Ivabradine reduces heart rate in stable angina and heart failure WITHOUT affecting myocardial contractility or blood pressure. Its mechanism is:
- A Blockade of cardiac L-type voltage-gated calcium channels, reducing pacemaker activity
- B Beta-1 selective antagonism in the SA node with no peripheral vascular beta-2 effects
- C Selective blockade of the funny current (If) through HCN4 channels in the sinoatrial node, reducing the rate of diastolic depolarisation ✓
- D Muscarinic M2 receptor agonism in the SA node increasing parasympathetic tone
Correct answer: C. Selective blockade of the funny current (If) through HCN4 channels in the sinoatrial node, reducing the rate of diastolic depolarisation
Explanation
Ivabradine specifically blocks HCN4 channels (hyperpolarisation-activated cyclic nucleotide-gated) which carry the funny current (If) that drives the slow phase 4 depolarisation of the sinoatrial node pacemaker cells. By reducing If, ivabradine slows the rate of diastolic depolarisation without affecting action potential plateau (no contractility change) or vascular tone (no BP change). Its action is purely rate-reducing (pure heart rate lowering), distinguishing it from calcium channel blockers and beta-blockers.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.