Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: There are low lung volumes which accentuates bibasilar atelectasis . Cardiomediastinal silhouette and hilar contours are unremarkable . A battery pack with pacemaker leads terminating in the right atrium and right ventricle are in unchanged position . A slight increase in the retrocardiac density may be due to low lung volumes versus early infectious process .
    OUTPUT:
    
Bibasilar atelectasis and low lung volumes . While ther is no overt evidence of pneumonia , a retrocardiac opacity in the appropriate clinical setting may be an early infectious process .