Atrial fibrillation and stroke prevention

Summary

Atrial fibrillation (AF) is a common arrhythmia that is associated with substantial morbidity and mortality, particularly due to stroke and thromboembolism. Anticoagulant therapy reduces the risk of stroke, and the greatest benefit is seen in patients at highest absolute risk. Aspirin is a less effective alternative, and any benefit of aspirin might be due to its favourable effects on arterial thrombosis caused by vascular disease. However, anticoagulant therapy remains underused, particularly in the elderly, who probably have the most to gain from stroke prevention owing to their high absolute risk. The underuse of anticoagulation might also be related to uncertain risk of thromboembolism in individual patients and a perceived overestimation of the benefit and underestimation of risk of bleeding with warfarin in clinical trials. In this Review, we summarise the data for and against warfarin and aspirin therapies and discuss the clinical assessments and risk stratifications that guide the use of antithrombotic therapy for stroke prevention in patients with AF. Possible barriers to the uptake of anticoagulation therapy are also discussed.

Introduction

Atrial fibrillation (AF) is a common arrhythmia, which is seen in everyday clinical practice. The prevalence of AF increases from less than 1% in patients younger than 60 years to almost 10% in patients over the age of 80 years.¹ Similarly, the incidence of AF increases from 0·2% per year in men under the age of 40 years to more than 2% per year in men aged 80–89 years, with a lower age-adjusted incidence in women.2, 3 Therefore, AF is predominantly a problem of the older population, and the prevalence of AF is projected to rise as the population ages and the prevalence of cardiovascular risk factors increases.⁴ Indeed, the rising prevalence and incidence of AF have already been reported in several studies of secular trends during the past two decades.5, 6 The authors of the Olmstead County study⁴ reported that the age-adjusted and sex-adjusted incidence of AF per 1000 person-years was 3·04 (95% CI 2·78–3·31) in 1980 and 3·68 (3·42–3·95) in 2000, with a relative increase of 12·6% (2·1%–23·1%) in total. This analysis estimates that the number of people with AF in the USA will be 12·1 million by 2050, assuming no further increase in age-adjusted incidence of AF, and 15·9 million if the increase in incidence continues.

AF accounts for more than 1% of health-care expenditure in the UK,⁷ and treatment of thromboembolic stroke incurs a significant share of the health-care costs associated with AF.⁸ On a population level, AF is associated with a fourfold to fivefold increase in the risk of stroke, and an estimated 15% of all strokes are caused by AF; importantly, this proportion increases substantially with age.⁹ In a selected population of patients with ischaemic stroke, AF was highly prevalent (almost 25%) and associated with longer stays in hospital, greater disability, higher rates of stroke recurrence, and higher rates of mortality compared with stroke patients without AF.¹⁰ The risk of stroke in patients with paroxysmal or persistent AF is comparable to the risk in patients with permanent AF¹¹ and, importantly, the absence of symptoms (eg, palpitations) does not imply lower risk of thromboembolism.¹²

The aim of this Review is to give an overview of antithrombotic therapy for stroke prevention in AF. We discuss risk factors for stroke, risk stratification, and new developments for stroke prevention in patients with AF.