How to determine cardiac width on chest X-ray (Chest X-ray)?

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Last updated: April 28, 2025 • View editorial policy

From the Research

To determine heart width on a chest X-ray, measure the widest transverse diameter of the cardiac silhouette on a standard posteroanterior (PA) chest radiograph, and compare it to the widest internal diameter of the thoracic cage to calculate the cardiothoracic ratio (CTR), with a normal CTR being less than 0.5, as suggested by the most recent study 1. This measurement is crucial in assessing cardiac enlargement, which may indicate conditions like heart failure, valvular disease, or cardiomyopathy.

  • The cardiothoracic ratio (CTR) is a commonly used parameter in the assessment of cardiomegaly, with a cut-off value of 0.5, as stated in the study 1.
  • A value of >0.5 should be interpreted as enlargement of the heart, according to the study 1.
  • Proper technique requires a PA view taken at full inspiration with appropriate distance (6 feet) between the X-ray source and film to minimize magnification.
  • The CTR is just one assessment tool and should be interpreted alongside clinical findings and other imaging studies when evaluating cardiac size.
  • The study 1 emphasizes the importance of considering the definition of the CTR and remembering to base measurements on PA radiographs, as attempts to mark it in other projections face many limitations.
  • It is essential to note that an increased CTR does not directly relate to heart function, as mentioned in the study 1.

References

Research

Radiological Cardiothoracic Ratio in Evidence-Based Medicine.

Journal of clinical medicine, 2021

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