This clinical investigation is a device-based open, prospective, multicenter two-arm randomized trial, comparing patients who are treated in the slow VT zone versus patients who are not treated in that zone.

The device intended to be used is the OVATIOTM CRT model 6750 but future generation of Sorin Group/ ELA Medical devices may be used provided they are CE marked. Ethics committees and health authorities will be informed prior to any use of a newer device if applicable.

All patients will have a 3-zone detection configuration programmed. The slow VT zone will be defined by programming the detection parameters as follows:

• Slow VT detection rate: 100 bpm (or if the resting rate is higher than 80 bpm, we recommend to adjust this parameter to: resting rate + 30 bpm)
• VT detection rate: 150 bpm

PARAD+ will be the first choice for SVT/ST and VT discrimination in the VT zones.

The Fast VT and VF limits are left to investigator's judgment. Therapy on VT, fast VT and VF are also left to the investigator's judgment.

Patients will be randomized at implant to have the slow VT zone programmed as a monitoring zone (monitoring arm) or to have therapies programmed within the slow VT zone (therapy arm). The randomization table will be generated by Sorin Group/ELA Medical.

Inclusion Criteria:

• Patient has been prescribed the implantation or replacement of a CRT-ICD system accordingly to the relevant currently-approved ACC/AHA15 (August 2005, Appendix §M.10) or ESC 16 (Update 2005, Appendix § M.11) guidelines or any relevant currently-approved local guidelines for the implantation or replacement of CRT-ICD.
• Patient has signed a consent form after he/she received the appropriate and mandatory information.

Exclusion Criteria:

• Clinical history of symptomatic or not symptomatic slow VT;
• Permanent Atrial Fibrillation (AF);
• Any contraindication to the implant or replacement of CRT-ICD;
• Pt is unable to attend the scheduled f-up visits at the implanting Centre;
• Pt is already included in another ongoing clinical study;
• Pt is unable to understand the objectives of the ITAC04 study;
• Pt refuses to cooperate;
• Pt is unable or refuses to provide informed consent;
• Pt is minor (less than 18-year old);
• Pt has life expectancy of less than 1 year;
• Pt is pregnant.