Widening of the subcarinal angle by pericardial effusion.

The subcarinal angle and transverse diameter of the cardiopericardial silhouette were measured on inspiratory posteroanterior radiographs of 54 patients (average age, 43.1 years) with pericardial effusion. The subcarinal angle was significantly greater (p less than 0.001) during effusion (81.0 degrees, n = 54) than either before (62.3 degrees, n = 14) or after (56.7 degrees, n = 21) effusion. A significant (p less than 0.05) positive correlation (r = 0.60, n = 118) was found between the magnitude of the subcarinal angle and the transverse diameter. This suggested that pericardial fluid accumulation displaces the heart and, in turn, splays the main bronchi. When pericardial fluid is not suspected clinically, a widened subcarinal angle, without other evidence of left atrial enlargement, may be a clue suggesting pericardial effusion.