You said: "Why would it cure AF? The heart is still dilated, which is one of the major risk factors for AF and why heart failure can cause it."
You are right in saying Chronic Heart Failure is a risk factor for Atrial Fibrillation (and vice versa). However, you have missed other important causes of AF such as Coronary Artery Disease (here Rex-L improved microvasculature though reducing inflammation) and Heart Attacks (here Rex-L as you are aware significantly reduced heart attacks).
The current medical theory would postulate Rex-L would have a positive effect on reducing the number of Chronic Heart Failure Patients that would otherwise go on to develop AF due to Rex-L halting/slowing the rate of structural damage progression to the heart's structure caused by unchecked inflammation.
In other words, a single injection of Rex-L in Stage II and Stage III Chronic Heart Failure patients will likely decrease the chance of the patient developing Atrial Fibrillation (assuming they did not already have it). Rex-L does this through improving cardiac microvasculature, decrease progressive loss of heart muscle (i.e. protect viable heart muscle), slowing of athlerosclerosis and plaque progression which reduces the chance of having a heart attack and further damaging heart muscle.
It would be interesting to know if SI has data pointing to a significant reduction in patients developing AF in the Rex-L arm of the trial. My thoughts would be that there would be a decrease because it would fit with current medical thinking and there are presumably enough patients in HRrEF NYHA Class II and III that were enrolled without both HF & AF (i.e. enough patients maybe to see a reduction in the development of AF - although I am not sure if enough follow-up time would allow for a significant finding?). Fingers crossed SI also has this data in hand (help with future uptake a little), but not the end of world if doesn't (would at least expect a trend towards reduced development of AF in the Rex-L trial arm). Definitely something worth considering in future trail designs if we also want to go down this path of investigating an alternative preventative treatment for AF (with or without CHF) some day down the road.
(20min delay)