Arrhythmias USMLE Step 1 Practice Question
A 71-year-old man with prior anterior myocardial infarction presents with palpitations and presyncope. Vital signs show BP 88/56, HR 170, RR 22, SpO2 98% on room air. ECG demonstrates regular wide-complex tachycardia at 170 bpm with uniform QRS morphology and absence of AV dissociation. Troponin is normal; chest X-ray shows no acute pulmonary process. He denies dyspnea. Which of the following is the most likely mechanism of this arrhythmia?
Answer choices
- AAccessory pathway conduction from atrium to ventricle
- BMultiple atrial foci with variable conduction
- CReentry confined to the AV node
- DAutomatic firing from the sinus node
- EReentry around a ventricular scarCorrect answer
- FTriggered activity from abnormal automaticity in the Purkinje fibers
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