Which one of the following patients with atrial fibrillation can be treated with aspirin alone?

1. A 60-year-old woman with rheumatic mitral valve disease

2.A 63-year-old man with no evidence of coronary artery disease (CAD) (Correct Answer)

3.A 65-year-old man with poor left ventricular systolic function

4.A 79-year-old woman with no evidence of CAD

5.An 80-year-old woman with a history of TIA

The correct answer is 2 not 4.
How come and Why?