Hi there Ness....
What you need to do is not try to correct your palpitations directly, but indirectly. You're getting palpitations from your panic attacks..which I'm sure you know...but I want to explain something to you that you might find interesting.
With panic attacks, yes they are psychological, but there is an actual physiological reason why they happen. When you are excited, need to fight, need to run, are scared etc. etc. etc. a division of your nervous system called the "sympathetic nervous system" is activated to help you perform better. Your heart starts beating faster, your pupils dilate to let in more light, you breathe faster, there is more blood flow to your muscles etc. etc. etc. As you can see, this is something that you would want if you were in a situation that required physical action; however, with panic attacks, what happens is that the sympathetic nervous system fires at a time where you are NOT in a situation that requires physical action. When this happens, it's very scary because all those changes happen in your body, and you get the feeling that you are about to die.....are you about to die? FAR FROM IT!
Anyway, what makes panic attacks worse is trying to fight them off, or trying to avoid them happening. What you have to do is allow yourself to have the panic attack (as scary as that is), but while you are having it, get used to the idea that the attack will NOT last forever....you will NOT die....you will not get hurt etc. etc. Trust me, they always pass. Eventually your mind and your body will be in sync again and you'll have less and less panic attacks. This is actually how psychiatrists first deal with panic attacks....if these methods don't work, there are certain anti-anxiety agents that you can be put on to help alleviate symptoms.
So what you need to do is not worry about your heart, but worry about a way to solve your panic attacks.