From the double weapon sidebar on Pg 10 of AV...
"Wielding a double weapon is like wielding a weapon in each hand. The first die given in the damage column of the table for a double weapon is for the primary end of the weapon; the second damage die is for the secondary end. You can use either end of a double weapon to deliver an attack unless a power specifies a main or off-hand weapon attack."
There are 4 double weapons in AV, if you have access to D&D insider look up double sword or urgrosh or double axe or double flail to see what the stats look like.
Oddly given the rules they were created by only the Urgrosh has 2 different ends the rest are basically dual wielding the same weapon in 2 hands.