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Anticoagulation and atrial fibrillation
  1. D S G CONWAY,
  2. G Y H LIP
  1. Haemostasis Thrombosis and Vascular Biology Unit
  2. University Department of Medicine
  3. City Hospital, Birmingham B18 7QH, UK
  4. G.Y.H.LIP{at}bham.ac.uk

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    Editor,—We would like to congratulate McNulty and colleagues on their excellent clinical audit of antithrombotic therapy in atrial fibrillation.1 Their approach to the methods of audit has been impeccable, completing the audit cycle by instigating a process of reaudit after the results from the original data set had been intensively presented to hospital colleagues, itself leading to a highly effective intervention.

    We would, however, appreciate this opportunity to provide a brief update in a few aspects of the current knowledge of stroke prevention in atrial fibrillation. The Lip and Lowe algorithm used for risk stratification was first published in 19962 and a refinement has since been proposed (box 1),3 which has been adapted for use in local and national guidelines.

    Box 1: Risk stratification and anticoagulation in non-valvular atrial fibrillation

    ASSESS RISK AND REASSESS REGULARLY:
    (1)
    High risk (annual risk of CVA = 8%–12%)
    All patients with previous transient ischaemic attack or CVA.
    All patients aged 75 or over with diabetes and/or hypertension.
    All patients with clinical evidence of valve disease, heart failure, thyroid disease, and/or impaired left ventricular function on echocardiography*.

    (2)
    Moderate risk (annual risk of CVA = 4%)
    All patients aged under 65 with clinical risk factors: diabetes, hypertension, peripheral arterial disease, ischaemic heart disease.
    All patients aged over 65 who are not in high risk group.
    (3)
    Low risk (annual risk of CVA = 1%)
    All patients under 65 with no history of embolism, hypertension, diabetes, or other clinical risk factors.
    TREATMENT
    • High risk: give warfarin (target INR 2.0–3.0) if no contraindications and possible in practice.

    • Moderate risk: either warfarin or aspirin 75–300 mg. In view of insufficient clear cut evidence, treatment may be decided on individual cases. Referral and echocardiography may help.

    • Low risk: give aspirin 75–300 mg daily.

      *Echocardiography: not needed for routine risk assessment but refines clinical risk stratification in case of impaired left ventricular function and valve disease. A large atrium per se is not an independent risk factor on multivariate analysis.

      CVA = cerebrovascular accident.

    The essential changes relate to the contribution of echocardiography and paroxysmal atrial fibrillation. In the Atrial Fibrillation Investigators overview on echocardiographic risk factors for thromboembolism, left atrial size per sedoes not appear to be an independent risk factor on multivariate analysis and is no longer used in the risk stratification schema3; indeed, left atrial dilatation rarely occurs independent of “other” pathology, such as hypertension or heart failure which themselves constitute high risk features.4In this analysis, moderate or severe left ventricular dysfunction on two dimensional echocardiography was the only significant abnormality which appeared to be an independent risk factor for thromboembolic stroke in non-valvular atrial fibrillation.4 Other studies using echocardiography for risk stratification have rarely found that the investigation significantly contributed to antithrombotic therapy management decisions, as many patients already had clinical risk factors allowing effective risk stratification.5 6

    Regarding other possible risk factors, hormone replacement therapy use may also increase risk while alcohol consumption may be protective.7 McNulty and colleagues do not specifically address the problem of paroxysmal atrial fibrillation,1but it should be emphasised that such patients carry the same stroke and thromboembolic risk as sustained atrial fibrillation, especially in the presence of clinical risk factors.8 In general, our recommendation is to use warfarin in patients with paroxysmal atrial fibrillation unless they can be classified as having “lone” atrial fibrillation or there are contraindications to the use of anticoagulation, where aspirin should be used instead.

    The safety and tolerability of long term anticoagulation titrated to conventional levels (international normalised ratio (INR) 2–3) is less clear in the very elderly (age older than 75 years), which is the age group encompassing perhaps half of the atrial fibrillation associated stroke patients. The elderly are also prone to more co-morbidity, polypharmacy, cognitive problems and frailty; indeed, biological age in some ways is more important than chronological age, and the decision must be based on the risk-benefit ratio, as with many things in clinical medicine. There have also been suggestions that an INR range of 1.6–2.5 can provide substantial, if partial efficacy (estimated to be nearly 90% of the highest intensities), and could be used for elderly patients to minimise haemorrhagic complications, although this has not been verified by any prospective study.9 Given the uncertainty about the safety of INRs >2.5 for patients with atrial fibrillation over the age 75, a target INR of 2.0 (range 1.6–2.5) may be a reasonable compromise between toxicity and efficacy for this age group, pending further data about the safety of higher intensities. Further information from our ongoing Medical Research Council funded BAFTA (Birmingham Atrial Fibrillation Treatment Assessment) study in elderly patients aged >75 years, with non-valvular atrial fibrillation in primary care, would provide further information.

    McNulty and colleagues extrapolate from their data the potential savings both in hospital admission days and financial cost,1 which may be achievable by a nationwide consensus approach to the problem. We wholeheartedly support this, and agree with their call for improved stroke prevention in atrial fibrillation, especially as there is now evidence the benefits and risks of anticoagulation seen in the clinical trials can realistically be translated into everyday clinical practice.10

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