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. This device includes atrial and ventricular detection and stimulation circuits. It can function in a DDD pacing mode or an AAI pacing mode with ventricular detection. The commutation of an AAI pacing mode towards a DDD pacing mode occurs when one of the following conditions is met: (i) the number of consecutive atrial events detected, not followed by a ventricular detection, exceeds an authorized number, for example 2 events; (ii) the number of non-consectutive atrial events not followed by a ventricular detection exceeds an authorized number over the duration of a monitoring window extending over a third number of given consecutive atrial events, for example, 3 events out of 12; (iii) 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 (iv) the interval separating two ventricular events exceeds an authorized predetermined delay, for example, 3 seconds. Atrial extrasystoles are not counted as atrial events.
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