Exercise test : Bruce protocol : exercise during 7 minutes, and rest during 6 minutes with registering of the electrocardiograms.

Exercise test and epinephrine test will be done at inclusion (day 1). The primary outcome of this study is to evaluate the best stress exam (exercise test versus epinephrine test), defined by a "positive" test to unmask long QT syndrome. Test is positive when QT interval lengthens 30 ms At the end of study inclusions, two reviewers will analyse, independently, electrocardiograms resulting from these tests to determine for each patient if a test was positive and which one. These reviewers will do this job without being informed of the patient status (mutated patient or not mutated patient (control)).

Exercise test and epinephrine test will be done at inclusion (day 1). The secondary outcome is to evaluate each test (exercise test and epinephrine test) characteristics. At the end of study inclusions, two reviewers will independently analyse electrocardiograms resulting from these tests to evaluate their characteristics.