care of patients with aortic dissection in the hospital, such as a cardiothoracic surgeon, cardiologist, ICU specialist, vascular surgeon, and/or vascular medicine specialist. After hospital discharge, regular outpatient follow-up should occur with at least one physician experienced in caring for patients with aortic dissection.Table 1. General instructions after aortic dissection.

Monitor your blood pressure at home.– Your blood pressure goal is 120/80 mmHg. Let your doctor know if it is above your goal, so that your medications can be adjusted.– Controlling your blood pressure is one of the most important things you can do to prevent additional problems with the aorta.– Beta-blockers help to reduce the stress on the aortic wall.– Take your blood pressure medications as prescribed.
Maintain a normal body weight.
Talk to your family about screening.– Since aortic dissection is sometimes inherited, your first-degree relatives (mother/father, sister/brother, son/daughter) may need to be screened to check the aorta.– First-degree relatives should discuss your aortic dissection with their health care providers.– Your first-degree relatives may need an echocardiogram and/or ultrasound of the abdominal aorta.
Avoid smoking and exposure to smoke.
Take your aspirin and statin, if prescribed.– If you have atherosclerosis (plaque) in the arteries, your doctor may have prescribed aspirin and a statin (cholesterol-lowering medication).
You should remain active.– Aim for 30 minutes/day of brisk exercise.– A good goal is 10,000 steps per day.
Avoid contact sports and overexertion.– Mild to moderate exertion is good for your overall cardiovascular health.– You should limit activities that require maximal exertion.– You should avoid contact sports, very strenuous exercise, and heavy lifting.– Overexertion can increase the blood pressure and the stress on the aortic wall.– Discuss your activity restrictions with your health care provider.

Initially, outpatient care will focus on getting back to a normal life after what is often a near-death experience. The physical and psychological recovery can be difficult, and rehabilitation may be needed.

The most important medical issue is usually the blood pressure. A normal blood pressure is 120/80 mmHg, and patients who have had an aortic dissection should aim for this goal. Beta-blockers are prescribed to lower the heart rate and the blood pressure, which reduces the stress on the aortic wall. Most patients will be on additional medications for blood pressure control.

Monitoring the aorta with imaging tests is important because the aorta can leak or the walls of the aorta can weaken and lead to an aneurysm (dilation or ballooning). Such complications can happen even without symptoms, and up to one-third of patients may require surgery later on. Periodic monitoring of the aorta may be with CT or MRI, depending on the preference of the specialist and depending on the specific patient situation. Some specialists will obtain a CT scan or MRI at 3, 6, and 12 months after an aortic dissection to evaluate the risk of growth of the dissected and weakened aorta. If everything looks stable at the 12-month follow-up visit, then imaging can be done once a year with CT or MRI.

Patients with aortic dissection may have atherosclerosis or plaque in the arteries, which requires additional medical treatment to reduce the risk of cardiovascular events such as heart attack and stroke. A blood-thinning medication such as aspirin is usually prescribed to reduce this risk. A statin is also prescribed to reduce the cholesterol and to reduce the risk of heart attack and stroke. Quitting smoking is absolutely essential. Diabetes should be controlled, and a normal body weight should be maintained.

What about family members?

Patients with aortic dissection may be referred to genetics counselors to look for an inherited cause, particularly if several family members have had problems with the aorta or if the dissection involved the ascending aorta. Even if formal genetic testing is not chosen, it is generally recommended that first-degree relatives be screened to check the aorta. This can be easily achieved with an echocardiogram and/or ultrasound of the abdominal aorta.

What precautions should be taken after aortic dissection?

Regular exercise is important for everyone. Adults should aim for at least 30 minutes per day of brisk exercise. Walking is a great way to start, with an ultimate goal of 10,000 steps per day. Mild to moderate exertion poses no problem after aortic dissection, but activities involving extreme or maximal exertion should be avoided. Contact sports, very strenuous exercise, isometric exercises (such as sit-ups, push-ups, or pull-ups), and heavy lifting should be avoided. Over-exertion can increase the blood pressure and the stress on the aortic wall.

It is important that patients who have survived an aortic dissection have a discussion with their doctors about their exercise plans and the amount of weight that is safe to lift. A good rule of thumb is that if something cannot be lifted easily at least 10 times in a row, then it is probably too heavy. In addition, straining should be avoided and exercise should not be performed to the point of exhaustion.6

Summary

Aortic dissection is an uncommon, life-threatening cause of chest pain. The symptoms often include a ripping or tearing pain, with the location depending on which part of the aorta is affected. Early diagnosis of aortic dissection is critical to improve survival. Emergency surgery is required for Type A aortic dissections, while medical management is the current standard for uncomplicated Type B dissections. Controlling blood pressure is the most important aspect of medical treatment of aortic dissection, especially in the chronic phase. Lifelong surveillance imaging and regular medical follow-up are required to monitor for complications and aneurysms after an aortic dissection.

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