Article history: Received 22 December 2016 Accepted 27 December 2016 clinically relevant increase in theQT interval, especially in consideration that these were LQTS patients, and thus expected to have a prolonged QT intervals to begin with. As analogy, the guidelines for LQTS indicate that whenever mexiletine shortens the QTc by at least 40 ms it should be added to beta-blockers for chronic th...