Bicuspid Aortic Foundation Aneurysm and Dissection Page

Thoracic Aortic Aneurysm and Dissection (TAAD)

Heart disease has historically been known as the number one killer of both men and women. However, there is another less well-known disease in the chest, aortic disease. Sudden death that seems "heart related" may sometimes actually have been caused by aortic disease. Following is information about the aorta, and the disease conditions that affect it.

About The Aorta

The aorta is the body's largest artery, carrying oxygen-rich blood away from the heart as it begins its journey through the circulatory system. It begins just above the aortic valve, rising out of the left ventricle of the heart, and then curves and bends down into the lower body. Other arteries branch off from it to supply blood to various parts of the body. The aortic root, ascending aorta, aortic arch, descending aorta, and thoracoabdominal aorta all are considered part of the thoracic (chest) aorta, and are treated by thoracic aortic specialists.

Aortic Root
The very beginning of the aorta, which is slightly larger in size, is called the root. The first two arteries that branch off the aorta, the coronary arteries, are found here. It is important to know this, because if surgery is needed on the aortic root, great care is needed in handling the coronary arteries, which supply blood to the heart. An important break through in aortic surgery was the development of the Bentall technique in 1968, which successfully allowed replacement of the aortic root followed by reattachment of the coronary arteries. This technique was later improved by using buttons of aortic tissue to attach the coronary arteries to the Dacron graft (Button Bentall).

Ascending Aorta
The ascending aorta is that section between the aortic root and the arch. No other arteries branch from it. This part of the aorta is under the most pressure, handles the greatest volume of blood, and also has very little support around it. Aneurysm and dissection are more likely to happen in this part of the aorta in those with bicuspid aortic valve disease and other connective tissue disorders.

Aortic Arch
The arch is the top of the aorta, where it curves as it bends down toward the lower body. The innominate, left common carotid, and left subclavian arteries, which carry blood to the head and upper body, branch off the arch.

Descending Aorta
The section of the aorta beginning just beyond the arch and ending at the diaphragm is called the descending aorta. Many little arteries, called the intercostal arteries, branch from this part of the aorta to supply the spinal cord with blood.

Thoracoabdominal Aorta
The part of the aorta that includes the lower descending aorta passing through the diaphragm and ending at the level of the renal arteries is called the thoracoabdominal aorta. Below this point, the aorta is called the abdominal aorta.

What is an Aortic Aneurysm?

In general, an aneurysm is a permanent enlargement or bulging of a blood vessel. This bulging or ballooning happens at a place where the walls of the vessel have become weak and thin.

The Society for Vascular Surgery has stated that an aneurysm exists when a blood vessel has enlarged to at least 1.5 times its normal diameter. It is reasonable that larger people will normally also have a larger aorta, and smaller people a smaller aorta. Therefore, the body size, as well as the gender and age of a person, help determine how big their aorta would normally be. If the normal size of the ascending aorta was 2.5 cm, enlargement to a diameter of 3.75 cm would be an aneurysm in that person.

For an aortic aneurysm, another definition is an enlargement of at least 4.0 cm in diameter in an average-sized adult.

If the aorta has begun to enlarge, before it is considered big enough to be an aneurysm, it is called dilated. The phrase aortic dilatation is used to describe this also.

•Whether aortic dilatation or an aneurysm is present, it is important to concentrate on getting an accurate measurement of the aorta.

• Enlargement of the aorta is considered a sign of aortic disease. It should be treated by medically addressing blood pressure and by checking aortic size periodically.

Thoracic Aortic Aneurysm

The medical terms used to describe an aortic aneurysm in the chest tell three things:

      • the shape of the aneurysm
      • where it is located
      • how big it is

There are two types of aortic aneurysm shapes:
      • saccular, where the enlargement is on one side of the aorta, like a sack or a pouch
      • fusiform, which means the enlargement is equal in all directions

Following are sample diagnoses of thoracic aortic aneurysms:

      • 5.1 cm fusiform ascending aortic aneurysm
      • 6.0 cm fusiform thoracoabdominal aortic aneurysm
      • 4.0 cm saccular arch aortic aneurysm

Pictured is an example of a fusiform ascending aortic aneurysm.

What is Aortic Dissection?

Aortic dissection involves the aortic wall, which has three layers:

      • intima, a thin inner layer
      • media, a thicker, elastic, middle layer
      • adventitia, a thin outer layer

When the inner layer of the aorta tears and separates from the outer layer (adventitia), it is called dissection. Blood enters the middle layer (media), separating the inner and outer layers. The blood remains inside the aorta and does not escape out into the body.

Dissection of the aorta may be Type A or Type B.

       • Type A dissection begins in the ascending aorta. It is quite common for Type A dissection to start just above the coronary arteries.

       • Type B dissection always affects the descending aorta but not the ascending aorta.

Risks of Aortic Aneurysm and Dissection

The earlier aortic disease is found, the greater the opportunity there is to use all available medical knowledge and surgical skill to treat it. Early detection, expert evaluation, and ongoing care provide the opportunity to continue living an active, productive life.

However, early detection can be difficult, and aortic disease is a serious condition.
The aorta is exposed to a much higher blood flow than any other blood vessel in the body. A healthy aorta is strong and flexible, handling well the volume of blood flowing through it under pressure. If the wall of the aorta is diseased, it is like having a bulging, weak area in a hose under pressure. The hose may tear or break open completely. When the "hose" is the aorta, filled with blood, this can be very damaging and often is fatal.

Aortic aneurysm and dissection are particularly treacherous because they give little, if any, warning. Unlike many illnesses, there usually is no ongoing pain or feeling of being sick. Some people do experience milder symptoms such as chest or back discomfort, a hoarse voice, a cough, difficulty swallowing, or asthma-like symptoms. These are symptoms that may be caused by many things, and the connection with the aorta is not obvious. When severe chest or back pain develops, it may already be an emergency situation involving dissection. Even if there is no dissection, careful investigation is needed to determine whether this pain is a sign of a weak aorta combined with uncontrolled hypertension, or an indication of the presence of an established aneurysm that is growing in size.

There is also danger because most people do not know that they have a condition that puts them at risk, such as a bicuspid aortic valve. They may have a history of aortic disease in their family and not realize it. If relatives have died suddenly and no autopsy was done, it often is assumed that they had a heart attack when they may actually have died of aortic dissection or rupture.

In the emergency room it is typical for a heart attack to be the first suspect when chest pain is present. When the pain is from the aorta, a heart attack will be ruled out. However, unless the aorta is scanned, the real reason for the pain will not be found. At this point, anxiety may be suggested as the reason for the symptoms. So this condition is dangerous because someone with aortic pain or full blown aortic dissection may die in the emergency room, or be sent home again not knowing that their life is at risk due to aortic disease.

Aortic dissection may happen whether or not the aorta is enlarged. When this tearing happens to the ascending aorta (Type A dissection), it is an emergency situation. Once it has torn, the thin outer layer is all that holds the aorta together. Emergency surgery is required.

Type B dissection (intimal tearing of the descending and thoracoabdominal aorta) in the short term is less dangerous, as long as it does not cut off the blood supply to the lower body and its organs. Often, lowering and stabilizing blood pressure may be all that is needed immediately. A dissected descending aorta must be monitored because it may enlarge, actually becoming an aneurysm, and eventually require surgery.

An aneurysm may either dissect or completely rupture. If an aneurysm dissects (intimal tear), survival will depend on where the tear happens and how quickly treatment is available. If an aortic aneurysm completely ruptures, bleeding is so severe that it is unlikely that anything can be done quickly enough.

What Causes Aortic Aneurysm and Dissection?

Several factors have been shown to cause thoracic aortic aneurysm and dissection. Knowing these risk factors is important, because they are clues that can lead to early detection of aortic disease.

The following are underlying factors that may result in the development of thoracic aortic aneurysm, dissection, or both:
          • Bicuspid aortic valve disease
          • Connective tissue disorders
             (Ehlers-Danlos, Marfan, Turners, Williams syndromes, etc.)
          • Other unspecified familial and connective tissue disorders
          • Hypertension
          • High blood pressure during heavy weight lifting or other strenuous activity
          • Atherosclerosis
          • Smoking
          • Infectious and inflammatory conditions
             (Takayasu's aortitis, giant cell arteritis, rheumatoid aortitis, syphilitic aortitis)
          • Injury

Injury and infection more commonly can cause pseudoaneurysm formation. A pseudoaneurysm is different from an actual aneurysm because there is a break in the aortic wall, and it is the support from neighboring structures that prevents free rupture.

Any medicine that exacerbates mild hypertension (such as those used as an appetite suppressant) can result in full hypertension. These types of medication are strongly discouraged for anyone with aortic disease and if used, careful supervision is needed.

In addition, using crack cocaine may result in thoracic aortic dissection. Cocaine usage can raise blood pressure to very high levels, and in some people has caused tearing of the aortic wall.

How Are Aortic Aneurysm and Dissection Found?

It is necessary to "see" inside the chest in order to check on the aorta there. Today's imaging technology makes this possible. There are tests that can be done which will show the aorta and whether or not it is enlarged or dissected. The test images should be of high quality and should be reviewed by aortic specialists, skilled in aortic measurement.

Echocardiogram
One test that may show part of the aorta is an echocardiogram. It uses sound waves to produce images of the heart, its valves, and also shows the root and ascending aorta. However, the most common form of this test (transthoracic echocardiogram or TTE) is done with a wand passed over the outside of the chest. This wand "sees" only a small area at a time, and this test is very dependent on how it is done. When an echocardiogram detects aortic enlargement, another test may be done to more precisely look at the entire aorta.
A tranesophageal echocardiogram (TEE) has a much better ability to reveal most of the thoracic aorta, and is an excellent tool to evaluate the heart's valves and chambers. However, it is invasive and requires sedation.

CT and MRI
Either a CT scan or an MRI gives the most accurate image of the entire aorta. Both of these tests are done with contrast, which is given intravenously. A CT scan uses x-rays to produce its images. An MRI uses a magnetic field. In the case of dissection, which usually occurs suddenly with great pain, the fastest way to get an image of the aorta is the CT scan.
Please see the Patients and Families page for additional information about diagnostic testing.

Emergencies

When aortic disease is known to be present, with proper care there should be a significant reduction in the number of emergencies. Medically maintaining lowered blood pressure is aimed at preventing emergency situations.

In an emergency, the odds of injury and death due to aortic dissection or rupture increase significantly.

     • When chest and/or back pain or other symptoms are present and there is no evidence of a heart attack, a CT scan of the aorta using intravenous contrast should be done. Alternatively, a high quality transesophageal echocardiogram (TEE) may also be equally informative.

     • Quickly finding out if an aortic aneurysm or dissection is present or not can make the difference between life and death.

     • The aorta itself "feels" pain that should not be ignored. Pain or feelings of pressure in the chest and back may come from the aorta, even if it has not dissected. This usually occurs with elevated systolic blood pressure (symptomatic aorta).

     • Medically, lowering blood pressure removes stress on the wall of the aorta and may relieve aortic pain.

     • Aortic pain and other aortic-related symptoms (such as pressure in the chest) are not due to anxiety. Anyone may be understandably anxious when experiencing chest pain. However, anxiety is most likely not the primary cause of the symptoms when aortic disease is present.

How Are Aortic Aneurysm and Dissection Treated?

Medical Treatment and Lifestyle Changes

Currently, there is no "cure" for aortic disease once there is degeneration of the tissue. It is possible to reduce the risk of ever developing an aneurysm due to something that can be controlled, such as hypertension and smoking.

Once aortic disease is present, regardless of the underlying cause, medical and surgical treatment is available. Aortic surgery has advanced significantly, over a period of three decades, saving many lives.

The main medical treatment for the enlarged aorta is maintaining blood pressure at appropriate levels. According to the new blood pressure classifications announced in 2003, normal blood pressure is below 120 systolic (top number), and at 120 pre-hypertension begins. This is meant for those with normal aortic tissue. For those with fragile aortic tissue, it is important to have a systolic blood pressure even lower than what is recommended for the general population. The following kinds of blood pressure medications may be used:

           • beta blockers
           • ARBs
           • ACE inhibitors
           • calcium channel blockers
           • alpha blockers
           • diuretics

Surgery

When Should I Have Surgery?
One of the first questions faced by anyone with a thoracic aortic aneurysm is, "When should I have surgery?" The decision to have aortic surgery is carefully made, considering risk factors for that individual, including their overall health and ability to tolerate surgery. Generally, surgery is suggested when the risk of aortic tear or rupture is greater than the risk of having surgery. Following are several things an aortic surgeon will consider regarding the timing of surgery:

     • Size of aneurysm
     • Aneurysm growth rate
     • Type of aortic disease present
     • Whether or not there are aortic symptoms such as chest or back pain
     • Family history (whether or not the aorta dissected or ruptured at small aortic sizes in other family members)

A great deal of attention is paid to the size of the aorta, because as the aorta gets larger, the odds are greater that it will tear or rupture. A great deal of attention is also paid to the risk of having surgery. The most experienced aortic surgery centers have successfully lowered the risk of aortic surgery. In these experienced centers, it should be possible to have surgery done sooner, at smaller sizes, before the aorta tears or ruptures.

The aortic aneurysm size at which surgery is suggested varies somewhat between surgeons and centers. When thinking about having thoracic aortic surgery, it is important to keep in mind that:

      • Surgery should be done in an experienced aortic surgery center with a low rate of complications and death and good long-term results.
      • Surgery decisions are made based on several factors, not just size alone.
      • Surgery decisions are made on an individual basis.
      • Surgery is generally offered to those with the most fragile aortic tissue earlier, at a smaller aneurysm size, due to a greater risk of rupture or dissection.

What is Aortic Surgery Like?
Generally, aortic surgery may seem like "open heart" surgery because the chest is opened and the heart lung machine is used. During aortic surgery, the weak, thin diseased tissue is removed, and a graft made of Dacron is put in its place. Modern Dacron grafts are strong, flexible, and treated with collagen so that blood cannot soak through them. The human body does not reject Dacron, and the graft does not become calcified. Over time, the graft is completely covered with a thin layer of human cells.

However, there are some special differences when surgery is done on the aorta. One of those differences is the need to temporarily stop not just the heart, but also the flow of blood, at a certain point while the aorta is open. In order to safely stop the flow of blood temporarily, the body temperature must be very cold. This is called total circulatory arrest, and can be safely done for up to about 40 minutes.

Over time, the results from aortic surgery have been studied, and it has become clearer which techniques have been the safest with the longest lasting solutions. This has allowed aortic surgery to advance to where it is currently, and additional efforts to improve techniques continue. The objective of surgery is to perform the safest, longest-lasting procedure that is possible with current technology.

How surgery is done depends on the part of the aorta affected.

Root, Ascending Aorta, and Aortic Valve
When the aortic valve, entire aortic root, and ascending aorta must all be replaced, a technique called the Button Bentall is currently available. Because the root is being removed, the arteries that branch off the root and provide blood to the heart (coronary arteries) need to be sewn to the new aorta, the Dacron graft. The "buttons" are the circles of aortic tissue that were left around the openings of these coronary arteries. The coronary arteries are attached to the Dacron aortic graft by sewing these buttons of aortic tissue to it.

The aortic valve is typically replaced either with a biological valve or a mechanical valve. The original Bentall technique used a mechanical valve. When the new aortic valve is made of biological tissue, this is called a Bio Bentall procedure.

      • The majority of aortic surgeons emphasize the importance of removing the entire ascending aorta, all the way to the beginning of the arch. When all of the ascending aortic tissue is removed, it cannot develop another aneurysm later. In order to do this safely, the aortic arch is left open and sewn to the Dacron graft without use of an aortic clamp (open anastomsis). This technique is done safely under total circulatory arrest and profound hypothermia (TCA), preferably in less than 40 minutes.

      • Following surgery on the ascending aorta, the diseased, aneurysmal tissue is completely removed. Earlier techniques kept the aneurysmal aortic tissue, and it was wrapped around the Dacron graft (inclusion technique). This technique has almost disappeared secondary to a higher incidence of pseudoaneurysm formation at the suture line. Therefore, this is no longer considered a desirable surgical approach.

If the aortic valve is appropriate for repair, the entire aortic root is removed and is replaced with a Dacron graft, leaving a small rim of aortic tissue attached to the aortic valve. The coronary arteries are re-attached to the side of the Dacron graft (aortic root remodeling technique).
In the majority of these cases:
      • the ascending aorta is removed all the way to the base of the innominate artery
      • total circulatory arrest is used
      • the aortic valve may be left as is, repaired, or replaced.

Aortic Arch
Surgery on the aortic arch requires special techniques because of the three major arteries that supply blood to the brain. Any disruption of the blood supply here can result in brain damage. The use of total circulatory arrest for aortic arch surgery, reported in 1975, was an important break through, allowing the safe removal of aortic arch aneurysms.

Descending and Thoracoabdominal Aorta
Many smaller vessels branch from this part of the aorta to supply blood to the spinal cord and organs such as the liver and kidneys. When surgery is done here, the main concerns are protecting the spinal cord and abdominal organs from harm. In order to avoid paraplegia and/or liver and kidney failure, more than one surgical technique has been used on this part of the aorta.
The use of total circulatory arrest under profound hypothermia for the past number of years has demonstrated significant promise in lowering paraplegia and renal failure. Other techniques such as left heart bypass or partial circulatory support, as well as the clamp and sew technique, are also in use in various centers.

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