By statistics cardiomegaly often implies ventricular enlargement (especially left ventricular) .Right ventricle generally do not enlarge the CT ratio until late stages .
More important is the impact of right atrial enlargement on the CT ratio. Here was a patient referred to echo lab for evaluation of cardiomegaly
The x-ray chest was suggesting a definite LV enlargement. To my surprise the LV was perfectly measuring a normal dimension .
The right atrium was huge and measuring more than 5 cms . This increased the CTR.
The following illustration tries to create echo equivalent of transverse CT diameter by rotating apical 4 chamber view by 90 degrees.
Cardimegaly in X- ray chest do not necessarily mean ventricular enlargement.
Pure atrio-megaly especially right atrial enlargement can dramatically increase the CT ratio.
This is not a big discovery , still fellows need to reinforce this fact , as mistakes are most often committed in well known things !