Subclinical atrial tachyarrhythmias, without clinical atrial fibrillation (AF), occurred frequently in patients with pacemakers and were associated with a significant increased risk of ischemic stroke or systemic embolism, according to the ASSERT trial published Jan. 12 in the New England Journal of Medicine.
One quarter of strokes are of unknown cause, and subclinical AF may be a common etiologic factor. Pacemakers can detect subclinical episodes of rapid atrial rate, which correlate with electrocardiographically documented AF.
In this study, Jeffrey S. Healey, MD, MSc, of McMaster University in Hamilton, Ontario, and colleagues evaluated whether subclinical episodes of rapid atrial rate detected by implanted devices were associated with an increased risk of ischemic stroke in patients who did not have other evidence of AF.
The researchers enrolled 2,580 patients, 65 years of age or older, with hypertension and no history of AF, in whom a pacemaker or defibrillator had recently been implanted. They monitored patients for three months to detect subclinical atrial tachyarrhythmias (episodes of atrial rate more than 190 beats per minute for more than six minutes) and followed them for a mean of 2.5 years for the primary outcome of ischemic stroke or systemic embolism. Patients with pacemakers were randomly assigned to receive or not to receive continuous atrial overdrive pacing.
During the course of the study, clinical AF developed in only 15.7 percent of the patients with subclinical atrial tachyarrhythmias, suggesting that there can be a lag between subclinical events and clinical detection, the authors wrote. The median time to the detection, by means of continuous device monitoring, of the occurrence of subclinical atrial tachyarrhythmias within the first three months was 36 days, indicating that Holter monitoring even for several days may fail to detect subclinical AF.
By three months, subclinical atrial tachyarrhythmias detected by implanted devices had occurred in 10.1 percent of the patient population. Subclinical atrial tachyarrhythmias were associated with an increased risk of clinical AF and of ischemic stroke or systemic embolism.
Of 51 patients who had a primary outcome event, 11 had subclinical atrial tachyarrhythmias detected by three months, and none had clinical AF by three months, according to Healey and colleagues. The population attributable risk of stroke or systemic embolism associated with subclinical atrial tachyarrhythmias was 13 percent. Subclinical atrial tachyarrhythmias remained predictive of the primary outcome after adjustment for predictors of stroke. Continuous atrial overdrive pacing did not prevent AF.
Of note, the study “did not analyze device-detected events of six minutes or less, which occurred frequently and which might be clinically important,” they wrote.
The results of the study did not show a benefit of continuous atrial overdrive pacing, according to the authors, but because the rate of development of clinical atrial fibrillation was low, the study was underpowered for this outcome.
Based on the results, Healey et al concluded that subclinical atrial tachyarrhythmias occurred frequently in patients with pacemakers who had a history of hypertension but no prior diagnosis of clinical AF. The subclinical atrial tachyarrhythmias often preceded the development of clinical AF. In patients with pacemakers who did not have clinical AF, the occurrence of subclinical atrial tachyarrhythmias was associated with a significantly increased risk of a subsequent stroke.
The study was funded by St. Jude Medical, based in St. Paul, Minn.