Cardiac electrical activity is detected on the body surface with conventional electrocardiography involving 12 leads (ECG 12). A limitation of the current ECG technique is that recordings are obtained from only 6 independent precordial leads pairs ; which may miss cardiac potentials from spatially limited regions. More extensive sampling of the body surface may contribute to additional clinical information. The present study investigates the additional sensitivity of ECG using 128 body surface leads (High Density (HD) ECG) in measuring global or regional cardiac activity.

Inclusion Criteria:

• Patient managed at the Bordeaux University Hospital for assessment of documented severe ventricular arrhythmia (VF, sudden resuscitated death) or suspected (syncope, family history of sudden death, ECG or Holter abnormality) or impaired ventricular conduction, OR
• Patients managed for prophylactic ventricular defibrillator implantation, according to international recommendations: Heart disease with ejection fraction < 35%, heart disease with sustained ventricular tachycardia, cardiomyopathies with high rhythmic risk,
• Women of childbearing age with effective contraception.

Exclusion Criteria:

• patients under 14 years old,
• pregnant or nursing woman.