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

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]

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

Saric M, Armour AC, Arnaout MS, et al. Guidelines for the Use of Echocardiography in the Evaluation of a Cardiac Source of Embolism. J Am Soc Echocardiogr 2016; 29: 1–42.
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