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[Cardiothoracic ratio]
1Department of Cardiology, JR Tokyo General Hospital.
Insights
The cardiothoracic ratio on chest X-rays is unreliable for diagnosing cardiac enlargement. Echocardiography is the accurate method for assessing cardiac dilatation, while chest X-rays are useful for follow-up.
Area of Science:
- Cardiology
- Radiology
- Medical Imaging
Background:
- The cardiothoracic ratio (CTR) on chest X-rays is a traditional indicator for cardiac size.
- A CTR of 50% is often considered the upper limit of normal, but this can lead to misdiagnosis, especially in certain populations.
- Factors like obesity, age, and technical variations can affect CTR accuracy.
Purpose of the Study:
- To evaluate the correlation between left ventricular dimension and cardiothoracic ratio in subjects with normal cardiac function.
- To assess the reliability of chest X-ray in diagnosing cardiac dilatation compared to echocardiography.
Main Methods:
- Correlation analysis was performed between left ventricular end-diastolic dimension and cardiothoracic ratio.
- Eighty consecutive subjects with normal physical, ECG, and Doppler echocardiography examinations were included.
- Standard chest X-ray measurements were compared with echocardiographic findings.
Main Results:
- No significant relationship was found between left ventricular end-diastolic dimension and the cardiothoracic ratio.
- The study highlights limitations of CTR in accurately reflecting cardiac size and potential for false positives.
- Echocardiography demonstrated superior accuracy in diagnosing cardiac dilatation.
Conclusions:
- Chest X-ray is essential for initial cardiac assessment but should be interpreted cautiously for cardiac dilatation.
- Echocardiography is the definitive diagnostic tool for cardiac enlargement.
- Chest X-rays remain valuable for monitoring and managing diagnosed cardiac conditions.
Abstract:
Cardiothoracic ratio has been a useful index of cardiac dilatation, and a value of 50% is generally considered to indicate the upper limit of normal cardiac size. However, this value is not always correct and increases the number of false-positive results, especially in obese or older subjects who may have a misdiagnosis of cardiac enlargement. The maximal transverse diameter of the cardiac shadow of chest X-ray film consists mainly of the diameters of the left ventricle and the right atrium as shown by X-ray computed tomography, but this ratio is influenced by many factors; not only left ventricular dilatation or hypertrophy, but also dilatation of the other cardiac chambers and the aorta, rotation and shift of the heart, respiratory phase, body posture, and measurement errors. In contrast, echocardiography is an accurate method for the diagnosis of cardiac dilatation. This study correlated left ventricular dimension with cardiothoracic ratio in 80 consecutive subjects with normal physical, ECG and Doppler echocardiography examinations. There was no relationship between left ventricular end-diastolic dimension and the cardiothoracic ratio. Chest X-ray is mandatory for initial cardiac examination. However, we must be careful about roentgenographic diagnosis of cardiac dilatation. Cardiac enlargement should be diagnosed by echocardiography, but follow-up and management can be based on chest X-ray films.