Temporal relationship between subclinical atrial fibrillation and embolic events.

BACKGROUND: Among patients with implantable pacemakers and defibrillators, subclinical atrial fibrillation (SCAF) is associated with an increased risk of stroke; however, there is limited understanding of their temporal relationship. METHODS AND RESULTS: The Asymptomatic Atrial Fibrillation and Stroke Evaluation in Pacemaker Patients and the Atrial Fibrillation Reduction Atrial Pacing Trial (ASSERT) enrolled 2580 pacemaker and defibrillator patients aged ≥65 years with a history of hypertension but without a history of atrial fibrillation. Pacemakers and implantable cardioverter-defibrillators precisely logged the time and duration of all episodes of SCAF and recorded electrograms that were adjudicated by experts. We examined the temporal relationship between SCAF >6 minutes in duration and stroke or systemic embolism. Of 51 patients who experienced stroke or systemic embolism during follow-up, 26 (51%) had SCAF. In 18 patients (35%), SCAF was detected before stroke or systemic embolism. However, only 4 patients (8%) had SCAF detected within 30 days before stroke or systemic embolism, and only 1 of these 4 patients was experiencing SCAF at the time of the stroke. In the 14 patients with SCAF detected >30 days before stroke or systemic embolism, the most recent episode occurred at a median interval of 339 days (25th to 75th percentile, 211-619) earlier. Eight patients (16%) had SCAF detected only after their stroke, despite continuous monitoring for a median duration of 228 days (25th to 75th percentile, 202-719) before their event. CONCLUSIONS: Although SCAF is associated with an increased risk of stroke and embolism, very few patients had SCAF in the month before their event. CLINICAL TRIAL REGISTRATION URL: http://www.clinicaltrials.gov. Unique identifier: NCT00256152.

Atrial overdrive pacing to prevent atrial fibrillation: insights from ASSERT.

BACKGROUND: Pacing algorithms to prevent atrial fibrillation (AF) have been tested in studies of modest size and duration with inconclusive results. OBJECTIVES: To prospectively evaluate the relationship between subclinical AF and stroke in patients 65 years of age or older with no previous AF receiving a first pacemaker or an implantable cardioverter-defibrillator for standard indications. Three months following device implantation, pacemaker patients were randomized to have continuous atrial overdrive pacing (CAOP) algorithm turned "ON" or "OFF." The primary study outcome was development of electrocardiogram-documented AF >6 minutes. RESULTS: A total of 2343 patients were randomized and followed for a mean of 2.5 years. The primary outcome occurred in 60 patients in the CAOP ON group (1.96% per year) and in 45 in the CAOP OFF group (1.44% per year; relative risk 1.38; 95% confidence interval 0.94-2.03; P = .10). Major clinical events (stroke, myocardial infarct, cardiovascular death, systemic embolism, heart failure hospitalization) occurred at similar frequencies in the 2 groups. In the CAOP ON group, 133 of the 1164 patients (11.4%) crossed over to CAOP OFF compared with 12 of the 1179 (1.0%) who crossed over from OFF to ON (P <.0001). False-positive device detections of AF were more common among patients assigned to CAOP ON (23%) than among patients assigned to CAOP OFF (7.7%; relative risk 2.99; 95% confidence interval 2.40-3.74; P <.001). Pacemaker generator replacement for battery depletion occurred in 4.4% of the subjects randomized to CAOP ON and in 2.5% of the patients assigned to CAOP OFF (relative risk 1.70; 95% confidence interval 1.08-2.67; P = .02). CONCLUSIONS: CAOP does not prevent new-onset AF, is poorly tolerated, and accelerates pulse generator battery depletion.

ASymptomatic atrial fibrillation and Stroke Evaluation in pacemaker patients and the atrial fibrillation Reduction atrial pacing Trial (ASSERT).

Asymptomatic atrial fibrillation (AF) is common and may have the same prognostic implications as symptomatic AF. Among patients receiving dual-chamber pacemakers, it is now possible to quantify asymptomatic AF accurately. Most of these episodes are of short duration, often lasting only seconds to minutes and are called atrial high-rate episodes (AHRE) to distinguish them from the longer episodes of overt AF. To understand properly the clinical importance of asymptomatic AF, a large study of pacemaker patients without clinically overt AF is required. ASSERT is a multicenter, cohort follow-up, and single-blinded randomized trial in elderly hypertensive patients with a pacemaker recently implanted for sinus or atrioventricular node disease. The goals of this trial are to evaluate whether the detection of AHRE with pacemaker telemetry predicts an increased risk of stroke and other vascular events and to evaluate if atrial overdrive pacing reduces symptomatic AF. ASSERT is evaluating the hypothesis that among pacemaker patients without a previous history of AF, detection of AHRE predicts an increased risk of stroke and systemic embolism. The second hypothesis to be tested is that overdrive atrial pacing will reduce the risk of symptomatic AF in pacemaker patients without a previous history of AF. Finally, a 400-patient substudy will use the noninvasive testing capabilities of the patients' pacemaker to evaluate changes in atrial electrophysiology over 2 years. This substudy will determine if atrial electrical remodeling is detectable in pacemaker patients and if it is associated with the development of AF.