A 77-year-old man presents with speech disturbances and weakness and numbness of his left arm. These symptoms started abruptly one hour ago and resolved slowly over the subsequent 30 minutes. He is currently asymptomatic. His medical history is significant for ischemic heart disease, atrial fibrillation, and sick sinus syndrome. He is currently on warfarin and metoprolol. He underwent implantation of a rate-responsive single-chamber ventricular demand pacemaker eight months ago. He only drinks socially and denies recreational drug use. His smoking history amounts to 40 pack-years. He lives in Italy and has been visiting his children for the last three weeks. During this period he has been poorly compliant with his medications. A full blood count, serum electrolyte assay, random capillary glucose, and noncontrast CT brain are all normal. A coagulation profile shows shows his INR to be 1.2 (target: 2.0-3.0).