Food for thought.
"It's easy to say two conditions are associated. Lots of things go together. It's much harder to claim one condition causes another.
In the US and other Western countries, obesity and atrial fibrillation are increasing in tandem. Ample evidence exists to associate the two diseases.
The question is: Does obesity cause AF? Or is it the other diseases that go with obesity, such as sleep apnea, hypertension, and diabetes? It's an important question because treatment (of any disease) is most successful when it targets the cause.
An elegant experiment  led by Dr Rajiv Mahajan (University of Adelaide, Australia) gets us very close to saying, yes, obesity does indeed cause AF.
As I tell you about this experiment, keep in mind what causes reentrant arrhythmia in the first place—multiple pathways, slowed conduction, and unidirectional block. In healthy cardiac muscle, conduction proceeds rapidly and smoothly through the cells; there is little chance of electrical reentry. In diseased muscle, inhomogeneity of conduction produces the milieu for reentry."
" The Study
The Australian research team compared electrical and structural cardiac properties of two groups of animals—obese (n=10) and lean (n=10) sheep. They created obese sheep by overfeeding. After 36 weeks of persistent obesity, researchers performed blood testing, echocardiography, electrophysiology testing, electroanatomic studies, and histology in both groups. They found significant differences:"