No evidence of automatic atrial overdrive pacing efficacy on reduction of paroxysmal atrial fibrillation.

AIMS: Paroxysmal atrial fibrillation (PAF) is frequently encountered in pacemaker patients, most commonly in sick sinus syndrome. The combination of site-specific pacing in conjunction with an overdrive algorithm combined with antiarrhythmic drugs on the incidence of PAF in patients with a conventional indication for pacing is unknown. METHODS AND RESULTS: Patients with pacemaker indication and PAF received a DDDR-pacemaker, which included an automatic atrial overdrive (AO) algorithm. The atrial lead was implanted in either the right atrial appendage (RAA) (n = 83) or the right low-atrial septum (LAS) (n = 94). The algorithm was switched on or off in a 3 month, single blind crossover design and antiarrhythmic drugs were kept stable. A control group of 96 patients (LAS, n = 14; RAA, n = 84) without PAF served as controls to assess any proarrhythmic effect of overdrive pacing. Atrial fibrillation (AF) burden defined as cumulative time in mode switch was not reduced during automatic AO from either the RAA or from the LAS. The reduction was not effective both for AF of short (<24 h) and long (> or =24 h) duration. There was no atrial proarrhythmia induced by the overdrive algorithm in the control group. CONCLUSIONS: We could not demonstrate a reduction of AF burden defined as cumulative time in AF by the AO algorithm, in patients who are paced for standard indications and PAF, neither from the RAA nor from the LAS.

Presence and development of atrial fibrillation in chronic heart failure. Experiences from the MERIT-HF Study.

BACKGROUND: Atrial fibrillation is common in heart failure, but data regarding beta-blockade in these patients and its ability to prevent new occurrence of atrial fibrillation are scarce. METHODS: Baseline ECGs in MERIT-HF were coded regarding baseline rhythm, and outcome was analyzed in relation to rhythm. Occurrence of atrial fibrillation during follow-up was also analyzed. RESULTS: At baseline atrial fibrillation was diagnosed in 556 patients (13.9%). Mean metoprolol CR/XL dose in patients in atrial fibrillation (154 mg) and sinus rhythm (158 mg) was similar, as well as decrease in heart rate (14.8 and 13.7 bpm, respectively). Only 61 (total of 362) deaths occurred in those in atrial fibrillation at baseline, 31 on placebo and 30 on metoprolol (RR 1.0; 95% CI 0.61-1.65). During follow-up, new atrial fibrillation was observed in 85 patients on placebo and 47 patients on metoprolol (RR 0.53; 95% CI 0.37-0.76; p=0.0005). CONCLUSION: First, given the wide confidence interval, it was impossible to detect an interaction between metoprolol and mortality in patients with atrial fibrillation and heart failure. Second, in patients with sinus rhythm at baseline, metoprolol reduced the incidence of atrial fibrillation during follow-up. However, we must be extremely cautious in over-interpreting effects in these subgroups.

Relationship between selected overdrive parameters and the therapeutic outcome and tolerance of atrial overdrive pacing.

There is a paucity of information on the influence of selected overdrive parameters on the clinical efficacy and tolerance of atrial overdrive algorithms to suppress atrial tachyarrhythmias. Data from a completed clinical trial investigating a new DDD+ overdrive algorithm implemented in a permanent pacemaker were analyzed. One-hundred patients with standard pacing indications and atrial tachyarrhythmias were enrolled and followed for 6 months in DDD and 6 months in DDD+ mode in a randomized, crossover fashion. The overdrive step size was programmed at the discretion of the investigators between 4 and 12 beats/min, overdrive plateau length between 10 and 32 beats, and maximum overdrive rate between 100 and 160 beats/min. The effects of DDD+ versus DDD mode on burden and incidence of atrial tachyarrhythmias stored in the mode switch memory were examined as a function of the programmed overdrive parameters. An overdrive step size between 7 and 12 beats/min, and higher a maximum overdrive rate between 121 and 160 beats/min were slightly more effective than lower programmed values, though > 500 randomized, crossover observations would have been necessary to verify statistical significance. Overdrive pacing related symptoms mandated early manual deactivation of overdrive pacing in 4.7% of 85 evaluated patients. Overdrive was disabled without testing tolerability of less aggressive overdrive values. There was no link between patient symptoms and programmed overdrive step size or overdrive plateau length values.

The influence of concomitant drug therapy on the efficacy of atrial overdrive stimulation for prevention of atrial tachyarrhythmias.

Data from the completed "Suppression of Atrial Fibrillation by DDD+ Overdrive Pacing with Inos2 CLS (closed-loop system) Pacemakers" multicenter trial were retrospectively evaluated to examine the influence of concomitant antiarrhythmic drugs on the clinical success of conventional single site right atrial overdrive pacing compared with DDD pacing. The DDD+ overdrive algorithm provided > 90% atrial pacing at a rate slightly above the intrinsic atrial rate. Seventy-five patients with conventional pacing indications and paroxysmal, recurrent atrial tachyarrhythmia have completed the study. They were randomized to 6 months of DDD or DDD+ pacing, followed by mode crossover and an additional 6-month follow-up in the alternate mode. The incidence of atrial tachyarrhythmia during each period was compared using data on sustained (> 60 s) mode switch episodes stored in the pacemaker memory. A stable antiarrhythmic drug regimen was allowed during the study. beta-Adrenergic blockers and Class III antiarrhythmics, prescribed to 54.7% and 40.0% of patients respectively, were linked to minimal or no benefit of overdrive pacing compared with DDD pacing. In contrast, patients untreated with beta-adrenergic blockers or Class III drugs had a significant reduction in atrial tachyarrhythmia burden of > 5 hours/patient per week (P < 0.05) during overdrive. Changes with Class I and Class IV antiarrhythmic drugs, prescribed to 18.7% and 13.3% of patients, respectively, were insignificant. Our data indicate that clinical trials that prohibit the use of beta-adrenergic blockers may record more favorable outcomes with dynamic atrial overdrive algorithms versus conventional DDDR pacing, than studies allowing concomitant beta-adrenergic blockade.