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AMSTERDAM -- Reducing atrial pacing didn't help prevent atrial fibrillation (Afib, or AF) in patients with sinus node dysfunction but did increase risk of fainting, the DANPACE II trial showed.

The proportion of patients who developed adjudication-confirmed, device-detected Afib episodes of at least 6 minutes' duration was an identical 46% whether dual-chamber pacemakers were set to a non-rate-adaptive base rate of 40 bpm or the usual rate-adaptive pacing at 60 bpm.

The results were the same when looking at longer or more persistent episodes of Afib and other outcomes, including quality of life, Mads Brix Kronborg, MD, PhD, of Aarhus University Hospital in Denmark, reported at the European Society of Cardiology (ESC) congress and in the .

However, reduced atrial pacing led to significantly more syncope and presyncope (22% vs 13%, P=0.01).

"Programming intended to minimize atrial pacing should not be used as routine in unselected patient with sinus node dysfunction," concluded ESC session study discussant Jose Luis Merino, MD, PhD, of La Paz University Hospital and Hospital Viamed Santa Elena in Madrid.

Prior observational studies had shown more Afib with more atrial pacing, but the trial suggests now that those were associations without causal links, Merino added.

Perhaps the findings mean that "pacing in any mode may have little effect on AF in patients with sinus node dysfunction, and the occurrence of AF in this population may be natural progression of a disease process that led to the sinus node dysfunction at the outset," suggested Ratika Parkash, MD, MSc, of Queen Elizabeth II Health Sciences Centre in Halifax, Nova Scotia, in an accompanying the paper.

While the results are clear that minimizing atrial pacing is not a good strategy for routine use, Kronborg told 番茄社区 that the results don't rule out individualized use.

"There are some patients who, especially when they are at rest, they feel their heart," he said, "and if they're used to having a lower pulse of 40, they might -- a little bit -- have discomfort or chest pain when you program it to 60. And for those patients I would individually reduce it to a lower base rate. If they then experience signs of syncope or presyncope, I would discuss with them if we should put the base rate up higher again to 50 or 60."

His study randomized 540 patients getting first-time dual-chamber pacemaker implantation at 11 sites in Denmark to the two atrial pacing strategies, stratifying by sex and history of prior paroxysmal Afib or atrial flutter, which 40% of patients had. Those with a history of permanent or persistent Afib at baseline were excluded.

Atrioventricular (AV) delays were programmed to avoid ventricular pacing, but did not exceed 260 ms, and no Afib suppression algorithms were utilized, Parkash noted.

The atrial pacing percentage was 1% in the 40 bpm atrial pacing group versus 49% among the controls. Ventricular pacing was 9% and 34%, respectively. "The higher ventricular pacing percentage is likely due to the rate-adaptive AV delay that was programmed at the outset in this group," Parkash noted, adding that this "could have contributed to higher rates of AF than would otherwise be seen, although this would have biased to a more positive result, which was not the case."

Crossover was more common in the 60 bpm atrial pacing group (23% vs 3%), which the discussant noted might have hampered the trial in showing a difference between strategies. Another limitation was the long duration of the trial -- enrolling from May 2014 to June 2021 -- that might suggest possible enrollment bias.