med for CHF/HTN in dialysis

I am wondering if anyone can shed some light on HTN/CHF in dialysis patients?
Firstly, it appears that most of my patients are on ARBs rather than ACEIs, is there a rationale on that? The MDs are resistant to changing these to ACEIs in spite of the fact that the ACEIs are cheaper and seems to me more studies with ACEIs rather than ARBs?
Secondly, I have a patient with LVH, CHF, HTN. Rx are amlodipine, hydralazine, losartan and nitropatch. BP still high pre and post dialysis. The MD switched her to irbesartan from losartan. What might be the rationale for that??
Any comments would be appreciated.