Cardiac Resynchronization Under Electroanatomical Guidance After Failure of Primary Implantation

Inclusion Criteria: * Patient with indication for implantation of a classic multisite pacemaker; * New York Heart Association II/IV patient despite optimal medical treatment; * Patient with left ventricular ejection fraction ≤35%; * Patient with a widened QRS \> 120ms; * Patient with at least one lateral coronary sinus vein visualized on angiography during the 1st procedure (if performed); * Patient with failure of resynchronization via the endovenous route due to difficulty in accessing the coronary sinus or instability in the coronary sinus; * Patient having been informed and having signed an informed consent form; * Patient able to understand the information related to the study (absence of linguistic, psychological, cognitive problem, etc.), and to complete questionnaires. Exclusion Criteria: * Patient with resynchronization failure due to occlusion of the superior vena cava; * Patient with no usable lateral coronary sinus vein; * Patient with a life expectancy \< 3 months; * Patient wearing a vena cava filter; * Patient with active sepsis; * Pregnant or likely to be pregnant (of childbearing age, without effective contraception) or breastfeeding; * Patient participating in another clinical trial, or in a period of exclusion from another clinical trial; * Patient not benefiting from a social security scheme.