I assume you had your heart checked; if your main symptom is palpitations, then a beta blocker might be more appropriate than Lexapro. But if you had a lot of problems and most have gone away, then stick with the Lexapro -- drugs don't cure, they just mitigate the symptoms. You'll always have symptoms unless you find a cure through some kind of therapy work.
If the Lexapro is helping with your anxiety, then it is doing what it is designed to do in my opinion. I have palpatations, but they are just a way of life. I have come to realize that they are just that...palpatations. If they bother you and contribute to your anxiety, have you have considered counseling? For me, gaining the knowledge to confront it and deal with it made it much easier to deal with it. Ativan is usually prescribed short term and you can build up a tolerance to it over time...keep us posted!