1. A process for processing signals representative of cardiac myocardium depolarization potentials, said signals being collected by a plurality of endocardial electrodes of an active implantable medical device including an implantable pacemaker, device for resynchronization, cardioversion and/or defibrillation, the process comprising: a) acquiring a plurality of endocardial electrogram signals (EGM) through a plurality of leads, each lead of the plurality of leads being collected between at least a pair of endocardial electrodes selected from the plurality of endocardial electrodes; b) calculating, through a combination of the plurality of endocardial electrogram signals (EGM) acquired at step a), a corresponding endocardial vectogram (VGM); d) estimating, based upon the endocardial vectogram calculated at step b), a reconstructed surface vectocardiogram (VCG reconstructed ); and e) reconstructing surface electrocardiogram signals (ECG) corresponding to said reconstructed surface vectocardiogram (VCG reconstructed ), wherein the step d) of estimating the reconstructed surface vectocardiogram (VCG reconstructed ) further comprises applying a linear filtering to the endocardial vectogram calculated at step b).