I've been a runner for more than 50 years, which also puts me at higher risk for A-Fib.
A 16%-18% increased risk because of low carbs really does not sound that important.
If 10% of people have A-Fib, an 18% increase is just 1.8 persons per hundred.
On the flip side, high carb intake had a definite impact on the severity of my A-Fib.
In hot weather, I used to drink as much as one gallon of orange juice per day (I love grove fresh OJ!).
Five years ago, my A-Fib suddenly became much worse. I completely cut OJ out of my diet and replaced it with water.
My A-Fib dramatically improved. I now go as long as a month with no symptoms at all.
OJ has lots of sugar, seems you were mainlining sugar into your blood stream, and not necessarily a problem with carbs.
I loooooove OJ. Unfortunately, I inherited the tree sloth metabolism on my mother’s side of the family, so the only caloric liquid that I usually drink is beer. Other than that, just black coffee, unsweetened tea and water.