Bos JM, et al. - Via this retrospective chart review, researchers investigated the potential role of sodium channel blockers in patients with potassium channel–mediated long QT syndrome (ie, LQT1 and LQT2). They analyzed 12 cases with genetically established LQT2 (10) or a combination of LQT1/LQT2 (1) or LQT2/type 3 long QT syndrome (LQT3)(1) who were treated with mexiletine (5 females; median age at diagnosis 14.1 years, median heart rate–corrected QT interval [QTc] at diagnosis 557 ms). They found that mexiletine, despite being a commonly prescribed medicine in patients with LQT3, led to shortening of QTc significantly in two-thirds of a small subset of patients with potassium channel–mediated LQT2. Added therapeutic efficacy to β-blocker therapy in patients with LQT2 may be provided by pharmacological targeting of the physiological late sodium current.