Circulation Journal Official Journal of the Japanese Circulation Society http://www. j-circ.or.jp acemaker diagnostics have become an important means of detecting and monitoring atrial tachyarrhythmias (ATA) in recipients of pacemakers implanted for bradyarrhythmias. State-of-the-art dual-chamber devices provide useful diagnostic information, including the number and duration of automatic mode switch episodes upon detection of ATA. In the recent ASSERT trial, with over 2.8 years of follow-up, (1) ATA were detected by the atrial high rate episode function in 36% of 2,580 pacemaker or implantable defibrillator recipients who had no history of ATA before device implantation, and (2) a 2.5-fold higher incidence of ischemic stroke or systemic embolism was observed in patients with than in patients without ATA detected by the atrial high rate function. 1,2 Therefore, accurate identification of ATA allows the planning of optimal antiarrhythmic and antithrombotic therapy. 3 However, the sensing of the far-field R-wave (FFRW) by the atrial channel may cause inappropriate mode switches from DDD to DDI mode, and trigger ATA or cause pacemaker syndrome. 4-14
Editorial p 582The right atrial appendage (RAA) is believed to be an unsuitable pacing site for the prevention of ATA, because it lengthens the inter-or intraatrial conduction time and increases the dispersion of atrial refractoriness. 15 Therefore, low atrial septal (LAS) pacing has been recommended instead of RAA pacing to prevent ATA, 16 though this remains to be confirmed by randomized clinical trial. 17 However, because the LAS region is closer to the ventricle than the RAA, it may be associated with a higher likelihood of FFRW oversensing, 16,18 though the prevalence and characteristics of FFRW sensing associated with LAS pacing have not been formally studied.We hypothesized that recipients of bipolar atrial leads with widely spaced tip-ring electrodes implanted in the LAS and who have left ventricular hypertrophy (LVH) on 12-lead ECG are at increased risk of FFRW sensing after ventricular pacing. To test this hypothesis, we measured the prevalence and examined the characteristics of FFRW sensing in recipients of dualchamber pacemakers, as well as the effects of the tip-ring Toshihisa Nagatomo, MD; Yutaka Otsuji, MD Background: Although low atrial septal (LAS) pacing may prevent atrial tachyarrhythmias in selected patients, farfield R-wave (FFRW) sensing in this region seems more likely than in the right atrial appendage.