Bipolar atrial sensing thresholds in sinus rhythm and atrial tachyarrhythmias - A comparative analysis in patients with DDDR pacemakers

Automatic mode switching (AMS) function in dual chamber pacemakers depends on adequate detection of atrial tachyarrhythmias. There are few data on sho wing how intra-operative atrial signal amplititude during sinus rhythm can predict atrial tachyarrhythmias after pacemaker implantation. In 43 patient s undergoing DDDR pacemaker implantation and atrioventricular nodal ablatio n for the treatment of drug-refractory paroxysmal atrial fibrillation, atri al sensing the thresholds during sinus rhythm and during induced atrial tac hyarrhythmias (24-48 h after device implantation) were analysed. Five diffe rent DDDR pacemaker systems were implanted (Chorus 7034(TM), Ela Medical n= 13; Meta DDDR 1254(TM), Telectronics Pacing Systems n=12; Vigor DR 1230(TM) , Guidant n=6; Trilogy DR 2364(TM), Pacesetter, n=2; Kappa DR 401(TM), Medt ronic USA n=10). Every patient received a steroid-eluting, screw-in, bipola r atrial lead (Medtronic, Capsure-Fix 4068(TM)). The mean P wave amplitude during implantation was 3.91 +/- 1.14 mV. The mean atrial sensing threshold during sinus rhythm and during all modes of induced atrial tachyarrhythmia s was 3.35 +/- 1.0 mV, and 1.52 +/- 0.92 mV, respectively (P<0.001). Atrial fibrillation was induced in 36 patients. The mean sensing threshold during sinus rhythm in this patient group was 3.39 +/- 1.01 mV, the mean sensing threshold during atrial fibrillation was 1.27 +/- 0.56 mV, reflecting a 63% reduction of sensing threshold compared with sinus rhythm (P<0.001). Atria l flutter was induced in seven patients. The mean sensing threshold during sinus rhythm was 2.92 +/- 1.19 mV, the mean sensing threshold during atrial flutter was 2.79 +/- 1.26 mV, reflecting a reduction of 5% (ns) compared w ith sinus rhythm. Atrial sensing thresholds during sinus rhythm were signif icantly correlated with sensing thresholds during atrial tachyarrhythmias ( r=0.44; P<0.002), but there were significant variations in intra-individual results. The reduction of atrial sensing thresholds between sinus rhythm a nd induced atrial tachyarrhythmias ranged from 30% to 82%. Conclusion: Bipolar atrial sensing thresholds during sinus rhythm are corre lated with sensing thresholds during atrial tachyarrhythmias, but there is a large degree of variance in individual patients. A 4:1 to 5:1 atrial sens ing safety margin based on sensing threshold during sinus rhythm is a predi ctor for adequate postoperative detection of atrial tachyarrhythmias and th e function of AMS devices.