Good question. If you need a new valve the medical staff should be able to manage your bloods with both the cardiac surgeons and heamatology. If you get a mechanical valve patients generally go on blood thinners so you dont have clots. But as your platlets are low, heam will probably advise the surgeons what meds to use. I personally dont see why you couldnt have the surgery... Depending on your age, other risk factors and how damaged the valve is.
On a side note, where I work they do trancatheter aortic valve implantations on elderly patients who might not recover well post surgery. So they can do implants through the groin. But yes depends on your case.
Now 30yr old. Diagnosed AML dec 2015 (Most likely MDS prior). Trisomy 6. Runx1 mutation also. Had induction and consolidation chemo. Marrow failure ++ so SCT on 21st of March with MUD. Married with a 1yr old!