Improved efficacy of mode switching during atrial fibrillation using automatic atrial sensitivity adjustment

Automatic mode switching (AMS) during atrial fibrillation (AF) in a dual ch amber pacemaker is dependent on the accurate detection of an atrial electro gram. As atrial amplitude is often reduced during AF compared with sinus rh ythm, this may result in failure of the AMS and a rapid ventricular respons e, in addition, undersensing of AF may result in competitive atrial pacing that sustains AF. We hypothesize that the use of automatic atrial sensitivi ty adjustment (ASA) may enhance AF sensing in a dual chamber pacemaker. We studied the AMS response with and without ASA of the Marathon DDDR (model 2 94-09, Intermedics, Inc.) pacemaker in 10 patients with paroxysmal AF. Intr acardiac atrial electrograms during sinus rhythm and induced AF were record ed onto an analog tape recorder. They were replayed into the pacemaker to a ssess the AMS response at various starting atrial sensitivities from 3.5 to 0.8 mV with ASA activated and without. Atrial amplitude was reduced during AF. The higher the initial atrial sensitivity, the better is the AMS respo nse and the lower the incidence of AF undersensing. The percentage of AMS b efore ASA ranged from 2.1% at an atrial sensitivity 3.5 mV to 95.6% at high est sensitivity of 0.5 mV (P < 0.05). After 10 minutes of ASA, the AMS resp onse was improved from 2.7% to 50.6% and from 9.5% to 50.9% at starting atr ial sensitivities of 3.5 mV and 2.5 mV, respectively (P < 0.05 in both inst ances). Undersensing during AF was also significantly reduced after ASA fro m 70% to 10% at a sensitivity of 3.5 mV and from 33.8% to 10.8 % at 2.5 m V . There was no increase in oversensing. In four patients with paroxysmal AF with an implanted pacemaker, ASA improved AMS response in patients with a low implant atrial amplitude. In conclusion, efficacy of mode switching and AF sensing are dependent on the programmed atrial sensitivity, which can b e enhanced with the use of ASA, particularly when P wave sensing during AF is borderline.