Ivabradine is used in stable angina and heart failure. Its mechanism differs from beta-blockers in that ivabradine:
- A Blocks L-type calcium channels in the SA node, reducing the slope of spontaneous depolarisation
- B Activates adenosine A1 receptors in the SA node, hyperpolarising the pacemaker cells
- C Selectively inhibits the funny current (If) by blocking HCN channels in the SA node, reducing heart rate without affecting contractility ✓
- D Inhibits adrenyl cyclase, reducing cAMP and slowing SA node discharge
Correct answer: C. Selectively inhibits the funny current (If) by blocking HCN channels in the SA node, reducing heart rate without affecting contractility
Explanation
Ivabradine selectively blocks hyperpolarisation-activated cyclic nucleotide-gated (HCN) channels responsible for the cardiac pacemaker 'funny current' (If) in the SA node. This reduces the rate of spontaneous diastolic depolarisation, lowering heart rate in a purely rate-dependent manner without affecting myocardial contractility, AV conduction, or vascular smooth muscle. Beta-blockers reduce heart rate via beta-receptor blockade with additional negative inotropic effects.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.