An apparatus and a system for seeking for an optimal configuration of a bi-, tri- or multi-ventricular cardiac resynchronization implantable medical device. This system includes ventricular pacing, a signal representative of an endocardial acceleration (EA) of a patient's heart, and isolating and pre-processing the EA signal to obtain an EA1 component and an EA2 component. The effectiveness of the current pacing configuration is evaluated by one or more composite indexes that combine at least two of the following parameters: peak-to-peak amplitude (PEA1) of the EA1 component; time occurrence (TstEA1) of the beginning of the EA1 component; time interval (LargEA1) between the beginning of the EA1 component and the moment of the energy peak of the EA1 component; and duration of systole (Syst), represented by the time interval between the beginning (TstEA1) of the EA1 component and the beginning (TstEA2) of the EA2 component.