Which of the following describes the mechanism of action of ivabradine in chronic heart failure with reduced ejection fraction?
- A Blockade of L-type calcium channels in vascular smooth muscle
- B Selective blockade of the sinoatrial funny current (If), slowing phase 4 depolarization ✓
- C Opening of ATP-sensitive potassium channels
- D Selective beta-1 receptor antagonism
Correct answer: B. Selective blockade of the sinoatrial funny current (If), slowing phase 4 depolarization
Explanation
Ivabradine selectively inhibits the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels carrying the funny current in the sinoatrial node, reducing heart rate without affecting contractility, blood pressure, or conduction. This makes it useful when resting heart rate remains 70 bpm or above despite maximally tolerated beta-blocker in HFrEF. Because it spares calcium channels entirely, it has no negative inotropic effect, which distinguishes it from the calcium channel blocker distractor.
Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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