A 52-year-old man comes to the emergency department (ED) due to 2 hours of burning substernal pain. Before coming to the ED, he took several tablets of antacid at home without any relief. The patient's other medical problems include hypertension and hyperlipidemia. His temperature is 36.7 C (98 F), blood pressure is 160/90 mm Hg, and pulse is 92/min. Cardiovascular examination shows normal S1 and S2 without any murmurs. There is no abdominal tenderness. ECG shows ST-segment depression in leads II, III, and aVF. Troponin is 0.06 ng/mL (normal

Question

A 52-year-old man comes to the emergency department (ED) due to 2 hours of burning substernal pain.  Before coming to the ED, he took several tablets of antacid at home without any relief.  The patient's other medical problems include hypertension and hyperlipidemia.  His temperature is 36.7 C (98 F), blood pressure is 160/90 mm Hg, and pulse is 92/min.  Cardiovascular examination shows normal S1 and S2 without any murmurs.  There is no abdominal tenderness.  ECG shows ST-segment depression in leads II, III, and aVF.  Troponin is 0.06 ng/mL (normal <0.01 ng/mL).  As part of this patient's treatment, enoxaparin therapy is initiated.  This drug is expected to bind to which of the following substances in this patient's blood?

Quizplus · Accepted Answer

11ec160b_3bd9_e609_9249_1b7f4df3e758_MD0001_00 This patient with chest pain, ST depressions, and mild troponin elevation appears to be experiencing a myocardial infarction. Enoxaparin is a form of low-molecular-weight heparin (LMWH) that, like heparin, functions by binding antithrombin III (AT III) via a pentasaccharide sequence. Once activated, AT III binds to factor Xa and stops factor Xa from converting prothrombin to thrombin. Less thrombin is produced, resulting in an anticoagulant effect. Unfractionated heparin has more molecules than LMWH, allowing it to bind factor Xa and thrombin; it is more effective than LMWH in inactivating thrombin. (Choices B and C) Tissue plasminogen activator (t-PA) converts plasminogen to plasmin. Plasmin functions to break down fibrin, resulting in thrombolysis. Because t-PA can only bind plasminogen strongly in the presence of fibrin, its thrombolytic action is clot specific. (Choice D) Protein C and protein S are endogenous antithrombotic molecules that are also vitamin K-dependent. Due to their shorter half-lives in the circulation, these molecules are depleted first during initiation of warfarin therapy, causing a transient procoagulant state. For this reason, patients are typically treated with heparin or LMWH during initiation of warfarin therapy. (Choice E) Prothrombin (factor II) is a vitamin K-dependent clotting factor. This factor, along with factors VII, IX, and X, is depleted by warfarin. LMWHs inhibit prothrombin production (through factor X inhibition), but they do not directly bind prothrombin. Educational objective: Enoxaparin is a low-molecular-weight heparin (LMWH) that functions like heparin in that it binds and activates antithrombin III (AT III). Activated AT III binds to factor Xa and stops factor Xa from converting prothrombin to thrombin. Due to its fewer number of molecules, LMWH acts primarily on factor Xa, not thrombin.

A 52-Year-Old Man Comes to the Emergency Department (ED) Due