An 86-year-old woman arrived in the emergency department complaining of 1 hour of chest pain. She had a history of myocardial infarction (MI), atrial fibrillation, placement of a dual-chamber pacemaker, stroke, gout, and hypertension.
On arrival, her blood pressure was 88/68 mm Hg, heart rate was 75 beats/min and irregular, respirations were 22/min, and blood oxygen saturation was 97% with 2 L/min supplemental oxygen. She looked uncomfortable and had no appreciable jugular venous distention, no abnormal heart sounds, clear lung fields, trace lower extremity edema, and weak radial pulses. The blood lactate level was 4.0 mg/dL (reference value, <2.3 mg/dL) (to convert to millimoles per liter, multiply by 0.111). A chest radiograph was normal except for pacemaker leads in the expected positions and an enlarged cardiac silhouette. An electrocardiogram (ECG) was obtained (Figure 1).