That shouldn't be a "?" Sorry. I'm certain I used mag glycinate. :)
I used magnesium glycinate?
I don't think it's the earth that has changed, but as we eat more and more processed foods, our diets often lack magnesium, which can be found in unprocessed vegetables (especially leaves), whole grains, nuts, etc.
That being said, I wouldn't be too optimistic to magnesium supplements as an antiarrhythmic. It's true that IV magnesium is used to control a severe arrhythmia known as torsades de pointes, and it's also true that magnesium has some mild calcium channel blocking abilities, which in theory can reduce ectopic beats, especially PACs. The problem is, most of the ingested magnesium will just be flushed through the body.
Ask your doctor if your magnesium levels are low. If they are, you should of course take magnesium supplements or increase your dietary magnesium. If not, I wouldn't bother. And don't trust everything you find on Google. Most alternative treatments are very financially motivated.