HP and atrial fibrillation: Of note, the protein disulfide-isomerase A3 (PDIA3), an important player in the response to endoplasmic reticulum stress and involved in the activation of the extrinsic apoptotic pathway; the acute-phase response reactant haptoglobin (HP); and peroxiredoxin-1 (PRDX1), an essential protein for fighting oxidative stress, were also deemed important to differentiate AF from SR.