Aortic Disease

 

The Aorta

The aorta is the largest artery in the body, rising from the heart's major pumping chamber, the left ventricle. Oxygen-rich blood enters the aorta with each contraction of the left ventricle and travels throughout the body through the smaller arteries branching from it.

The walls of the aorta are made up of three different layers of tissue: a thin inner layer (intima); a thick, elastic middle layer (media); and a thin outer layer (adventitia). The structure of these layers is important to the proper functioning of the aorta. As the heart contracts, forcing blood through the open aortic valve into the aorta, the walls of this artery must be flexible enough to absorb the force as blood surges into it.

The aorta is said to be an elastic blood vessel. Connective fibers within the aortic wall allow it to stretch as it experiences pressure, returning to its relaxed state as the force subsides. In the normal aorta these elastic fibers are present throughout and are especially dense in the wall of the ascending aorta, which experiences the greatest force with each heartbeat.

 

Structure of the Aorta


 


 

(Click on image to view the structure of the aorta.)

  • Aortic root - The root is the beginning of the aorta. Starting from the aortic valve (annulus) and becoming slightly wider in diameter (sinuses of Valsalva), it gives rise to two coronary arteries and ends at the beginning of the ascending aorta (sinotubular junction). The two coronary arteries are responsible for carrying oxygen-rich blood to the heart muscle itself.
  • Ascending aorta - This segment extends upward from the aortic root to the point where the innominate artery branches off the aorta, and the aorta begins to form an arch. It is within the heart sack (pericardium) by itself and no arteries branch from it. There is little support from surrounding tissue and it must face the entire cardiac output volume (minus the coronary arteries), making the ascending segment the most vulnerable part of the aorta.
  • Aortic arch - The arch represents the curved portion at the top of the aorta. The innominate, left common carotid, and left subclavian arteries, which supply blood to the head and upper body, branch from the arch. It is outside the pericardial sack and generally has better support from surrounding structures.
  • Descending aorta - This section begins just beyond the arch as the aorta bends down into the body. The descending aorta ends at the diaphragm. It contains the intercostal arteries that feed the spinal cord. The beginning portion of the descending aorta is vulnerable to injury (intimal tear) during deceleration conditions.
  • Thoracoabdominal aorta - This section begins at the diaphragm and ends at the visceral vessels (celiac, superior mesenteric and renal arteries).
  • Abdominal aorta - The abdominal aorta begins below the renal arteries, which supply blood to the kidneys. The aorta ends where it divides into the two iliac arteries. It contains a small artery named the inferior mesenteric artery.

 

Aortic Aneurysm and Dissection Overview

Diseased aortic tissue is characterized by degeneration of the cells composing the aortic wall. This diseased tissue is weak, lacking sufficient elastic components to stretch and contract well. The first indication of this abnormality may be a localized enlargement in the area of weakness. When it reaches a certain size this enlarged area is referred to as an aneurysm.

Aortic tissue may also tear, even if the aorta is not enlarged. Tearing of the inner layer of the vessel wall allows blood to leak into the middle layer of the aorta, separating the inner and outer layers. This is called dissection.

 

Thoracic Aortic Aneurysms

The permanent enlargement of some portion of a blood vessel is often described as bulging, ballooning or dilated. The diameter of the enlargement will determine whether or not it is considered an aneurysm. Traditionally for the aorta, any permanently dilated section measuring 4.0 cm or greater in diameter has been called an aneurysm.

The definition of an aneurysm may also be based on comparison with the normal blood vessel size for an individual. When the permanent enlargement of some part of a blood vessel is at least 1.5 times greater than normal size, it may be termed an aneurysm. Applying this to the aorta, if an individual's normal aorta is 2.5 cm, then dilation of 3.75 cm or greater represents an aneurysm in that person. A variation of this defines an aneurysm when the enlarged aorta is at least twice its normal size.

Whether the aorta is called "dilated" or the word "aneurysm" is used, any enlargement of the aorta, regardless of its size, is an indication of aortic disease and requires treatment. Aortic enlargement, although perhaps not yet qualified for the term aneurysm, should be monitored, treated medically, and the lifestyle and diet of the patient addressed.

Identifying dilation of the aorta implies the ability to determine the aorta's normal size for an individual. It is understood that the aorta's size will vary across any given population based on age, gender and body size. Broad ranges of aortic diameters sometimes listed as the normal size of the aorta necessarily span a large variation of body sizes in the population and may be misleading regarding a given individual. It is important that every effort is made to determine the normal aortic diameter for each individual in order to detect the early stages of aortic expansion due to underlying aortic disease. Generally, in the majority of patients that part of the aorta that is not enlarged may be used as an indicator of what is normal for that individual.

 

Aneurysm Types

Thoracic aortic aneurysms are described according to their location, size and shape. Location indicates the sections of the aorta affected (i.e., the root, ascending, arch, descending or thoracoabdominal). The size of the aneurysm is the diameter at the widest point of enlargement and is usually measured in centimeters. There are generally two different shapes for aneurysms: fusiform and saccular.

Fusiform Aneurysms

As depicted in the drawing at the left, a fusiform aneurysm is enlarged equally in all directions. As an example, a diagnosis of an aortic aneurysm might be: a fusiform aneurysm of the ascending aorta, measuring 5.2 cm.
 


 


  (Click on image to view fusiform aneurysm.)
 

Saccular Aneurysms

The saccular aneurysm gets its name due to a bulge, or sack, occurring on only one side of the aorta, as pictured at the left.


 


 

(Click on image to view saccular aneurysm.)
 

Psuedoaneurysms

A pseudoaneurysm is an aneurysm that does not have some or all of the aortic wall layers, often due to some injury to the inner aortic wall. They are also sometimes called false aneurysms. These aneurysms are more unpredictable, with a higher tendency to rupture at smaller sizes. Usually there is a greater inflammatory process involved in the surrounding tissue, which potentially can complicate a redo operation. Some pseudoaneurysms are the result of infection, which increases the risk of embolization and stroke.

 

Causes and Risk Factors for Thoracic Aortic Aneurysms:

  • Bicuspid aortic disease
  • Marfan syndrome and Ehlers-Danlos syndrome
  • Other connective tissue disorders (Marfanoid)
  • Atherosclerosis
  • Miscellaneous infectious and inflammatory conditions
  • Hypertension
  • Smoking
  • Trauma

 

Thoracic Aortic Dissection

Aortic dissection is the tearing of the inner layer of the aortic wall, allowing blood to leak into the wall itself and cause the separation of the inner and outer layers. It is usually associated with severe chest pain radiating to the back.

Type A Dissection

Dissection beginning in the ascending aorta is called Type A dissection. As depicted in the drawing, Type A dissection often begins just above the coronary arteries. Dissection occurring here, where the aorta is the largest, thinnest, lacks support from surrounding structures and experiences the greatest amount of wall tension, is life threatening. Type A dissection is always treated as a surgical emergency.

(Click on image to view Type A dissection.)

 

Type B Dissection

Whenever the ascending aorta is not involved, it is referred to as Type B dissection. This type always involves the descending aorta. The drawing at the left illustrates a Type B dissection beginning just beyond the aortic arch. Type B dissection is initially stabilized medically. However, if complications with blood flow to the lower body arise, whether as a result of narrowing of the true aorta (true lumen) or disruption and blockage of one of the aortic branches, the patient will require an interventional procedure.

(Click on image to view Type B dissection.)
 

Chronic aneurysmal enlargement of 4.5 cm in Marfan patients and 5 cm in non-Marfan patients will require surgical correction or endovascular stent placement if appropriate. Continued medical therapy is the best approach in Type B dissection when most of the blood flows into the true aorta (true lumen) and the aortic diameter is less than 4 cm. In these situations the patient is treated with blood pressure medication and the status of the aorta is periodically monitored through diagnostic testing.

Causes and Risk Factors for Both Type A and Type B Thoracic Aortic Dissections:

  • Bicuspid aortic disease
  • Marfan syndrome and Ehlers-Danlos syndrome
  • Other connective tissue disorders (Marfanoid)
  • Atherosclerosis
  • Miscellaneous infectious and inflammatory conditions
  • Hypertension
  • Crack cocaine usage
  • Smoking
  • Trauma

 

Thoracic Aortic Injury (Trauma)

Rapid deceleration of a moving person will cause a movement gradient across the junction of the aortic arch and the beginning of the descending thoracic aorta. Frequently the inner layer (intima) breaks, and the integrity of the aorta is maintained only by the thin outer layer (adventitia). This deceleration injury is seen in motor vehicle and motorcycle accidents, motor vehicle and pedestrian accidents, airplane crash landings and free falls from buildings, trees or mountains.

Aortic trauma is most common in severe motor vehicle and motorcycle accidents. Motor vehicle accidents in which aortic injury should be suspected include those in which:

  • Rollover of the vehicle occurs
  • A fatality is involved
  • A person is ejected from the vehicle
  • The vehicle sustains a dent of more than 12 inches
  • A prolonged period of time was required to extricate the victim from the vehicle
  • The jaws of life are used
  • A pedestrian is struck by a car going more than 20 miles per hour

This patient will require emergent diagnosis and scanning, usually done by spiral CT with contrast or transesophageal echo. Less frequently, aortography may be required. If a positive diagnosis is made, the patient will require either surgical resection of 2 to 3 inches of the aorta and replacement with a Dacron graft or the use an endovascular stented graft.

 

Thoracic Aortic Coarctation

Coarctation of the aorta is a narrowing of a section of the aorta, typically just beyond the arch as it bends down to descend to the lower body. Blood pressure is lower beyond the narrowed section. This is a congenital condition usually diagnosed and treated in infancy and childhood. It may be present with other congenital conditions such as bicuspid aortic valves.

Coarctation may be present in adults without causing symptoms due to the presence of collateral circulation. This means that over time smaller blood vessels have enlarged and provide an alternative pathway for blood flow. If the mean pressure gradient across the narrowing is greater than 25 mm, surgery may be needed. It is particularly important for adult patients with coarctation to receive treatment for upper body hypertension. Long standing upper body hypertension will cause severe left ventricular thickening (hypertrophy) and increase the risk of stroke as a result of intra-cerebral bleeding. Untreated significant adult coarctation will cause premature death as a result of hypertension complications.

 

Diagnosis

Thoracic aortic disease is discovered in different ways. Sometimes there is pressure or pain in the chest or back, but most often there are no warning symptoms. A dilated aorta or aneurysm may be discovered in the course of testing for something else or perhaps as part of a routine physical. Patients may have been advised that the existence of a bicuspid aortic valve puts them at risk for aortic aneurysm or dissection. A patient may also have been told that a connective tissue disorder, such as the Marfan's syndrome, is affecting the aorta and the valves of the heart.

Diagnostic testing is the first step in establishing a treatment strategy. A high degree of accuracy in the performance and interpretation of these tests is particularly critical in the evaluation of aortic disease.

 

Echocardiography

Echocardiograms use sound waves to produce pictures showing the heart chambers and valves as well as the aorta. This technology is particularly useful in evaluating valve function. Transthoracic echocardiograms (TTE) have the advantage of being noninvasive with a good level of accuracy for evaluating the ascending aorta, as well as the cardiac chambers and valves. Transesophageal echocardiography (TEE), although invasive and requiring general sedation, is more accurate in evaluation of aortic dissection, the descending aorta and overall cardiac and valve function.

 

Computed Tomography (CT) Scans

Spiral CT scans will require an intravenous contrast agent to rule out aortic dissection. This technology is widely available and an excellent tool for sizing of the aorta. However, it does not measure function of the heart or valves. It requires X-ray exposure, and the intravenous contrast may have an adverse affect on already borderline renal failure patients.

 

Magnetic Resonance Imaging (MRI)

MRI technology, an alternative to the CT scan, uses magnetic fields in creating images of the aorta. MRI shows blood flow, as well as details of the aorta and heart valves. Although more expensive than CT scans, the resultant images display much finer detail. There is no X-ray exposure, and the intravenous contrast has no adverse affect on the kidneys. It is not possible to use this test in critically ill patients or those with implanted pacemakers or ICDs.

Aortography

Presently there is very little indication for the use of aortography in the diagnosis of aortic disease unless it is done at the point of interventional treatment (balloon fenestration, endovascular stented graft placement). Routine use of coronary angiography in aortic dissection and connective tissue disorders (Marfan syndrome or bicuspid aortic disease) is not advised as these patients have a natural protection against atherosclerosis. Unless patients have a high risk factor for coronary artery disease, they are usually free of any significant plaque formation.

Additional Tests

Additional testing may include nuclear medicine (adenosine thallium myocardial viability tests) to evaluate any pre-existing coronary artery problems. Addition of carotid artery ultrasound (duplex scan) will delineate any pre-existing carotid problems. Patients who are surgical candidates will require dental clearance to avoid any postoperative infection of their prosthesis.

 

Treatment

Medical Treatment

Medical treatment and lifestyle changes are specified for each individual and will include blood pressure optimization and lifestyle recommendations. Blood pressure medications, such as beta blockers, ACE inhibitors, ARBs and calcium channel blockers, are commonly prescribed. However, use of diuretics may be beneficial in patients who are prone to weight gain as a result of water retention. Generally, an optimal systolic blood pressure range prior to surgery is between 105 and 110 during normal activity.

Lifestyle recommendations address diet, exercise and smoking cessation. It is very important that those with aortic disease do not smoke either actively or passively. A diet low in fat and carbohydrates and high in fiber and protein is recommended. Exercise is generally extremely helpful for aortic aneurysm patients, and they are encouraged to be active. Usually power walks of 15 to 30 minutes two to three times daily are recommended. However, heavy lifting, which puts pressure on the aorta, is prohibited.

Surgical Treatment

When the risk of aortic dissection or rupture is greater than that associated with surgery, elective surgery is offered to replace the diseased section of the aorta with a Dacron graft. If necessary the aortic valve may also be either repaired or replaced. Details regarding the surgical approach based on the segment of the aorta involved may be found on Cedars-Sinai's web page.

 

Ongoing Postsurgical Care

The continuation of medical treatment following surgery is aimed at protecting the graft, the remaining aorta, the aortic valve and the cardiovascular system generally. It is also to eliminate left ventricular hypertrophy (thickening) and diastolic dysfunction (where the heart muscle becomes very stiff and inefficient) as a result of long-standing under-treatment of hypertension. Beta blockers and other blood pressure medications, including ACE inhibitors and ARBs, are the best medications with the longest beneficial affect on survival at the present time. Calcium channel blockers and diuretics may also be added as indicated.

A CT scan or MRI is done following surgery and then at intervals going forward. The functioning of the heart and valves may also be viewed periodically by echocardiography. Good dental and oral hygiene, including regularly scheduled dental cleanings, is strongly recommended to maintain a healthy oral cavity. In summary:

  • Postsurgery MRI or CT scan benchmark
  • Annual MRI or CT scan check-up
  • Ongoing blood pressure optimization
  • PT/INR monitoring if on the anticoagulant Coumadin
  • Lifestyle recommendations continue generally the same as prior to surgery

 

For More Information and Appointments

To view some frequently asked questions about aortic disease, click here. For more information, contact:

Thoracic Aortic Surgery Program
Cedars-Sinai Medical Center
8700 Beverly Blvd., Suite 6215
Los Angeles, CA 90048
Phone: 1-800-CEDARS-1 (233-2771)
Fax: (310) 423-0127
Send Us a Message
To schedule an appointment, contact:
Division of Cardiothoracic Surgery
Phone: (310) 423-3851
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