Stents due to graph failure

My 78 year old Mom is scheduled to have a heart cath and stents will be put into place if possible. She had a 4-way bypass 6 years ago and they think some of her graphs have failed. She is on one baby aspirin per day and takes plavix. When I asked if she should stop taking these for the procedure, they told me "no."  But for all of her other procedures like knee artheroscopy, etc. she had to stop the blood thinners. Why not with this procedure?

[kenkeith]

Anti-platelet medication delays clotting of blood.  A clot can occlude vessels causing a heart attack and the cardiologist doesn't believe there will be any ruptures, etc. The risk may be excessive bleeding in the event of any detrimental circumstances.