A new study published in the New England Journal of Medicine sheds some much-needed light on the precise role of subclinical atrial fibrillation (AF) in the prognosis and development of ischemic stroke. ASSERT (Asymptomatic Atrial Fibrillation and Stroke Evaluation in Pacemaker Patients and the Atrial Fibrillation Reduction Atrial Pacing Trial) followed 2580 patients with a newly implanted pacemaker or ICD and with no previous diagnosis of AF.
At 3 months, subclinical AF lasting longer than 6 minutes had been detected in 10.1% (261) of the subjects. During 2.5 years of follow-up, 51 patients in the study had an ischemic stroke or systemic embolism. Of these, 11 were in the group with subclinical AF by 3 months. Patients with subclinical AF had more than double the risk for stroke or systemic embolism:
- HR 2.49; CI 1.28 – 4.85, p = 0.007
Subclinical AF accounted for 13% of the population attributable risk for ischemic stroke or systemic embolism, according to the ASSERT investigators. Patients with subclinical AF and a CHADS-2 score above 2 had nearly a 4% per year risk for stroke or systemic embolism.
In a second portion of the study, half of the patients with pacemakers were randomized to continuous atrial overdrive pacing, but this intervention had no significant impact on any of the endpoints in the study.
In an accompanying editorial, Gervasio Lamas praises the study but argues that the clinical implications are unclear: “The current evidence simply does not address the question of whether treatment with warfarin or other anticoagulants is justifiable for the asymptomatic patient who has had a 6-minute episode of atrial fibrillation.” Lamas recommends the CHADS-2 score as an aide in deciding which patients should receive anticoagulation.