Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: The lung volumes are low which causes crowding of the bronchovascular structures . There is a left retrocardiac opacity which may represent atelectasis or infection . No large pleural effusion or pneumothorax is identified . Mild pulmonary edema appears relatively unchanged since ___ . Cardiomegaly and calcification of the aortic knob is also relatively unchanged . A pacer with leads in the right atrium and right ventricle is redemonstrated . There is no free air beneath the right hemidiaphragm .
    OUTPUT:
    
Retrocardiac opacity is incompletely assessed and could represent atelectasis and or pneumonia . Please refer to subsequent CTA chest results for further details .