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Is cardiomegaly on chest radiograph representative of true cardiomegaly: a cross-sectional observational study comparing cardiac size on chest radiograph to that on echocardiography.

AIMS
To determine whether or not cardiomegaly identified on chest radiograph (CXR) is indicative of true cardiomegaly as determined using echocardiography (echo) as the gold standard tool, and therefore whether or not cardiomegaly on CXR should be investigated further.


METHODS
CXR and echocardiogram reports were reviewed for the presence of cardiomegaly in a population following non-ST segment elevation myocardial infarction (NSTEMI). Data was evaluated to determine whether cardiomegaly reported on CXR did indeed represent true cardiomegaly. Exploratory analysis was undertaken to determine whether or not Body Surface Area (BSA) was a significant explanatory variable.


RESULTS
Data was collected for 244 patients. Thirty-nine were reported to have cardiomegaly on CXR, 22 of those also had cardiomegaly on echo, giving a true positive rate of 56% and a false positive rate of 44%. Fifty-five were reported to have cardiomegaly on echo, of which 33 (60%) did not have cardiomegaly identified on CXR. Sensitivity of CXR to identify cardiomegaly was 40% and specificity was 91% with a positive predictive value of 56% and negative predictive value of 84%. BSA does not appear to be a significant explanatory variable for the discrepancy between the CXR and echo estimates of cardiomegaly.


CONCLUSIONS
In patients following an NSTEMI, the true positive rate of cardiomegaly identified on CXR is not too dissimilar to the false positive rate, thereby suggesting that reporting "cardiomegaly" based on CXR findings is inaccurate and rather reporting should simply focus on the cardiothoracic ratio and defining this as an enlarged cardiac silhouette rather than true cardiomegaly. In clinical practice the data indicates that the number needed to investigate to identify true cardiomegaly on echo is only two, thereby concluding that all patients post-NSTEMI with cardiomegaly on CXR should go on to have an echo, consistent with current national guidelines. As the study population were all post-MI, further study is necessary to evaluate whether this association holds true in a wider population.