Arrhythmias USMLE Step 1 Practice Question
A 72-year-old woman with long-standing hypertension presents with palpitations and dyspnea. Vital signs show BP 148/92 mmHg, HR 118/min, RR 22/min, temperature 36.8°C, and SpO2 98% on room air. ECG demonstrates QRS duration of 160 milliseconds with broad monophasic R waves in leads I and V6, and deep broad S waves in V1. Chest X-ray shows no acute pulmonary pathology. She denies recent chest pain. Which of the following is the most likely diagnosis?
Answer choices
- AAtrial fibrillation
- BMobitz I block
- CLeft bundle branch blockCorrect answer
- DWolff-Parkinson-White syndrome
- ERight bundle branch block
- FAcute myocardial infarction
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.