The goal of this research is to prospectively evaluate the performance of the electromechanical window according to a phonographic method, as a mean of diagnosis of long QT syndrome, and to compare its performance with routine tests used.

Familial long QT syndrome (LQTS) is a hereditary cardiac disorder in which most affected family members have delayed ventricular repolarization manifest on the electrocardiogram (ECG) as QT prolongation. This disease is associated with an increased propensity to palpitations, syncope, polymorphous ventricular tachycardia and sudden arrhythmic death. The diagnosis relies mostly on resting ECG findings and on genetic testing. In clinical practice however, this diagnosis is complicated by 2 main reasons: 1) a significant overlap in ECG findings between healthy and diseased individuals and 2) a frequent identification of genetic variants of unknown significance. Recent studies have suggested that echocardiographic measurement of the electromechanical window (EMW - the delay between the end of mechanical contraction and electrical activation of the heart) has better performance in the diagnosis of LQTS. The echocardiographic technique is however too complicated for routine clinical use. Preliminary work conducted at the University Hospital of Bordeaux and at the University Hospital of Reunion Island has demonstrated that a phonocardiographic approach leads to similar results with an improved feasibility and a good reproducibility.

Inclusion Criteria:

• Propositus patients with genetically proven LQTS and their relatives,
• Patients of both sexes aged 12 and over,
• Free, informed and written consent of the patient and the two holders of parental authority for minors.

Exclusion Criteria:

• Inability to consent,
• Person deprived of liberty by judicial or administrative decision,
• Majors subject to a legal protection measure,
• Person participating in another research including an exclusion period still in progress,
• Severely impaired physical and / or psychological health, which, according to the investigator, may affect the participant's compliance with the study.