Revision 10 for 'Cardiothoracic ratio'All Revisions
The CTR is measured on a PA chest x-ray, and is the ratio of maximal horizontal cardiac diameter to maximal horizontal thoracic diameter (inner edge of ribs / edge of pleura). A normal measurement should be less than 0.5.
It should be noted that this is a coarse marker of disease. If the patient is symptomatic then echocardiography is required but the yield of echocardiography is low if performed just for an increased CTR 3.