Pacemaker Causing Fainting Spells?

My mother is 83, had CABG x 5 six weeks ago; about 12 days post-op had dual chamber pacemaker. Morning after pacemaker implant had first incident of orthostatic hypotension. Has had it since: If she doesn't stand still for a minute after rising from chair before walking somewhere, she'll pass out or nearly pass out, with change in mental status. Doctors don't know cause; pacemaker team insists it can't be "pacemaker syndrome" because it's dual chamber. She's had head/chest CT, chest X rays, blood tests, echocardiogram - all normal. Tilt table test confirms OH. No diabetes or other problems. Nonsmoker.

Current meds: amiodarone, Effexor (been on that for a year), Zocor, aspirin. Docs say meds aren't the cause. She just started midodrine yesterday. CABG went without a hitch, no complications other than just this OH day after pacemaker implant. Please help! She doesn't always wait the full minute and thus, she's at risk for serious falls unless I'm at her side constantly to catch her.

[Jerry_NJ]

I will assume one reason she has a pacemaker is her un-paced heart beats too slowly, and the PM gives it more beats at some level.  I don't wear a PM, so I'm trying to help from memory on what I have read in the past.  If my memory is correct it would seem very possible that it takes some time for the PM to pick up the HR.  And if the happens only sometimes, it could be because she has a lower HR just before rising on those occasions.

It would seem reasonable to me to discuss what the PM is set at, i.e., when does it "kick in'"?  Perhaps they can set it to kick in at a higher HR.  Just thinking with you and hope you get better results, you mother does that is.