Does Atrial Fibrillation cause renal failure?

This article, published very recently in Circulation excites me! It describes a retrospective study from Japan of patients with atrial fibrillation who also happen to have  diminished renal function. This renal impairment improves after successful ablation.
Either something important and new is being described (which is exciting) or confounding factors (such as change of drug regimen) have been missed. The sceptic in me would go for the latter whereas the optimist would go for the former. The hypothesis could be confirmed or dismissed by a properly conducted trial.
If AF is proven to make renal function worse AND ablation reverses this decline, then the case for ablation is strengthened - which is also good, as ablation for AF (concomitant with other cardiac surgery) is one of my interest - hence the nerdish excitement!