As a PvP healer, i wouldn't focus my spec for damage. You already do good damage with HS/BS/Shiv and Snipe/EP, not to mentition Orbital Strike. I've even gotten 5k damage medal with EP a few times (uncommon though).
Med Shield is a pretty worthless talent in my opinion. The probe only absorbs a certain amount of damage and then it's gone. If you are being attacked, the probe will be gone before you can even get off a heal.
I really like Slip Away, but now I spec into Infiltrator instead. As a healer you are constantly under attack in PvP and I'd rather have 15% extra run speed constantly, but I guess that pretty individual.