Stroke type and severity in patients with subclinical atrial fibrillation: An analysis from the Asymptomatic Atrial Fibrillation and Stroke Evaluation in Pacemaker Patients and the Atrial Fibrillation Reduction Atrial Pacing Trial (ASSERT)
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BACKGROUND: The Asymptomatic Atrial Fibrillation and Stroke Evaluation in Pacemaker Patients and the Atrial Fibrillation Reduction Atrial Pacing Trial (ASSERT) demonstrated that subclinical atrial fibrillation (SCAF) was associated with a 2.5-fold increased risk of stroke. However, the absolute stroke rate was only 1.7% per year and fewer than 20% patients with stroke had SCAF in the preceding 30 days. This raises the possibility that SCAF is merely a risk marker for stroke rather than the cause. Systematic characterization of stroke subtypes among patients with SCAF would help clarify this issue. METHODS: All ischemic strokes that occurred in the ASSERT trial were blindly adjudicated by stroke neurologists, classified as cortical versus subcortical, and subtyped using modified TOAST criteria. Stroke severity was measured using the modified Rankin Score. RESULTS: Of the 44 participants who had an ischemic stroke, 14 had SCAF before stroke. Among patients with SCAF who had stroke, 57% of strokes (n = 8) were judged to be cardioembolic, 36% to be lacunar (n = 5), and 7% (n = 1) to be large artery disease. However, of 5 patients who had SCAF detected within 30 days before their index stroke, 4 patients had a cardioembolic stroke. The average duration of SCAF in these 4 patients was 6.0 ± 6.1 h/d. The modified Rankin score at 30 days was similar between patients with (2.7 ± 2.3) and without SCAF (2.3 ± 2.0; P = .68). CONCLUSIONS: In patients with SCAF and stroke, SCAF seems probably causal in many cases; however, in more than 40%, it seems to be acting only as a risk marker.