[Atrial fibrillation: incidence and prognostic factors of embolic risk].

Atrial fibrillation (AF) carries a high risk of systemic embolism, in particular stroke. This is true not only when AF is associated with rheumatic valvular heart disease, but also in the so-called nonvalvular AF (NVAF). The recent randomized clinical trials assessing antithrombotic therapy as primary prevention in NVAF have shown that, untreated, disabling stroke occurs in 2.5%/year, ischemic stroke in 5%/year, stroke and transient ischemic attack in 7%/year, and stroke, transient ischemic attack and silent stroke in > 7%/year. All AF does not carry identical stroke risk. A risk stratification is important in order to decide long-term antithrombotic prophylaxis. A number of important clinical predictors of stroke have been identified. They include age, hypertension, congestive heart failure, previous arterial thromboembolism and previous myocardial infarction. Idiopathic or "lone" AF in patients < 60 years old, without hypertension and diabetes mellitus, carries an extremely low risk of stroke. Also in paroxysmal AF, when patients are < 60 years old and without organic heart disease, the embolic risk is low. The recent onset of AF does not seem to be associated with an excess of embolic risk, in comparison with long-standing AF. In conclusion, the underlying heart disease represents the main determinant of embolic risk. Within the broad spectrum of patients with NVAF a satisfactory risk stratification for thromboembolism can be accomplished by the analysis of clinical risk factors, possibly in association with echocardiographic variables.