CARDIOVASCULAR JOURNAL OF AFRICA • Vol 21, No 5, September/October 2010
274
AFRICA
The reliability of chest radiographs in predicting left
atrial enlargement
SJ QUINTON, JA KER, P RHEEDER, A DEFFUR
Summary
Introduction:
Estimates of left atrial size in patients with
suspected cardiac disease play an important role in predict-
ing prognosis and events, as well as treatment decisions. Two
methods are commonly used to estimate left atrial size: chest
radiography and cardiac ultrasound. This study aims to
determine the test characteristics by comparing the use of
radiographs to cardiac ultrasound (the gold-standard test).
Methods:
Data from patients older than 18 years admitted
to Steve Biko Academic Hospital during 2000–2003 who
had both chest radiographs and cardiac ultrasound were
included in this cross-sectional, retrospective analysis. Chest
radiographs were classified into three quality classes, and
the sub-carinal angle (SCA) and sub-angle distance (SAD)
were measured twice in all available radiographs by two
observers. Intra- and inter-observer variability (three meth-
ods) as well as the predictive value of the carinal angle and
sub-angle distance measurements were determined using
logistic regression (with left atrial enlargement – determined
by ultrasound as comparator).
Results:
Data for 159 patients were available (154 cardiac
ultrasounds and 178 chest radiographs). Intra-observer
variability for chest radiograph measurements was low with
almost perfect concordance (
p
=
0.000). Inter-observer vari-
ability was higher for supine radiographs. Using logistic
regression, a linear model was identified which was statisti-
cally significant only for erect radiographs. While goodness-
of-fit analysis showed that the model fits the data, perform-
ance characteristics were poor, with high sensitivity and low
specificity, and an area under the ROC curve of 0.62–0.63,
depending on type of radiograph and measurement (SCA
or SAD). Linearity in the logit of the dependent variable
was assessed, and found to be present at the extremes of
SCA measurements for the supine radiograph data and in
the first three quartiles for erect radiograph data. A non-
linear model determined by fractional polynomial analysis
did not perform significantly better than the original linear
model. Cut-off values for the SCA of 72° and 84° (erect and
supine radiographs, respectively) were found to give the best
compromise between sensitivity and specificity. The corre-
sponding cut-off values for SAD were 24.1 and 26.9 mm.
Conclusion:
Assessment of either SCA or SAD to determine
left atrial size was equivalent and repeatable, both with the
same observer and between two observers (less so for supine
radiographs). While this measure was precise, it was found
not to be very accurate. Therefore, chest radiographs are not
reliable in predicting left atrial enlargement.
Keywords:
sub-carinal angle, sub-angle distance, chest radio-
graph, left atrial size
Submitted 10/12/09, accepted 10/3/10
Cardiovasc J Afr
2010;
21
: 274–279
DOI: CVJ-21.008
Left atrial size can be useful in clinical medicine both as a
prognostic marker and in the prediction of clinical events.
Postoperative symptomatic improvement following surgery for
aortic stenosis may be predicted using left atrial size.
1
An
echocardiographic study
2
found a significant correlation between
left atrial size and atrial natriuretic peptide levels after acute
myocardial infarction both at 10 to 12 days post infarction as
well as at six months. Based on a correlation coefficient of 0.70,
it was concluded that the percentage change in the size of the
left atrium could reliably predict the percentage change in atrial
natriuretic peptide after an acute myocardial infarction.
In a long-term study of patients with dilated cardiomyopathy,
echo-derived atrial dimension was found to be the major predic-
tor of cardiac death and clinical outcome compared to other
echocardiographic, clinical and haemodynamic parameters at
time of entry into the study.
3
Left atrial appendage area is increased in patients with atrial
fibrillation,
4
a known increased risk of cardioembolic stroke. An
increased left atrial size also correlates with an increased risk
of stroke in patients with sinus rhythm.
5
In an ethnically mixed
population, left atrial size is proportionate to the risk of ischae-
mic stroke.
6
Left atrial size is an important determinant in the response
to treatment of atrial fibrillation, such as cardioversion for atrial
fibrillation where left atrial size decreased after restoration of
sinus rhythm in all patients.
7
Left atrial size may indicate which
patients could benefit from anti-arrythmic therapy. Sinus rhythm
can be maintained after cardioversion with left atrial sizes vary-
ing between 45 and 60 mm, and with greater left atrial dimen-
sions, atrial fibrillation was likely to return.
8
Biplane two-dimensional echo is accurate for determining
left atrial size
9
but is not widely available or affordable. Chest
radiographs are often used to estimate left atrial size, being
cheaper and more readily available, and clinical decisions are
often based on this without regard to the accuracy and precision
of this measurement.
Department of Internal Medicine, School of Medicine,
University of Pretoria, and Steve Biko Academic Hospital,
Pretoria, South Africa
SJ QUINTON, MB ChB, Dip Datametrics,
A DEFFUR, MB ChB, MMed (Int), DTH
Faculty of Health Sciences, University of Pretoria, Pretoria,
South Africa
JA KER, MB ChB, MMed (Int), MD
Department of Clinical Epidemiology, School of Medicine,
University of Pretoria, Pretoria, South Africa
P RHEEDER, MB ChB, MMed (Int), FCP, MSC (Clin Epidem), PhD
(Utrecht)
