If you are a Paladin you can Shield Swipe when you know Chaos Breath is coming and prevent it entirely. You need to land it between the time when you get marked and when he uses the breath. It's been a while since the last time I did CT, but I think you wait like 3 seconds after being marked and then swipe and it'll prevent the breath. You can use Bulwark for a chance to extend your swipe uptime to 10s.