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European Journal of Echocardiography 2004 5(1):86-92; doi:10.1016/S1525-2167(03)00046-5
© 2004 by European Society of Cardiology
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Copyright © 2003, The European Society of Cardiology

A rapid method to quantify left atrial contractile function: Doppler tissue imaging of the mitral annulus during atrial systole

B Hessea, S.U Schueleb, M Thamilasarana, J Thomasa and L Rodrigueza,*

aDepartment of Cardiology, The Cleveland Clinic Foundation, Cleveland, OH, USA
bDepartment of Neurology, The Cleveland Clinic Foundation, Cleveland, OH, USA

Received 3 March 2003; received in revised form 9 May 2003; accepted after revision 16 May 2003.

* Corresponding author. Department of Cardiology, Desk F 15, 9500 Euclid Avenue, Cleveland, OH 44195, USA. Tel.: +1-216-444-4150; fax: +1-216-445-7306. rodrigl{at}ccf.org


   Abstract
Top
 Abstract
1. Introduction
 2. Methods
 3. Results
 4. Discussion
 References
 
Aims: Assess the value of peak atrial systolic mitral annular velocity (Aann) measured by Doppler tissue echocardiography to quantify left atrial systolic function.

Methods: We studied a total of 61 adults; 10 subjects without history of heart disease and 51 patients with a history of atrial fibrillation or undergoing evaluation for left ventricular systolic or diastolic dysfunction. Aann was obtained by averaging peak atrial systolic mitral annular velocities from the septal, lateral, anterior, and inferior annulus. Left atrial fractional area change (FAC) and fractional volume change (FVC) during atrial systole were calculated. The correlation between peak atrial systolic mitral annular velocity (Aann) and left atrial systolic FAC and FVC was determined.

Results: Mean FAC and FVC were 27±12 and 40±14%, respectively; mean Aann was 11.2 ± 3.2 cm/s. Linear regression analysis showed correlation between Aann and FAC (r = 0.71; p<0.001) and between Aann and FVC (r = 0.74; p<0.001).

Conclusions: Peak systolic mitral annular velocity correlates well with left atrial systolic FAC and FVC, thus providing an easy means to assess left atrial systolic function.

Keywords: left atrial function; Doppler tissue imaging; mitral regurgitation


   1. Introduction
Top
 Abstract
 1. Introduction
2. Methods
 3. Results
 4. Discussion
 References
 
The importance of the contribution of atrial contraction to ventricular filling has been known since William Harvey.1 It has been suggested that normal atrial systole can keep the mean atrial pressure significantly lower than left ventricular end diastolic pressure and therefore, ‘protect’ the patient from pulmonary congestion. Experimental and clinical data have characterized the determinants of atrial function, but quantitative assessment is difficult, requiring invasive pressure–volume loops, thus precluding routine clinical use.2–4 Estimation of left atrial ejection fraction by two-dimensional (2D) echo has been used to assess left atrial function in patients with dilated cardiomyopathy, but this method is tedious and requires accurate measurements from multiple views.

Doppler tissue imaging (DTI) is a relatively new technology, allowing measurement of myocardial velocities. Although numerous studies have been published using DTI for assessing left ventricular relaxation, little is known about the significance of myocardial velocities during atrial contraction.5 The purpose of this study was to:

1. Evaluate in a larger group of patients the relation between peak mitral annular systolic velocity during atrial contraction and left atrial ejection fraction, measured as left atrial systolic fractional area and volume change (FAC and FVC).
2. Assess the correlation of peak mitral annular systolic velocity with other non-invasive indices of atrial function.


   2. Methods
Top
 Abstract
 1. Introduction
 2. Methods
3. Results
 4. Discussion
 References
 
2.1 Patient population sample
We examined 61 consecutive patients, aged 55 ± 16, who underwent 2D echocardiography including DTI of the mitral annulus at the Cleveland Clinic Foundation, Cleveland, OH. These patients underwent echocardiography including DTI for evaluation of left ventricular systolic or diastolic function, or follow-up examinations for a history of paroxysmal atrial fibrillation. Of these 61 patients, 10 had no echocardiographic evidence of heart disease. Left ventricular systolic dysfunction, isolated diastolic dysfunction, and a history of atrial fibrillation were present in 16, 9, and 26 patients, respectively. Mitral regurgitation (MR) was found in 44 of these patients. All patients were in normal sinus rhythm at the time of the examination. The Cleveland Clinic Foundation Institutional Review Board has approved performing research on the routine and tissue Doppler imaging data obtained from the echocardiographic laboratory.

2.2 Echocardiography
Echocardiograms were obtained with the patient placed in the left lateral decubitus position by an Acuson 128 XP/10 Sequoia (Mountain View, CA) with a multifrequency transducer equipped with DTI technology. A simultaneous electrocardiogram was recorded in all subjects. Mitral inflow velocities were recorded by standard pulsed-wave Doppler at the tips of the mitral valve leaflets. Left atrial outlines and diameters were obtained from the apical two-chamber view and the four-chamber view at maximal atrial dimension, pre-atrial systole and end-atrial systole, as determined by the onset of the P-wave on the electrocardiogram and at the point of mitral valve closure before left ventricular systole.

Left atrial volumes were calculated using the biplane area–length modified Simpson formula: V (cm)3 = 8A1A2/3{pi}l; where A1 and A2 represent the enclosed area of the atrial chamber from the two orthogonal views, and l is the common diameter directed from apex to base.6

Besides the routine 2D-echocardiographic evaluation, the following specific indices of left atrial function were directly measured or calculated:

1. Aann—septal and lateral (from the apical four-chamber view), and anterior and inferior (from the apical two-chamber view) peak atrial systolic mitral annular velocities were measured during atrial contraction. Data from all four measurements were averaged to obtain Aann.
2. FAC during atrial systole, calculated as FAC (%) = (Apre-a — Amin)/Apre-a, where Apre-a is the left atrial area (cm2) prior to atrial systole, and Amin is the minimal left atrial area (cm2) at the end of atrial systole.
3. FVC during atrial systole, calculated as FAC (%) = (Vpre-a — Vmin)/Vpre-a, where Vpre-a is the left atrial volume (ml) prior to atrial systole and Vmin is the minimal left atrial volume (ml) at the end of atrial systole.
4. Peak transmitral A wave velocity.
5. Atrial ejection force (AEF), using the previously6,7 described formula: AEF=0.5x{rho}xMOAxpA2 (gcm/s2 = dynes), where {rho} is the specific gravity of blood (1.06 g/cm3), MOA the mitral valve opening area (cm2), and pA is the peak transmitral A wave velocity (cm/s).

2.3 Statistical analysis
The indices of left atrial function were described as mean±SD, and differences between the groups were assessed using one-way ANOVA. We used uni- and multilinear regression analysis to relate Aann to the following parameters: transmitral peak E and peak A wave velocity; E/A ratio; transmitral flow deceleration time; AEF; left atrial end-diastolic, pre-systolic and end-systolic areas and volumes; left atrial systolic FAC and FVC; heart rate; and left ventricular ejection fraction. Patients with MR were stratified according to the degree of its severity (none, mild, moderate, and severe) and their mean Aann was compared using one-way ANOVA.

2.4 Interobserver variation
To assess interobserver variation, 10 echocardiograms were read by two independent investigators. Interobserver variability for each parameter was calculated as the difference between the two measurements divided by the average of the two, and expressed in percent ±SD (%).


   3. Results
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
4. Discussion
 References
 
3.1 Baseline characteristics
We examined 35 men and 26 women with a mean age of 55 ± 16 (see Table 1). Of these 61 patients, 26 had a history of atrial fibrillation, 16 had evidence of left ventricular systolic dysfunction, and nine had evidence of left ventricular diastolic dysfunction; 10 had no heart disease. At the time of echocardiography all patients were in sinus rhythm. MR was found in 44 of these patients: trivial to mild in 24 patients, moderate in 15 patients, and severe in five patients. Mean age, heart rate, and left ventricular ejection fraction at the time of the echocardiographic examination are listed in Table 1. Subjects with no history of heart disease were younger. Patients with a history of atrial fibrillation had a lower heart rate than patients with left ventricular systolic or diastolic dysfunction. Compared with the other groups, left ventricular ejection fraction was lower in the group with known systolic heart failure.


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  		Table 1 Descriptive statistics—all values expressed as mean±SD

 
3.2 Atrial dimensions
Mean left atrial pre-systolic and end-systolic areas (related to the atrial cycle) as measured from the apical four-chamber view, as well as the corresponding calculated left atrial volumes were greatest in the heart failure group, and smallest in the group without known heart disease (see Table 1).

3.3 Atrial function
3.3.1 Doppler tissue and 2D-echocardiographic imaging
Mean Aann was greatest in the normal group and smallest in the heart failure group (see Table 1). Mean FAC and FVC during left atrial systole were lowest in the heart failure group. The SD was larger in the group with diastolic dysfunction and likely reflects the broad range of left atrial systolic function in this group.

3.3.2 Doppler flow derived parameters
Mean transmitral peak E and A wave velocity, deceleration time, as well as the calculated E/A ratio are listed in Table 1. There was no statistically significant difference between the groups.

3.4 Regression analysis
3.4.1 Univariate linear regression analysis
There was a good correlation between Aann and left atrial systolic FVC (y = 4.7+0.2x; r = 0.74; p<0.001, see Fig. 1), and between Aann and left atrial systolic FAC (y = 6.3+0.2x; r = 0.71; p<0.001) (see Table 2). Aann showed better correlation with FAC or FVC than the individual (septal, lateral, inferior, and anterior) annular velocities. Peak transmitral A wave velocity, deceleration time, AEF, and left ventricular ejection fraction correlated weakly positively with Aann; a weak negative correlation was noted between Aann and peak transmitral E wave velocity, E/A ratio, left atrial areas, and left atrial volumes. There was no correlation between Aann and heart rate or age. Comparing the different patient groups, Aann correlated best with left atrial systolic FVC in the group with left ventricular diastolic dysfunction (r = 0.93; p<0.001), followed by patients with a history of atrial fibrillation (r = 0.68; p<0.001) and left ventricular systolic dysfunction (r = 0.66; p = 0.005). There was no correlation for the group without heart disease (r = 0.10; p = 0.78), which is most likely related to the narrow scatter of values in this relatively small patient group. Values were similar for the correlation between Aann and left atrial systolic FAC.


Figure 1
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  		Figure 1 Correlation of left Aann (in m/s) with left atrial systolic FAC (in %).

 


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  		Table 2 Univariate linear regression analysis—correlation of Aann with other left atrial parameters

 
3.4.2 Multivariate linear regression analysis
We examined two different models including either left atrial systolic FAC or FVC. In the model including area parameters, the following variables were independently predictive of Aann and were included in a stepwise forward fashion in the multilinear regression model: left atrial systolic FAC, age, peak transmitral A wave velocity, and deceleration time (F-ratio 22.9; r = 0.79; p<0.001). In the volumetric model, the predictive variables were: left atrial systolic FVC, age, left ventricular ejection fraction, and transmitral peak E and A wave velocities (F-ratio 18.5; r = 0.80; p<0.001). The most powerful predictors of Aann in each model were left atrial systolic FAC and FVC, respectively.

3.5 Peak atrial systolic mitral annular velocity in mitral regurgitation
Mean Aann in the patients with no or mild MR was 11.4±3.6 and 12.6±2.2 m/s, respectively. Compared to the group with mild MR, Aann was decreased in patients with moderate (9.6±3.2 m/s) or severe (8.7±2.9 m/s) MR (see Fig. 2).


Figure 2
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  		Figure 2 Left Aann (in m/s) stratified according to the degree of MR. The values above the x-axis reflect the mean Aann±SD in patients with no MR, mild MR, moderate MR, and severe MR.

 
3.6 Interobserver variation
The mean interobserver variation (in % ±SD) was 8.9±6.1% for measurement of 2D indices, 7.1±6.2% for transmitral Doppler parameters, and 4.5±4.3% for assessment of peak left atrial systolic mitral annular velocity.


   4. Discussion
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
References
 
The major finding of this study is that Aann measured by DTI correlates with left atrial systolic FAC and FVC, thus providing an easy means to assess left atrial systolic function. While DTI has been more widely assessed for its ability to evaluate ventricular function, this study supports the additional role of DTI in quantitating atrial systolic function.

Multiple studies have examined left atrial systolic function using a variety of parameters, namely left atrial emptying volume or left atrial emptying volume fraction;8–10 left atrial fractional shortening or FAC;11–13 Doppler transmitral flow parameters such as peak A wave velocity and its time–velocity integral, or the E/A ratio;14–16 left atrial work load;17,18 left atrial appendage flow velocities;19–21 AEF;6,14,22 and left atrial kinetic energy.22 However, some of these require cumbersome invasive procedures15,22 while others are highly sensitive to changes in cardiac loading conditions, left ventricular systolic function, and autonomic state.2,6,11,23,24 The assessment of left atrial function is thus complex and the accuracy of these parameters to measure atrial contractility is limited.

DTI is a relatively new technology that allows direct and non-invasive measurement of myocardial velocities.5 To our knowledge, no previous attempt has been made to evaluate the utility of DTI to assess atrial systolic function in humans. In a recent animal experiment, Nagueh et al. found that Aann was directly related to atrial contractility (left atrial dP/dt) and inversely related to left ventricular end-diastolic pressure.25 In our study, Aann was related to left atrial systolic FACs and FVCs. Furthermore, it correlated positively with traditional parameters reflecting atrial systolic function such as transmitral peak A wave velocity and AEF; and inversely with parameters going along with decreased myocardial contractility, such as impaired left ventricular ejection fraction. Although the subgroups with MR were small, there appears to be a decline in Aann with worsening degrees of MR. The significance of these findings deserves further investigation in a larger number of patients with chronic MR.

Previous reports have yielded differing results concerning the relationship between left atrial function and left atrial size, patient age, heart rate, or underlying cardiac morbidity.8,10,14,26 We could not confirm the previously described decline of left atrial function expressed as Aann with age or heart rate, which has been previously noted.10 Maximal atrial area or volume predicted Aann in the univariate linear analysis, but not after including other atrial functional parameters. This indicates the possible importance of adjusting left atrial dimensions for body surface area.26,27

Given the simplicity of the measurement, left atrial peak mitral annular velocity was associated with a smaller interobserver variability than the measurement of traditional parameters; these often require several measurements and calculations which multiply the risk of error.

The major limitation of this study is the lack of a gold standard measurement of left atrial function. The measurement of atrial ejection fraction has limitations similar to the ventricular ejection fraction, and the annular motion itself may be influenced by other factors such as annular interdependence.11,28,29 Left atrial appendage function was not assessed, and we performed only 2D-transthoracic echocardiographic measurement of the left atrium. Compared to angiographic data this has been shown to underestimate true left atrial volume.27 Recent publications are proposing the use of echocardiographic atrial volume as parameter of atrial size.30

As can be depicted from Fig. 1, the standard error of the estimate is significant, and the application of this method may be problematic in an individual patient. Therefore, further evaluation of Aann regarding its reproducibility and robustness is needed.31 The individual patient groups were small and we included patients who were diagnosed at different stages of their disease, which limits the statistical significance of their comparison. This may explain the fact that the mitral inflow velocities did not significantly differ between patients with or without diastolic dysfunction (stages I–IV). However, the goal of this report was to establish the correlation between Aann and various LA functional parameters in a group of patients with various clinical conditions.

In spite of these limitations, Aann provides a potentially useful means to determine left atrial systolic function; it can easily be assessed echocardiographically by direct measurement and is valid in a variety of cardiac conditions. Further research is needed to apply this method in a larger group of patients with altered contractile patterns such as hypertrophic cardiomyopathy, and in the same individual patient after loading and inotropic conditions have changed.


   References
Top
 Abstract
 1. Introduction
 2. Methods
 3. Results
 4. Discussion
 References
 

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