Circulation: European Perspectives

T he well-known fact that atrial fibrillation (AF) confers a substantial mortality and morbidity from stroke and thromboembolism, and is an increasing public health problem, is repeatedly emphasised from sound epidemiological and clinical studies.Similarly, the benefits of anticoagulation therapy as thromboprophylaxis are well established from many clinical trials, 1 and have been ingrained in various clinical management guidelines for AF. 2 Despite the strong evidence of the problem, and the good evidence that we can reduce the burden of stroke due to AF with anticoagulation, repeated surveys still clearly show the continued suboptimal use of thromboprophylaxis for AF.Can we do better?Problems With Risk Stratification Most cardiologists recognise that the stroke risk in AF is not homogeneous, and different risk stratification criteria have been proposed, as reviewed by Lip and Boos. 2 The recent EuroHeart Survey 3 for AF shows that cardiologists do not undertake risk stratification well, and many low-risk patients (who can be treated with aspirin) are prescribed warfarin, whilst some high-risk patients (who need warfarin) are treated with aspirin.This is along the same lines as work that has shown that consultant physicians can be poor at estimating stroke and bleeding risks.4 Aspirin Is not a Viable Alternative to WarfarinThere is also the misconception -one might even say conspiracy -that aspirin is a viable alternative to warfarin.Pathophysiologically, thrombus in AF is fibrin-rich ("red clot"), rather than platelet-rich ("white clot").Abnormalities of coagulation and haemostasis are well-documented in AF in keeping with the presence of a prothrombotic state with this arrhythmia, which seems unrelated to structural heart disease or aetiology of AF. 5 Some platelet abnormalities may also be found, but are more associated with the vascular disease commonly found with this arrhythmia, rather than being due to AF per se.Clinically, aspirin reduces the risk of stroke by 22%, but much of this was driven by the results of only one clinical trial, the Stroke Prevention in Atrial Fibrillation study (Circulation.1991:84:527-539).If strokes do occur in aspirin-treated AF patients, they are usually more severe, with a greater in-hospital mortality and disability.On another note, the relative risk reduction of stroke by aspirin compared to placebo is similar to the stroke risk reduction (also 22%) seen for the use of antiplatelet therapy in high-risk vascular disease patients in the Antithrombotic Trialists' Collaboration.6 As AF commonly coexists with vascular disease, the benefit of aspirin as thromboprophylaxis in AF may simply reflect the beneficial effect on vascular disease rather than on AF specifically. Paroxysmal AF Is not a Lower Stroke RiskMany clinicians also erroneously regard those with paroxysmal AF as being at lower stroke risk and dispense with the need for anticoagulation.7 Indeed, patients who sustain one short paroxysm once a year may well be at a different risk to a patient getting long, daily paroxysms.However, many patients with paroxysmal AF do get many asymptomatic Gregory Y.H. Lip, MD, professor of cardiovascular medicine at the City Hospital, Birmingham, England, questions whether thromboprophylaxis for atrial fibrillation could be improved in the United Kingdom.