REN and atrial fibrillation: The increased concentration of pro-inflammatory cytokines in the serum of patients with CHF compared to healthy controls is a circumstance that can be caused by some relevant processes in the context of CHF, among others: global aging, metabolic syndrome, chronic obstructive pulmonary disease (COPD), chronic kidney disease (CKD), atrial fibrillation and neurohormonal hypothesis of renin-angiotensin-aldosterone system (23–26).