Subclinical Atrial Fibrillation and the Risk of Stroke
Do asymptomatic episodes of atrial tachyarrhythmia (AT) detected by a pacemaker or implanted cardioverter-defibrillator (ICD) increase the risk of stroke?
The subjects of this study were 2,580 patients who underwent implantation of a pacemaker or ICD. The selection criteria were age ≥65 years (mean age 76 years), hypertension, and no history of atrial fibrillation (AF). A subclinical AT was defined as an asymptomatic atrial high-rate event >190 bpm lasting >6 minutes. Patients in whom ATs were noted at 3 months of follow-up were randomly assigned to receive or to not receive continuous atrial overdrive pacing. The primary outcome was ischemic stroke or systemic embolism.
Subclinical ATs (median of two/patient, mean rate 480 bpm) were noted in 10.1% of patients at 3 months of follow-up. During the entire follow-up, subclinical ATs were noted in 34.6% of patients and clinical AF occurred in 15.7% of patients. During a mean of 2.5 years of follow-up, the annual risk of stroke/embolism was significantly higher in patients with than without a subclinical AT detected at 3 months (1.7% vs. 0.7%, hazard ratio [HR], 2.5). During follow-up, AT episodes >6 minutes, >6 hours, and >24 hours in duration were associated with a similar degree of increased risk of stroke/embolism (HRs 1.8, 2.0, and 2.0, respectively). Continuous atrial overdrive pacing did not prevent ATs.
The authors concluded that asymptomatic AF detected by cardiac devices is associated with an increased risk of stroke/embolism.
Because only AT episodes longer than 6 minutes were included in the analysis, the minimum duration of subclinical ATs associated with thromboembolic complications is unclear. Whether anticoagulation has a net benefit in patients with subclinical ATs also remains to be determined.
Keywords: Risk, Stroke, Defibrillators, Follow-Up Studies, Heart Atria, Tachycardia, Thromboembolism, Blood Coagulation, Cardiology, Pacemaker, Artificial, Hypertension
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