Sometimes, a doctor will diagnose GERD based on symptoms and history alone, but pH probe tests can also be used to diagnose this, as well as endoscopic evaluations, imaging studies, and esophageal manometry (to test for weakness in the sphincter between the stomach and esophagus. Since you also have a history of conduction problems with the heart, blood test and CBC, chest imaging studies (xray, CT, MRI), EKG (electrocardiogram), and exercise stress test might be appropriate as well to rule out cardiac problems as contributing to your chest pain. That esophagitis has already been seen is a very good indication that you do have GERD, however. Technically, any type of "itis" (esophagitis, gastritis) means that the tissue is simply inflammed. The trick is to determine the cause for this inflammation. Esophagitis can be inflammation of the esophagus from repeated exposure to stomach acid, or even from bacterial or fungal infections, or both.

It's true that there are a lot of bacteria in the intestinal tract, and they serve very useful purposes. At normal levels, they won't cause a problem, but when a person's immune system is weakened for some reason or another (stress, illness, damage to the tissue of the GI tract), these bacteria are capable of multiplying too quickly and can cause an infection by invading the tissue in that area. If the tissue is already inflammed or damaged from something like excessive acid exposure, it's much easier for the bacteria to invade the tissue and cause an infection. If left untreated, these infections can spread to nearby tissues or blood stream, and set off the whole body, as you mentioned.

And yes, intestinal health does help the immune system. The entire immune system isn't based on the intestines alone, but research suggests that normal levels of certain "friendly" bacteria in the intestines help strengthen the immune system. Bacteria such as Lactobacillus acidophilus and Bifidobacterium bifidum,which are normally found in the intestines, assist the body by defending it against toxins, bacteria and allergens. Some people take supplements called "probiotics" for this reason, and certain types of probiotics are used to even treat GERD, but the effectiveness hasn't been evaluated by the FDA at this time. You can read more about them here: http://en.wikipedia.org/wiki/Probiotic

Were you treated for the H. pylori found from your endo procedure? This is a type of bacteria that is not a part of the normal flora of bacteria in the stomach, and can lead to gastritis, esophagitis, and acid reflux. In fact, this might be the cause of your symptoms. H. pylori loves the stomach environment, and isn't likely to go away on its own without treatment. Minor infections can be treated with bismuth solutions, such as Pepto-bismol that you find over-the-counter, which kills the bacteria. If the infection is more severe, however, oral antibiotics will be required to kill them efficiently.

I hope this helps!