I used to check my pulse all the time. Eventually though, I did figure out how to stop doing it. And my advice is completely useless. Never the less, it did work, so..
You just have to stop. You have to force yourself to not do it. You have to do anything but that. Its hard. Its scary. And everything about you is screaming to do so. But you can't do it. Once you check, your sympathetic nervous system floods you with adrenaline. Because it doesnt take chances, and if you werent in danger, why would you be checking? So every time you do it, you actually make it worse.
But the other side is that, every time you resist doing it, it gets easier to resist next time, and the time after that, and so on.
Its not easy, it took me a long time to do. But its what must happen