Ivabradine lowers heart rate without affecting myocardial contractility or blood pressure because it selectively inhibits:

• A L-type calcium channels in SA node cells
• B Beta-1 adrenergic receptors in the SA node
• C Inward rectifier potassium channels (IK1)
• D The funny current (If) mediated by HCN channels during diastolic depolarisation ✓

Explanation

Ivabradine specifically blocks HCN (hyperpolarisation-activated cyclic nucleotide-gated) channels responsible for the pacemaker 'funny current' (If) in SA node cells, slowing the rate of diastolic depolarisation and reducing heart rate without negative inotropy or vasodilation. This pure rate-lowering effect makes it valuable in stable angina and heart failure with reduced EF when beta-blockers are contraindicated. It does not affect L-type calcium channels or beta-receptors.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.