An aortic dissection is a medical event where a tear occurs in the inner layer of the aorta, the body’s main artery that carries blood from the heart. This tear allows blood to flow between the layers of the aortic wall, forcing them apart. To diagnose this condition, doctors use an echocardiogram, a non-invasive imaging test that uses sound waves to create pictures of the heart and surrounding blood vessels. This procedure provides a rapid way to visualize the aorta and identify signs of a dissection.
The information from an echocardiogram helps medical teams make swift decisions about patient care. The imaging can reveal not just the presence of a dissection but also its impact on the heart’s function. This guides the immediate course of treatment for this time-sensitive condition.
The Echocardiogram Procedure for Aortic Dissection
Two main types of echocardiograms are used to diagnose an aortic dissection. The first is the transthoracic echocardiogram (TTE), which is the initial imaging test performed in an emergency setting. For a TTE, a technician places a handheld device called a transducer on the chest wall. This device sends sound waves through the skin to the heart and aorta, which bounce back to create moving images.
The TTE is valued for its speed and non-invasive nature, allowing for a quick preliminary assessment at the patient’s bedside. It provides views of the aortic root and the proximal portion of the ascending aorta, which are common sites for dissections to originate.
A transesophageal echocardiogram (TEE) offers a more detailed view and is employed when a TTE is inconclusive. For this procedure, the patient is sedated, and a small, flexible probe with a transducer is guided down the throat into the esophagus. Since the esophagus lies directly behind the heart and aorta, this placement provides an unobstructed view, free from interference from the ribs or lungs. This proximity allows the TEE to produce high-resolution images of nearly the entire thoracic aorta.
Identifying the Intimal Flap
The definitive sign of an aortic dissection on an echocardiogram is the presence of an intimal flap. This flap is the torn inner lining of the aorta, known as the intima, which has separated from the middle layer of the aortic wall. On the ultrasound screen, it appears as a thin, mobile, and often undulating line within the aorta, moving with the rhythm of the heartbeat.
The creation of the intimal flap divides the aorta into two distinct channels: the “true lumen” and the “false lumen.” The true lumen is the original pathway for blood flow, while the false lumen is the new channel created between the layers of the aortic wall where blood should not be. The false lumen is often larger and may show slower or even reversed blood flow.
To confirm the presence and nature of these two lumens, technicians use Doppler imaging. Color Doppler helps visualize the direction of blood flow, clearly showing blood entering the false lumen through an entry tear in the intima. This technique can also identify any exit tears where blood might rejoin the true lumen further down the aorta.
Assessing Aortic Dissection Complications
An echocardiogram is also used to evaluate immediate complications that can arise from an aortic dissection. A primary concern is aortic regurgitation, which occurs when the dissection damages the aortic valve. The tear can distort the valve’s structure, preventing its leaflets from closing properly and causing blood to leak backward into the heart’s left ventricle. An echo can visualize this valve dysfunction and quantify the severity of the leakage.
Another complication an echocardiogram can detect is pericardial effusion, which can lead to cardiac tamponade. This happens when the dissection ruptures outward, causing blood to leak into the pericardial sac surrounding the heart. The accumulation of blood in this sac increases pressure on the heart, restricting its ability to fill and pump effectively. An echo can identify the presence and volume of this fluid.
The echocardiogram can also provide information about how the dissection affects the coronary arteries, which supply blood to the heart muscle. If the dissection extends into the aortic root, it can obstruct the openings of these arteries, leading to a heart attack. The imaging can reveal wall motion abnormalities, where parts of the heart muscle are not contracting properly, suggesting a blockage of blood flow.
Diagnostic Accuracy and Follow-Up Imaging
The diagnostic accuracy of an echocardiogram for aortic dissection varies between the two methods. A transthoracic echocardiogram (TTE) is a rapid first step, but its sensitivity for detecting a dissection in the ascending aorta is between 59% and 83%. Its effectiveness is lower for dissections in the descending aorta, so a negative TTE does not completely rule out a dissection if clinical suspicion is high.
A transesophageal echocardiogram (TEE) offers significantly higher accuracy, with a sensitivity that can reach 99%. The clear, high-resolution images it provides make it a more definitive tool for confirming a diagnosis. However, TEE has limitations, including a “blind spot” in a small portion of the distal ascending aorta that can be difficult to visualize.
Due to these limitations and the need for a complete anatomical map for surgical planning, other imaging tests are often ordered. A computed tomography (CT) angiogram is frequently used for its ability to visualize the entire aorta from its root to its distant branches. This allows doctors to determine the full extent of the dissection and identify any involvement of branch vessels. An MRI may also be used, offering excellent detail without the use of radiation.