The Correlation between Chest X-ray and Cardiac Magnetic Resonance Imaging in the Assessment of Left Atrial Enlargement

Objective: Left atrial enlargement (LAE) is common in cardiovascular disease and is associated with heart failure, atrial fibrillation, and stroke. Chest X-ray (CXR) is widely available; however, its diagnostic value for LAE has not been validated against cardiac magnetic resonance imaging (CMR). We evaluated the correlation and diagnostic performance of conventional CXR signs for detecting LAE using CMR as the reference standard. Materials and Methods: We retrospectively analyzed 110 patients who underwent CMR and had a posteroanterior CXR within 6 months. Left atrial volume was calculated by the biplane area–length method and indexed to body surface area. CXR signs assessed were the subcarinal angle, double density sign, and left atrial appendage prominence (“third contour”). Sensitivity, specificity, and diagnostic accuracy were calculated against CMR-defined LAE. Results: CMR identified LAE in 85 patients (77.3%). The third contour had the highest sensitivity (78.8%) but poor specificity (8.0%), whereas a subcarinal angle > 90° had the highest specificity (92.0%) with low sensitivity (8.2%). Overall diagnostic accuracy for individual or combined CXR signs was 27.3%–62.7%, with no correlation between CXR findings and CMR-derived left atrial volume index (all P > 0.05). Conclusions: To our knowledge, this is the first study validating CXR parameters against CMR for detecting LAE, revealing that conventional radiographic signs have limited diagnostic performance. Despite its accessibility and routine use, CXR demonstrated low sensitivity and specificity for LAE compared with CMR.