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Visualization of left atrial appendage and assessment of its function by transthoracic second harmonic imaging and
1Department of Cardiology, A. Manzoni Hospital, Lecco, Italy. maxpozz@libero.it
Insights
Transthoracic echocardiography with contrast reliably measures left atrial appendage flow velocity, aiding thromboembolism risk assessment in atrial fibrillation patients. This non-invasive method shows promise for serial screening.
Area of Science:
- Cardiology
- Medical Imaging
- Echocardiography
Background:
- Low flow velocity in the left atrial appendage (LAA) predicts thromboembolism and cardioversion failure in atrial fibrillation.
- Transoesophageal echocardiography (TEE) assesses LAA flow but is limited for serial screening due to its invasive nature.
Purpose of the Study:
- To evaluate transthoracic echocardiography (TTE) with second harmonic imaging and Doppler, including contrast enhancement, for assessing LAA visualization and flow velocity.
- To compare TTE findings with transoesophageal echocardiography (TEE) in patients with atrial fibrillation.
Main Methods:
- Investigated 51 patients undergoing TEE using transthoracic second harmonic imaging and pulsed Doppler with and without Levovist contrast.
- Assessed LAA visualization, flow velocity measurements, and thrombus detection.
- Correlated TTE and TEE measurements of peak emptying velocity and flow patterns.
Main Results:
- LAA was visualized by TTE in 46/51 patients; interpretable Doppler tracings were obtained in 39 at baseline and 45 with contrast.
- Peak emptying velocity correlations were 0.81 (standard TTE) and 0.91 (contrast TTE) versus TEE.
- Agreement in flow velocity patterns between contrast TTE and TEE was 93%; contrast TTE identified low flow (<30cm/s) in most patients with LAA thrombus or spontaneous contrast on TEE.
Conclusions:
- Transthoracic echocardiography with second harmonic imaging and pulsed Doppler can visualize the LAA and reliably measure flow velocity in many patients.
- Contrast enhancement significantly improves the feasibility and accuracy of TTE for evaluating LAA flow velocity.
- Prospective studies are needed to confirm the clinical utility of this non-invasive method for predicting thromboembolic risk and cardioversion success.
Background:
Low flow velocity within the left atrial appendage, as assessed by transoesophageal echocardiography, is a predictor of thromboembolism and of a low success rate of cardioversion of atrial fibrillation. However, the semi-invasive nature does limit its serial application as a screening technique.
Methods And Results:
We investigated the value of transthoracic second harmonic echocardiography and pulsed Doppler at baseline and after intravenous contrast injection to visualize the left atrial appendage and assess blood flow velocities within its cavity. We studied 51 consecutive patients undergoing transoesophageal echocardiography. After transoesophageal echocardiography, transthoracic second harmonic imaging was performed and the left atrial appendage was visualized in 46 patients. Interpretable pulsed Doppler tracings of left atrial appendage flow were obtained at baseline in 39 patients and in 45 patients during Levovist administration. The correlations between peak emptying velocity of left atrial appendage as measured by transoesophageal echocardiography and by transthoracic standard and contrast-enhanced Doppler were 0.81 and 0.91, respectively. The agreement between transoesophageal echocardiography and transthoracic contrast-enhanced pulsed Doppler echocardiography in classifying left atrial appendage flow velocity patterns was 93%. Left atrial appendage thrombus was detected by transthoracic second harmonic imaging in only one of the eight patients shown by transoesophageal echocardiography to have a thrombus. However, all but one of the patients with left atrial appendage thrombus and/or spontaneous echocardiographic contrast at transoesophageal echocardiography had <30cm/s left atrial appendage flow velocity by transthoracic Doppler.
Conclusions:
This study shows that left atrial appendage can be visualized by transthoracic second harmonic imaging and that the flow velocity within its cavity is reliably measured by pulsed Doppler in a substantial fraction of patients. Contrast enhancement improves the feasibility and the accuracy of transthoracic evaluation of left atrial appendage flow velocity. The practical value of these results in predicting thromboembolic risk and success of cardioversion of atrial fibrillation needs to be proved by prospective studies.