Current status of stroke risk stratification in patients with atrial fibrillation.

Identifying independent risk factors for stroke in patients with atrial fibrillation is important for 2 main reasons: it sheds light on stroke pathogenesis associated with this common cardiac dysrhythmia, and it allows stratification of stroke risk for individual patients. Both are keys to prevention of the unduly large cardioembolic brain infarcts that complicate atrial fibrillation. Among nonvalvular atrial fibrillation patients, the absolute risk of stroke averages 3% to 4% per year, but it varies 20-fold depending on patient age and other clinical features.1,2 Hence, stroke risk stratification allows the absolute benefits of prophylactic antithrombotic therapy to be estimated for individual patients. Since the initial analysis of the pooled control groups of 5 randomized clinical trials in 1994,3 several studies analyzing stroke risk factors in nonvalvular atrial fibrillation patients using multivariate analysis have yielded 4 consistent predictors: increasing age, hypertension/systolic blood pressure, diabetes, and prior embolism (Table 1).1 Prior stroke/TIA is the most powerful risk factor and is associated with high rates of stroke ( 5% per year, averaging 10% per year) warranting anticoagulation, even in atrial fibrillation patients without other risk factors.1 Female sex has been less consistently linked to stroke risk, although independently predictive in 3 studies.1 Unexpectedly, heart failure has not been an independent predictor of stroke in atrial fibrillation patients. Further, a recurrent paroxysmal pattern (as opposed to persistent or permanent atrial fibrillation) in elderly patients was not independently predictive of reduced stroke risk in any of 4 studies in which it was assessed. What are the pathogenetic implications? The 4 most consistent risk factors for stroke in atrial fibrillation patients (ie, prior stroke/TIA, advancing age, hypertension, and diabetes) are also risk factors for stroke among persons without atrial fibrillation. However, the absolute stroke rates associated with these risk factors are several times higher among atrial fibrillation patients compared with risk factor–specific ageadjusted rates in patients without atrial fibrillation. Hypertension is associated with stasis of flow and thrombus in the left atrial appendage and with cardioembolic strokes in atrial fibrillation patients (Figure).9–11 Left atrial appendage flow velocities, strongly and inversely associated with appendage thrombi, decrease with advancing age.11 Diabetes may be a marker of a prothrombotic state favoring left atrial thrombus formation.12 The large relative risk reduction of ischemic strokes by anticoagulation over aspirin in atrial fibrillation Table 1. Independent Risk Factors for Stroke in Atrial Fibrillation Patients: Summary of Studies Using Multivariate Analysis*