This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
Atrial fibrillation may occur in all of the following conditions, except - 
Select and explain. 
A. Mitral stenosis, B. Hypothyroidism, C. Dilated cardiomyopathy, D. Mitral regurgitation
B: Hypothyroidism
Answer: B: Hypothyroidism 
Explanation: None