ABIM IM Practice Test 2

A 74-year-old woman is evaluated in the emergency department 6 hours after the sudden onset of right hand weakness and difficulty finding words, and new difficulty seeing objects to her left. She has hypertension and type 2 diabetes mellitus. Medications are lisinopril and metformin. She does not smoke. Blood pressure is 152/86 mm Hg, and pulse rate is 96/min. Examination shows nonfluent aphasia, mild right hand weakness and a left homonymous hemianopia. MRI of the brain shows small acute cortical infarcts in the left middle cerebral artery territory and the right posterior cerebral artery territory, without hemorrhage. CT angiography of the head and neck shows no carotid, vertebral or intracranial stenosis. Creatinine is 0.9 mg/dL [0.50–1.10]. A rhythm strip is shown. Which of the following is the most likely mechanism of her stroke?