Arrhythmias USMLE Step 1 Practice Question
A 19-year-old college student presents with recurrent episodes of palpitations (HR 180 bpm, BP 110/70 mmHg, RR 20, SpO2 98% on room air). Between episodes, ECG demonstrates a short PR interval and slurred QRS upstroke consistent with ventricular preexcitation. During the acute episode, rhythm strip shows regular narrow-complex tachycardia at 190 bpm. Troponin levels are normal. Which mechanism best explains the tachycardia during this episode?
Answer choices
- ATriggered activity from delayed afterdepolarizations
- BFocal atrial automaticity from the pulmonary veins
- CAntegrade conduction through the AV node and retrograde conduction through the accessory pathwayCorrect answer
- DAntegrade conduction through the accessory pathway and retrograde conduction through the AV node
- EReentry entirely within the AV node
- FTriggered activity from delayed afterdepolarizations in the accessory pathway
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