1. An method for an active implantable medical device that provides cardiac resynchronization by biventricular pacing, comprising: using processing circuitry of the implantable medical device to detecting atrial and ventricular events; using the processing circuitry to stimulate the right and left ventricles; applying an atrioventricular delay (AVD) counted from the detection of a spontaneous or paced atrial event, at the end of which, a right ventricular pacing is applied in the absence of detected spontaneous ventricular event; applying an interventricular delay (VVD) between the respective times of stimulation of the left and right ventricles; selectively operating the stimulation such that the device operates in either a right mode (RV only) wherein only the right ventricle is paced, or a left mode (LV only) wherein only the left ventricle is stimulated, or in a biventricular mode (BiV) wherein both ventricles are stimulated together with or without the application of a VVD; using a sensor coupled to the processing circuitry to provide an endocardial acceleration signal EA; extracting, from the EA signal, at least one predetermined characteristic EA parameter; using the EA parameter to evaluate the biventricular stimulation, the evaluation comprising comparing the values of the EA parameter in biventricular mode and in left only mode or right only mode and using the comparison and an assessment of the variability of the EA parameter as a function of the AVD in the left or right mode to distinguish between cases comprising: (a) normal operation, (b) a loss of RV or LV capture, (c) possible anodal stimulation; and conducting at least one update to operational parameters of the device based on the determined case.