100 QUESTIONS IN CARDIOLOGY

71 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?

Suzanna Hardman and Martin Cowie

Age is an important determinant of the risk of thrombo-

embolism, 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 thrombo-

embolism 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/m^2 body surface area) or global left

ventricular systolic dysfunction on transthoracic echo-

cardiography also identifies patients at a higher risk of thrombo-

embolism. 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.