This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Other topics and Adverse effects, Subject name: Anatomy
Mechanism of action of digitalis in atrial fibrillation is 
Select and explain. 
A. By Causing bradycarlia, B. Na+ K+ ATPase inhibition, C. Increase in refractoriness of AV nodal tissue, D. By Causing bradycarlia
C: Increase in refractoriness of AV nodal tissue
Answer: C: Increase in refractoriness of AV nodal tissue 
Explanation: (Ref: KDT 6/ep502) Digitalis acts in CHF by inhibiting Na+-K+-ATPase whereas in AF, it acts by decreasing the conduction through AV node.