This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S, Subject name: Pharmacology
Mechanism of digitalis in atrial fibrillation: 
Select and explain. 
A. Decrease in contractility, B. Na+ K+ ATP ase pump inhibition, C. Increase refractoriness of AV node, D. Bradycardia
C: Increase refractoriness of AV node
Answer: C: Increase refractoriness of AV node 
Explanation: Ans. C. Increase refractoriness of AV nodeDigoxin is inotropic agent used in heart failure. It has positive inotropic effect and negative chronotropic effect. Inotropic effect is due to blockade of Na+K+ATPase pump. Chronotropic effect is due to vagomimetic effect which increase the refractoriness of AV node. This mechanism is utilized in atrial flutter and fibrillation. Answer is C