Ivabradine reduces heart rate in heart failure patients by acting on which specific channel?

• A L-type voltage-gated calcium channel in SA node pacemaker cells
• B Delayed rectifier potassium channel (IKr) prolonging phase 3 repolarisation
• C Fast sodium channel reducing phase 0 depolarisation rate
• D HCN4 channels carrying If (funny current) in SA node pacemaker cells ✓

Explanation

Ivabradine selectively inhibits HCN4 (hyperpolarisation-activated, cyclic nucleotide-gated) channels in the SA node that carry the I(f) or 'funny' pacemaker current. This current is responsible for the slow spontaneous diastolic depolarisation (phase 4) in pacemaker cells; blocking it reduces the slope of depolarisation and decreases heart rate without affecting myocardial contractility or blood pressure. It is used in HFrEF with persistent tachycardia despite beta-blockers.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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