How do I assess the risk of CVA or TIA in a patient with chronic atrial fibrillation and in a patient with paroxysmal atrial fibrillation?

Age is an important determinant of the risk of thromboembolism, and hence of transient ischaemic attack (TIA) and of cerebrovascular accident (CVA) in patients with atrial fibrillation. If the patient is aged less than 60 years, and has no evidence of other cardiac disease (such as coronary artery disease, valve disease or heart failure) the risk of thromboembolism is low (of the order of 0.5% per year). This risk is lower than the risk of a serious bleed if the patient is anticoagulated with warfarin (1.3% per year or higher depending on the quality of anticoagulation control). If the patient is older than the 60 years, or has evidence of other cardiovascular disease, the risk of thromboembolism increases.

In the Stroke Prevention in Atrial Fibrillation Study clinical features indicating a higher risk of thromboembolism were: age over 60 years; history of congestive heart failure within the previous 3 months; hypertension (treated or untreated); and previous thromboembolism. The more of these features present in a patient the higher the risk of thromboembolism. A large left atrium (>2.5cm diameter/m2 body surface area) or global left ventricular systolic dysfunction on transthoracic echocardiography also identifies patients at a higher risk of thromboembolism. Such abnormalities may not be suspected clinically and wherever possible echocardiography should be performed in patients with AF in order to determine more precisely the risk of thromboembolism.

Paroxysmal (as opposed to chronic) atrial fibrillation covers a wide spectrum of disease severity with the duration and frequency of attacks varying markedly between and within patients. Although the clinical trials of anticoagulation in patients with atrial fibrillation were inconsistent in including patients with paroxysmal atrial fibrillation, there was no evidence that such patients had a lower risk of thromboembolism than those with chronic atrial fibrillation. It is likely that as the episodes become more frequent and of longer duration that the risk approaches those in patients with chronic atrial fibrillation.