Investigating severe interscapular pain

A 52 year old woman presented with a sudden onset (two hour history) of severe interscapular burning pain associated with shortness of breath. Her medical history was unremarkable except for a strong family history of coronary heart disease.

Examination was normal apart from a blood pressure of 150/80 mm Hg and heart rate of 110 beats/min. The respiratory rate was 14 breaths/min, and the patient was afebrile with otherwise normal cardiorespiratory examination. Chest radiography showed borderline widened mediastinum and upper lobe venous congestion. Electrocardiography showed non-specific changes in the T waves. Blood gas analysis showed the patient to be hypoxic (PaO₂ = 8 kPa (normal 8-14 kPa)), with no evidence of carbon dioxide retention. Her full blood count and biochemical profile were normal except for mildly raised C reactive protein and positive D-dimers. Baseline level of troponin I was <0.01 ng/ml.

Chest pain was partially relieved by glyceril trinitrate spray; subsequently the patient was given a morphine injection to ease her pain.