To provide an active implantable medical device for cardiac rhythm management such as a pacemaker, defibrillator and/or cardioverter, having an improved DDD/AAI operating mode that automatically switches between operating in an AAI and a DDD pacing mode for cardiac rhythm management.

Switching from the AAI pacing mode to the DDD pacing mode occurs when one of the following conditions is met: the number of consecutive atrial events detected, not followed by a ventricular detection, exceeds an authorized number, for example 2 events; the number of atrial events not followed by a ventricular detection exceeds an authorized number over the duration a monitoring window extending over a third number of given consecutive atrial events, for example, 3 events out of 12 ; the number of atrial events followed by a ventricular detection occurring after a delay is longer than one predetermined duration exceeds an authorized value, for example, six events for a 300 ms delay; or the interval separating two ventricular events exceeds an authorized predetermined delay, for example, 3 seconds.