Detection of ventricular tachycardia in an active implantable medical device having an AAI operating mode

An active implantable medical device, such as a pacemaker, cardioverter and/ or defibrillator of AAI or AAI/DDD type, with detection of ventricular tachycardiae. This device senses spontaneous ventricular and atrial events; delivers atrial pacing pulses; and is able to apply, after delivery of an atrial pacing pulse, concurrently with sensing ventricular events, a refractory period (PR) and a safety window (FS) of predetermined durations; and determining the beginning of a spontaneous ventricular cycle in response to sensing of a ventricular event out of the safety window (R0, R1, R2, R3). It further includes detecting ventricular tachycardiae in response to sensing of ventricular events occurring both within and out of the safety window, conditioned notably by the detection of a sequence of events including, between two consecutive atrial pacing pulses (A1, A2; A2, A3), one ventricular event occurring within the safety window (r1; r2) and one subsequent ventricular event occurring out of the safety window (R1, R2).