This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Rheumatic Hea disease & infective endocarditis, Subject name: Medicine
Which of the auscultatory sign is absent in mitral stenosis in the presence of atrial fibrillation? 
Select and explain. 
A. Mid diastolic murmur, B. Presystolic accentuation, C. Variable first hea sound, D. Loud P2
B: Presystolic accentuation
Answer: B: Presystolic accentuation 
Explanation: The presystolic accentuation of the mid-diastolic murmur of atrial fibrillation is due to atrial contraction against a closed mitral valve. With the onset of atrial fibrillation, since atrial will be twitching, pre-systolic accentuation will disappear. Other changes in findings of mitral stenosis with an onset of atrial fibrillation are: The first hea sound becomes variable in intensity as hea rhythm is irregularly irregular Opening snap continues to occur as long as the valves are pliable and non-calcified. Length of the diastolic murmur varies.