For instance, certain serum inflammatory markers such as C-reactive protein (CRP), interleukin-6 (IL-6), interleukin-2 (IL-2), endothelin-1, matrix metalloproteinase-2, and tumor necrosis factor-alpha have been considered relevant to the early recurrence of AF after RFCA [24,25,26,27]. Here, IL6 is linked to atrial fibrillation.