A novel approach to the diagnosis of left atrial appendage thrombus using contrast echocardiography and power Doppler imaging
Cardiovascular Department, Medical College of Georgia, BBR-6518 Augusta, GA 30912, USA
Received 1 October 2007; accepted after revision 14 October 2007.
* Corresponding author. Tel: +1 706 721 2736; fax: +1 706 627 7903. E-mail address: ararango{at}mcg.edu
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Abstract |
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Background: Transesophageal echocardiography is performed routinely among patients with atrial fibrillation (AF) in order to exclude left atrial appendage (LAA) thrombus prior to cardioversion. Because assessment for LAA thrombus is dependent upon the experience of the operator and is therefore subjective, there remains a subset of patients in whom the diagnosis may not be definitive. The purpose of this report is to present a novel technique which may aid in the confirmation and/or exclusion of LAA thrombus using contrast echocardiography (CE) and power Doppler (PD) imaging.
Methods: TEE imaging of the LAA appendage was performed in 3 patients. By visual inspection, the presence of the thrombus was absent (patient one), equivocal (patient two) and definite (patient three). Contrast echocardiography with Definity® and power Doppler imaging was performed to aid in the confirmation and/or exclusion of thrombus in these 3 patients.
Results: CE alone was useful in confirming the absence and presence of LA thrombus determined by visual inspection in patients one and three, respectively. CE in conjunction with PD imaging was useful in identifying the presence of LAA thrombus (by showing a filling defect and the absence of flow in the tip) in the patient with equivocal results by visual inspection
Conclusion: Contrast echocardiography alone may be useful in confirming and/or excluding the presence of LAA thrombus among patients with AF. CE with PD imaging provides incremental information in aiding in the diagnosis when the conventional images are equivocal.
Keywords: Left atrial appendage thrombus; Contrast echocardiography; Power Doppler
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Background |
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Atrial fibrillation (AF) is a common cause of systemic embolization. The left atrial appendage (LAA) is the most common site for thrombus formation among patients with AF.1 Published guidelines recommend anticoagulation for 3–4 weeks and/or exclusion of LAA thrombi by transoesophageal echocardiography (TEE) prior to cardioversion to decrease the risk of systemic embolization.2,3 Identification of LAA thrombi by TEE has been predominantly by visual inspection and therefore dependent upon the experience of the observer. Indirect evidence for the presence of a thrombus has been provided by colour flow Doppler, pulsed-wave Doppler, and tissue Doppler of the LAA.3,4 Despite these available techniques, however, the assessment of LAA thrombus remains subjective, resulting in a subset of patients in whom the presence of LAA thrombus remains questionable. Although echo contrast agents have been used to aid in the diagnosis of LV thrombus,5 very limited data currently exist evaluating the use of such contrast agents for the assessment of atrial appendage thrombus.6 When combined with echocardiographic contrast agents, power Doppler has proven useful as a tool to assess blood flow in low flow states.7 When used in conjunction with standard colour Doppler, power Doppler has shown to provide complementary information regarding blood flow within mass lesions, vessel stenoses, and thromboses.7
In this report, we present a novel approach to aid in the confirmation and/or exclusion of LAA thrombus in three patients in AF using contrast echocardiography in conjunction with power Doppler imaging. In order to demonstrate this technique, we present three patients: Patient 1 had no LAA thrombus by visual inspection; Patient 2 had an equivocal thrombus by visual inspection; Patient 3 had a definite thrombus by visual inspection. We demonstrate how the use of contrast echocardiography (CE) with power Doppler imaging helped to confirm the presence of thrombus in Patient 2 in whom the diagnosis was equivocal by visual inspection alone. This technique may play an integral and complementary role to standard conventional imaging, particularly in cases where the presence of a thrombus is indeterminate by visual inspection.
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Methods |
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Transoesophageal echocardiography (TEE) was performed using a multiplane TEE probe (Philips Medical Systems, Andover, MA, USA). Imaging was performed using a Philips Sonos 7500 (Philips Medical Systems, USA) ultrasound machine and a standard preset protocol for TEE imaging. Contrast echocardiography and power Doppler was performed during real-time standard imaging. The LAA was assessed according to the following protocol.
- Visual inspection with and without colour flow Doppler.
- Contrast echocardiography: 0.5 cc of Definity® (Definity®, Bristol Myers Squibb, Inc.) was diluted in 9.5 cc of normal saline. Using slow i.v. push, 0.5 cc of the dilution was injected, followed by 10 cc bolus of normal saline. Continuous imaging was performed, with careful observation for the appearance of contrast from the pulmonary veins into the left atrium (LA) and LAA. The authors note that it is imperative that the initial wash-in phase of the contrast into the LAA be observed carefully. Even in the presence of a definite thrombus, the contrast may eventually fill around the mass, thereby potentially obscuring a thrombus (Figure 4B).
- Application of power Doppler imaging during wash-in phase of the contrast into the LA and LAA.
Three experienced echocardiographers from our laboratory were shown the images of all three patients. Consensus as to the presence or absence of thrombus or indeterminate status was agreed on by all three readers.
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Cases |
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The three patients are categorized according to the initial assessment by TEE based on visual inspection and colour Doppler alone. All patients were in AF at the time of the TEE.
Patient 1: no evidence of LAA thrombus by visual inspection and colour Doppler.
Patient 2: equivocal findings for LAA thrombus based on the presence of spontaneous contrast without definite organized thrombus formation within the tip of the LAA.
Patient 3: definite evidence of LAA thrombus visual inspection and colour Doppler.
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Results |
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The results of visual inspection, Definity® assessment, and power Doppler are illustrated in Table 1 for the absence (–), equivocal (+/–), and definite (+) presence of thrombus within the tip of the LAA.
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A description of the echocardiographic findings is presented below.
Patient 1
Visual inspection using conventional imaging with and without colour Doppler shows no evidence of thrombus within the LAA (Figure 1A and B). With Definity®, there is immediate and complete opacification of the LAA. Power Doppler shows normal flow within the entire appendage to the tip (Figure 2A and B).
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Patient 2
Visual inspection using conventional imaging and colour Doppler demonstrates the presence of dense spontaneous contrast in the LA and appendage without a definite organized thrombus (Figure 3A and B). With Definity®, there is delayed opacification of the appendage with a suggestion of a filling defect at the tip (Figure 4A). After several cardiac cycles, the Definity® fills in around the defect (Figure 4B). Power Doppler demonstrates a consistent absence of flow in the tip of the appendage, suggesting the presence of a thrombus (Figure 4C).
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Patient 3
Visual inspection using conventional imaging with and without color Doppler shows a definite thrombus in the LAA (Figure 5A and B). With Definity®, there is delayed opacification of the appendage with a filling defect at the tip (Figure 6A). Power Doppler demonstrates a consistent absence of flow in the tip of the appendage, confirming the presence of thrombus (Figure 6B).
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Discussion |
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Several studies have reported the utility of TEE in the assessment of LAA thrombus in patients with AF,3,8 mitral stenosis,6,9 and suspected cardiac source of embolism.3 The diagnosis of LAA thrombus is typically made by direct visual inspection. The presence of spontaneous echo contrast is a marker of increased risk of thrombus formation.4,9 In our experience, however, there appears to be a spectrum from dense spontaneous contrast to organized thrombus formation often making the definitive diagnosis of LAA thrombus difficult. The problem with establishing a definitive diagnosis is that pathological confirmation is typically not possible. Prior studies have suggested that colour Doppler, tissue Doppler imaging, and pulse Doppler may aid in the diagnosis of LAA thrombus.10 Colour Doppler assessment with an area of reduced or absent colour flow is also highly suggestive of thrombus. Evidence of decreased LAA ejection fraction >25% measured by planimetry was also found to be an independent predictor of LAA clot formation.9 Techniques such as pulsed-wave Doppler to assess for low flow velocities within the LAA and tissue Doppler imaging to assess LAA function remain inconclusive for the assessment of clot formation.4 In this report, we have demonstrated a novel approach for the assessment of LAA thrombus using CE in conjunction with power Doppler imaging. This technique has allowed us to more definitively ‘rule in’ the presence of LAA thrombus when visual inspection, colour Doppler, and pulsed-wave Doppler are equivocal. Although the absence of flow by power Doppler does not definitively confirm the presence of a well-organized thrombus, the absence of flow may suggest someone at similar increased risk for a cardio-embolic event. In these circumstances, one is often faced to make a decision to either ‘rule in’ or ‘rule out’ LAA thrombus, especially prior to cardioversion. Hence, this technique may aid in the decision-making process in either a positive or negative direction. Power Doppler is a superior technique compared with pulsed-wave and colour Doppler for evaluation of blood flow in circumstances where the angle of insonation, movement, or anatomy is the limiting factor in the ultrasonic assessment of a region of interest.2,7 To our knowledge, this is the first report using CE and power Doppler for the assessment of LAA thrombi. Because of the subjective nature of conventional techniques used to diagnose LAA clot, this technique may provide more objective information, particularly when the diagnosis remains questionable. The use of contrast echo and power Doppler have promise in helping to enhance the positive and negative predictive value of TEE in the assessment of LAA thrombus. This technique will benefit from more extensive evaluation in a larger scale population.
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Acknowledgements |
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Conflict of interest: none declared.
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References |
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- Goswami KC, Yadav R, Bahl VK. Predictors of left atrial appendage clot: a transesophageal echocardiographic study of left atrial appendage function in patients with severe mitral stenosis. Indian Heart J (2004) 56:628–35.[Medline]
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[Abstract/Free Full Text] - Parvathaneni L, Mahenthiran J, Jacob S, Foltz J, Gill WJ, Ghumman W, Gradus-Pizlo I, Geigenbaum H, Sawada SG. Comparison of tissue Doppler dynamics to Doppler flow in evaluating left atrial appendage function by transesophageal echocardiography. Am J Cardiol (2005) 95:1011–4.[CrossRef][Web of Science][Medline]
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- Ha JW, Lee BK, Kim HJ, Pyun WB, Byun KH, Rim SJ, Chung N. Assessment of left atrial appendage filling pattern by using intravenous administration of microbubbles: comparison between mitral stenosis and mitral regurgitation. J Am Soc Echocardiogr (2001) 14:1100–6.[CrossRef][Web of Science][Medline]
- Hamper UM, DeJong MR, Caskey CI, Sheth S. Power Doppler imaging: clinical experience and correlation with color Doppler US and other imaging modalities. Radiographics (1997) 17:499–513.[Abstract]
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- Goswami K, Yadav R, Bahl V. Predictors of left atrial appendage clot: A transesophageal echocardiographic study of left atrial appendage function in patients with severe mitral stenosis. Indian Heart J (2004) 56:628–35.[Medline]
- Manganaro A, Ando' G, Salvo A, Consolo A, Coppolino F, Giannino D. A comparison of Power Doppler with conventional sonographic imaging for the evaluation of renal artery stenosis. Cardiovasc Ultrasound (2004) 14:1.
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