Which of the following should be ordered next in the treatment of this patient?

A 75-year-old woman presents to the emergency department complaining of generalized pain and edema in her left leg. She denies chest pain, shortness of breath, and hemoptysis. She takes 2.5 mg warfarin daily for atrial fibrillation and her INR is 2.6. Lower extremity ultrasound reveals the presence of a deep venous thrombosis in the left popliteal vein. Which of the following should be ordered next in the treatment of this patient?

1.Increase warfarin dose
2.CT angiogram of the chest
3.Ventilation/perfusion lung scan
4.Inferior vena cava filter
5.IV heparin

Exp:

This patient is suffering from a deep vein thrombosis (DVT). The fact that the patient is already on a therapeutic dose of anticoagulant makes inferior vena cava (IVC) filter placement necessary.
Anticoagulation is the primary prophylaxis and treatment for DVT. The patient is taking warfarin and has reached a therapeutic level of anticoagulation (INR 2.0 - 3.0). The appropriate action is to have an IVC filter placed as she has failed anticoagulation. An IVC filter would also be indicated if the patient had a contraindication to anticoagulation. Notably, anticoagulation does not dissolve the existing DVT. Thrombolytic therapy (i.e. tPA) may be used in cases of hemodynamically significant pulmonary embolism (PE).

Illustration A shows a DVT on a doppler study.