GPs should consider all patients over 75 for anticoagulation therapy because of the poor performance of NICE-approved tools for predicting stroke risk in older patients with atrial fibrillation, researchers conclude.
A study published online by the BMJ found several risk tools used in primary care to assess the risk of stroke, and recommended in NICE guidance on atrial fibrillation, ‘failed to show an increase in risk at the upper range of scores', and that all had ‘a similar limited ability to predict the risk of stroke'.
Consequently the researchers – including a member of the NICE guideline development group who helped write its 2006 guidance – argued ‘there could be a pragmatic rationale for classifying all patients over 75 as high risk until better tools are available'.
The research comes after a GP-led advisory committee to NICE recommended new QOF indicators to increase the prescribing of warfarin to patients with atrial fibrillation should be added to the QOF – but warned of a controversy over which tool GPs used to assess stroke risk.
Researchers compared the performance of the most commonly used stroke risk stratification scores in a population of 665 patients aged 75 or over with atrial fibrillation, who were not taking warfarin either throughout or for part of the median 2.2-year study period.
Seven systems were evaluated, including CHADS2, Framingham, NICE guidelines, and the more recently developed CHADS2-VASC tool, all of which classify patients in low, moderate and high risk categories.
NICE guidance recommends that anticoagulation with warfarin should be given to all atrial fibrillation patients at high risk of stroke, and anticoagulation or aspirin considered for patients at moderate risk.
The distribution of patients classified into the three risk categories was similar across the tools, with 65%-69% classified as at moderate risk.
After adjustment for all other factors in the model, only history of diabetes and previous stroke or transient ischaemic attack were identified as significant risk factors for future stroke, with hazard ratios of 2.1 and 2.6, respectively.
Professor Richard Hobbs, head of primary care health sciences at the University of Birmingham and a GP in the city, concluded: ‘Current risk stratification schemes in older people with atrial fibrillation have only limited ability to predict the risk of stroke.
‘Given the systematic under-treatment of older people with anticoagulation, and the relative safety of warfarin versus aspirin in those aged over 70, there could be a pragmatic rationale for classifying all patients over 75 as at high risk until better tools are available.'
NICE is currently assessing the use of dabigatran, the first of a new generation of anticoagulants, for use in the NHS, though the initial cost is expected to be high.
But the researchers argued: ‘Even if patients and physicians remain reluctant to prescribe warfarin, accurate identification of those at high thromboembolic risk remains a priority as effective management alternatives to warfarin options, that don't require monitoring, become available. Offering such patients aspirin is an inappropriate option.'
BMJ 2011, online 23 June.
