A 73-year-old woman presents with mild dyspnea and dizziness. She has a history of deep venous thrombosis and hypertension and is taking maintenance doses of warfarin and lisinopril.

Her physical exam reveals a blood pressure of 130/80 mm Hg, a heart rate of 114 beats/min and irregularly irregular, and a respiratory rate of 18 breaths/min. She is in no acute distress, has no jugular venous distention, and her lungs are clear.

Her cardiac exam reveals an irregularly irregular rhythm; no murmurs or extra sounds are heard on auscultation. Bilateral lower extremities have no edema or tenderness. Her neurological exam is normal.

Diagnostic testing reveals a normal basic metabolic profile, normal cardiac biomarkers, normal thyroid function studies, an international normalized ratio (INR) between 2 and 3, and a negative chest x-ray. A 12-lead electrocardiogram reveals mild left ventricular hypertrophy and atrial fibrillation, with no other abnormal findings. Chest computed tomography (CT) is negative for pulmonary emboli. Subsequent echocardiography reveals findings consistent with mild left ventricular hypertrophy and atrial fibrillation, but no other abnormalities.