Just read 'The haywire heart' by Chris Case ,John MandrolaMD and Lennard Zinn, a book which I found to be quite fascinating. It is aimed at Super athletes but it contains a lot of well reasoned information and advice on dealing with Afib, and compares the super fit with other sufferers and ordinary individuals.
Surprisingly the professional super athletes who stop at about 35 tend not to suffer from afib as their hearts adapt to less flat out exercise and tend to shrink back to a more normal size. The authors identify studies which show that between 30 minutes to one hour exercise a day is sufficient to maintain heart health.
However those who do go on can slide into Afib and their hearts resemble those who are obese - they have larger left atria and electrical and structural problems, i.e. fibrosis, dilation, stretch and inflammation.
There are plenty of thought provoking case studies and the takeaway chapter has a good look at supplements, e.g. coq10, L-carnitine, Iodine (especially for those who don't eat fish but do eat lots of bread and pastas, Garlic, Magnesium, Aspirin, Hawthorn and Nsaids.
As they say in their conclusion 'if you are well informed, persistent and patient, a rich life awaits you'