Single-chamber AAI mode

A single-chamber pacemaker operates in AAI mode when a single lead is positioned in the atrium; the AAI mode can also be programmed in a dual-chamber pacemaker. This tracing allows highlighting the main characteristics of this pacing mode:

1. sensing and pacing of the atrium, inhibition due to a spontaneous atrial event; the preferred indication is therefore a pure sinus node dysfunction without ventricular conduction disorder. An AAI pacemaker allows limiting the number of implanted leads as well as ensuring a physiological rate at rest and during exercise after programming of the rate response while avoiding unnecessary ventricular pacing;
2. absence of ventricular sensing or pacing. AAI single-chamber pacemakers or the programming of the AAI mode in a dual-chamber pacemaker are formally contraindicated in patients with permanent or paroxysmal atrioventricular conduction disorders. They should also be avoided in patients with vagal symptoms or carotid sinus syndrome.

A recent study has reported unfavorable results in 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 is greater in patients implanted with an AAI with the need to add a ventricular lead as a result of the occurrence of an atrioventricular conduction disorder. Hence, the indications for the implantation of a single-chamber AAI pacemaker are nowadays relatively limited. 

In this patient, the prolonged post-atrial pacing PR interval is not propitious to the programming of AAI pacing in the long term.