Why am I not surprised the ER didn't find anything? I've only been through a couple of years of testing that didn't find anything and suffered a heart attack, that's why. I now refuse stress tests because I've had 4 that didn't show anything and I am sure they are useless unless you are unable to walk across the room. I had to figure my causes and cures out for myself. Fortunately I have a bit of an education in biology and worked in some pharmacology labs and a hospital ICU lab, but I'm certainly not a doctor and don't play one on TV.
Hardly any doctors are aware that the stomach and esophagus can have an effect on the heart. It works the other way around too, according to severalthe studies I read. Not surprising since just about everything has a connection to the vagus nerve.
Here's one new study: http://ajpheart.physiology.org/cgi/content/full/290/5/H2085 . This was written after my heart attack, but it says what I already figured out on my own. I recommend printing it and taking it to your cardiologist. No, maybe not. Patients aren't supposed to know anything, so don't push it too much. Once you find your triggers you may be able to stop the symptoms yourself.
Now here's what I did: On the recommendation of my allergist, who said, "Of course you have food allergies, I've been in practice over thirty years, and I see this all the time!" I started keeping a detailed food journal - including all the things I put on the hamburger, not just that I ate a hamburger, and so forth.
Then I did challenge testing of the foods that I thought were giving me symptoms. (My problem was that I would get reflux and then get tachycardia.) The method is to eat a tsp of a suspect substance, wait 20 minutes. Then if there were no symptoms you double the dose 2 tsp, wait 20 minutes. Then double again 4 tsp, 20 minutes, then 8 tsp, then 16 and stop. Some foods take a little more, so you might start with a tablespoon. I knew a teaspoon of jello was not a problem, but a cereal bowl was sure to set me off. You have to separate foods too. The waffle wasn't a problem, but the maple syrup was. I had problems with mixed seasonings, pepper, garlic, mustard and ketchup, vinegar.
When I got my very long list of foods identified - nearly a page typed - I searched the internet. I knew some things like wine and beer would bring up a hit when searched with "allergy." I found all my foods on sulfite allergy websites. But that's my triggers, not necessarily anyone else's. When I went back to my allergist, she didn't know about sulfite in particular, but she has since found other patients with the same problem. A lot of medications have sulfites too! I'm glad I found out that generic propofol has sulfite preservative because last year I needed 3 surgeries and giving me that could have killed me. I have a typed list of my intolerances and another of meds containing sulfites.
Maybe all this has nothing to do with your symptoms, but it doesn't cost anything but your time - lots of your time. I spent 2 months just getting the first list done, then weeks more on challenge testing. I've spent years continuing my personal research. I used to have tach every day. Now it's not that often, only when I cheat on my diet.