Arrhythmias USMLE Step 1 Practice Question
A 27-year-old man with no prior cardiac history presents with regular narrow-complex tachycardia. Vital signs show HR 180 bpm, BP 95/60 mmHg, RR 20, SpO2 98% on room air. He receives intravenous adenosine and briefly experiences flushing and substernal chest discomfort before the rhythm terminates to normal sinus rhythm. ECG demonstrates no delta waves or evidence of preexcitation. Which of the following best describes the mechanism of this medication?
Answer choices
- ABlocks delayed rectifier potassium channels throughout the ventricle
- BInhibits Na-K-2Cl cotransport in the thick ascending limb
- CBlocks fast sodium channels in ventricular myocardium
- DIncreases vagal tone and transiently blocks AV nodal conductionCorrect answer
- EStimulates beta-1 receptors in the AV node
- FBlocks L-type calcium channels in the sinoatrial node
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.