Mexiletine shortens the QT interval in a pedigree of KCNH2 related long QT syndrome

A 23‐year‐old female had been suffering from recurrent syncopal episodes during sleep since her childhood. She had a family history of sudden death and her QTc interval was remarkably prolonged to 537 ms A Holter ECG revealed torsade de pointes, corresponding to syncope. She was started on mexiletine and her QTc interval shortened. Her symptoms were controlled after β‐blockers and Ca‐blockers were added. A genetic analysis with a next generation sequencer identified a frameshift mutation at the C terminus of the KCNH2 gene. Here we present a type 2 long QT syndrome case in which mexiletine was effective. This is a unique case report of a familial long QT syndrome (LQT2) patient. We initially thought this was a LQT3 family since syncope occurred during sleep. Mexiletine was effective for controlling the symptoms and shortening the QT interval in this family.