cardiac source of embolism
A common question asked when a patient has an embolic event (i.e. stroke, mesenteric ischemia, femoral artery occlusions) is whether there was a cardiac source of embolus.
In this tutorial we will go over the principles of left atrial appendage interrogation using trans-esophageal echocardiography (TEE), looking for a nidus for clot (spontaneous echo contrast, low flow stasis).
left atrial appendage (laa)
The left atrial appendage (LAA) is difficult to interrogate using trans-thoracic echo (TTE), given the it is a posterior structure within the left atrium. However, the LAA is more easily interrogated by TEE, with the esophagus in close proximity to the left atrium. This will overview the principles of LAA interrogation, including:
- Views (mid-esophageal 2-chamber view)
- Colour and spectral Doppler interrogations (flow velocities)
- Appearance of spontaneous echo contrast (SEC or “smoke”) and intra-cardiac thrombus
laa INTERROGATION USING TEE
With the transducer in the mid-esophageal 2-chamber position (ME2C) with the omni-plane angle ~90 degrees and the transducer in the same rotation as ME4C. This view provides further interrogation of the: left atrium (LA), left ventricle (LV), mitral valve (MV), left atrial appendage (LAA), Coumadin ridge and left pulmonary veins.

2D/Colour/Spectral Doppler
- We interrogate the LAA looking at the: (in ME2C)
- 2D structures:
- Zoom in on the LAA
- Look for spontaneous echo contrast (“smoke”) or intra-cardiac thrombus in LAA
- 2D structures:
- Colour Doppler
- Turn on colour box – adjusting the Nyquist limit (to determine what velocity flows enter the LAA): see video to the right
- High [~67cm/s]
- Medium [~45cm/s]
- Low [~20-23cm/s]
- Turn on colour box – adjusting the Nyquist limit (to determine what velocity flows enter the LAA): see video to the right
- Spectral Doppler (pulse wave [PW])
- Place PW into LAA (see figure to the right)
- Check the velocities of the waveforms coming into and out of the LAA (be mindful of the ~20cm/s cutoff)

Spectral Doppler velocity
- Spectral Doppler pulse wave [PW] into LAA
- Left panel: reassuring LAA velocities of > 20cm/s
- Right panel: non-reassuring LAA velocities of < 20cm/s (nidus of clot formation)


Spotaneous echo contrast and intracardiac thrombus
Sponatenous echo contrast (SEC) or “smoke” has been described in the echocardiography literature in multiple heart conditions suggestive of sluggish flow (e.g. post-cardioversion, AFib, mitral stenosis, etc.)
Intracardiac thrombus was defined as a “mass of echoes in an [intracardiac chamber] with a well circumscribed, defined border…distinct (echocardiographic texture) between the underlying myocardium and thrombus”.
Cardiac source of embolism tutorial
In this tutorial, we will breakdown performance and interpretation of LAA interrogation.
REFERENCES
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- Douglas PS, Khandheria B, Stainback RF, Weissman NJ, Brindis RG, Patel MR, Khandheria B, Alpert JS, Fitzgerald D, Heidenreich P, Martin ET, Messer JV, Miller AB, Picard MH, Raggi P, Reed KD, Rumsfeld JS, Steimle AE, Tonkovic R, Vijayaraghavan K, Weissman NJ, Yeon SB, Brindis RG, Douglas PS, Hendel RC, Patel MR, Peterson E, Wolk MJ, Allen JM. ACCF/ASE/ACEP/ASNC/SCAI/SCCT/SCMR 2007 Appropriateness Criteria for Transthoracic and Transesophageal Echocardiography: A Report of the American College of Cardiology Foundation Quality Strategic Directions Committee Appropriateness Criteria Working Group, American Society of Echocardiography, American College of Emergency Physicians, American Society of Nuclear Cardiology, Society for Cardiovascular Angiography and Interventions, Society of Cardiovascular Computed Tomography, and the Society for Cardiovascular Magnetic Resonance Endorsed by the American College of Chest Physicians and the Society of Critical Care Medicine. J Am Soc Echocardiogr 2007;20:787–805.