Left Atrial Appendage

 

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Evaluation of the left atrium and left atrial appendage is one of the most common indications for a transesophageal echocardiogram, particularly in the context of atrial arrhythmias and electrical cardioversion. Because the left atrium is the most posterior structure in the heart, it is difficult to comprehensively evaluate using a transthoracic echocardiogram scanning from the anterior chest wall.

Transthoracic Imaging

Typically, the left atrial appendage can only be seen in the apical 2 chamber and in some instances the apical 4 chamber views and even if visualized, the resolution of transthoracic echocardiography is insufficient to adequately exclude appendage thrombus. Below is an example of the left atrial appendage seen in a 2 chamber transthoracic view.

Transesophageal Imaging

  1. TEE has three principle advantages over transthroacic echocardiography in evaluating the LA appendage:

    1. The first is that the esophagous sits immediately posterior to the left atrium and thus a TEE probe is ideally positioned to evaluate the LA and LA appendage.

    2. With TEE, we are able to scan electronically to evaluate the appendage in a number of planes.

    3. The spatial resolution of TEE is slightly higher than that of transthoracic imaging.

 

The left atrial appendage is generally initially visualized from a high mid-esophageal view at 0 degrees, using moderate anteflexion on the probe. The appendage is seen at the lateral left atrium at 0 degrees. The morphology of the appendage is often described as "comma" or "boot" shaped.

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In a typical examination to exclude appendage thrombus, the appendage is then visualized in a zoomed view in multiple planes, electronically scanning in increments of 30-40 degrees until the entire appendage is visualized or view of the appendage is lost. Note that in 80% of patients, the left atrial appendage will be multi-lobed.

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Using an angle where the long axis of the appendage is roughly parallel to the direction of the probe (60-90 degrees), it is customary to image the appendage with color and pulse wave Doppler. Note in the color images at left that color flow is vigorous through the appendage. Also note the left superior pulmonary vein to the right of the appendage in this view. In the pulse wave image (below left), note the normal Doppler velocities in the appendage. Doppler velocities <0.5 m/s are suggestive of stasis.

 

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As you continue to increase the angle by electronically scanning, you will often notice that the LA appendage will have multiple lobes, which was not evident when viewing the appendage in a single plane. In this view at 120 degrees, note the bi-lobed appendage and the ridge at the top of the appendage, known as the "coumadin ridge" which can sometimes be confused with an appendage mass or thrombus. Also note the fine processes at the left edge of the appendage which are pectinate muscles and should not be confused with thrombus.

 

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Increasing the scanning angle further to 130-180 degrees, a "reverse boot" view of the appendage can be obtained in many patients, though this can sometimes be challenging to achieve. Again note the trabeculation in the appendage consistent with normal pectinate muscle.