A 70-year-old man comes to the office due to palpitations. He has felt an irregular and fast heartbeat on multiple occasions over the last month. The patient has not had chest pain, dyspnea, dizziness, or weakness. His medical history includes hypertension and type 2 diabetes mellitus. Temperature is 36.7 C (98.1 F), pulse is 102/min and irregular, blood pressure is 140/82 mm Hg, and respirations are 16/min. Cardiopulmonary auscultation reveals clear lungs and no heart murmurs. ECG shows an irregularly irregular rhythm with absent P waves. The patient is started on metoprolol and apixaban. Which of the following is likely to be directly affected as the result of this therapy?

Question

A 70-year-old man comes to the office due to palpitations.  He has felt an irregular and fast heartbeat on multiple occasions over the last month.  The patient has not had chest pain, dyspnea, dizziness, or weakness.  His medical history includes hypertension and type 2 diabetes mellitus.  Temperature is 36.7 C (98.1 F), pulse is 102/min and irregular, blood pressure is 140/82 mm Hg, and respirations are 16/min.  Cardiopulmonary auscultation reveals clear lungs and no heart murmurs.  ECG shows an irregularly irregular rhythm with absent P waves.  The patient is started on metoprolol and apixaban.  Which of the following is likely to be directly affected as the result of this therapy?

Quizplus · Accepted Answer

11ec160b_3cc7_f05d_9249_91f08c4f608b_MD0001_00 This patient has palpitations, an irregular pulse, and ECG findings consistent with atrial fibrillation. Treatment with a rate control medication (eg, metoprolol) reduces atrioventricular conduction and limits ventricular tachycardia, which helps prevent symptoms (eg, palpitations, dizziness) and risk of cardiomyopathy. However, rate control agents do not inhibit uncoordinated atrial contraction, so patients remain at risk for atrial thrombus and embolic stroke. As a result, most patients are also initiated on anticoagulation. Direct factor Xa inhibitors (eg, apixaban) are often used for stroke prevention in atrial fibrillation as they are administered orally and do not require monitoring of drug levels (unlike warfarin). This class of medications blocks the active site of factor Xa, which prevents it from converting prothrombin to thrombin. Direct factor Xa inhibitors are denoted by names that end in "Xa-ban." (Choice A) The conversion of factor X to factor Xa is the beginning the final common pathway of the coagulation cascade and is triggered by factor VIIIa (intrinsic pathway) and tissue factor (extrinsic pathway). Factor Xa inhibitors block conversion of prothrombin to thrombin, not factor X to factor Xa. (Choice B) Factor Xa inhibitors reduce the conversion of fibrinogen to fibrin. However, this is a downstream (not direct) effect that occurs as a result of decreased thrombin levels. (Choice C) Tissue plasminogen activator is a fibrinolytic enzyme that increases the conversion of plasminogen to plasmin. It is primarily used to lyse ongoing clots in patients with acute ischemic strokes. (Choice E) Warfarin inhibits vitamin K epoxide reductase, which decreases the reduced form of vitamin K and limits gamma-carboxylation of vitamin K-dependent coagulation factors (II, VII, IX, X). Educational objective: Direct factor Xa inhibitors (eg, apixaban) are anticoagulants that block the active site of factor Xa, which leads to reduced conversion of prothrombin to thrombin. This class of medications is administered orally and requires no drug level monitoring.

A 70-Year-Old Man Comes to the Office Due to Palpitations