A 68-year-old man comes to the emergency department due to lightheadedness, generalized weakness, and palpitations. The patient has a prolonged history of hypertension and takes amlodipine. He does not use tobacco or alcohol. His blood pressure is 110/60 mm Hg and pulse is 144/min and irregular. ECG shows an irregularly irregular rhythm and absent P waves. The patient is started on beta blocker therapy for rate control, with improvement in his heart rate. Long-term anticoagulation is initiated to prevent atrial thrombus formation, and he is eventually discharged home on warfarin. Which of the following is the best test to monitor the anticoagulation effect of warfarin in this patient?

Question

A 68-year-old man comes to the emergency department due to lightheadedness, generalized weakness, and palpitations.  The patient has a prolonged history of hypertension and takes amlodipine.  He does not use tobacco or alcohol.  His blood pressure is 110/60 mm Hg and pulse is 144/min and irregular.  ECG shows an irregularly irregular rhythm and absent P waves.  The patient is started on beta blocker therapy for rate control, with improvement in his heart rate.  Long-term anticoagulation is initiated to prevent atrial thrombus formation, and he is eventually discharged home on warfarin.  Which of the following is the best test to monitor the anticoagulation effect of warfarin in this patient?

Quizplus · Accepted Answer

11ec160b_3bd9_49c8_9249_2d3243db8350_MD0001_00 This patient's ECG (irregularly irregular rhythm with absent P waves) suggests atrial fibrillation (AF), which alters cardiac flow dynamics, making thrombus formation more common. If this thrombus detaches from the atrial wall, there is a risk of stroke. The oral anticoagulant warfarin (Coumadin) reduces thrombus formation risk by inhibiting the activation of vitamin K-dependent clotting factors II, VII, IX, and X (vitamin K antagonist). This leads to decreased levels of these factors, particularly factor VII, and therefore prolongs the prothrombin time (PT). Another useful laboratory value is the International Normalized Ratio (INR), a ratio of the patient's PT to a control (usual INR target for AF: 2.0-3.0). Examples of indications include AF, deep venous thrombosis, and pulmonary thromboembolism. Outpatients who take warfarin typically have their INR checked every few weeks (more frequently initially). The most common side effect is excessive anticoagulation leading to bleeding (which can require vitamin K and fresh frozen plasma if rapid reversal is needed). Skin necrosis can occur during the first few days of treatment due to a transient hypercoagulable state (reduction in protein C anticoagulant activity before affecting other factors' procoagulant activity); for this reason, heparin is typically administered temporarily at the start of warfarin therapy ("heparin bridge"). Warfarin should not be used during pregnancy because it is teratogenic and can cause fetal bleeding. (Choice A) Activated partial thromboplastin time (aPTT) is used to monitor unfractionated heparin, which primarily affects the intrinsic coagulation pathway. (Choice B) Bleeding time is used for the assessment of platelet function. Increased bleeding time can be seen with thrombocytopenia, von Willebrand disease, defects of platelet aggregation, disseminated intravascular coagulation (DIC), and aspirin therapy. (Choices C and D) The combination of a decreased fibrinogen level and the presence of fibrin split products (such as D-dimer) is characteristic of DIC. Educational objective: Warfarin is an oral anticoagulant that inhibits the carboxylation of vitamin K-dependent coagulation factors II, VII, IX, and X. It is used in atrial fibrillation, deep venous thrombosis, and pulmonary thromboembolism. Prothrombin time (PT)/International Normalized Ratio (INR) should be monitored regularly during treatment with warfarin. Activated partial thromboplastin time (aPTT) is used for monitoring unfractionated heparin.

A 68-Year-Old Man Comes to the Emergency Department Due to Lightheadedness