MPO and atrial fibrillation: Considering the versatile roles of neutrophil degranulation linked to pathophysiology of AF, and MPO as a prerequisite factor for structural remodelling as well as its capacity to promote electrical instability in the atria and vulnerability to AF26, neutrophil degranulation in atrial tissue may precede or coincide with AF onset, and subsequently alter the cardiac tissue homeostasis and eventually contribute to the tenacity of AF.