Summarize the radiology report findings into an impression within 3 sentences.
    INPUT: Left - sided pacemaker device is re - demonstrated with leads terminating in the right atrium and right ventricle . Mild enlargement of the cardiac silhouette is again noted . Marked enlargement of the main pulmonary artery is similar . Lung volumes are low compared to the previous study . There is crowding of the bronchovascular structures without overt pulmonary edema . Patchy opacity within the right lung base likely reflects atelectasis . No pleural effusion or pneumothorax is present . There are mild degenerative changes noted in the thoracic spine .
    OUTPUT:
    
Patchy opacity in the right lung base , likely atelectasis in the setting of low lung volumes . Infection can not be completely excluded in the correct clinical setting .