The ability with the really long cast time that kills you instantly if he finishes casting. Interrupt it.
The stuff that does moderate damage - let it through, if your finding he gets your health down too quick, use force wave to interrupt a couple of the non-lethal ones.
I died once, figured out that I need to interrupt the really long one that one shot me - interrupted it everytime, profit.
If you really still can't do it then ask for someone to tag along with you.
But believe me if Vivicar is causing you problems then the end boss on Corellia will make you cry. Master your interrupts now.
(oh I did it as Shadow too - I honestly can't see how you can find it hard as Sage with healing abilities on top of an interrupt)