This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S, Subject name: Medicine
Most common cause of cardioembolic stroke is 
Select and explain. 
A. Non rheumatic atrial fibrillation, B. Myocardial infarction, C. Ischemic cardiomyopathy, D. Prosthetic valves
A: Non rheumatic atrial fibrillation
Answer: A: Non rheumatic atrial fibrillation 
Explanation: Nonrheumatic atrial fibrillation is the most common cause of cerebral embolism overall. The presumed stroke mechanism is thrombus formation in the fibrillating atrium or atrial appendage, with subsequent embolization. Patients with atrial fibrillation have an average annual risk of stroke of ~5%.MI, prosthetic valves, rheumatic hea disease, and ischemic cardiomyopathy are other causes.Ref: Harrison 19e pg: 2564