A 72-year-old man comes to the emergency department due to left-sided weakness and speech difficulty upon awakening this morning. Medical history includes hypertension and persistent atrial fibrillation. His anticoagulant medication was stopped 6 months ago after an episode of gastrointestinal bleeding. Blood pressure is 160/90 mm Hg and pulse is 88/min and irregular. Examination shows mild dysarthria, left lower facial weakness, and left hemiparesis. CT scan of the head shows no evidence of intracranial bleeding. Transthoracic echocardiogram shows left atrial enlargement, normal left ventricular systolic function, and mild mitral regurgitation. The patient's symptoms are determined to be caused by a thromboembolic event. Which of the following is the most likely source of the thrombus?

Question

A 72-year-old man comes to the emergency department due to left-sided weakness and speech difficulty upon awakening this morning.  Medical history includes hypertension and persistent atrial fibrillation.  His anticoagulant medication was stopped 6 months ago after an episode of gastrointestinal bleeding.  Blood pressure is 160/90 mm Hg and pulse is 88/min and irregular.  Examination shows mild dysarthria, left lower facial weakness, and left hemiparesis.  CT scan of the head shows no evidence of intracranial bleeding.  Transthoracic echocardiogram shows left atrial enlargement, normal left ventricular systolic function, and mild mitral regurgitation.  The patient's symptoms are determined to be caused by a thromboembolic event.  Which of the following is the most likely source of the thrombus?

Quizplus · Accepted Answer

11ec160b_3553_ac71_9249_1b58cdcfe86c_MD0001_00 Atrial fibrillation is associated with significant risk of systemic thromboembolism; therefore, long-term anticoagulation is often recommended in patients without any confounding contraindications (eg, recent gastrointestinal bleeding). Several factors contribute to thrombus development in atrial fibrillation, including left atrial enlargement, blood stasis due to ineffective atrial contraction, and atrial inflammation and fibrosis (exerts a procoagulant effect). The left atrial appendage is a small saclike structure in the left atrium that is particularly susceptible to thrombus formation. Approximately 90% of left atrial thrombi are found within the left atrial appendage in patients with nonvalvular atrial fibrillation. These clots can then systemically embolize and lead to stroke (as in this patient), acute limb ischemia, or acute mesenteric ischemia. (Choice A) The crista terminalis refers to a thick band of atrial muscle that separates the smooth sinus venosus from the right atrial appendage and atrium proper. It is the site of origin of the atrial pectinate muscles and is not a significant region of thrombus formation in atrial fibrillation. (Choice C) A left ventricular (LV) apical thrombus poses risk of systemic embolization and stroke, but it typically only develops in patients with LV aneurysm or severe LV systolic dysfunction. It is not associated with atrial fibrillation. (Choice D) Prosthetic valve thrombosis can occur with bioprosthetic or mechanical mitral valves in patients without adequate anticoagulation. Thrombus formation on a native mitral valve is extremely rare, especially when valve function is normal or near normal. (Choices E and G) Thrombosis of the pulmonary veins or sinus of Valsalva (aortic sinus) is rare and not associated with atrial fibrillation. (Choice F) Thrombus formation can occur in the right atrial appendage with atrial fibrillation, though less frequently than in the left atrial appendage. A right atrial thrombus poses risk of embolization to the pulmonary (rather than systemic) circulation, resulting in pulmonary embolism. Educational objective: Atrial fibrillation is associated with increased risk of systemic thromboembolism. The left atrial appendage is the most common site of thrombus formation in atrial fibrillation.

A 72-Year-Old Man Comes to the Emergency Department Due to Left-Sided