Conference Coverage

Shift From Atrial Overdrive Pacing for AF Prevention Urged



BOSTON – Continuous atrial overdrive pacing does not prevent the development of new atrial fibrillation and is not a useful feature of pacemakers for patients with no history of AF, a researcher said at the annual meeting of the Heart Rhythm Society.

A secondary analysis of data from the Asymptomatic Atrial Fibrillation and Stroke Evaluation in Pacemaker Patients and the Atrial Fibrillation Reduction Atrial Pacing Trial (ASSERT) of atrial pacing in older patients with no history of AF showed that continuous atrial overdrive pacing (CAOP) had "no discernible effect" on the incidence of new atrial tachyarrhythmia, AF longer than 6 minutes, or AF burden, reported Dr. Stefan Hohnloser, director of clinical electrophysiology at J.W. Goethe University in Frankfurt, Germany.

Dr. Stefan Hohnloser

Atrial preventive pacing "was associated with a high rate of crossover to alternate pacing mode, an increase in AF burden in patients with minimal ventricular pacing, more false-positive detection of atrial fibrillation by the pacemaker, and more frequent pacemaker generator replacement," Dr. Hohnloser said.

There have been 24 small or moderately sized studies of atrial preventive pacing in more than 10,000 patients, yet the results of those studies have been muddied by relatively short follow-up, the use of many different devices from different manufacturers, different pacing algorithms, and variations in atrial lead placements, hence the rationale for the secondary goal of ASSERT, he said.

ASSERT was a randomized study of 2,343 patients aged 65 and older with a history of hypertension but no history of AF or prior use of a vitamin K antagonist. The primary hypothesis that subclinical AF detected by pacemakers or implantable cardioverter defibrillators (ICDs) could predict increased risk of stroke or systemic embolism was borne out by the results.

The same could not be said, however, for the secondary hypothesis that CAOP could prevent development of AF and clinical end points, Dr. Hohnloser said.

After a 3-month run-in period to determine the presence or absence of subclinical AF, patients were randomized in a single-blind fashion to have the CAOP feature of their devices switched on or kept off. Patients were followed every 3 months. Independent adjudicators read all device-stored electrograms longer than 6 minutes.

Over 2.5 years of follow-up, there were no significant differences between the CAOP-on or -off groups in time to atrial tachyarrhythmia or to a composite clinical end point of stroke, myocardial infarction, cardiovascular death, systemic embolism, or heart-failure hospitalization, he said.

A subgroup analysis showed that atrial lead position, atrioventricular node disease with or without sinus node disease, sinus node disease alone, or history of heart failure were not significant predictors of treatment effect by randomization. However, patients who spent less than the median time in ventricular pacing at 6 months (59%) had significantly more of the primary outcome events, compared with patients who spent more than 59% of the time in ventricular pacing, he reported.

In all, 11.4% of patients assigned to CAOP on at study entry were crossed over to CAOP off, compared with only 1.0% of patients in the off group who were crossed over to continuous atrial overdrive pacing, a significant difference.

One or more false-positive AF detections occurred in 23% of patients with continuous pacing, compared with 7.7% of those with it turned off, for a significant relative risk of 2.99.

Dr. Richard I. Fogel

Pacemaker generator replacement was required in 4.4% of patients with CAOP on, compared with 2.5% of those with it off (relative risk, 1.70; P = .02). This result was expected, Dr. Hohnloser said, because of the extra workload on the pacemakers in continuous overdrive.

The results confirm that patients not already in atrial fibrillation do not appear to benefit from CAOP, but the study did not address whether the strategy benefits patients who already have AF, commented Dr. Richard I. Fogel from the St. Vincent Medical Group, Indianapolis, in an interview.

"The question didn’t address whether it decreases the atrial fibrillation burden. But I think it’s very clear that if you don’t have atrial fibrillation and you have had it, you shouldn’t use this algorithm. Although you have to wonder whether there aren’t some subsets of patients who might benefit," he said. Dr. Fogel moderated the late-breaking abstracts session but was not involved in the study.

The ASSERT trial was funded by St. Jude Medical. Dr. Hohnloser disclosed serving as a consultant, member of the steering committee, and speakers bureau member for St. Jude Medical and other companies. Dr. Fogel disclosed that he has received grants for clinical research and grants for educational activities from St. Jude Medical, Medtronic, and Guidant and owns stock in Medtronic and Guidant.

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