Problem: A 67-year-old woman is brought to the emergency department for evaluation of palpitations and dizziness. A diagnosis of atrial fibrillation is made, and the patient is started on warfarin for prophylaxis against future embolic events. Four days after initiating warfarin, she develops well-defined, purpuric, and bullous lesions over her thighs (see image below). Inhibition of which of the following components of the coagulation cascade is likely responsible for this woman's lesions? Need Professional Help?
Credit: Wikimedia Commons Elimination tool Factor IX Protein S Protein C Factor II Factor VII