single-chamber AAI mode

N° 5
Manufacturer Abbott Device PM Field Pacing Modes

Same patient as in tracing 1; change of pacing mode (the leads function normally).

Graph and trace

Programming in AAI mode 60 beats/minute; sensing of a stable atrial activity with inhibition of pacing (it is therefore not an AAT or AOO mode); absence of sensing of QRS complexes (it is therefore not an ODO or VDD mode).


A single-chamber pacemaker operates in AAI mode when only one lead is positioned in the atrium; the AAI mode can also be programmed in a dual-chamber pacemaker. The AAI mode provides single-chamber atrial pacing at the programmed pacing rate unless inhibited by a sensed event. Sensing only applies to the atrium.

Single-chamber AAI pacemakers or AAI mode programming on a dual-chamber pacemaker are formally contraindicated in patients with a permanent or paroxysmal atrioventricular conduction disorder. They should also be avoided in patients with vagal symptoms or carotid sinus syndrome. The preferred indication is therefore pure sinus dysfunction without atrioventricular conduction disorder. An AAI pacemaker allows limiting the number of implanted leads, ensures a physiological rate at rest and during exercise after programming of the rate response and avoids any unnecessary ventricular pacing. A recent study, however, reported unfavorable results for the implantation of a single-chamber AAI pacemaker compared to the implantation of a dual-chamber pacemaker in patients with sinus dysfunction. Indeed, the rate of re-intervention was higher in patients implanted with an AAI pacemaker with the need to add a ventricular lead secondarily to the occurrence of an atrioventricular conduction disorder. More surprisingly, the incidence of atrial fibrillation episodes was also higher. The indications for implantation of a single-chamber AAI pacemaker are thus nowadays relatively limited.

Message to remember

The programming and operation of the AAI mode are essentially similar to that of a VVI pacemaker. However, it is necessary to program a higher sensitivity (lower programmed value) since the amplitude of the atrial complexes are often lower than that of the ventricular complexes. Similarly, the refractory period must be longer to avoid oversensing of ventricular complexes. The sensing of the R wave by an AAI pacemaker leads to a decrease in pacing rate, with the R wave recycling the escape interval. In the presence of oversensing of the far-field R wave, it is possible to render the pacemaker less sensitive and/or to prolong the refractory period.