When pursuing complex PCI of the RCA (especially when lesion preparation is required), when do you consider placing a transvenous pacemaker in anticipation of conduction abnormalities?  

There are a few options when using roto for the RCA or a dominant LCX. Upfront TVP if you want to play it safe. Pretreatment with aminophylline 100-250 mg 10 minutes. Test run without pre-treatment and having atropine and/or TVP nearby at the ready. Which you choose depends on gut instinct a...

In the presence of LBBB.

Use of Rotablator would require a temporary pacemaker.

I usually have central venous access prior to starting any PCI with rotablator. With RCA rotational atherectomy (especially) the TV pacer is still standard of care. 

The routine premedication with aminophylline 250mg IV prior to RCA atherectomy has drastically reduced the need for TVP in my practice. On occasions, it is not effective and TVP is needed. This has been confirmed in published studies.