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A 68-year-old man comes to the emergency department because of a 5-hour history of palpitations and light-headedness. He states that he has experienced shorter episodes of palpitations before, but nothing so severe. After admission to the hospital, the patient receives a full cardiac work-up and is diagnosed with rapid atrial fibrillation, most likely secondary to a moderately stenosed mitral valve. Medical treatment to convert him to sinus rhythm is unsuccessful. However, his heart rate is well controlled with various atrioventricular node blocking agents. The patient is prescribed a regimen of daily medications including drugs to control potentially disastrous complications of atrial fibrillation. Which of the following drugs is most likely prescribed long-term to prevent such complications?

(A) Aspirin
(B) Protamine sulfate
(C) Streptokinase
(D) Unfractionated heparin
(E) Warfarin


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The correct answer is E. Chronic atrial fibrillation is a risk factor for clot formation and systemic embolization. This man needs ongoing anticoagulation to prevent possible complications, such as cerebrovascular accidents or mesenteric infarction. Warfarin inhibits gamma-carboxylation of vitamin K-dependent clotting factors and is used for chronic anticoagulation. It is taken orally and has a long half-life. The degree of anticoagulation must be followed by measuring the International Normalized Ratio.

Answer A is incorrect. Aspirin works by irreversibly inhibiting cyclooxygenase, thereby preventing the conversion of arachidonic acid to prostaglandins. The four effects of aspirin are antiplatelet (thereby inhibiting thrombus formation), antipyretic, analgesic, and anti-inflammatory. Aspirin is not used to prevent clot formation in the setting of atrial fibrillation, but rather to prevent myocardial infarction. In the setting of atrial fibrillation, the patient needs a drug that prevents activation of the clotting cascade, whereas aspirin acts only on platelet aggregation.

Answer B is incorrect. Protamine sulfate is used for rapid reversal of heparinization in the setting of overzealous anticoagulation.

Answer C is incorrect. Streptokinase is a thrombolytic used to break down existing clots. This could be used in the setting of a myocardial infarction. It would not be used prophylactically to prevent clot formation in atrial fibrillation.

Answer D is incorrect. Heparin is taken parenterally and is used for immediate, not long- term, anticoagulation. This patient was likely given heparin on admission to the hospital and was then converted to warfarin for chronic anticoagulation before his discharge.