I would definitely get checked out by a cardiologist before ANY more races or training for that matter. Do you want to be that guy that drops dead during the latest IM race? I didn't think so. You have to be responsible given the situation. As another poster said, you have to think of your family. Triathlon is a lifestyle, but at the end of the day it is for health and enjoyment. Doing something counterproductive to your overall goals isn't sensible.

Transfer the registration to another race. Support your family at the race and perhaps volunteer as well. I had to get checked out once too. EKG, blood work, halter monitor, echocardiogram, stress test and tilt table test. It turned out everything was fine, but I am really glad moving forward that I was checked out. The peace of mind you will enjoy moving forward is invaluable.

UPDATE-I just read your last post. I'm really glad to see that you decided to pull the plug (no pun intended) on IMMT and get checked out. No matter the result, you won't regret it. If something is found then it's the best decision you ever made. If they don't find anything then you were being responsible to yourself and family. I'm glad you made the right decision. Good luck and I'm sure everything will work out fine!