Mechanism of action of digitalis in atrial fibrillation is:: (A) By decreasing cardiac contractility, (B) Na+ K+ ATPase inhibition, (C) Increase in refractoriness of AV nodal tissue, (D) By causing bradycardia
Answer is C. Digoxin reduces ventricular rate in A. Fib. by decreasing the number of impulses that are able to pass down the A-V node and bundle of His. It increases ERP of A-V node by direct, vagomimetic and antiadrenergic actions --> Minimum interval between consecutive impulses that can successfully traverse the conducting tissue is prolonged.