Are you just having a resting ECG done? Just remember, that those things can show a lot of false positives, so if your doctor is not concerned, I would not be either. For example, I just went in for my physical a couple of months ago and it spit out that I had had a prior heart attack. They did it again and it said I had heart disease...I was like, sheesh...I eat right, do cardio every day and I'm young. The doctors were not concerned and they gave me a few other conclusive tests and the end result was I just had a really strong heart beat because of all the long distance running I have don over the past 15 years. My point is, don't get too overly worked up about this test. It's painless, quick and easy. Even if something comes back 'abnormal,' quite often it is normal for you:). Just keep your lines of communication open with your doctor and ask as many questions as you like with him/her.
i dun think the food u ate will affect ur ecg result,i have done a lot of ecgs due to those anxiety chestpain etc,the main point is do not move alot while ur in the test cause trembling might affect ur ecg result,this is wat my doc told me b4