An active implantable medical device of the cardiac prosthesis type for stimulation, resynchronization and/or defibrillation, comprising: - an acceleration sensor adapted to deliver an endocardial acceleration signal, representative of the cyclic contractions of the myocardium; and - means for analyzing the EA signal, adapted to recognize and isolate in the EA signal an EA4 component corresponding to the fourth peak of endocardial acceleration associated with atrial activity, characterized in that the device is a device lacking means for collecting an atrial EGM signal, and in that it further comprises: - means for detecting ventricular events by analysis of a ventricular electrogram signal; - means for ventricular stimulation; - means adapted to apply, to the means for ventricular stimulation, an atrioventricular delay counted from an atrial event and at the end of which a ventricular stimulation is delivered in the absence of detection of a spontaneous ventricular event; and - means for determining (146; 164) a search window of the EA4 component in the EA signal; - means adapted to confirm the presence or absence of an EA4 component in the search window; and - means adapted to apply (142; 144; 160; 168) to the ventricular stimulation means: • the AVD, in the presence of a confirmed EA4 component; or • a predetermined escape interval in the absence of a confirmed EA4 component, and wherein the means for determining the search window comprises means adapted to: a) in the presence of atrioventricular conduction: • detect the time of occurrence of a ventricular event from the ventricular EGM signal; • detect in the EA signal EA1 and/or EA2 components corresponding to the respective first and/or second peaks of endocardial acceleration associated with the ventricular event; and • determine the search window of the EA4 component depending on the temporal position of the detected EA1 and/or EA2 components, and b) in the absence of atrioventricular conduction: • apply a masking delay of the EA1 and/or EA2 components in the EA signal, counted from a stimulated ventricular event; and • determine the search window of the EA4 component after the masking delay. - an acceleration sensor adapted to deliver an endocardial acceleration signal, representative of the cyclic contractions of the myocardium; and - means for analyzing the EA signal, adapted to recognize and isolate in the EA signal an EA4 component corresponding to the fourth peak of endocardial acceleration associated with atrial activity, - means for detecting ventricular events by analysis of a ventricular electrogram signal; - means for ventricular stimulation; - means adapted to apply, to the means for ventricular stimulation, an atrioventricular delay counted from an atrial event and at the end of which a ventricular stimulation is delivered in the absence of detection of a spontaneous ventricular event; and - means for determining (146; 164) a search window of the EA4 component in the EA signal; - means adapted to confirm the presence or absence of an EA4 component in the search window; and - means adapted to apply (142; 144; 160; 168) to the ventricular stimulation means: • the AVD, in the presence of a confirmed EA4 component; or • a predetermined escape interval in the absence of a confirmed EA4 component, • the AVD, in the presence of a confirmed EA4 component; or • a predetermined escape interval in the absence of a confirmed EA4 component, a) in the presence of atrioventricular conduction: • detect the time of occurrence of a ventricular event from the ventricular EGM signal; • detect in the EA signal EA1 and/or EA2 components corresponding to the respective first and/or second peaks of endocardial acceleration associated with the ventricular event; and • determine the search window of the EA4 component depending on the temporal position of the detected EA1 and/or EA2 components, and • detect the time of occurrence of a ventricular event from the ventricular EGM signal; • detect in the EA signal EA1 and/or EA2 components corresponding to the respective first and/or second peaks of endocardial acceleration associated with the ventricular event; and • determine the search window of the EA4 component depending on the temporal position of the detected EA1 and/or EA2 components, and b) in the absence of atrioventricular conduction: • apply a masking delay of the EA1 and/or EA2 components in the EA signal, counted from a stimulated ventricular event; and • determine the search window of the EA4 component after the masking delay. • apply a masking delay of the EA1 and/or EA2 components in the EA signal, counted from a stimulated ventricular event; and • determine the search window of the EA4 component after the masking delay.