If there is cardiomegaly - look for other signs of heart failure
It may be possible to determine which chamber is enlarged
An obscured heart border may indicate disease of the adjacent lung
Cardiomegaly and heart failure
The heart size should be assessed on every chest radiograph. The heart is enlarged if the cardiothoracic ratio (CTR) is greater than 50% on a PA view. If the heart is enlarged, check for other signs of heart failure such as pulmonary oedema, septal lines (or Kerley B lines), and pleural effusions.
Upper zone vessel enlargement (1) - a sign of pulmonary venous hypertension
Pulmonary oedema (2) - bilateral increased lung markings (classically peri-hilar and shaped like bats wings - more widespread in this case)
Septal (Kerley B) lines (3) - See next picture
Pleural effusions (4)
Worsening exercise tolerance
Chronic uncontrolled hypertension
Rapid onset of shortness of breath
Left ventricular failure with pulmonary oedema
Septal (Kerley B) lines
Septal lines, also known as Kerley B lines, are due to fluid accumulating between the secondary lobules of the lungs. They are an elusive sign, but once spotted, pulmonary oedema is almost always the cause, especially in a patient with a cardiac history.
Septal lines - a specific sign of pulmonary oedema
Occasionally conditions that cause lymphatic obstruction may cause septal lines - such as sarcoidosis or lymphangitis carcinomatosa
Heart chamber enlargement
If there is cardiomegaly it is sometimes possible to determine which chamber is enlarged. For example, signs of left atrial enlargement include a double right heart border, bulging of the left heart border, and splaying of the carina to greater than 90 degrees.
Left ventricular aneurysm - an uncommon complication of myocardial infarction
Obscured heart contours
An obscured heart border may be due to disease of the adjacent lung. Just as right middle lobe consolidation obscures the right heart border (right atrial edge), so consolidation of the lingula (an anterior segment of the left upper lobe) leads to an obscured left heart border (left ventricular edge).