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Reduction of Atrial Fibrillation by Pacing Mode
Abstract & Commentary
By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.
Source: Sweeney MO, et al. Minimizing ventricular pacing to reduce atrial fibrillation in sinus-node disease. N Engl J Med. 2007;357:1000-1008.
This paper reports the results of the Search AV Extension and Managed Ventricular Pacing for Promoting Atrioventricular Conduction (SAVE PACe) Trial. This study evaluated the use of pacing algorithms that were designed to minimize the percentage of ventricular pacing in patients with symptomatic sinus-node dysfunction. Eligible patients had symptomatic bradycardia due to sinus-node disease and a normal QRS interval. At the time of implant, they could AV conduct 1:1 during atrial pacing at a rate of at least 100 bpm. Patients with a history of 2 or more cardioversions for atrial fibrillation, or second or third degree AV block, were excluded. Patients randomized to the minimal ventricular pacing group had pacemaker programming that permitted automatic lengthening of, or elimination of, the pacemaker's AV interval in order to withhold ventricular pacing. Patients in the conventional pacing group had an AV interval programmed between 120 and 180 m/sec. Several different pacemaker models were used, so the minimal ventricular pacing algorithm was not constant. The primary end point was time-to-persistent atrial fibrillation defined as one of the following: 2 consecutive visits in which atrial fibrillation was present, at least 22 hours of atrial fibrillation for at least 7 consecutive days recorded by the pacemaker diagnostic data log, or atrial fibrillation of shorter duration, which had been terminated by an electrical or pharmacologic intervention. Secondary end points included hospitalizations for heart failure and the percentage of atrial and ventricular paced beats over time.
A total of 1,065 patients were enrolled and underwent randomization after successful implantation of a dual chamber pacemaker. The mean age was 72 years, with approximately equal numbers of males and females. The mean ejection fraction was 58%, with 37% of the patients having a prior history of atrial fibrillation. The mean lower rate limit was 61 beats in both groups. The duration of follow-up was 1.7 ± 1 year.
During follow-up, the median percentage of ventricular paced beats was 9.1% in the minimal ventricular pacing group vs 99% in the conventional pacing group. The median percentage of atrial beats was similar in the 2 groups (71.4% vs 70.4%). Persistent atrial fibrillation developed in 68 of 535 patients in the conventional dual chamber pacing group (12.7%) compared to 42 of 530 in the minimal ventricular pacing group [(7.9%); P = 0.004]. Kaplan-Meier estimates of time-to-persistent atrial fibrillation showed absolute reductions in the rates of development of persistent atrial fibrillation of 3.8% at one year, 6.9% at 2 years and 7.0% at 3 years. By multivariate analysis, minimal ventricular pacing was shown to be an independent predictor of protection from persistent atrial fibrillation, with a hazard ratio of 0.6 (P = 0.009). Subgroup analysis showed a consistent pattern of benefit with minimal ventricular pacing. There was no significant difference in mortality between the 2 groups (4.9% minimal ventricular pacing vs 5.4% conventional pacing). Hospitalization for heart failure also did not differ between the groups, but more patients in the conventional pacing group underwent late catheter ablation of the AV node, or pulmonary vein isolation, for the management of atrial fibrillation.
Sweeney and colleagues conclude that pacing algorithms that minimize ventricular pacing in patients with sinus-node dysfunction are associated with a reduction in the risk of developing persistent atrial fibrillation.
Prior studies on the optimal mode of pacing in patients with sinus-node dysfunction have indicated that atrial-based pacing modes reduce the occurrence of atrial fibrillation during follow-up. Other studies have shown that unnecessary ventricular pacing can be associated with clinical worsening of heart failure, and that a higher proportion of paced ventricular beats is associated with both heart failure and atrial fibrillation. This study is the first large study to test prospectively the hypothesis that a pacing algorithm in patients with sinus-node dysfunction, which was specifically designed to reduce the proportion of ventricular pacing, will reduce the incidence of atrial fibrillation. The incidence of atrial fibrillation was indeed reduced, and favorable trends were noted in mortality, stroke rate, hospitalization, and the need for ablation procedures for atrial fibrillation management. Sweeney et al hypothesized that this is due to a decrease in ventricular dyssynchronization induced by right ventricular pacing, but it must be recognized that dyssynchronization and ventricular function were not specifically measured in this trial. However, the observations here strongly support the clinical practice of programming pacemakers in patients with sinus-node disease in such a way that unnecessary ventricular pacing is avoided, if that can be achieved without producing hemodynamic consequences due to changes in AV conduction.