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Lyme disease — USMLE Step 2 CK MCQ

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HardInternal MedicineLyme diseaseUSMLE Step 2 CK

A 24-year-old with intermittent palpitations develops an irregular wide-complex tachycardia at 220/min. Prior electrocardiography showed a short PR interval and delta waves. Blood pressure is 118/72 mm Hg, mentation is normal, and there is no chest pain or pulmonary edema. Which acute treatment is most appropriate?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: E — Give intravenous procainamide with continuous electrocardiographic monitoring

Explanation lettering: C = shown as A · E = shown as C · A = shown as E

A is correct: this is hemodynamically stable pre-excited atrial fibrillation, recognized by a very rapid irregular wide-complex rhythm in a patient with ventricular pre-excitation. Procainamide slows conduction through the accessory pathway and can terminate the arrhythmia; continuous monitoring is required for hypotension and QRS or QT prolongation. B, C, D, and E predominantly block the atrioventricular node, which can shift conduction toward the accessory pathway, accelerate the ventricular rate, and precipitate ventricular fibrillation.

Reference: 2023 ACC/AHA/ACCP/HRS guideline for atrial fibrillation. https://www.ahajournals.org/doi/10.1161/CIR.0000000000001193