Ivabradine reduces heart rate by a unique mechanism relevant to sinoatrial node automaticity. It blocks the:

• A L-type calcium channels in phase 0 of the sinoatrial action potential
• B HCN (hyperpolarization-activated cyclic nucleotide-gated) channels carrying the funny current If ✓
• C Delayed rectifier K+ channels (IKr) prolonging phase 3 repolarization
• D T-type calcium channels responsible for phase 4 spontaneous depolarization

Explanation

Ivabradine selectively blocks HCN channels (specifically HCN4 isoform in the SA node) which carry the hyperpolarization-activated funny current If. If is a mixed Na+/K+ inward current that activates during diastolic hyperpolarization and drives slow phase-4 depolarization in the SA node pacemaker. Blocking If prolongs the time between action potentials, reducing heart rate without affecting contractility, conduction velocity, or repolarization. This spares blood pressure and is particularly valuable in stable angina and HFrEF where beta-blockers are insufficient or contraindicated.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.