Each week, Osmosis shares a USMLE® Step 1-style practice question to test your medical knowledge. Today’s case involves a 66-year-old woman who suddenly develops left-sided weakness. She has a history of hypertension and hyperlipidemia. Neurologic examination reveals right-sided gaze deviation and weakness in her left limbs. Can you identify the most common origin of the thrombus related to her condition?
A 66-year-old woman presents to the emergency department after developing acute onset, left-sided weakness. The patient’s daughter reports she found her mother sitting in a chair, unable to lift her left arm or leg. The patient’s past medical history includes hypertension and hyperlipidemia, for which she takes hydrochlorothiazide and atorvastatin. The patient’s temperature is 37°C (98.6°F), pulse is 110/min, respirations are 18/min, blood pressure is 177/86 mmHg, and O2 saturation is 97% on room air. Neurologic examination demonstrates a right-sided gaze deviation and 2/5 strength in the left upper and left lower extremity. An initial electrocardiogram is shown below.
Which of the following structures of the heart is the most common origin of the thrombus implicated in this patient’s clinical condition?
A. Left atrial appendage
B. Right ventricle
C. Left ventricle
D. Mitral valve
E. Tricuspid valve
Scroll down for the correct answer!
The correct answer to today’s USMLE® Step 1 Question is…
A. Left atrial appendage
Before we get to the Main Explanation, let’s look at the incorrect answer explanations. Skip to the bottom if you want to learn more about the correct answer right away!
Incorrect Answer Explanations
B. Right ventricle
The right ventricle is not the most common site of thrombus formation resulting in ischemic stroke. Thrombus formation and subsequent ischemic stroke do not commonly occur from the right heart unless a patent foramen ovale is present.
C. Left ventricle
Left ventricular aneurysms following myocardial infarction can serve as the site of thrombus formation and subsequent ischemic stroke; however, it is not the most common site of thrombus formation.
D. Mitral valve
The left atrial appendage, not the mitral valve, is the most common site of thrombus formation and subsequent ischemic stroke from atrial fibrillation.
E. Tricuspid valve
The tricuspid valve is not the most common site of thrombus formation resulting in ischemic stroke. Thrombus formation and subsequent ischemic stroke do not commonly occur from the right heart unless a patent foramen ovale is present.
Main Explanation
This patient presents with evidence of an ischemic stroke–a major complication of untreated atrial fibrillation, which is depicted on this patient’s electrocardiogram.
Atrial fibrillation is the most common sustained arrhythmia in clinical practice and results from unpatterned depolarization of atrial tissues caused by multiple micro-reentry circuits. These reentry circuits can be caused by progressive fibrosis and atrial dilation. Electrocardiographically, atrial fibrillation is characterized by irregular QRS complexes with absent P-waves.
Diastolic filling and subsequent cardiac output may decrease when rapid ventricular response occurs with rates >100 beats per minute. These changes can result in chest pain, shortness of breath, dizziness, and lightheadedness. In addition, hemostasis in the atria can result in thrombus formation, most commonly at the left atrial appendage, owing to its shape and internal trabeculations.
Major Takeaway
Ischemic stroke is a major complication of untreated atrial fibrillation. Thrombus formation secondary to atrial fibrillation most commonly occurs in the left atrial appendage.
Want to learn more about this topic?
Watch the Osmosis video: Ischemic Stroke video
References
- Al-Saady NM, Obel OA, Camm AJ. Left atrial appendage: structure, function, and role in thromboembolism. Heart. 1999 Nov;82(5):547-54. doi: 10.1136/hrt.82.5.547. PMID: 10525506; PMCID: PMC1760793.
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