That scary term just means you had an abnormality on the EKG, with the ryhthym of your heart, and YES, that absolutely can be caused by anxiety or a panic attack. I've been hooked up to a monitor while having a panic attack, my heart rate was almost 200, and I was having skipped beats (called PVC's), but that was from the panic.
You've already had a thorough work up from a cardiologist, an echo is a great test, they can visualize all of the parts of the heart while it is beating. If there is anything big and bad going on, most likely an echo would have shown something.
Nothing to be overly concerned about at this point. It's good that your doc wants you to follow up with the cardiologist. I think that will help to put your mind at ease.
Try not to worry too much. If there was something BAD going on, you'd be in the hospital, not at home.