How do I assess the heart on a chest X‑ray?

Assessing the Heart on Chest X-Ray

The chest radiograph provides a rapid, inexpensive overview of cardiac size, configuration, and pulmonary vascularity, but has significant limitations in detecting cardiac chamber enlargement and should prompt echocardiography when abnormalities are suspected. 1

Technical Requirements for Reliable Assessment

• Only posteroanterior (PA) and lateral views provide reliable cardiac measurements 2, 3
• Anteroposterior (AP) portable radiographs magnify the cardiac silhouette and cannot reliably assess true cardiac size 2, 4
• Verify proper technique before interpretation: adequate inspiration, minimal rotation (check medial clavicular heads equidistant from spinous processes), and appropriate penetration 3

Systematic Cardiac Evaluation

Cardiac Size and Contour

• Measure the cardiothoracic ratio (CTR): maximum transverse cardiac diameter divided by maximum thoracic diameter 1, 2
• CTR >0.50 (50%) traditionally suggests cardiomegaly, though this has poor correlation with actual left ventricular size 2, 5
• Critical limitation: CTR primarily reflects right ventricular and right atrial dimensions, not left ventricular function 2, 5, 6
• Research demonstrates no significant correlation between CTR and left ventricular end-diastolic dimension on echocardiography (r=0.011, p=0.879) 5
• Chest radiography has only 54-61% sensitivity and 54-90% specificity for detecting cardiomegaly compared to echocardiography 4, 7

Specific Cardiac Chamber Assessment

Right Heart Enlargement:

• Increased convexity of the right heart border suggests right atrial enlargement 1
• Loss of retrosternal clear space on lateral view indicates right ventricular enlargement 1
• However, chest radiographs fail to reliably detect right ventricular or right atrial enlargement in restrictive lung disease 6

Left Heart Enlargement:

• Straightening or convexity of the left heart border suggests left atrial enlargement 1
• Lateral displacement of the cardiac apex suggests left ventricular enlargement 1
• Double density sign (left atrial border visible through right atrium) indicates left atrial enlargement 1

Pulmonary Vascularity Assessment

Pulmonary Artery Evaluation:

• Main pulmonary artery (MPA) diameter >35 mm from midline to left lateral border indicates pulmonary hypertension with 96% sensitivity 1
• Right descending pulmonary artery >15 mm (women) or >16 mm (men) has 93% sensitivity and 88% specificity for pulmonary hypertension 1, 3
• Left descending pulmonary artery >18 mm on lateral view suggests pulmonary hypertension but with lower specificity (67%) 1

Pulmonary Vascular Patterns:

• Cephalization (upper lobe vessel prominence) indicates pulmonary venous hypertension 1
• Rapid tapering ("pruning") of peripheral vessels with enlarged central arteries suggests pulmonary arterial hypertension 1
• Kerley B lines indicate interstitial edema from elevated left atrial pressure 1

Additional Cardiac Features

• Assess for pericardial effusion: globular cardiac silhouette with sharp borders 1
• Evaluate for calcifications: valvular, coronary, or pericardial 1
• Check for surgical clips, prosthetic valves, pacemakers, or other devices 1, 3
• Assess aortic contour and width for dilation or tortuosity 1, 3

Critical Pitfalls and Limitations

Major Limitations:

• Normal chest radiograph does not exclude significant cardiac disease 1
• Chest radiography performs poorly in detecting mild cardiac abnormalities 1
• Serial chest radiographs are not recommended for routine heart failure management due to insensitivity for detecting fluid status changes 2
• AP radiographs magnify the heart by 15-20% and cannot be used for reliable CTR measurement 2, 4

When to Proceed to Advanced Imaging:

• Order echocardiography for: suspected cardiomegaly, assessment of ejection fraction, chamber dimensions, valvular function, and estimation of pulmonary artery pressure 1, 2
• Order cardiac MRI for: precise volumetric measurements, tissue characterization, and functional assessment when echocardiography is inadequate 1
• Order CT/CTA for: coronary artery evaluation, pulmonary embolism, aortic pathology, or when echocardiography windows are poor 1

Practical Clinical Algorithm

1. Obtain PA and lateral chest radiographs (not AP if avoidable) 1, 2
2. Assess technical quality before interpretation 3
3. Measure CTR but recognize its limitations for left ventricular assessment 2, 5
4. Evaluate pulmonary artery dimensions if pulmonary hypertension suspected 1, 3
5. Assess pulmonary vascularity patterns for congestion or hypertension 1
6. If CTR >0.50, pulmonary artery enlargement, or abnormal cardiac contour detected, proceed directly to echocardiography 1, 2
7. Do not rely on chest radiography alone for cardiac diagnosis or management decisions 1, 5