American Board of Internal Medicine (ABIM) Certification Practice Exam

Which medication can effectively reduce heart rate in symptomatic inappropriate sinus tachycardia?

1. Atenolol

2. Bisoprolol

3. Ivabradine

4. Metoprolol

The correct answer is: Ivabradine

In the context of symptomatic inappropriate sinus tachycardia (IST), ivabradine is specifically designed to reduce heart rate by inhibiting the hyperpolarization-activated cyclic nucleotide-gated channel (I_f) in the sinoatrial node. Unlike beta-blockers, ivabradine acts selectively on the pacemaker current in the heart, leading to a decrease in heart rate without affecting myocardial contractility or electrical conduction, which makes it particularly useful in patients where beta-blockers may not be appropriate or well-tolerated. Additionally, ivabradine has been demonstrated to have efficacy in reducing symptoms such as palpitations and fatigue associated with IST, providing a targeted approach to treatment. Its mechanism allows it to effectively lower the resting heart rate without the side effects commonly associated with beta-blocker therapy, making it an ideal option for managing this condition. In selecting ivabradine, clinicians prioritize addressing the underlying mechanism of IST while minimizing potential adverse effects, showcasing the utility of this medication in effectively managing elevated heart rates in affected patients.