Abstract
BackgroundCardiothoracic ratio (CTR) in chest radiographs is still widely used to estimate cardiac size despite the advent of newer imaging techniques. We hypothesise that a universal CTR cut-off value of 50% is a poor indicator of cardiac enlargement. Our aim was to compare CTR with volumetric and functional parameters derived from cardiac magnetic resonance imaging (MRI).Methods309 patients with a chest radiograph and cardiac MRI acquired within a month were reviewed to assess how CTR correlates with multiple cardiac MRI variables: bi-ventricular EDV (absolute and indexed to body surface area), EF, indexed total heart volume and bi-atrial areas. In addition, we have also determined CTR accuracy by creating multiple ROC curves with the described variables.ResultsAll cardiac MRI variables correlate weakly but statistically significantly with CTR. This weak correlation is explained by a substantial overlap of cardiac MRI parameters in patients with normal and increased CTR. For all variables, CTR was only mildly to moderately better than a chance to discriminate cardiac enlargement (AUC 0.6–0.7). Large CTR values (> 55%) are specific but not sensitive, while low CTR values (< 45%) are sensitive but not specific. Values in between are not sensitive nor specific.ConclusionsCTR correlates weakly with true chamber size assessed by gold standard cardiac MRI and has a weak discriminatory power. Thus, clinical decisions based on intermediate CTRs (45–55%) should be avoided. Large CTRs (> 55%) are likely indicative of true heart chamber enlargement. Low CTRs (< 45%) are likely indicative of normal heart size.
Highlights
Cardiothoracic ratio (CTR) in chest radiographs is still widely used to estimate cardiac size despite the advent of newer imaging techniques
This study aims to determine the reliability of CTR to predict cardiac enlargement by comparing the CTR values to cardiac parameters
Our results have shown a weak but statistically significant correlation between CTR and cardiac magnetic resonance imaging (MRI) defined parameters related to cardiac size
Summary
Cardiothoracic ratio (CTR) in chest radiographs is still widely used to estimate cardiac size despite the advent of newer imaging techniques. Cardiothoracic ratio (CTR) is a simple method to evaluate the heart size on chest radiographs. Despite having been introduced more than 100 years ago [1], it is still commonly reported nowadays, even though new imaging techniques have been developed. This is probably because CTR can be measured and interpreted on a widely available and inexpensive imaging study. CTR depends on multiple technical and anatomic factors that can contribute to an inaccurate assessment of the real heart size. There are other cardiac and noncardiac aspects such as sub-optimal inspiratory effort, patient’s or thoracic cage abnormalities that could influence the value of CTR [2,3,4]
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