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Review Article
Left Atrial Volume - A New Index in Echocardiography
Biswajit Paul
Abstract
Prediction of cardiovascular outcomes by non-invasive techniques remains a priority in patients with cardiovascular
disease. The left ventricular ejection fraction, which is a parameter of systolic function has been the most sought
after index for a long time. The importance of diastolic function has come to the foreground. Left atrial volume,
is an index of long-standing diastolic function. This review discusses the methodology of estimation of left atrial
volume and its clinical implications.
F
Introduction
filling of LV is approximately 40%, 35% and 25% respectively.2
As LV relaxation gradually worsens, the relative contribution
of LA reservoir and contractile function increases while conduit
function decreases. But with advanced diastolic dysfunction the
LA serves predominantly as a conduit.
or long, the estimated ejection fraction (EF) of left ventricle
(LV) determined by echocardiography has been used to
predict cardiovascular outcomes. Recent evidence highlights
the importance of left atrial (LA) volume with regards to
prediction of cardiovascular outcomes. The LA volume has been
compared to the “glycated hemoglobin of diabetes mellitus”, as
it is a reflection of long-standing hemodynamic condition. This
review aims to discuss the parameters used to determine LA
phasic function, methodology of LA volume estimation and its
usefulness in clinical practice.
Assessment of LA size
LA is not a symmetrically shaped three-dimensional (3D)
structure. Furthermore, LA enlargement may not occur in a
uniform fashion. Therefore anteroposterior measurement of
LA by M-mode echocardiography is likely to be an insensitive
assessment of any change in LA size. In contrast, LA volume
by two-dimensional (2D) or 3D echocardiography provides a
more accurate and reproducible estimate of LA size as compared
to magnetic resonance imaging (MRI) and cine-computerised
tomography (CT). The LA size is measured at the ventricular
end-systole when the LA chamber is at its greatest dimension.
It is imperative to avoid foreshortening of the LA for computing
LA volume. The confluence of the pulmonary veins and LA
appendage should be excluded, when performing planimetry.3
For assessment of left atrial ‘reservoir’, ‘conduit’ and ‘contractile’
function, LA volumes should be measured at specified phases
of the cardiac cycle. They are a) end-systolic frame just before
mitral valve opening ; b) end-diastolic frame just before mitral
Mechanical Function of Left Atrium
The mechanical function of LA has been traditionally
described in three phases within the cardiac cycle: the ‘reservoir’,
the ‘conduit’ and the ‘contractile’ machinery. During ventricular
systole and isovolumic relaxation, the LA functions as a
‘reservoir’ receiving blood from pulmonary veins. The early
phase of ventricular diastole sets the stage for LA operating as
a ‘conduit’ for blood passing from the pulmonary veins into the
LV. This is followed by atrial ‘contraction’ during which the LV
stroke volume is augmented by approximately twenty percent.1
Various LA volumes have been used to describe LA phasic
function.
1.
Reservoir volume, is calculated as the difference between
maximal and minimum LA volumes. Maximal LA volume
occurs at ventricular end-systole just before the opening
mitral valve; while minimum LA volume occurs at enddiastole, just before closure of mitral valve.
2.
Conduit volume, is calculated as the difference between
maximum and pre-atrial contraction LA volume.
3.
Contractile volume, is calculated as the difference between
minimum and pre-atrial contraction LA volume.
The relative contribution of LA phasic function to LV filling
is dependent upon the diastolic properties of LV. In subjects
with normal diastolic function, the relative contribution of the
reservoir, conduit and contractile function of the LA to the
Consultant Cardiologist, Escorts Heart Institute & Research Centre,
Okhla, New Delhi - 110025
Received: 8.11.2008; Accepted: 9.3.2009
© JAPI • JUNE 2009 • VOL. 57 Fig. 1: Panel A: LA volume by Simpson’s method. Panel B: LA
volume by bi-plane area length method
463
pathology. In a non-compliant LV, as the LA is exposed to
the pressures of the LV during diastole, LA pressure rises
to maintain adequate LV filling.5 It is the increase in LA
wall tension which leads to chamber dilatation. LA volume
is therefore an expression of the chronicity of exposure to
abnormal filling pressures.6 Thus LA volume reflects an
average of LV filling pressures over time. It is thus useful
for monitoring long-term hemodynamic control.
Fig. 2: LA volume by 3-dimensional echocardiography
valve closure; c) last frame just before mitral valve reopening
i.e. pre-atrial contraction. Echocardiographic assessment of LA
volume is done by Simpson’s method, area –length method and
real time 3D echocardiography.
Simpson’s method: Estimation of LA volume by Simpson’s
method of disc is well validated and recommended by the
American Society of Echocardiography (ASE) guidelines 3
(Figure 1A).
3.
Atrial fibrillation: It is difficult to establish a causal
relationship between atrial fibrillation and LA volume.
Structural alterations in LA, may be related to the underlying
pathophysiology or solely to the arrhythmia itself. Data from
experimental animal studies do lend evidence to the fact
that atrial arrhythmias induce structural remodeling.9
4.
Volume overload: Chronic volume overload associated with
large shunts, valvular regurgitation and high output states
including athletic heart10 can contribute to LA enlargement.
However myocardial relaxation physiology is usually
normal as compared to abnormal myocyte relaxation seen
in pressure overload situations.
Atrial fibrillation (AF) is a serious cardiac arrhythmia
associated with increased morbidity and mortality. Data from
the Framingham11 and Cardiovascular Health Study12 have
incriminated an increased anteroposterior LA diameter as
the harbinger of AF. It has been confirmed that LA volume
represents a superior measure over LA diameter for predicting
outcomes inclusive of AF. The prognostic information provided
is incremental to clinical risk factors.
Increased LA volume is also a predictor of stroke and death.
An indexed LA volume of ≥32 ml/m2 is associated with an
increased risk of stroke independent of age and other clinical risk
factors for cerebrovascular disease.13 An increased LA volume
is also the predictor of first stroke in elderly who are in sinus
rhythm and without any history of ischemic neurological events,
AF or valvular heart disease.
Real time 3D echocardiography:4 Full volume 3-dimensional
images are obtained with the matrix array transducer. Zoom
function gain adjustments are used to clarify the endocardial
border. The three- dimensional dataset is transferred to a
Q-LAB system for offline analysis. For calculation of LA
volume, a semiautomated tracing of the LA endocardial
border is performed by marking five atrial points : the anterior,
inferior, lateral, septal mitral annuli and the LA apex (Figure 2).
Modifications are made to correct automatic tracings if necessary.
LA volume is the barometer of LV filing pressure and reflects
the burden of diastolic dysfunction. Because a large number
of individuals with LV dysfunction are in a pre-clinical phase
of the disease, methods to quantify the risk of progression to
symptomatic heart failure would be clinically useful. LA volume
≥ 32 ml/m2 is associated with increased incidence of heart failure
which is independent of age, myocardial infarction, diabetes
mellitus, hypertension, LV hypertrophy and mitral inflow
velocities.14,15 Even in subjects with a normal ejection fraction,
an increment in LA volume is observed from baseline to the
diagnosis of heart failure.
Reference Values
Normal indexed LA volume has been determined in several
studies involving several hundred patients using the preferred
biplane technique. Most trial results indicate a value of 22 ± 6 ml/
m2 as the normal range and the same is recognized by ASE.3
Determinants of LA size
464
Anthropometry and age: LA size should be indexed to body
surface area as body size is a major determinant of LA
size. It is the variation in body size which accounts for
gender difference in LA size.7 The left atrial volume index
(LAVI) is independent of age from childhood onwards.8
The age related LA enlargement is a reflection of the
pathophysiologic changes that accompany advancing age
rather than a consequence of chronologic aging
Prediction of Cardiovascular
Outcomes
Biplane area- length method: Orthogonal apical views, apical
four and two–chamber views are obtained for determination of
LA area and length. The length is determined from the middle of
the plane of mitral annulus to posterior wall. Left atrial volume is
calculated on the basis of the algorithm 0.85 × A1 × A2 ÷ L ; where
A1 and A2 are the areas of LA in four and two chamber views
and L is the shortest of the lengths obtained from the orthogonal
views and indexed to body surface area.3 This method has also
been recommended by the ASE guidelines for estimation of LA
volume (Figure 1B ).
1.
2.
LAVI is a predictor of survival after acute myocardial
infarction. An exponential increase in mortality with increasing
LA volume has been documented.16 Moreover, the prognostic
information is incremental to clinical data and standard
Left ventricular filling pressures: The increase in LA volume
is a reflection of elevated LV filling pressures in the absence
of congenital heart disease, mitral valve or primary atrial
© JAPI • JUNE 2009 • VOL. 57
echocardiographic measures of LV systolic and diastolic
function.
dimensional echocardiography to measure left atrial volume:
comparison with other echocardiographic techniques. J Am Soc
Echocardiogr 2005;18:991-7.
There is evidence that LAVI ≤ 28 ml/m2 is strongly predictive
of normal stress echocardiogram.17 Although a robust data
in this perspective is awaited, it holds promise to provide a
simple means of identifying patients with low ischemic risk.
LA volume is intimately related to LV mass/hypertrophy,
systolic and diastolic dysfunction. The incremental value of each
parameter for the prediction of death is expected to diminish
when considering others. But LAVI derives its importance in
providing incremental value in predicting mortality.
5.
Greenberg B, Chatterjee K, Parmley WW, Werner JA, Holly AN. The
influence of left ventricular filling pressure on atrial contribution
to cardiac output. Am Heart J 1979;98:742–51.
6.
Tsang TS, Barnes ME, Gersh BJ, Bailey KR, Seward JB. Left atrial
volume as a morphophysiologic expression of left ventricular
diastolic dysfunction and relation to cardiovascular risk burden.
Am J Cardiol 2002;90:1284 –9.
7.
Knutsen KM, Stugaard M, Michelsen S, Otterstad JE. M-mode
echocardiographic findings in apparently healthy, nonathletic
Norwegians aged 20–70 years. Influence of age, sex and body
surface area. J Intern Med 1989;225:111–5.
8.
Pearlman JD, Triulzi MO, King ME, Abascal VM, Newell J, Weyman
AE. Left atrial dimensions in growth and development: normal
limits for two-dimensional echocardiography. J Am Coll Cardiol
1990;16:1168 –74.
9.
Allessie M, Ausma J, Schotten U. Electrical, contractile and
structural remodeling during atrial fibrillation. Cardiovasc Res
2002;54:230–46.
Limitations
The major limitation in any imaging modality is its image
quality. The atria are located in the far field of apical views.
The image quality of LA is therefore not optimal. Modification
of gain settings may not improve image quality as increase in
gain will further reduce LA lumen size. Inadvertent planimetry
of a foreshortened LA would introduce considerable errors in
volume estimation. Therefore it is necessary that maximal LA
size be obtained during volume estimation. These pitfalls can
not be negated by 3-D imaging owing to decreased resolution
thus making LA trace problematic.
10. Hoogsteen J, Hoogeveen A, Schaffers H, Wijn PF, van der Wall EE.
Left atrial and ventricular dimensions in highly trained cyclists. Int
J Cardiovasc Imaging 2003;19:211–7.
11. Vaziri SM, Larson MG, Benjamin EJ, Levy D. Echocardiographic
predictors of nonrheumatic atrial fibrillation. The Framingham
heart study. Circulation 1994;89:724 –30.
Certain questions need to be answered. Does regression of
LA size with therapy translate into improved outcomes?18 What
is the natural history of LA remodeling? Future studies are
warranted to further our understanding.
12. Gardin JM, McClelland R, Kitzman D, et al. M-mode
echocardiographic predictors of six- to seven-year incidence
of coronary heart disease, stroke, congestive heart failure, and
mortality in an elderly cohort (the Cardiovascular Health Study).
Am J Cardiol 2001;87:1051–7.
Conclusion
LA volume is a valuable tool for clinical and prognostic
implications. It should be routinely incorporated in clinical
practice. It is an evolving science and more data is required to
understand the natural history of LA remodeling and the impact
on outcomes after LA size reduction.
13. Barnes ME, Miyasaka Y, Seward JB, et al. Left atrial volume in the
prediction of first ischemic stroke in an elderly cohort without atrial
fibrillation. Mayo Clin Proc 2004;79:1008 –14.
14. Takemoto Y, Barnes ME, Seward JB, et al. Usefulness of left atrial
volume in predicting first congestive heart failure in patients ≥ 65
years of age with well-preserved left ventricular systolic function.
Am J Cardiol 2005;96:832– 6.
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2.
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humans. Am J Cardiol 1998; 82: 756-61.
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17. Alsaileek AA, Osranek M, Fatema K, McCully RB, Tsang TS,
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echocardiography. J Am Coll Cardiol 2006 ; 47: 1024-28.
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Jenkins C, Bricknell K, Marwick TH. Use of real-time three
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