KCNA3 and Prolonged QT interval: An association between repolarization heterogeneity and mechanical contraction assessed by GLS, in the absence of underlying myocardial fibrosis, has been shown in observational studies in subjects with long QT syndrome (Haugaa et al., 2010; Leren et al., 2015), a condition that is characterized by loss of function potassium channel mutations leading to prolonged action potential duration (APD).