A 44-year-old man presents with dyspnea and chest discomfort for two weeks. These symptoms have markedly worsened over the last four days. There is no history of paroxysmal nocturnal dyspnea or orthopnea. No other symptoms are present. His medical, surgical, and family histories are unremarkable. He only drinks socially and does not smoke. An ECG is obtained. This shows a rate of 106 bpm with a regular rhythm. All leads have low voltage QRS complexes with electrical alternans.