Left Atrial Appendage Flow Velocity Research Articles

Role of Left Atrial Appendage in Left Atrial Reservoir Function as Evaluated by Left Atrial Appendage Clamping During Cardiac Surgery

We evaluated the role of left atrial appendage (LAA) in the left atrial (LA) reservoir function by assessing the changes in LA flow dynamics after LAA clamping during cardiac surgery. The subjects were 8 patients who had undergone coronary artery bypass grafting (CABG) and 7 who had undergone mitral valvular surgery due to mitral regurgitation. We recorded transmitral, pulmonary venous and LAA flow velocity patterns by intraoperative transesophageal pulsed Doppler echocardiography, monitoring LA pressure before and 5 minutes after LAA clamping. The maximal LAA area was significantly greater, and the peak late diastolic LAA emptying flow velocity was significantly lower before LAA clamping in the mitral regurgitation group than in the CABG group. In both groups, the peak early and late diastolic transmitral and pulmonary venous flow velocities significantly increased, and the peak second systolic pulmonary flow velocity significantly decreased during LAA clamping. There were no significant changes in heart rate and systemic systolic blood pressure during LAA clamping, whereas mean LA pressure and maximal LA dimension significantly increased in both the groups. The LA pressure-volume relation during ventricular systole shifted upward and to the left during LAA clamping, and the slope was steeper in the MR group than in the CABG group. We conclude that the LAA is more compliant than the LA main chamber, and plays an important role in LA reservoir function in the presence of LA pressure and/or volume overload.

Relationship between flow dynamics in the left atrium and hemostatic abnormalities in patients with nonvalvular atrial fibrillation.

To investigate the relationship between left atrial (LA) flow dynamics and hemostatic markers in nonvalvular atrial fibrillation (AF), 45 patients with nonvalvular AF who had not received anticoagulants were evaluated by transesophageal echocardiography. We determined the LA appendage flow and the presence of LA spontaneous echo contrast (SEC) or thrombus. We measured plasma levels of thrombin-antithrombin III complex (TAT), fibrinopeptide A, D-dimer, beta-thromboglobulin, and platelet factor 4 in peripheral blood as hemostatic markers. The patients were divided into a low-velocity group (n = 19; sum of peak emptying and filling LA appendage flow velocities < 40 cm/s) and a high-velocity group (n = 26; > or = 40 cm/s). The maximum LA diameter was significantly greater and the LA expansion fraction was significantly smaller in the low-velocity group than in the high-velocity group. LA SEC or thrombus was observed in 11 patients (58%) in the low-velocity group, but not in any patients in the high-velocity group (p < 0.001). The plasma levels of TAT, fibrinopeptide A, D-dimer, beta-thromboglobulin, and platelet factor 4 were significantly higher in the low-velocity group than in the high-velocity group. The plasma levels of TAT, fibrinopeptide A, beta-thromboglobulin, and platelet factor 4 were significantly higher in 8 patients without LA SEC or thrombus in the low-velocity group than in 26 patients in the high-velocity group. Patients with nonvalvular AF accompanied by an enlarged and dysfunctioning LA and a decreased LA appendage flow velocity had increased intravascular coagulation-fibrinolysis activity and platelet activation. These abnormalities may be closely related to the thrombogenetic state in patients with nonvalvular AF.

Transthoracic Versus Transesophageal Two-Dimensional Echo Doppler Determination of Flow Velocity in the Left Atrial Appendage.

The assessment of flow velocity (FV) in the left atrial appendage (LAA) by transesophageal echocardiography (TEE) has been reported to be a useful tool as a high risk marker for systemic emboli. The analysis of FV in LAA by transthoracic echocardiography (TTE) has not yet been validated. The purpose of this study was to compare FV measurements in the LAA by TEE and TTE in 30 consecutive patients (age 19-87 years, mean = 55) sent for echocardiographic study with the following diagnosis: stroke (11 patients), mitral stenosis (6 patients), congenital heart disease (4 patients), mitral prosthetic function assessment (2 patients), and other pathologies (7 patients). FV was measured at the outlet and mid-portion of the LAA with TTE, from the apical two-chamber view and with biplane TEE, from the longitudinal two-chamber view. Satisfactory measurements were obtained with TTE from the outlet of the LAA in 96.7% and from the mid-portion of the LAA in 90% of patients. One third of patients were in atrial fibrillation (AF) during the study. The mean FV in the outlet of the LAA was 32.7 +/- 2.5 (SE) cm/sec with TTE and was 33.7 +/- 3.04 (SE) cm/sec with TEE (r = 0.95). The mean FV in the mid-portion of the LAA was 40.9 +/- 3.3 and 42.7 +/- 3.9 with TTE and TEE respectively (P = NS) (r = 0.95). There was no difference in the LAA FV determination by TTE and TEE in the subgroup with AF. TTE was able to detect FV < 30 cm/sec with a sensitivity of 88% and specificity of 81% and a positive predictive value of 84% compared with TEE.

Left Atrial Appendage “Stunning” After Electrical Cardioversion of Atrial Flutter: An Attenuated Response Compared With Atrial Fibrillation as the Mechanism for Lower Susceptibility to Thromboembolic Events

Objectives. This study sought to determine whether left atrial appendage stunning occurs in patients with atrial flutter and to compare left atrial appendage function in the pericardioversion period with that in patients with atrial fibrillation.Background. Left atrial appendage stunning has recently been proposed as a key mechanistic phenomenon in the etiology of postcardioversion thromboembolic events in atrial fibrillation. Atrial flutter is thought to be associated with a negligible risk of thromboembolic events; therefore, anticoagulation is commonly withheld before and after cardioversion in these patients.Methods. Sixty-three patients with atrial flutter (n = 19) or atrial fibrillation (n = 44) underwent transesophageal echocardiography immediately before and after electrical cardioversion. In addition to assessing the presence of thrombus and spontaneous echo contrast, we measured left atrial appendage emptying velocity and calculated shear rates by pulsed wave Doppler and two-dimensional echocardiography.Results. Patients with atrial flutter exhibited greater left atrial appendage flow velocities before cardioversion than those with atrial fibrillation (42 ± 19 vs. 28 ± 15 cm/s [mean ± SD], p < 0.001). Left atrial appendage shear rates were also higher in patients with atrial flutter (103 ± 82 vs. 59 ± 37 s−1, p < 0.001). After cardioversion, left atrial appendage flow velocities decreased compared with precardioversion values in patients with atrial fibrillation (28 ± 15 before to 15 ± 14 cm/s after cardioversion, p < 0.001) and atrial flutter (42 ± 19 to 27 ± 18 cm/s, respectively, p < 0.001). Shear rates decreased from 59 ± 37 before cardioversion to 30 ± 31 s−1after cardioversion in atrial fibrillation (p < 0.001), and from 103 ± 82 s to 65 ± 52 s−1, respectively (p < 0.001), in atrial flutter. This decrease in flow velocity from before to after cardioversion occurred in 36 (82%) of 44 patients with atrial fibrillation and 14 (74%) of 19 with atrial flutter. The impaired left atrial appendage function after cardioversion was less pronounced in the group with atrial flutter (27 ± 18 cm/s for atrial flutter vs. 15 ± 14 cm/s for atrial fibrillation, p < 0.001). New or increased spontaneous echo contrast occurred in 22 (50%) of 44 patients with atrial fibrillation versus 4 (21%) of 19 with atrial flutter (p < 0.05).Conclusions. Left atrial appendage stunning also occurs in patients with atrial flutter, although to a lesser degree than in those with atrial fibrillation. These data suggest that patients with atrial flutter are at risk for thromboembolic events after cardioversion, although this risk is most likely lower than that in patients with atrial fibrillation because of better preserved left atrial appendage function.(J Am Coll Cardiol 1997;29:582–9)

Evaluation of left atrial appendage function by measurement of changes in flow velocity patterns after electrical cardioversion in patients with isolated atrial fibrillation

We investigated temporary changes in left atrial appendage (LAA) flow velocity patterns in patients undergoing electrical cardioversion for chronic isolated atrial fibrillation, and evaluated the role of active LAA contraction in directing blood flow to the left atrial main chamber and left ventricle. The study consisted of 26 patients with chronic isolated atrial fibrillation treated with electrical cardioversion and 20 normal controls in sinus rhythm. Using transthoracic and transesophageal Doppler echocardiography, we recorded transmitral, pulmonary venous, and LAA flow velocity patterns before, 24 hours, and 1 week after cardioversion in all subjects. In the 15 patients who underwent successful cardioversion, the maximal LAA area 24 hours after cardioversion was smaller than the area before cardioversion, whereas LAA ejection fraction during atrial systole and peak atrial systolic emptying velocity of the LAA flow were lower 24 hours after cardioversion than those in the control group. One week after cardioversion, maximal LAA area and LAA peak atrial systolic emptying velocity were restored to levels approximately equivalent to those in the control group, although LAA ejection fraction was lower than in the control group. Maximal LAA area and LAA peak atrial systolic emptying velocity correlated negatively and positively with LAA ejection fraction, respectively, 24 hours and 1 week after cardioversion. These results suggest that LAA and the left atrial main chamber show stunning 24 hours after cardioversion, and the atrial systolic emptying wave of LAA flow is generated by active LAA contraction.

Prediction of outcome of electrical cardioversion by left atrial appendage flow velocities in atrial fibrillation.

We evaluated the usefulness of left atrial appendage (LAA) flow velocity during atrial fibrillation as an objective measure for prediction of the outcome of electrical cardioversion. Left atrial appendage peak velocities were measured by transesophageal echocardiography before cardioversion in 56 patients. Left atrial thrombus was demonstrated in 6 (11%) of these patients. Cardioversion was then performed in the 50 patients who did not have a thrombus and in 1 patient whose left atrial thrombus disappeared after anticoagulant therapy (n = 51). Thirty-eight patients converted to sinus rhythm which remained stable until discharge (initial success group). Of these, long-term (> 6 months) maintenance of sinus rhythm was achieved in 31 patients (82%). Five patients with almost no detectable appendage contractions during atrial fibrillation were classified in the initial failure group. The peak LAA flow velocity was significantly higher in patients with the initial success group compared with the patients in the initial failure group (25.6 +/- 12.0 vs 15.3 +/- 10.7 cm/s, respectively; p < 0.01). Left atrial appendage flow velocity during atrial fibrillation may be useful for identifying candidates for electrical cardioversion.

Transesophageal echocardiographic prediction of initially successful electrical cardioversion of isolated atrial fibrillation. Effects of left atrial appendage function.

Left atrial appendage (LAA) flow velocities prior to electrical cardioversion were recorded using transesophageal pulsed Doppler echocardiography to predict initially successful cardioversion of isolated atrial fibrillation (AF). Patients with AF were placed into either a success group (19 patients) in which sinus rhythm was maintained for at least 2 days or a failure group (12 patients). The duration of AF was shorter in the success group. The maximum left atrial diameter was the same for the two groups. The maximum LAA area was smaller in the success group. The maximum forward and backward LAA velocities were greater in the success group, as were the mean forward and backward LAA velocities. In the patients with mean LAA flow velocities greater than 19 cm/sec, the success of cardioversion could be predicted with high sensitivity (80%) and specificity (88%). We conclude that the duration of AF, the maximum LAA area, and LAA flow velocities prior to cardioversion predict the initial recovery of sinus rhythm for isolated AF.

Influence of left atrial pressure on left atrial appendage flow velocity patterns in patients in sinus rhythm

To examine changes in left atrial appendage flow velocity patterns in relation to left atrial pressures during sinus rhythm, transesophageal echocardiography and cardiac catheterization were performed in 31 patients with myocardial diseases in sinus rhythm and 20 control subjects without cardiovascular disease. The 31 patients were divided into two groups according to mean pulmonary capillary wedge pressure: the group with high wedge pressure (19.9 ± 5.8 mm Hg) and the group with low wedge pressure (8.6 ± 2.9 mm Hg). The left atrial appendage peak early emptying velocity was decreased significantly in the groups with both high and low wedge pressure compared with the control group. The left atrial appendage peak late emptying velocity was significantly greater in the group with low wedge pressure compared with the control group, whereas it was decreased significantly in the group with high wedge pressure compared with the control group. The left atrial appendage peak late emptying velocity had a significant negative correlation with wedge pressure. The maximum left atrial appendage area at end systole in the group with high wedge pressure was significantly greater than that in both the group with low wedge pressure and the control group. There was a significant positive correlation between the maximum left atrial appendage area and the wedge pressure, as well as a significant negative correlation between the left atrial appendage ejection fraction during atrial contraction and the wedge pressure. In the group with high wedge pressure, one patient had evidence of left atrial appendage thrombi and two had spontaneous echo contrast. These results suggest that even in patients in sinus rhythm, a marked elevation in the left atrial pressure is likely to reduce the left atrial appendage peak early and late emptying velocities. These changes may be accompanied by an increased incidence of thrombus formation in the left atrial appendage compared with individuals with normal or only slightly elevated left atrial pressures.

Integrated backscatter for quantification of left atrial spontaneous echo contrast

Objectives. This study was designed to develop a quantitative method of spontaneous echo contrast (SEC) assessment using integrated backscatter and to compare integrated backscatter SEC measurement with independent qualitative grades of SEC and clinical and echocardiographic predictors of thromboembolism.Background. Left atrial SEC refers to dynamic swirling smoke-like echoes that are associated with low flow states and embolic events and have been graded qualitatively as mild or severe.Methods. We performed transesophageal echocardiography in 43 patients and acquired digital integrated backscatter image sequences of the interatrial septum to internally calibrate the left ventricular cavity and left atrial cavity under different gain settings. Patients were independently assessed as having no, mild or severe SEC. We compared intensity of integrated backscatter in the left atrial cavity relative to that in the left ventricular as well as to the independently assessed qualitative grades of SEC. Fourier analysis characterized the temporal variability of SEC. The integrated backscatter was compared with clinical and echocardiographic predictors of thromboembolism.Results. The left atrial cavity integrated backscatter intensity of the mild SEC subgroup was 4.7 dB higher than that from the left ventricular cavity, and the left atrial intensity of the severe SEC subgroup was 12.5 dB higher than that from the left ventricular cavity. The left atrial cavity integrated backscatter intensity correlated well with the qualitative grade. Fourier transforms of SEC integrated backscatter sequences revealed a characteristic dominant low frequency/high amplitude spectrum, distinctive from no SEC. There was a close relationship between integrated backscatter values and atrial fibrillation, left atrial size, left atrial appendage flow velocities and thrombus.Conclusions. Integrated backscatter provides an objective quantitative measure of SEC that correlates well with qualitative grade and is closely associated with clinical and echocardiographic predictors of thromboembolism. The relationship between integrated backscatter measures and cardioembolic risk will be defined in future multicenter studies.

Influence of aging on left atrial appendage flow velocity patterns in normal subjects

Transesophageal pulsed Doppler echocardiography was performed to examine changes with age in the left atrial appendage flow velocity patterns in 50 normal subjects (15 to 80 years) in sinus rhythm. There was a significant negative correlation between the peak early diastolic forward and backward left atrial appendage flow velocities and age, as well as a significant positive correlation between the peak early diastolic forward left atrial appendage flow velocity and the peak early diastolic transmitral and pulmonary venous flow velocities. Although there was a significant positive correlation between the peak atrial systolic transmitral flow velocity and age, there was a negative correlation between the peak atrial systolic forward and backward left atrial appendage flow velocities and age. There was a positive correlation between both the maximum left atrial diameter and the amplitude of the interatrial septal motion during atrial systole and age. There was a significant negative correlation between the left atrial appendage ejection fraction during atrial systole and age. Left atrial appendage thrombi and spontaneous echo contrast were detected in two subjects with low peak early diastolic and atrial systolic left atrial appendage flow velocities. In conclusion, both peak early diastolic and atrial systolic left atrial appendage flow velocities decreased with age. A decrease in the peak atrial systolic flow velocity appeared to be an important sign of left atrial appendage thrombus formation even in normal elderly subjects in sinus rhythm.

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

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. 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). 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). 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.

1021-59 Influence of Cardiac Pacing Mode on Left Atrial Appendage Function: Implication for the Cause of Systemic Embolism in VVI Pacing

A higher incidence of systemic embolism has been observed in patients with VVI pacing compared to DDD pacing. However, the cause of systemic embolism in VVI pacing remains unclear. Previous studies have demonstrated that thrombus formation and systemic embolization are related to left atrial appendage (LAA) dysfunction. To investigate the influence of pacing mode on LAA function, we performed transesophageal echocardiography in 16 patients (mean age 65) with permanent DDD pacemakers. The indications for pacemaker implantation were third degree atria-ventricular block (A-V block, n = 10) and sick sinus syndrome (SSS, n = 6). All had shown sinus rhythm at implantation. We measured peak LAA emptying and filling flow velocities during both DDD and VVI pacing at 60 beats/min. The data are summarized below: Peak LAA flow velocity (cm/s) p value DDD VVI A-V block (n = 10) 58 ± 18 40 ± 19 &lt;0.01 SSS (n = 6) 41 ± 13 24 ± 7 &lt;0.05 Total (n = 16) 52 ± 18 34 ± 18 &lt;0.01 Peak LAA flow velocities decreased significantly when a pacemaker was reprogrammed from DDD to VVI pacing mode, especially in patients with SSS. LAA function was impaired in VVI pacing compared with that in DDD pacing. These results suggest that impaired LAA function in VVI pacing may predispose the chamber to thrombus formation, which may playa role in the mechanism of the embolization.

Influence of acutely altered loading conditions on left atrial appendage flow velocities

Objectives. The purpose of this study was to identify the effects of altered loading conditions on left atrial appendage flow velocities.Background. Although studies have suggested that Doppler analysis of left atrial appendage blood flow may have clinical utility, the hemodynamic and cardiac mechanical determinants of left atrial appendage flow are poorly understood.Methods. Transesophageal Doppler echocardiography was performed in eight atrially paced anesthetized dogs instrumented with sonomicrometers on the left atrial appendage and the left ventricular minor axis and with left atrial and left ventricular micromanometers. Left atrial appendage emptying and filling velocities corresponding to early and late ventricular diastole, respectively, were measured using volume expansion and phenylephrine infusion.Results. Volume infusion caused a significant decrease in the early to late emptying and filling ratios (mean ± SD 0.85 ± 0.24 vs. 0.46 ± 0.17 and 0.80 ± 0.50 vs. 0.40 ± 0.20, both p < 0.05). By contrast, phenylephrine infusion did not significantly alter either filling or emptying ratio. The independent determinants of each flow wave were identified with multiple regression analysis: early emptying velocity—time constant of left ventricular relaxation, left ventricular end-systolic dimension and aortic pressure (r = 0.75, p < 0.001); late emptying velocity—left ventricular peak positive time derivative of left ventricular pressure (dPdt) and fractional shortening (r = 0.74, p < 0.001); early filling velocity—left atrial appendage shortening fraction (r = 0.45, p = 0.01) and late filling velocity—left atrial appendage lengthening rate and left ventricular fractional shortening (r = 0.56, p < 0.01).Conclusions. These results indicate that 1) both the magnitude and the pattern of left atriai appendage emptying and filling velocities are dependent on loading conditions, and 2) left atrial appendage velocities are influenced to a greater extent by changes in left ventricular than in left atrial appendage function. These findings may have implications for the pathogenesis of left atrial appendage thrombi.

Hemodynamic and hemorheologic determinants of left atrial spontaneous echo contrast and thrombus formation in patients with idiopathic dilated cardiomyopathy

The purpose of the present study was to evaluate the specific role of hemorheologic and hemodynamic parameters for spontaneous echo contrast and thrombus formation in vivo. We therefore investigated the association between the presence of left atrial spontaneous echo contrast and thrombus formation by transesophageal echocardiography and multiple clinical, hemodynamic, and hemorheologic parameters in 70 patients with idiopathic dilated cardiomyopathy. Transesophageal echocardiography showed left atrial spontaneous echo contrast and left atrial thrombi in 33% and 19% of patients, respectively. Patients with left atrial spontaneous echo contrast had a lower cardiac index (2.1 ± 0.9 versus 2.6 ± 0.9 L/min/m 2; p < 0.02), a lower left atrial (21 ± 8 versus 38 ± 10 cm/sec; p < 0.001) and left atrial appendage flow velocity (17 ± 14 versus 39 ± 13 cm/sec; p < 0.001), a larger left atrial diameter (53 ± 6 versus 46 ± 10 mm; p < 0.002), and more often presented with atrial fibrillation (62% versus 32%; p < 0.02). Plasma fibrinogen concentration (4.0 ± 1.1 versus 3.5 ± 0.7 gm/L; p < 0.02) and plasma viscosity (1.83 ± 0.10 versus 1.76 ± 0.15 mPa · sec; p < 0.05) were higher in patients with spontaneous echo contrast. Multivariate analysis revealed an association between the presence of spontaneous echo contrast and left atrial flow velocity ( p < 0.0001) and plasma viscosity ( p < 0.01). In patients with left atrial (appendage) thrombus or a history of embolism, left atrial appendage flow velocity was lower (15.0 ± 8.2 versus 29.6 ± 14.5 cm/sec; p < 0.005) and spontaneous echo contrast was more frequently observed (52% versus 23%; p < 0.05). Hemorheologic parameters were not significantly different between patients with and without left atrial thrombus. In conclusion, left atrial thrombi and spontaneous echo contrast represent frequent findings in idiopathic dilated cardiomyopathy. They are both primarily related to a low left atrial blood flow velocity. Hemorheologic factors may contribute to spontaneous echo contrast formation in vivo, but are unlikely to play a significant role for thrombus formation.

Left atrial appendage flow velocity assessment using transesophageal echocardiography in nonrheumatic atrial fibrillation and systemic embolism

Fifty-four patients with nonrheumatic atrial fibrillation (AF) were studied: 16 patients with (group I) and 38 patients without (group II) documented systemic embolism. Transesophageal echocardiography (TEE) was performed to evaluate the presence of left atrial (LA) appendage thrombus and LA spontaneous contrast, LA size, systolic and diastolic peak velocity of the left pulmonary vein, and forward and backward peak velocity of the LA appendage. No difference was observed in the presence of LA thrombus between the 2 groups. The occurrence of LA spontaneous contrast was significantly (p = 0.01) higher in the group with embolism. LA size, measured by atrial length (4.96 ± 0.84 vs 4.79 ± 1.38 cm; p = NS) and atrial width (4.50 ± 0.96 vs 4.31 ± 1.24 cm; p = NS), was the same for both groups and thus not associated with embolism. There was no difference in systolic peak velocity (0.39 ± 0.22 vs 0.44 ± 0.22 m/s; p = NS), and a trend toward a higher diastolic peak velocity (0.50 ± 0.17 vs 0.42 ± 0.15 m/s; p = 0.08) was seen in the left pulmonary vein in the group with embolism. Forward (0.25 ± 0.19 vs 0.39 ± 0.23 m/s; p < 0.05) and backward (0.23 ± 0.15 vs 0.33 ± 0.16 m/s; p < 0.05) peak velocities of the LA appendage were significantly lower in the embolism group. Assessment of LA appendage flow velocity may potentially identify patients with nonrheumatic AF at high risk for systemic embolism.