This prospective study will evaluate in patients, fulfilling implant criteria for Cardiac Resynchronisation Therapy (CRT) implant, the optimal atrial contribution to the resynchronised ventricles in the event of right atrial pacing.

All patients will undergo advanced echocardiographic examination pre-operative, pre-discharge after implantation and at 3 and 6-months follow-up. AV-delay optimization will be performed using aortic VTI measured by continuous wave Doppler in a modified 4-chamber view. During optimisation aortic VTI will be measured at different heart rates reached by increasing atrial pacing 10, 20 and 30 beats above intrinsic heart rate (IHR).

Inclusion Criteria:

• Symptoms of heart failure
• Left ventricular dysfunction
• Ventricular dyssynchrony
• 18 years or of legal age in order to give informed consent according to national laws
• Able to understand the nature of the procedure
• Available for follow-up on a regular basis at an approved investigational center

Exclusion Criteria:

• Atrial Fibrillation
• Life expectancy of less than six months due to other medical conditions
• For women: pregnancy or absence of medically accepted birth control
• Inability or refusal to sign the Patient Informed Consent
• Inability or refusal to comply with the follow up schedule or protocol requirements
• Inability to undergo device implant, including general anaesthesia if required
• Mechanical tricuspid prosthesis
• Currently enrolled in another investigational study, including drug investigations
• Hypertrophic Obstructive Cardiomyopathy (HOCM)
• Not meeting the inclusion criteria

Adverse events were assessed only at implant, 3 months and 6 months follow-up. Events observed between these visits were not provided by the investigator.