The research aims to compare the response of Cardiac Resynchronisation Therapy (CRT) using HF ECG guided or the conventional method of Q-LV measurement guided optimisation for left ventricular, pacing site.

The study aims to demonstrate that left ventricular (LV) pacing site optimisation using high frequency (HF) ECG improves LV reverse remodeling response to Cardiac Resynchronization Therapy (CRT), compared with Q-LV (Q-wave on the surface ECG to LV Electrogram) measurement after 6 months of treatment.

Participants will be implanted with a Cardiac Resynchronisation Therapy device with either pacemaker or defibrillator function.

The study is a single-Centre, randomized, prospective trial. One hundred and eighty participants will be assigned to either the treatment (HF-ECG guided LV pacing site optimisation) or control (Q-LV guided LV pacing site optimisation) arm, employing a 1:1 randomization. The participants will be followed up for a period of 6 months.

Inclusion Criteria:

• • Eligible for implantation of a CRT-D device according to published relevant ESC and CCS guidelines;

  • In sinus rhythm;
  • NYHA class II, III or IV
  • Have reviewed, signed and dated an informed consent.
  • Age 18

Exclusion Criteria:

• Previous implant with a pacemaker, an ICD or a CRT device. (except upgrade from single chamber ICD with a fully functional defibrillation lead) not under recall or surveillance);
• Persistent atrial arrhythmias (or cardioversion for atrial fibrillation) within the past month;
• Ventricular tachyarrhythmia of transient or reversible causes such as acute myocardial infarction (MI), digitalis intoxication, drowning, electrocution, electrolyte imbalance, hypoxia or sepsis, uncorrected at the time of the enrolment;
• Incessant ventricular tachyarrhythmia;
• Unstable angina, or acute MI, Coronary Artery Bypass-Grafting (CABG), or Percutaneous Coronary Intervention (PCI) within the past 4 weeks;
• Correctable valvular disease that is the primary cause of heart failure;
• Indication for valve repair or replacement;
• Recent Cerebro-Vascular Accident (CVA) or Transient Ischemic Attack (TIA) (within the previous 3 months);
• On transplant waiting list;
• Previous heart transplant;
• Already included in another clinical study that could confound the results of this study;
• Life expectancy less than 1 year;
• Inability to understand the purpose of the study;
• Unavailability for scheduled follow-up or refusal to cooperate;
• Age of less than 18 years;
• Pregnancy;
• Drug addiction or abuse;
• Under guardianship.