A 34-year-old woman with a history of migraine without aura is evaluated in the emergency department for acute dyspnea and pleuritic chest pain. She has been on combined oral contraceptive pills for 3 years. Two weeks ago, she developed left calf swelling and pain; compression ultrasonography of the left lower extremity confirmed a popliteal vein thrombosis. She was started on warfarin monotherapy and achieved an INR of 2.1 on day 5 of treatment. Today she presents with acute onset of dyspnea, tachycardia (HR 112 bpm), tachypnea (RR 24), oxygen saturation 91% on room air, and pleuritic chest pain. Repeat compression ultrasound of the left lower extremity shows stable thrombosis with no new clot extension. Electrocardiography shows sinus tachycardia without ST-segment changes. Which of the following best explains her acute clinical deterioration?

1. A)Inadequate anticoagulation despite therapeutic INR, allowing continued thrombus propagation
2. B)Warfarin-induced protein C deficiency causing hypercoagulability in the first week of therapy
3. C)Pulmonary embolism arising from the known deep vein thrombosisGABARITO
4. D)Heparin-induced thrombocytopenia from prior heparin exposure
5. E)Myocardial infarction secondary to estrogen-mediated coronary vasospasm