Two-dimensional echocardiographic imaging of left atrial appendage thrombi

The utility of two-dimensional echocardiography in the diagnosis of left atrial thrombi is well documented. One major limitation of this technique, however, has been the failure to successfully image left atrial appendage thrombi. This report discusses the presumptive diagnosis in three patients of pathologically confirmed left atrial appendage thrombi using a modified short-axis parasternal two-dimensional echocardiographic view.     

Characterization of Doppler flow of the left atrial appendage and its relation to thrombi. A transesophageal echocardiographic study]

OBJECTIVE: The characteristics and clinical implications associated with Left Atrial Appendage (LAA) flow have not been clearly analyzed. The purpose of this transesophageal pulsed doppler study was to evaluate the importance of rhythm and echo doppler parameters on LAA thrombus formation. DESIGN: Prospective study. SETTING: Patients in a follow-up transesophageal echocardiographic study at Gregorio Maranon General Hospital, Madrid. PATIENTS: Through a transesophageal echocardiographic color Doppler prospective study we evaluated 44 consecutive patients. INTERVENTIONS: In each patient we measured presence of atrial fibrillation, presence of LAA thrombi and LAA doppler flow pattern parameters (peak velocity and area enclosed by the pulsed doppler filling and emptying waves). MEASUREMENTS: We identified three types of LAA doppler flow: Type I, clearly defining biphasic flow, was present only in sinus rhythm patients and not associated to LAA thrombus; Type II saw-fish active flow pattern was detected only in atrial fibrillation patients not associated also with LAA thrombus. Type III low flow pattern occurred only in atrial fibrillation patients and is associated to the majority of LAA thrombus. CONCLUSIONS: These findings document the importance of LAA doppler factors when transesophageal echocardiography is used to study LAA thrombus formation.     

Predictors of left atrial appendage clot: a transesophageal echocardiographic study of left atrial appendage function in patients with severe mitral stenosis

BACKGROUND: The purpose of this study was to prospectively evaluate a large group of consecutive, non-anticoagulated patients with severe rheumatic mitral stenosis and to analyze the left atrial appendage function in relation to left atrial appendage clot and spontaneous echo contrast formation. METHODS AND RESULTS: We prospectively studied left atrial appendage function in 200 consecutive patients with severe mitral stenosis who underwent transesophageal echocardiography and correlated it with spontaneous echo contrast and left atrial appendage clot. The mean age was 30.2 +/- 9.4 years. Fifty-five (27.5%) patients were in atrial fibrillation. Left atrial appendage clot was present in 50 (25%) patients and 113 (56.5%) had spontaneous echo contrast. The older age, increased duration of symptoms, atrial fibrillation, spontaneous echo contrast, larger left atrium, depressed left atrial appendage function and type II and III left atrial appendage flow patterns correlated significantly (p<0.05) with the left atrial appendage clot. Left atrial appendage ejection fraction was significantly less in patients with clot (21.8 +/- 12.8% v. 39.1 +/- 13.2%, p<0.0001) and in those with spontaneous echo contrast (30.3 +/- 16.2 % v. 40.3 +/- 11.8%, p<0.001). Left atrial appendage filling (18.0 +/- 11.7 v. 27.6 +/- 11.8 cm/s, p <0.0001) and emptying velocities (15.4 +/- 7.0 v. 21.5 +/- 9.6 cm/s, p<0.001) and filling (1.4 +/- 1.0 v. 2.5 +/- 1.4 cm, p<0.0001) and emptying (1.5 +/- 1.2 v. 2.1 +/- 1.2 cm, p <0.05) velocity time integrals were also significantly lower in patients with clot as compared to those without clot. On multivariate regression analysis, atrial fibrillation (odds ratio 6.68, 95% CI 1.85-24.19, p=0.003) and left atrial appendage ejection fraction (odds ratio 1.06, 95% CI 1.00 - 1.11, p=0.04) were the only two independent predictors of clot formation. Incidence of clot was 62.59% in patients with left atrial appendage ejection fraction < or = 25% as compared to 10.4% in those having left atrial appendage ejection fraction >25%. Similarly patients with spontaneous echo contrasthadlower filling (21.7 +/- 11.5 v. 29.4 +/- 12.7 cm/s, p<0.0001) and emptying (17.0 +/- 8.1 v. 23.9 +/- 10.9 cm/s, p<0.0001) velocities, as well as filling (1.9 +/- 1.3 v. 2.7 +/- 1.3 cm, p<0.01) and emptying (1.7 +/- 1.0 v. 2.3 +/- 1.4 cm, p<0.01) velocity time integrals as compared to patients without spontaneous echo contrast. In a subgroup of the patients with normal sinus rhythm, the left atrial appendage ejection fraction was significantly less in patients with clot compared to those without clot (31.2 +/- 13.2 v. 41.3 +/- 11.5 %, p<0.01). CONCLUSIONS: In the patients with severe mitral stenosis, besides atrial fibrillation, a subgroup of patients in normal sinus rhythm with depressed left atrial appendage function (left atrial appendage ejection fraction < or = 25%) had a higher risk of clot formation in left atrial appendage and these patients should be routinely anticoagulated for prevention of clot formation.     

Diagnosis of left atrial appendage thrombi by multiplane transesophageal echocardiography: interlaboratory comparative study.

BACKGROUND: Transesophageal echocardiography (TEE) is regarded as the method of choice for imaging left atrial appendage thrombi (LAAT). However, the interobserver variability among 2 independent echocardiographic laboratories in diagnosing LAAT by multiplane TEE has not yet been assessed. METHODS AND RESULTS: The videorecordings of 50 patients in atrial fibrillation (25 from each laboratory) were blindly reviewed by 1 experienced observer from each institution. LAAT were assessed as present, absent or questionable. Indications for TEE were: cardioversion (n=17), valve disease (n=13), endocarditis (n=12), or embolism (n=8). The prevalence of LAAT was 10% (observer 1) vs 12% (observer 2). A questionable LAAT was assessed in 6% vs 12% and a LAAT was excluded in 84% vs 76%, respectively. By head-to-head comparison, disagreement occurred in 11 cases (22%, kappa=0.5). Discrepant results were not related to the echocardiographic equipment. Problems occurred because of reverberation artifacts of the ridge between the left atrial appendage and left upper pulmonary vein (n=5), and in differentiating LAAT from spontaneous echocardiographic contrast (n=4) or an echogenic atrioventricular groove (n=1). The differentiation of pectinate muscles from LAAT was the reason for disagreement in only 1 case. Eliminating the category of questionable thrombi increased the kappa value to 0.65. In 5 patients undergoing cardiac surgery, both observers had agreed on the presence (n=1) or absence (n=4) of LAAT, and intraoperatively the results of TEE were confirmed. CONCLUSION: Even with multiplane TEE, interobserver variability among 2 independent echocardiographic laboratories for diagnosing LAAT remains high because of problems in differentiating LAAT from spontaneous echocardiographic contrast and reverberation artifacts.     

Left atrial appendage function and thrombus formation in atrial fibrillation-flutter: A transesophageal echocardiographic study

Objectives. The purpose of this study was to investigate left atrial appendage size, function and thrombus prevalence in patients with atrial “fibrillation-flutter.”Background. Thrombus formation and peripheral embolization in atrial fibrillation are related to left atrial appendage dysfunction. Embolization occurs less frequently in atrial flutter. It is not known whether the atrial appendage in fibrillation-flutter, which has an intermediate appearance on the surface electrocardiogram (ECG), has distinct characteristics that could affect thrombus formation.Methods. Sixty-one patients with atrial tachyarrhythmias underwent transesophageal echocardiographic examination of the left atrial appendage. Appendage area, peak emptying velocity and the presence of thrombus and spontaneous echo contrast were determined. The results for 14 patients with fibrillation-flutter (based on ECG fibrillatory wave characteristics) were compared with those for 30 patients with atrial fibrillation and 17 patients with atrial flutter.Results. Both fibrillation-flutter and atrial fibrillation were associated with chaotic appendage flow patterns with similarly low peak emptying velocities (18 ± 8 and 17 ± 10 cm/s, mean ± 1 SD, respectively). Atrial flutter was associated with a regular pattern of appendage contraction and a significantly higher peak emptying velocity (42 ± 18 cm/s, p < 0.0001). Mean appendage area was similar for fibrillation-flutter and fibrillation (6.3 ± 2.2 and 6.7 ± 2.1 cm², respectively) but was significantly smaller for atrial flutter (5.3 ± 1.4 cm², p < 0.05). The prevalence of left atrial appendage thrombus was similar for fibrillation-flutter and atrial fibrillation (40% and 29%, respctivdy), whereas no patient with atrial flutter had a thrombus (p < 0.05). Similarly, the presence of spontaneous echo contrast was higher for fibrillationflutter (50%) and atrial fibrillation (40%) than for atrial flutter (6%, p < 0.05).Conclusions. Left atrial appendage size and function in atrial fibrillation-flutter are indistinguishable from those of typical atrial fibrillation, and the frequency of thrombus and spontaneous echo contrast is similarly high. This is in contrast to atrial flutter, which is characterized by a smaller, more contractile left atrial appendage and a lower frequency of thrombus and spontaneous echo contrast.     

华法林溶解左心耳血栓机制的研究

目的探讨华法林溶解左心耳血栓的机制。方法慢性非瓣膜性房颤患者18例,经食管超声心动图(TEE)检查证实有左心耳血栓形成,华法林治疗3~6个月,观察其对左心耳血栓的影响,测定治疗前后血浆纤维蛋白原(Fg)、血管性血友病因子(vWF)、D二聚体(DD)、血小板颗粒膜糖蛋白140(GMP140)、凝血酶抗凝血酶Ⅲ复合物(TAT)和纤溶酶原激活物抑制物1(PAI1);应用TEE测定治疗前后左心耳血流速度和左室射血分数。结果华法林治疗(INR210±014)后,9444%患者左心耳血栓消失;与治疗前比较,血浆DD明显减低〔(182±083)mg/Lvs(133±041)mg/L,P<005〕;左心耳充盈血流速度〔(4271±1470)cm/svs(5622±1753)cm/s,P<005〕和排空血流速度〔(3215±1405)cm/svs(4536±1682)cm/s,P<005〕显著增加,左室射血分数增加〔(053±016)vs(058±016)P<001〕。结论华法林抗凝治疗可使非瓣膜性房颤患者左心耳血栓溶解消失,其机制可能是华法林抑制凝血系统后,抗凝纤溶活性相对增强使血栓溶解,左心耳血流动力学改善。     

Prevalence of left atrial thrombus in rheumatic mitral stenosis with atrial fibrillation and its response to anticoagulation: a transesophageal echocardiographic study

BACKGROUND: The frequency of occurrence of left atrial thrombi, and the effect of anticoagulation in patients with rheumatic mitral stenosis and atrial fibrillation is not well established. This study was conducted to evaluate the occurrence of left atrial body and left atrial appendage clots in patients with rheumatic mitral stenosis and atrial fibrillation, and to document the effect of long-term anticoagulation on clot dissolution. METHODS AND RESULTS: Consecutive patients with severe rheumatic mitral stenosis and atrial fibrillation were assessed by transesophageal echocardiography. Those with left atrial body or left atrial appendage clots were anticoagulated with oral nicoumalone. Transesophageal echocardiography was then repeated in patients on anticoagulation who were on regular follow-up, and in whom percutaneous transvenous mitral commissurotomy could be considered. Of the 490 patients studied, 163 had left atrial body or left atrial appendage clots. A repeat transesophageal echocardiographic examination was done in 50 patients who had optimal anticoagulation for a period of 6 months. Only 2 of the 17 patients who had left atrial body clots had successful clot dissolution after long-term anticoagulation, while the left atrial appendage clots disappeared in 31 of 33 patients (p<0.001). CONCLUSIONS: Left atrial clots are present in a third of patients with severe rheumatic mitral stenosis and atrial fibrillation. Isolated left atrial appendage clots in patients with rheumatic mitral stenosis and atrial fibrillation can disappear with long-term anticoagulation, while thrombi that extend into the left atrial body may persist despite optimal anticoagulation.     

Role of left atrial appendage obliteration in stroke reduction in patients with mitral valve prosthesis: a transesophageal echocardiographic study

OBJECTIVES: The aim of our study was to assess whether left atrial appendage (LAA) ligation in patients undergoing mitral valve replacement is associated with the risk of future embolisms. BACKGROUND: Previous studies show that the LAA plays an important role in the development of intracardiac thrombus. According to this decisive role, LAA surgical closure in patients undergoing cardiac surgery may be an attractive choice for reducing stroke. METHODS: We retrospectively studied 205 patients with previous mitral valve replacement and referred for echocardiography study. Patients were excluded if other causes of systemic embolism were found. The main outcome measure was the occurrence of an embolic event. RESULTS: Ligation of LAA was performed in 58 patients. However, an incomplete ligation was verified in six patients. During a median time from valve replacement to echocardiography study of 69.4 months (1 to 329), 27 patients had an embolism. Multivariate analysis identified the absence of LAA ligation (odds ratio [OR] 6.7 [95% confidence interval [CI] 1.5 to 31.0]; p = 0.02) and the presence of left atrial thrombus as the only independent predictors of occurrence of an embolic event. Moreover, when the identification of an incomplete LAA ligation was considered together with the absence of LAA ligation, risk of embolism increased up to 11.9 x (OR 11.9 [95% CI 1.5 to 93.6]; p = 0.02). CONCLUSIONS: Our study shows that LAA ligation during surgery of mitral valve replacement, performed in a high-risk population, is consistent with a reduction of the risk of late embolism and supports this technique if a mitral valve replacement is indicated.     

Prediction of left atrial appendage thrombi in non-valvular atrial fibrillation.

AIMS: There is little knowledge about the predictors of left atrial appendage (LAA) thrombi in non-valvular atrial fibrillation (NVAF). We investigated the ability of D-dimer to predict LAA thrombi. METHODS AND RESULTS: In this study, 925 patients with NVAF were enrolled. At the time of transoesophageal echocardiography (TEE), D-dimer levels were measured simultaneously. Significant independent predictors of LAA thrombi were the presence of congestive heart failure [odds ratio (OR) 3.10, 95% confidence interval (CI) 1.77-5.50, P < 0.0001), a history of recent embolic events (OR 3.39, 95% CI 1.90-6.04, P < 0.0001), and D-dimer levels (OR 97.6, 95% CI 17.3-595.8, P < 0.0001). Receiver operating characteristic analysis yielded an optimal cutoff value of 1.15 microg/mL for D-dimer to detect LAA thrombi. LAA thrombi were detected in 21.8% of patients with higher D-dimer values, whereas it was detected in only 3.1% of patients with lower D-dimer values. D-dimer cutoff level of 1.15 microg/mL had a negative predictive value of 97% for identifying LAA thrombi. CONCLUSION: In patients with NVAF, D-dimer may be helpful for predicting the absence of LAA thrombi. D-dimer level was clinically useful to guide the management of patients with NVAF, especially for those complicated with congestive heart failure and/or recent embolic events.     

Transthoracic echocardiographic predictors of left atrial appendage thrombus

Transesophageal echocardiography (TEE) is commonly performed to detect the presence of a left atrial appendage (LAA) thrombus in the setting of an embolic event or before an anticipated electrical cardioversion for atrial fibrillation. The predictive value of transthoracic echocardiographic (TTE) findings in these patients has not been well defined. This study evaluated whether TTE findings can predict LAA thrombi using TEE as the gold standard for the identification of LAA thrombi. From November 1995 to March 2003, 10,753 patients underwent TEE to exclude LAA thrombi after embolic events or before cardioversion. Of these, 3,768 patients had complete TTE examinations performed <2 weeks before undergoing TEE. Demographics, TTE, and cardiac rhythm variables were analyzed using univariate and multivariate logistic regression to identify predictors of LAA thrombi diagnosed on subsequent TEE. LAA thrombi were identified by TEE in 199 patients (5.3%). Several TTE variables predicted LAA thrombi by TEE, including mitral stenosis, atrial fibrillation, tricuspid regurgitation, valvular prosthesis, left ventricular dysfunction, and right ventricular dysfunction. Mitral regurgitation was associated with a reduced risk for LAA thrombi (odds ratio 0.61, p = 0.003). A structurally normal heart in sinus rhythm (n = 247, 6.9%) had a 100% negative predictive value for LAA thrombi. In conclusion, several TTE variables were found to be predictive of LAA thrombi. The likelihood of LAA thrombi being found on TEE was infinitely small in the absence of these variables and the presence of sinus rhythm.     

Surgical left atrial appendage ligation is frequently incomplete: a transesophageal echocardiograhic study

OBJECTIVES: This study sought to determine the incidence of incomplete ligation of the left atrial appendage (LAA) during mitral valve surgery. BACKGROUND: Ligation of the LAA to prevent future thromboembolic events is commonly performed during mitral surgery. However, success in completely excluding the appendage from the circulation has never been systematically assessed. METHODS: Using transesophageal Doppler echocardiography, we studied 50 patients who underwent mitral valve surgery and ligation of the LAA. Thirty patients were studied immediately postoperative, and 20 patients were studied 6 days to 13 years after surgery. Incomplete ligation was detected by demonstrating a color jet traversing the separation between the left atrial body and appendage. RESULTS: Transesophageal echocardiography detected incomplete LAA ligation in 18 of 50 (36%) patients. The incidence of incomplete ligation was not significantly different between patients studied immediately postoperative and patients studied at various times after surgery. Type of mitral surgery (repair vs. replacement), operative approach (sternotomy vs. port access), left atrial size or degree of mitral regurgitation did not significantly correlate with the incidence of incomplete appendage ligation. However, the power to detect a significant difference in left atrial size was only 64%. Spontaneous echo contrast or thrombus was identified within appendages in 9 of 18 (50%) patients with incomplete ligation, while 4 of these 18 (22%) patients had thromboembolic events. CONCLUSIONS: Surgical LAA ligation is frequently incomplete. The similar incidence of incomplete ligation detected immediately postoperative and at various times thereafter suggest that this results from an intraoperative phenomenon rather than from gradual dehiscence of sutures over years. The incidence of incomplete left atrial ligation was unrelated to type of surgery, surgical approach, left atrial size or degree of mitral regurgitation. Residual communication between the incompletely ligated appendage and the left atrial body may produce a milieu of stagnant blood flow within the appendage and be a potential mechanism for embolic events.     

Role of oral anticoagulation and inoue balloon mitral valvulotomy in presence of left atrial thrombus: a prospective serial transesophageal echocardiographic study

BACKGROUND AND AIMS OF THE STUDY: Left atrial (LA) and/or left atrial appendage (LAA) thrombi are often found in patients with rheumatic mitral stenosis (MS). The fate of these thrombi on optimal oral anticoagulation, and the feasibility of balloon mitral valvulotomy (BMV) is not well established. The study aims were to assess the efficacy of oral anticoagulation in the resolution/organization of these thrombi, and the feasibility and safety of Inoue BMV in these patients. METHODS: All consecutive patients with severe MS and a mitral valve suitable for BMV, but found to have LA/LAA thrombus on transesophageal echocardiography (TEE) between January 1999 and January 2001 were included. Anticoagulation was carried out with oral nicoumalone; the INR was maintained at 2.5-3.5. Follow up TEE was performed at intervals of two months for a maximum of six months. BMV using the Inoue balloon technique was performed as soon as possible after resolution or organization of thrombus. RESULTS: Sixty-six patients with MS (41 females, 25 males, mean age 33.1+/-10.4 years) and LA thrombus on TEE were studied. Thrombi were categorized into three groups: type I, thrombi localized to LAA (n = 36; 54.6%); type II, LAA thrombi protruding just beyond the LAA mouth (n = 22; 33.3%); and type III, LAA thrombi extending into the LA cavity (n = 8; 12.1%). Mean thrombus size was 27.6+/-9.1 mm (range: 15-35 mm). Complete resolution was seen in 22 patients (33.3%), and organization in 38 (57.6%). No significant change was observed in six patients (9.1%). Resolution was most common in the first two months, and in type I thrombi (41.7%, 27.2% and 12.5% in type I, II and III thrombi, respectively). BMV was performed in 90.9% of patients, and was uneventful in all. BMV was performed in the presence of organized thrombus in 63% of patients. CONCLUSION: Anticoagulant therapy is effective in resolution and/or organization of LA thrombi in patients with MS. Six months' duration of anticoagulation appears optimal. BMV using the Inoue balloon technique can be performed safely after resolution or organization of thrombus, with no additional risk of complication.     

Influence of pacing-induced myocardial ischemia on left atrial regurgitant jet: A transesophageal echocardiographic study

Objectives. We investigated the influence of pacing-induced myocardial ischemia on systolic regurgitant jet in the left atrium, using simultaneous transesophageal echocardiography and transesophageal atrial pacing.Background. In vitro studies have shown that ischemia-induced mitral regurgitation may occur as a result of mitral leaflet malcoaptation or (global) left ventricular dysfunction. However, no transesophageal echocardiographic study has thus far been performed to demonstrate the mechanism and extent of mitral regurgitation during myocardial ischemia in patients.Methods. In 24 patients (mean [±SD] age 57 ± 10 years) with (15 patients) and without (9 control subjects) coronary artery disease, heart rate, blood pressure and systolic regurgitant jet were assessed before and immediately after pacing. Pacing was increased stepwise up to 160 beats/min to provoke wall motion abnormalities while the left ventricular short axis was monitored at the midpapillary muscle level. Other variables obtained before and at peak pacing included left ventricular end-diastolic and end-systolic areas and left ventricular end-diastolic and end-systolic endocardial segmental lengths.Results. Heart rate and blood pressure before and after pacing were not significantly different in control subjects or in patients. At baseline, a jet was present in all but three control subjects. New or increased anterior or posterior wall motion abnormalities were observed during pacing in seven and eight patients, respectively. End-systolic left ventricular areas and segment lengths were significantly reduced in control subjects compared with patients with coronary artery disease at peak pacing (p < 0.05). The increase in systolic regurgitant jet was significantly greater in patients (2.0 ± 1.1 to 3.1 ± 1.8 cm²vs. 0.7 ± 0.7 to 0.9 ± 0.9 cm²[after pacing], p < 0.01). This effect was greater in patients with posterior than with anterior wall motion abnormalities (3.5 ± 1.6 vs. 2.1 ± 1.2 cm²[after pacing], p < 0.05).Conclusions. Quantitative changes in geometry and function of the left ventricle caused by pacing-induced myocardial ischemia augments systolic regurgitant jet size. An increase in the jet during atrial pacing is associated with new or increased wall motion abnormalities, especially of the posterior wall. Pacing-induced anterior wall motion abnormalities appear not to be related directly to an increase in the jet.     

Prediction of embolism in atrial fibrillation: classification of left atrial thrombi by transesophageal echocardiography

The current study was undertaken to clarify the relationship between cerebral/arterial embolism and the morphology of left atrial thrombi. Forty-one patients with atrial fibrillation and left atrial thrombi were followed for 1 year, using transesophageal echocardiography (TEE) to study how the shape, site, movability, number and maximum dimension of left atrial thrombi are related to embolism. Left atrial thrombi were classified by their shape and movability into movable ball (MB) type (n=13), fixed ball (FB) type (n=17) and mountain (MN) type (n=11). The thrombi were also classified by location into the interior section (n=3), middle section (n=8), and the entrance section (n=19) of the left atrial appendage, and the section outside of the left atrial appendage (n=11). The rate of embolism in the MB-type group was significantly higher than that in the other groups (ie, MB 76.9% vs FB 17.6% (p<0.01) vs MN 9.1%; p<0.01), which indicates that the MB-type thrombus is an important risk factor for cerebral/arterial embolism.     

Implantation of left atrial appendage occlusion devices and complex appendage anatomy: the importance of transesophageal echocardiography

Percutaneous delivery of left atrial appendage (LAA) occluding devices represents a novel approach for stroke prevention in patients with atrial fibrillation. Transesophageal echocardiography (TEE) has a pivotal role throughout these procedures, facilitating device size selection and ensuring optimal deployment of the device. We report a case of an LAA occluding device implantation in which apparent proper positioning on fluoroscopy was determined by TEE to be malpositioning with a nonocclusive, perpendicular orientation to the plane of the LAA ostium. This problem appeared to be related to a complex, multilobed LAA anatomy and was readily resolved by repositioning of the device under TEE guidance.     

Interobserver variability in the detection of spontaneous echo contrast, left atrial thrombi, and left atrial appendage thrombi by transoesophageal echocardiography.

OBJECTIVE--To assess the interobserver variability between two observers from different echocardiographic laboratories. DESIGN--Two observers reviewed video recordings blinded to the other's diagnosis. In part I (n = 88), they determined interobserver variability for spontaneous echo contrast, left atrial thrombi, and appendage thrombi. No diagnostic criteria for thrombi were defined. In part II (n = 85), diagnostic criteria for thrombi were defined. RESULTS--Part I: Both observers agreed in diagnosing spontaneous echo contrast in 97%, left atrial thrombi in 90%, left atrial appendage thrombi in 94%. Part II: With predefined criteria no disagreement occurred in diagnosing left atrial thrombi. In the diagnosis of left atrial appendage thrombi both observers agreed in 89%. The mean diameters of the 10 thrombi on which the observers agreed were greater than of the nine appendage thrombi on which they disagreed. CONCLUSIONS--Interobserver variability in the diagnosis of spontaneous echo contrast is low. Defined criteria decrease interobserver variability for left atrial and appendage thrombi, although one third of the thrombi diagnosed by one observer were not confirmed by the other. Interobserver variability is high in the assessment of small structures (< 15 mm) within the left atrial appendage.