i began having worsening episodes of arrhythmias about 6 mos ago.
mine usually lasted no longer than 45". i had a lot of the same tests. i tried wearing a couple of different monitors but could never catch it at the right time.

finally my dr ordered a monitor that i wore for a month. that did the trick. i was dx'd with A Fib or atrial fibrillation. untreated it can increase the risk for cardiac blood clots because the heart is quivering and blood tends to pool which can make a clot. i ended up on an anti arrhythmic. i also had to start on a blood thinner. i didn't want to but i understood the risks.

make sure your dr really documents what kind of arrhythmia you have. not treating unless you're "passing out" doesn't seem right to me. the fact that you're symptomatic should count for something.

advocate for getting more information, and, get copies of your test results and dr dictations. you might learn a lot.

I had tachycardia starting at 17, on and off. Later in life, I switched over to the atrial fibrillation which NurseNancy has. Mine is paroxysmal, that is, I don't have it all the time.
I agree that it can be triggered by food additives. I am much more likely to get it if I have
had food additives, which means I don't eat out in many places. Also I am more likely to get it if I eat a meal heavy in fat (like red meat) which I'm not supposed to do on the Swank diet anyway. A-fib is different than tachycardia, and I recognized the difference right away, but when I had my first attack about six years ago I just felt exhausted and could not tell what was going on. I checked my heart rate and it was very fast and weak, so I called 911. I take l5 mg a day of Propanalol, a Beta blocker, in 5 mg increments (with each meal, or take at bedtime if I forget the one at dinner time). I am in danger of clots from Polycythemia Vera, too. I believe following the Swank diet and
curtailing excess salt has kept me so far from clots, but I probably do have tiny clots in my toes, where the thick blood from PV may clog my microvascular system and irritate the nerves, thus increasing neuropathy to the acute pain level sometimes.

Once I got Tachycardia from a big dose of Vitamin C--probably with an additive, as it came from a health food store which I learned later has products with a lot of additives.
I read labels.