AAI pacemaker

In summary, the patient receiving an AAI pacemaker shonld be in sinus rhythm without evidence of AV conduction abnoimaUties. 

Fig. 3.1 Normal function in the AAI mode. P refers to a sensed atrial event. A refers to a paced atrial event. Two successive events may be described as one of the following intervals AA, PP, PA, and AP. The LRL (also called the low rate timer) in the example shown is 60bpm. Thus, the PA and AA intervals are 1,000ms. The P wave is sensed and after 1000ms the low rate timer expires. An atrial paced event occurs (A). A second atrial paced event occur after 1000ms. Sensing atrial activity inhibits the pacemaker output and resets the low rate timer. In the AAI mode, timing is based on the time between atrial events.

Lower Rate Limit. The most basic interval in the AAI mode is the LRL. The LRL determines the maximum length of time the pacemaker circuitry will wait for intrinsic atrial activity (P wave) to occur before initiating an atfial output stimulus (Fig. 3.1). When there is no hysteresis (see the following), this interval applies both to the period from the last intrinsic event to the first paced event or the period from the last paced event to the next paced event. 

Brandt J, Fahraeus T, Schuller H, Ear-field QRS complex sensing via the atrial pacemaker lead, I Mechanism, consequences, differential diagnosis and countermeasures in AAI and VDD/DDD pacing, PACE 1988 11 1432-1438. 

In a series of 136 consecutive patients being transplanted with the bicaval anastomosis technique in our department only one (0.7%) needed permanent pacemaker implantation (AAI mode) because of sinus node dysfunction. 

---