Left atrial volume role for CRT response and for arrhythmic events (VT/VF/AT/AF) onset

Inclusion Criteria:

• Patient with left ventricular ejection fraction ≤ 35%, II, III or IV NYHA Class, even if optimal medical therapy.
• Patients with standard indication to CRT according current guideline, sinus rhythm at implantation, LBBB and QRS duration >= 120 ms
• Patients who will undergo to a new CRT-defibrillator system implantation
• Patients who are able to understand and sign the informed consent
• Patients who are able to attend all required follow-up visits at the study centerfor 24 months

Exclusion Criteria:

• Age < 18 years
• Women who are pregnant or who are planning to become pregnant
• Patients with permanent Atrial Fibrillation or persistent Atrial Fibrillation in the 90 days preceding the implantation
• Patients with organic mitral valve disease
• Patients with prosthetic heart valves
• Patients who will undergo to upgrading from other devices (PM or ICD) to CRT, heart transplantation, patients with CRT devices

Patients implanted with cardiac resynchronization therapy defirbillator devices and who meet the inclusion and exclusion criteria