Does Septal Atrial Lead Location Reduce Atrial Fibrillation Burden in Patients with Dual Chamber Pacemakers?
Abstract & Commentary
Edward P. Gerstenfeld, MD
Professor of Medicine, Chief, Cardiac Electrophysiology, University of California, San Francisco
Source: Lau CP, et al. Prospective randomized study to assess the efficacy of site and rate of atrial pacing on long-term progression of atrial fibrillation in sick sinus syndrome: Septal pacing for atrial fibrillation suppression evaluation (SAFE) study. Circulation 2013;128:687-693.
Implanted pacemakers with atrial leads are often used to detect asymptomatic episodes of atrial fibrillation (AF). In addition, over the last 2 decades various algorithms have been attempted to use atrial pacing to reduce AF burden in patients with paroxysmal AF. These algorithms have included overdrive atrial pacing (i.e., pacing faster than the intrinsic sinus rate in order to overdrive suppress AF "triggers"), septal atrial pacing to abbreviate atrial activation time, and multisite atrial pacing. The current study examines two strategies for reduction of AF in a 2 × 2 randomized design: pacing from the left atrial septum vs standard lead positioning in the right atrial appendage and overdrive suppression pacing vs standard demand pacing. Patients with documented paroxysmal AF in the 6 months prior to randomization undergoing implantation of a pacemaker with an atrial lead were enrolled. Patients were prospectively randomized in a 2 × 2 factorial design to placement of the atrial lead either in the low atrial septum or standard right atrial appendage and to an atrial overdrive pacing algorithm either ON or OFF. Patients were followed every 6 months up to a minimum of 3 years after enrollment. At each visit, all episodes of device-detected AF were recorded in addition to any clinical AF events. Atrial high rate episodes lasting > 6 minutes duration were considered to indicate an AF event. From May 2005 to November 2011, 385 patients were enrolled from 21 centers. Patients were randomized to pacing from the RA appendage with (n = 98) or without (n = 99) continuous atrial overdrive pacing and to pacing from the low atrial septum with (n = 92) or without (n = 96) continuous atrial overdrive pacing. Successful implantation was achieved in 99% of patients. As designed, RA septal pacing significantly reduced P wave duration and continuous atrial pacing significantly increased the percentage of atrial pacing. After a mean of 3.1 years of follow-up, there was no difference in AF burden with septal vs right atrial appendage pacing (hazard ratio [HR], 1.18; 95% confidence interval [CI], 0.79-1.75; P = 0.65) or with continuous atrial pacing ON vs OFF (HR 1.17; 95% CI, 0.79-1.74; P = 0.61). Persistent AF developed in 20% of patients in the study, with no difference in the development of persistent AF among the four randomized groups. Adverse events did not differ among the four groups (P > 0.05). The authors concluded that neither continuous overdrive atrial pacing nor atrial septal pacing reduced the development of persistent AF in patients with pacemakers for sick sinus syndrome.
Reduction in AF burden through the use of atrial pacing algorithms in patients with implanted pacemakers with atrial leads has been investigated for the past 2 decades. The incidence of AF is certainly higher in patients with sinus node dysfunction or other conduction disease, and monitoring of AF burden can easily be accomplished with modern pacemakers. Simple overdrive suppression of the premature atrial complexes that trigger AF makes good sense and has been tried in the postoperative and permanent pacemaker populations. Although new pharmaceutical agents require extensive randomized prospective trials to ensure efficacy and safety, these overdrive atrial pacing algorithms have become included in pacemaker software with little oversight or documentation of efficacy. The Septal Pacing for Atrial Fibrillation Suppression Evaluation (SAFE) trial confirms that overdrive atrial pacing has no role in the prevention of AF. Such algorithms also increase battery usage and may worsen symptoms in patients because of the increased pacing rate during sinus tachycardia. Therefore, such algorithms should be abandoned in future pacemaker software. Early studies also showed that conduction delay in the triangle of Koch may contribute to the initiation of AF with premature beats, and that pacing in the triangle of Koch prevented initiation of AF from remote atrial premature beats.1 Abbreviating P wave duration also may reduce heterogeneity of refractoriness and preexcite regions of slow conduction also reducing the propensity to AF. However, the SAFE trial also confirms that septal pacing has no advantage over standard right atrial appendage pacing for the prevention of AF.
What lessons have we learned from the SAFE trial? First, when indicated, atrial lead placement should be located at a safe stable location that allows stable thresholds and good sensing, ideally the right atrial appendage. There is also no role for atrial overdrive pacing to prevent AF in patients with paroxysmal AF. This should help eliminate some unneeded software in the next generation of pacemakers. Other algorithms, such as burst pacing to terminate atrial flutters or multisite atrial pacing, still require further investigation. But in this case, simpler is better.
REFERENCE
1. Papageorgiou P, et al. Site-dependent intra-atrial conduction delay. Relationship to initiation of atrial fibrillation. Circulation 1996;94:384-389.
