A 64-year-old woman with a longstanding diagnosis of mixed connective tissue disorder and pulmonary fibrosis is admitted with symptoms of recent increase in postprandrial retrosternal distress, heaburn, and nocturnal cough. Her ECG shows nonspecific T-wave changes and she finds minimal relief of her symptoms with sublingual NTG. On examination, she is not in any acute distress and is afebrile. Chest exam reveals bilateral crackles. CXR is shown . The cause of this patient's acute symptoms may be