There are many threads here on this forum about AVRT. I especially like this one:
http://www.soberrecovery.com/forums/...ined-long.html
There are also several other threads: Here is part 5 of AVRT discussion:
http://www.soberrecovery.com/forums/...-part-5-a.html
I'll bump them both for you so you can either click on them here or go straight to the threads on this forum.