1. An active implantable medical device for stimulation, defibrillation and/or cardiac resynchronization therapy, the device comprising: a processor configured to: control stimulation of the heart; detect at least one of a ventricular depolarization signal or an atrial depolarization signal on a channel at a plurality of distinct instants; and perform a morphological analysis in which the at least one of the ventricular depolarization signal or the atrial depolarization signal at the distinct instants are compared, wherein the processor is configured to perform the morphological analysis by: inhibiting the controlled stimulation; collecting at least two EGM signals of endocardial electrogram during a spontaneous rhythm cardiac cycle, wherein the EGM signals are collected concurrently on a plurality of separate respective channels; deriving at least two respective distinct temporal components from the at least two EGM signals; combining the at least two temporal components into at least one parametric 2D characteristic representative of the cardiac cycle, from the variations of one of the temporal components as a function of the other temporal component; analyzing the 2D characteristic by deriving, from the 2D characteristic or from an average of the 2D characteristics collected over successive cardiac cycles, at least one intrinsic descriptor parameter representative of the 2D characteristic; periodically performing a historical analysis by evaluating a variation over time of the at least one intrinsic descriptor parameter of a current 2D characteristic with respect to a previous reference 2D characteristic stored by the device; comparing the variation assessed by the historical analysis to a predetermined threshold; and selectively triggering an alert based on the result of the comparison.