Digoxin controls the rapid ventricular rate in atrial fibrillation primarily through which action?
- A Enhancement of vagal tone, which decreases AV nodal conduction velocity ✓
- B Direct blockade of L-type calcium channels in the AV node
- C Sympatholytic action mediated by central alpha-2 receptors
- D Blockade of potassium channels, prolonging AV nodal refractory period
Correct answer: A. Enhancement of vagal tone, which decreases AV nodal conduction velocity
Explanation
Digoxin inhibits Na+/K+-ATPase throughout the autonomic nervous system, enhancing vagal (cholinergic) activity. At the AV node this reduces conduction velocity and lengthens the effective refractory period, slowing ventricular response to atrial fibrillation. Its positive inotropy comes from the same pump inhibition raising intracellular sodium and secondarily calcium, but rate control in atrial fibrillation is chiefly vagomimetic. It has no direct calcium channel or potassium channel blocking action.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 13th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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