Without extreme caution heat should be avoided because you can screw up the resins that make the carbon fibers of the arrow stay together. Cutting from the back is a much better solution. If you've got to get the insert out, then try putting a drill bit inside the shaft and swinging it hard. Be careful, because when it does break the glue loose the insert and drill bit become projectiles in a furious way. They were most likely installed with Goat Tuff glue if done at a shop or possibly the Easton epoxy that comes with the inserts; either one is a very hard but brittle glue that can be broken by the drill trick. Cutting from the back is still the best option, though.