Echocardiographic "smoke" is produced by an interaction of erythrocytes and plasma proteins modulated by shear forces

Cardioembolic stroke

Cardioembolic stroke accounts for 1 out of every 5 to 6 ischemic strokes. A potential cardiac source should be considered in all patients presenting with ischemic neurologic deficits. a clear understanding of the various types of cardiac conditions associated with cardioembolic stroke is important. This article reviews potential cardiac sources of emboli and discusses the role of anticoagulation in both primary and secondary prevention of cardioembolic stroke. The role of echocardiography in evaluating patients with possible cardioembolic stroke is also addressed, and an algorithm is proposed for the use of echocardiography in evaluating patients with ischemic neurologic deficits.

Transesophageal echocardiographic assessment of embolic sources: intracardiac and extracardiac masses and aortic degenerative disease

The increased sensitivity of transesophageal echocardiography (TEE) makes it complementary and, in many cases, superior to transthoracic echocardiography in the detection of various sources of embolism. These sources include intracardiac thrombus, tumors, spontaneous echocardiographic contrast, and others. TEE is also helpful as an adjunctive test for the diagnosis of pulmonary embolisms.

Effects of heart rate on flow velocity of the left atrial appendage in patients with nonvalvular atrial fibrillation

BACKGROUND AND HYPOTHESIS

Flow velocity of the left atrial appendage (LAA) is thought to be important in thrombus formation in association with blood stasis and the development of spontaneous echo contrast. The effects of heart rate on peak flow velocity of LAA have not been studied in patients with nonvalvular atrial fibrillation.

METHODS

Using transesophageal Doppler echocardiography, peak flow velocity of the LAA was measured at the junction between the left atrium and the LAA during left ventricular (LV) systole and diastole in 21 patients with nonvalvular atrial fibrillation. In six cases, the average peak flow velocity of the LAA for 10 consecutive beats with moderately long R-R intervals (LI beats) was compared with those of 3-5 consecutive beats with extremely short R-R intervals (SI beats).

RESULTS

Average peak flow velocity of the LAA during LV diastole was significantly higher than that during LV systole (26.5 +/- 15.7 vs. 19.3 +/- 10.4 cm/s, p < 0.01). In SI beats, average peak flow velocity of the LAA was significantly lower than that in LI beats (17.1 +/- 12.1 vs. 21.2 +/- 12.9 cm/s, p < 0.01).

CONCLUSION

An increased heart rate reduced the peak flow velocity of the LAA in patients with nonvalvular atrial fibrillation, which would promote blood stasis in the LAA.

Reduction of left ventricular spontaneous echo contrast in cardiomyopathy by acute inotropic intervention or aggressive therapy

The purpose of this study was to determine whether improvement of left ventricular (LV) systolic function could reduce the severity or eliminate LV spontaneous echo contrast found with transthoracic echocardiography in a group of patients with advanced cardiomyopathy. A successful reduction of this by hemodynamic means might indicate an additional beneficial method of helping prevent thromboembolism in advanced cardiomyopathy. Six patients with advanced cardiomyopathy and demonstrating spontaneous echo contrast on transthoracic echocardiography were treated with acute inotropic drug infusions or aggressive medical therapy to improve LV systolic function to determine whether reduction in spontaneous contrast could be achieved by such means. A spontaneous echo contrast scoring system was devised: 0 to 4, indicating absent to severe. Six observers, unacquainted with the study plan, were blinded as to the source of the 12 pre- and post-therapy two-dimensional echocardiograms obtained and re-recorded in a random sequence, and were asked to grade the degree of spontaneous echo contrast. In all six patients, LV spontaneous echo contrast was reduced by improvement in LV systolic function (average score lowered from 2.94 to 1.25, p < 0.005). Among patients with cardiomyopathy at high risk for LV thromboembolism, as indicated by the presence of LV spontaneous echo contrast, improvement in LV systolic function may serve as an adjunct to anticoagulation or, in some cases, as a substitute when the latter is contraindicated in the prevention of thromboembolism. The results obtained suggest merit in prospective, long-term studies of a larger group of such patients.

Hemodynamic correlates of spontaneous echo contrast in the descending aorta

To identify the hemodynamic association of spontaneous echo contrast (SEC) in the descending aorta (DA), we measured aortic flow parameters in 102 consecutive patients studied with transesophageal echocardiography. SEC in the DA was identified in 19 of 102 patients (19%). Patients with SEC in the DA were older (67 +/- 9 vs 57 +/- 17 years; p = 0.001), had a higher proportion of chronic atrial arrhythmia (13 of 19 vs 11 of 83; p = 0.000001), and had a higher frequency of decreased left ventricular performance (10 of 19 vs 19 of 83; p = 0.01). Patients with SEC in the DA had larger aortic diameters (2.9 +/- 0.5 vs 2.3 +/- 0.4 cm; p = 0.0001), lower maximal velocity in the DA (42.6 +/- 12.8 vs 75.6 +/- 34.4 cm/s; p = 0.0001), and lower maximal shear rate (61.6 +/- 20.3 vs 139.9 +/- 78.8 s-1; p = 0.0001). There was no difference in volumetric flow in the DA between groups. In multivariate analysis, only arrhythmia (p = 0.008) and maximal shear rate (p = 0.002) were identified as significant independent predictors of SEC in the DA. We conclude that SEC in the DA is related to chronic atrial arrhythmia and shear rate but not to volumetric flow.

Spontaneous echocardiographic contrast in the thoracic aorta: factors associated with its occurrence and its association with embolic events

Spontaneous echocardiographic contrast is associated with embolic events when it occurs in the left atrium. Because little is known about spontaneous echocardiographic contrast in the aorta, we investigated this association retrospectively in 343 patients without aortic dissection or aneurysm who had undergone transesophageal echocardiography. Two independent readers concurred on the presence of spontaneous echocardiographic contrast in the aorta in 93% of the study patients, with the remainder agreed on by consensus. Spontaneous echocardiographic contrast was found in 65 patients (19%) and was associated with older age (p < 0.0001), male sex (p < 0.0001), slightly larger aortas (p < 0.0001), and complex aortic atherosclerosis (p = 0.0001). Thirty-four (28.6%) of 119 patients with clinical embolic events had spontaneous echocardiographic contrast in the aorta in contrast to 31 (13.8%) of 224 patients referred for other reasons (p = 0.0001). This finding remained significant when spontaneous echocardiographic contrast in the aorta was the only abnormality allowed (n = 207, p = 0.0065) or when other echocardiographic variables known to be related to embolic events were included in a multivariate analysis. Thus, spontaneous echocardiographic contrast in the aorta can often be detected by transesophageal echocardiography and is associated with a higher prevalence of embolic events.

Cardioversion of atrial fibrillation

Cardioversion to sinus rhythm should be considered for all patients in atrial fibrillation in order to improve cardiac performance and perhaps to reduce the long-term risk of thromboembolic complications. Different methods of cardioversion, whether electrical or pharmacological, exist and there is often uncertainty about performing the procedure. In particular, there is often confusion about the use of anti-arrhythmic drugs and the suitable length of anticoagulant therapy required pre- and post-cardioversion. This review discusses the current understanding of electrical and pharmacological cardioversion of atrial fibrillation, the clinical effects and the role of prophylactic anti-arrhythmic and anticoagulant therapy in this procedure.

Effect of aspirin on spontaneous contrast in the brachial veins of normal subjects

Blood cell aggregates are thought to be the cause of spontaneous echo contrast (SEC), although there is disagreement as to whether red cell or platelet aggregates produce this effect. One way to differentiate between these 2 possibilities is to evaluate the effect of aspirin on SEC because aspirin would not be expected to affect red cell aggregates. To eliminate the need to perform repetitive transesophageal echocardiographic studies, and the possible effect of the underlying disease process on SEC, the effect of aspirin on SEC in the brachial vein was studied in normal volunteers using a single-blind, before-and-after study design. Other factors known to affect blood echogenicity including hematocrit, sedimentation rate, and the presence of platelet aggregates by microscopy were also studied. The amount of SEC was quantitated by image analysis and expressed as the aggregate score. The results in 10 volunteers showed that all had SEC in brachial veins before aspirin, but there was no significant day-to-day variation in the amount of SEC during the control period (mean +/- SEM 104,248 +/- 23,088, 153,722 +/- 35,664, and 124,568 +/- 22,827 for days 1, 3, and 5, respectively). A significant decrease in the aggregate score occurred after 7 days of aspirin, 650 mg twice a day (51,690 vs 127,513, p = 0.002); this was accompanied by a striking decrement in the size of the largest platelet aggregate found in venous blood. Aspirin caused no significant change in the hematocrit or sedimentation rate. These results indicate that there is a component of SEC that is aspirin-sensitive and is likely to represent platelet aggregates.

Transesophageal echocardiographic determinants of embolism in nonrheumatic atrial fibrillation

The purpose of the study was to determine the relation of transesophageal echocardiographic findings to symptoms of systemic embolism in patients with nonrheumatic atrial fibrillation. Transthoracic and transesophageal echocardiography were used to study 107 patients with atrial fibrillation including 49 patients without embolic complications and 58 patients who had suffered from previous cerebral or peripheral embolism. A multiple logistic regression analysis revealed that left atrial thrombi (odds ratio 9.0, 95% CI 2.4-33.6, p < 0.005) and the presence of dense left atrial spontaneous contrast (odds ratio 8.4, 95% CI 1.3-53.1, p < 0.05) were independently related to embolic symptoms. Intensive left atrial spontaneous contrast was associated with an increased left atrial diameter (odds ratio 2.0, 95% CI 1.1-3.6, p < 0.05), the presence of chronic atrial fibrillation (odds ratio 6.9, 95% CI 1.6-29.8, p < 0.01) and aortic atherosclerosis (odds ratio 2.6, 95% CI 1.2-5.5, p < 0.05). It was further negatively correlated to mitral regurgitation (odds ratio 0.4, 95% CI 0.2-0.9, p < 0.05). In conclusion, dense spontaneous echo contrast and left atrial thrombi are associated to thromboembolic complications in patients with nonrheumatic atrial fibrillation. Classifying of spontaneous contrast seems to be useful when estimating the thromboembolic risk in atrial fibrillation.

Quantification of blood echogenicity: evaluation of a semiquantitative method of grading spontaneous echo contrast

Spontaneous echo contrast (SEC) is an echogenic, swirling pattern of blood flow which may be observed by transesophageal echocardiography (TEE) in the left atrium in low flow states, such as atrial fibrillation (AF). The presence of SEC has been proposed as a marker of increased thromboembolic risk. Evaluation of the severity of SEC might be useful in stratification of thromboembolic risk. The aim of this study was to validate a semiquantitative method of grading SEC against quantitative videodensitometric analysis. TEE studies were performed in 50 patients with AF. The severity of left atrial SEC was graded by three independent observers and by videodensitometry. There was a strong, positive correlation between the semiquantitative grades of SEC and quantitative videodensitometric scores (r = 0.85, P < 0.0001). Inter- and intraobserver correlations in the grading of SEC were very high (observer 1 vs. 2: r = 0.98, P = 0.0001; observer 1 vs. 3: r = 0.93, P = 0.0001; observer 1 vs. 1: r = 0.97, P = 0.0001). Semiquantitative grading of SEC can be performed rapidly and reliably by experienced observers. These results support the use of semiquantitative grading in studies of the pathogenesis and prognostic implications of SEC.

Ultrasound backscatter at 30 MHz from human blood: influence of rouleau size affected by blood modification and shear rate

High frequency intravascular ultrasound may show a high intensity backscatter from blood which hampers the discrimination between lumen and arterial wall. In this study, the acoustic behaviour of blood at 30 MHz in relation to rouleau size was analyzed. In a Couette viscometer, high frequency (20-40 MHz) backscatter data from normal and modified blood samples from eight volunteers were obtained at shear rates from 0 to 1000 s-1. The acoustic behaviour of blood was quantified by the integrated backscatter power and the spectral slope of the backscatter coefficient. Backscatter from blood depended on rouleau size. At a shear rate of zero, both whole blood and rouleau-enhanced blood showed a 11-dB-higher integrated backscatter power than rouleau-suppressed blood, which itself was 10 dB higher than that of hemolysed blood, the latter showing a 6-dB-higher backscatter than saline. Platelets did not contribute to the backscatter power. Plasma and saline produced no detectable integrated backscatter power other than noise. The spectral slope of whole and rouleau-enhanced blood was small (1 and 0.5, respectively), whereas rouleau-suppressed blood and hemolysed blood (both with a slope of 3.3) behaved almost like a Rayleigh scattering medium (slope = 4). The backscatter from rouleau-suppressed blood showed no shear rate dependence. At low shear rates ( < 0.8 s-1 for integrated backscatter power and < 0.2 s-1 for the spectral slope), whole blood and rouleau-enhanced blood tended to the results from the static situation (no shear). At high shear rates ( > 80 s-1 for integrated backscatter power and >11 s-1 for spectral slope), these samples tended to the results of rouleau-suppressed blood. Ultrasound backscatter at 30 MHz from human blood is only caused by red blood cells. With increasing aggregate (rouleau) size, the integrated backscatter power increased by 11 dB, and the spectral slope decreased from 3.3 to 1.

Non-smoke spontaneous contrast in left atrium intensified by respiratory manoeuvres: a new transoesophageal echocardiographic observation

OBJECTIVE

To elucidate why different types of contrast appear in the left atrium during transoesophageal echocardiographic contrast studies. This should lead to a more uniform definition of true patent foramen ovale.

BACKGROUND

The Valsalva manoeuvre and cough are routinely used to enhance right to left shunt for the detection of patent foramen ovale. No information is, however, available on the effect of these manoeuvres on the intrinsic echogenicity of blood in the left atrium.

METHODS

30 consecutive patients referred for transoesophageal echocardiography were studied. Gain settings were relatively high so that no details were lost. The appearance of contrast during normal respiration, cough, and the Valsalva manoeuvre was looked for in the left atrium with and without venous injection of 10 ml of 5% dextrose. Frequency of contrast appearance in the left atrium was expressed as a percentage. Intensity of contrast, when present, was graded 1 (mild), 2 (moderate), or 3 (equal to right atrial contrast during injection). Timing was assessed in cardiac cycles after the end of respiratory manoeuvres.

RESULTS

Left atrial contrast appeared as a "snowstorm" flowing from the right pulmonary veins towards the middle of the left atrium. It was present respectively with and without contrast injection in eight and five patients during normal respiration, in 15 and seven during a cough, and in 20 and 14 during the Valsalva manoeuvre. When present, the mean intensity of contrast was 1.0 during normal respiration, 1.4 during a cough, and 1.4 during the Valsalva manoeuvre. The mean delay of contrast appearance was 3-4 cycles after release of the Valsalva manoeuvre and after onset of cough.

CONCLUSIONS

Respiratory manoeuvres frequently induce the transient appearance of mild to moderate contrast in the left atrium, most often independently of venous injections. Mild contrast was seen only with high gain settings. This contrast is likely to be related to transient stasis in the pulmonary circulation. In some cases peripheral venous injections of dextrose solution produced, without any respiratory manoeuvre, a similar contrast after the first four cardiac cycles of the right atrium filling, which is likely to represent recirculation of the injected bolus through the pulmonary capillary bed. Therefore respiratory manoeuvres should always be performed before contrast injections to allow better distinction between this background and true patent foramen ovale or pulmonary arteriovenous fistula.

A prospective study of left atrial spontaneous echo contrast and thrombus in 100 consecutive patients referred for balloon dilation of the mitral valve

The aim of this study was to determine the clinical, echocardiographic, and hemodynamic predictors of left atrial spontaneous echo contrast (SEC) and thrombus, respectively, in patients referred for balloon dilation of the mitral valve and to establish the relationship between the two phenomena in this group of patients. One hundred consecutive patients (mean age 57 +/- 14 years) referred for mitral balloon (Inoue) dilation were studied prospectively with transthoracic and transesophageal (83 biplane and 17 single plane) echocardiography (TEE) combined with spectral and color Doppler modalities, immediately before the procedure. TEE was repeated within 24 hours of valvotomy in the first 55 patients. All patients also underwent comprehensive left- and right-sided heart catheterization. TEE was performed successfully in 96 patients. SEC was detected in all 65 patients in atrial fibrillation and in 14 (45%) of 31 patients in sinus rhythm. Patients with SEC were significantly older (61 +/- 13 vs 45 +/- 12 years; p < 0.001) and had larger left atrial volume (98 +/- 48 vs 64 +/- 24 ml; p < 0.001), higher mitral valve echocardiographic scores (7.4 +/- 3.2 vs 5.3 +/- 2.6; p = 0.016), lower cardiac output (3.5 +/- 1.1 versus 4.6 +/- 0.9 L/min; p < 0.001), lower peak systolic pulmonary vein flow velocity (SVm) (24 +/- 12 versus 45 +/- 11 cm/sec; p < 0.001), and correspondingly lower systolic velocity-time integral (4.0 +/- 2.6 vs 7.9 +/- 2.9 cm; p < 0.001) than had patients without SEC. There were no significant associations between SEC and either mitral valve area or anticoagulant therapy. SVm and atrial fibrillation were found to be independent predictors of SEC. In patients in sinus rhythm, SVm was the only independent predictor of SEC. After mitral balloon dilation, SEC disappeared in only two of 35 patients in atrial fibrillation and in five of eight patients in sinus rhythm. Significant mitral regurgitation occurred in the two patients in atrial fibrillation. TEE detected left atrial thrombus in 14 patients. Thrombus was significantly associated with age, mitral valve area, and the severity of SEC. The latter was found to be an independent predictor of thrombus. Two patients in sinus rhythm had evidence of left atrial mechanical dysfunction. Both patients had left atrial SEC and one had thrombus in the appendage. It is concluded that SEC in patients with severe mitral stenosis is dependent on left atrial systolic function and peak systolic pulmonary vein velocity. It is not related to mitral valve area or anticoagulant therapy.(ABSTRACT TRUNCATED AT 400 WORDS)

Spontaneous echo contrast and hemorheologic abnormalities in cerebrovascular disease

BACKGROUND AND PURPOSE

Spontaneous echo contrast (SEC) is thought to represent a risk factor for cardioembolic stroke. In vitro studies suggest that SEC results from interaction between red cells and fibrinogen. To better understand the relation between SEC and stroke and to investigate the in vivo genesis of SEC, we examined the relation between SEC, the constituents of the blood, and plasma and serum viscosity in patients with acute stroke or chronic cerebrovascular disease.

METHODS

Fifty patients with acute stroke or chronic cerebrovascular disease referred for transesophageal echocardiogram (TEE) were studied by transthoracic echocardiography and TEE. Complete blood count, fibrinogen, albumin, gamma-globulin, and plasma and serum viscosity determinations were made. Left atrial SEC was graded as absent, mild, or marked by means of TEE.

RESULTS

SEC was absent in 31 patients, mild in 10 patients, and marked in 9 patients. Higher grade of SEC was associated with a significantly greater percentage of patients with atrial fibrillation and larger left atrial dimension. Atrial fibrillation was present in 23% of the patients in the SEC absent group, 50% of the patients in the mild SEC group, and 78% of the patients in the marked SEC group (P < .01). Left atrial diameter averaged 3.8 +/- 0.6 cm in the SEC absent group, 4.3 +/- 1.1 in the mild SEC group, and 4.9 +/- 0.7 in the marked SEC group (P < .001). Hematocrit, white blood cell count, and platelet count did not differ among the three groups. Fibrinogen, gamma-globulin, plasma viscosity, and serum viscosity values were all significantly higher in the presence of SEC (P < .05). Fibrinogen values were 361 +/- 97 mg/dL in the SEC absent group and 427 +/- 135 mg/dL in the marked SEC group. gamma-Globulin levels were 0.75 +/- 0.23 g/dL in the SEC absent group and 1.06 +/- 0.48 g/dL in the marked SEC group. Both plasma viscosity (1.97 cp) and serum viscosity (1.64 cp) were higher in the marked SEC group than in the SEC absent group (1.77 and 1.50 cp, respectively).

CONCLUSIONS

In patients with acute stroke or chronic cerebrovascular disease, the severity of SEC was not related to albumin, hematocrit, white cell count, or platelet count but rather to elevated fibrinogen levels and concomitant increases in both plasma and serum viscosity. Moreover, increasing grade of SEC was associated with significantly increased left atrial diameter and a higher percentage of patients in atrial fibrillation.

Significant mitral regurgitation is protective against left atrial spontaneous echo contrast formation, but not against systemic embolism

The prevalence of left atrial spontaneous echo contrast (SEC) and the occurrence of systemic embolism were prospectively studied in 176 consecutive patients. All had significant mitral regurgitation (MR) and underwent transesophageal echocardiographic (TEE) studies. Left ventriculography was performed in all patients to document the severity of MR. The underlying causes of MR included rheumatic heart disease in 84 patients, ruptured chordae tendineae in 37, mitral valve prolapse in 18, infective endocarditis in 20, coronary artery disease in 8, congenital heart disease in 5, and dilated cardiomyopathy in 4. No patient was found to have left atrial thrombus. Left atrial SEC was observed in three patients (1.7 percent), all of whom had atrial fibrillation, concomitant mitral stenosis, and huge left atria. Color flow mapping revealed that left atrial SEC was prominent in regions where the turbulent flow of MR was not present. Systemic embolism occurred in ten patients (5.7 percent). The underlying disease was infective endocarditis, rheumatic heart disease, and dilated cardiomyopathy in 6, 3, and 1 patient, respectively. The sites of embolization involved the central nervous system in eight patients and the spleen in the remaining two. Three patients with rheumatic heart disease and the one with dilated cardiomyopathy were in atrial fibrillation and had dilated left atria (diameter > 45 mm) when systemic embolism occurred. Only one patient with rheumatic heart disease was found to have left atrial SEC. The remaining six, with infective endocarditis, all had sinus rhythm. In conclusion, left atrial SEC or thrombus detected by TEE is uncommon in patients with significant MR. Clinical conditions may be of help to identify the subsets of patients at higher risk for systemic embolism.

Hematologic correlates of spontaneous echo contrast in patients with atrial fibrillation and implications for thromboembolic risk

Spontaneous echo contrast has been observed in conditions of low blood flow velocity, such as rheumatic mitral stenosis and atrial fibrillation (AF). The phenomenon has been attributed to increased echogenicity due to aggregation of blood cells at low shear rates. The aim of this study was to determine whether abnormalities of blood composition also might contribute to spontaneous echo contrast formation by promoting cellular aggregation. Transesophageal echocardiography was performed in 185 patients with AF (31 with valvular and 154 with nonvalvular AF). The left atrium was examined for thrombus and spontaneous echo contrast, which was graded from 0 (nil) to 4+ (severe) by 2 independent observers. Forty milliliters of venous blood was obtained from each patient for hematologic analysis. Spontaneous echo contrast was observed in 46% of patients (74% with valvular and 41% with nonvalvular AF). In linear regression analysis, positive correlations were found between grade of spontaneous echo contrast and erythrocyte sedimentation rate (p < 0.001), low-shear blood viscosity (p < 0.001) and anticardiolipin antibody (p = 0.02) in the total study population, and in patients with nonvalvular AF. Spontaneous echo contrast correlated with mitral valve area (p < 0.01) and gradient (p = 0.03), but not with hematologic parameters in patients with valvular AF. Left atrial thrombus was present in 6 patients, all of whom had spontaneous echo contrast. Age (< 0.01), spontaneous echo contrast (p = 0.03) and the fibrinogen concentration (p = 0.03) correlated with previous embolic events.(ABSTRACT TRUNCATED AT 250 WORDS)

Relations between left atrial appendage blood flow velocity, spontaneous echocardiographic contrast and thromboembolic risk in vivo

OBJECTIVES

The aim of this study was to determine the relations between spontaneous echo contrast, left atrial appendage blood flow velocity and thromboembolism.

BACKGROUND

Left atrial thrombus and spontaneous echo contrast, a putative marker of thromboembolic risk, are frequently located in the left atrial appendage. Measurement of left atrial appendage outflow Doppler velocity by transesophageal echocardiography is a recent technique for assessment of left atrial appendage function, which may be important in thrombus formation.

METHODS

Transthoracic and transesophageal echocardiographic studies were performed in 140 patients with atrial fibrillation (chronic in 80 patients, paroxysmal in 50 patients, first episode < 2 weeks in 10 patients). The left atrium and appendage were inspected for thrombus and spontaneous echo contrast, which was graded from 0 (none) to 4+ (severe). Outflow velocity profiles were obtained by pulsed wave Doppler at the orifice of the left atrial appendage.

RESULTS

Left atrial spontaneous echo contrast was present in 78 patients (56%). In multivariate logistic regression analysis, spontaneous echo contrast was the only significant correlate of left atrial thrombus and was present in 14 (93%) of 15 patients. Spontaneous echo contrast and age were associated positively, and anticoagulant therapy was associated negatively, with previous thromboembolic events. Increasing grades of spontaneous echo contrast were associated with decreasing left atrial appendage blood velocity. The velocity in patients with thrombus was not significantly different from that in patients with 4+ spontaneous echo contrast. In multivariate linear regression analysis, the grade of spontaneous echo contrast was significantly and negatively associated with left atrial appendage velocity (p = -0.0001) and mitral regurgitation (p = -0.0002) and significantly and positively associated with left atrial area (p = 0.0005). The odds ratio for spontaneous echo contrast was 28:1 for low left atrial appendage blood flow velocity (< 35 cm/s) and 96:1 for low velocity and the absence of mitral regurgitation.

CONCLUSIONS

Spontaneous echo contrast is the cardiac factor most strongly associated with left atrial appendage thrombus and embolic events. Spontaneous echo contrast formation is promoted by reduced blood flow velocity and increased left atrial size but is diminished by mitral regurgitation.

Cause of spontaneous echocardiographic contrast as assessed by scanning electron microscopy

Spontaneous echo contrast ("echocardiographic smoke") is known to occur in low-flow states and to require the presence of red cells and plasma proteins. Limited morphologic information regarding the microanatomic structure of red cells exhibiting spontaneous echo contrast is known. The study was designed to evaluate the microanatomic features of red cells exhibiting spontaneous echocardiographic contrast with scanning electron microscopy. With human blood, a beaker, and a stirring bar, a simple model for demonstration of spontaneous echo contrast and its reversal was devised. Blood elements were "sampled" from within this model at times of high and low spontaneous echogenicity by adherence of blood elements to poly-L-lysine-coated slides that were subsequently fixed and examined with scanning electron microscopy. Spontaneous echo contrast was maximal at complete stasis or low-flow states and could be abolished by agitation of blood with continuous stirring. Sampling during low-flow states with high echogenicity showed a preponderance of clumped red cells, whereas at high-flow and low echogenicity states red cells were dispersed and usually solitary. No morphologic features suggestive of activation of the coagulation system were noted. Spontaneous echo contrast is caused by reversible red blood cell clumping, which occurs in fresh human blood at low-flow (low shear rate) states and can be abolished by increasing flow. This phenomenon is independent of activation of the clotting system.

The role of echocardiography in the evaluation of cardiac source of embolism: left atrial spontaneous echo contrast

Left atrial (LA) spontaneous echo contrast, also known as "smoke," is a frequent transesophageal echocardiographic finding characterized by swirling, smokelike echoes in the LA cavity or appendage. LA smoke is associated with conditions favoring stasis of LA blood, including atrial fibrillation, mitral stenosis, the absence of mitral regurgitation, and LA enlargement. LA spontaneous echo contrast is a marker of previous embolic events in patients with atrial fibrillation, mitral stenosis, or mitral valve replacement. Most LA thrombi are accompanied by smoke. Recent studies show that LA spontaneous echo contrast is also associated with increased fibrinogen, hematocrit, and blood viscosity, indicating a relatively hypercoagulable state in addition to stasis. These findings suggest that LA spontaneous echo contrast is a manifestation of erythrocyte aggregation, and that hematologic factors may contribute to the association between spontaneous echo contrast and thromboembolism.