Coronary Artery Disease USMLE Step 1 Practice Question
A 25-year-old healthy volunteer participates in a cardiac physiology experiment and receives an intravenous infusion of a beta-1 agonist. Vital signs show HR 98 bpm, BP 128/76 mmHg, RR 16, temp 37°C, SpO2 98% on room air. ECG demonstrates increased slope of phase 4 depolarization in sinoatrial node pacemaker cells. The volunteer denies chest pain or dyspnea. Which of the following changes is the most direct result of enhanced automaticity?
Answer choices
- AProlonged QT interval due to delayed repolarization
- BFaster heart rate from enhanced SA node automaticityCorrect answer
- CLoss of the ventricular plateau phase
- DComplete AV block due to suppressed conduction
- ESlower heart rate from reduced automaticity
- FIncreased peripheral vasoconstriction leading to elevated diastolic blood pressure
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