Diagnostic performance of chest radiography measurements for the assessment of cardiac chamber enlargement

Background:The cardiothoracic ratio (CTR) is commonly assessed on chest radiography for detection of cardiac chamber enlargement, but the traditional cutpoint of 0.5 has low specificity. We sought to evaluate the diagnostic accuracy of new measurement techniques for the detection of cardiac enlargement on chest radiographs.Methods:We obtained retrospective cross-sectional data on consecutive patients who underwent both chest radiography and cardiac magnetic resonance imaging (MRI) within a 14-day interval between 2006 and 2016 at a large academic hospital network. We established the presence of cardiac chamber enlargement using cardiac MRI as the reference standard. We evaluated the diagnostic performance of different techniques for measuring heart size and CTR on frontal chest radiographs.Results:Of 152 patients included, 81 (53%) were men and the mean age was 52 years. Maximum heart diameter had the highest area under the receiver operating characteristic curve for detection of cardiac enlargement (0.827, 95% confidence interval 0.760–0.894). In the subgroup of posteroanterior chest radiography studies (n = 101), a CTR cutpoint of 0.50 had only moderate sensitivity (72%) and specificity (72%). In men, a maximum heart diameter cutpoint of 15 cm had a sensitivity of 86% and a negative likelihood ratio of 0.24, and a cutpoint of 19 cm had a specificity of 100% and a positive likelihood ratio of infinity. In women, a maximum heart diameter cutpoint of 13 cm had a sensitivity of 91% and a negative likelihood ratio of 0.15, and a cutpoint of 17 cm had a specificity of 91% and a positive likelihood ratio of 3.5.Interpretation:A traditional CTR cutpoint of 0.5 has limited diagnostic value. Simple heart diameter measurements have higher diagnostic performance measures than CTR.

Cardiac chamber enlargement is important to identify, given that it is a predictor of poor outcomes and may reflect potentially treatable underlying disease.¹ Cardiac chamber size can be assessed using multiple imaging modalities, including chest radiography, echocardiography, computed tomography and cardiac magnetic resonance imaging (MRI).^2–4 Although cardiac MRI is considered the reference standard for the evaluation of cardiac size and function, it is rarely performed as an initial investigation because of its relatively high cost and limited availability.⁵ On the other hand, chest radiography is frequently performed as the initial imaging investigation for suspected pulmonary and cardiac disease, including in patients presenting with shortness of breath and chest pain.^6,7 Therefore, accurate and reproducible measures of cardiac enlargement on chest radiography would help to identify patients with underlying cardiac disease who might benefit from further investigation.Cardiac enlargement is frequently evaluated on chest radiography using the cardiothoracic ratio (CTR), which was originally described in 1919.⁸ Although this sign is an accepted and frequently used marker of cardiac enlargement, it has not been validated against cardiac MRI or other contemporary methods of objectively assessing cardiac chamber size. Some studies have shown that the CTR, as assessed using the originally described cutpoint of 0.5, has low specificity and diagnostic accuracy for cardiac enlargement, and therefore may be of limited clinical utility.^9–11 The purpose of this study was to evaluate new measurement techniques and cutpoints for the detection of cardiac chamber enlargement on chest radiography in comparison with MRI.