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BCS Statement on Screening for Atrial Fibrillation to Prevent Stroke 31 October 2014British Cardiovascular Society statement in response to the National Screening Committee’s decision not to recommend screening for Atrial Fibrillation for the prevention of stroke in adults aged 65 and older. We were surprised that the National Screening Committee (NSC) rejected the proposal to screen people for atrial fibrillation (AF) in order to prevent stroke. [1,2] We believe that it would be in the public interest for the NSC to reconsider their decision before their scheduled review date of 2017, because, in our view, it was based on a misinterpretation of the evidence. The case for screening for AF for the prevention of stroke AF is both a cause of stroke (embolism) and a marker of atherosclerosis, which is a cause of stroke. Between ages 65 and 74 both the prevalence of AF and the annual incidence of stroke in people with AF are about 5%. [3,4] Both rates increase with age. Of all patients with stroke 17% have AF. [5] Electrocardiographic rhythm recording is a simple and safe screening test with a detection rate of about 90% for a 1% false positive rate. [6] Anticoagulation using warfarin (or novel oral anticoagulants) is effective in reducing the risk of stroke. From combined data from five randomised trials (in which 94% of the subjects had no history of stroke), stroke occurred in 27/1225 warfarin treated and 81/1236 control patients, an incidence of 1.4% and 4.5% per year, respectively; stroke was reduced by 68% (95% CI 50% to 79%). [5] Warfarin prevented 3.1 strokes per 100 patients treated per year, at a cost of 0.3 major haemorrhages (mainly gastrointestinal). [5] The costs of screening and medical care are probably outweighed by the costs of strokes prevented, provided that screening is not taken as an opportunity for additional unevaluated investigations. [7] Overall, the screening and treatment of AF is an effective strategy for reducing the incidence of stroke in the population; it could prevent about 12% of all strokes (0.17 x 0.68). The National Screening Committee’s objections to screening for AF The committee based their decision not to screen for AF on the premise that people with asymptomatic AF, who would be detected through screening, may have a lower risk of stroke than people with symptomatic AF. They cited, as their most “useful” supporting evidence, data from the AFFIRM study, [8] stating that “the authors [of the AFFIRM study] did not take account of the greater number of patients with a history of stroke or transient ischaemic attack (TIA) among the group with asymptomatic AF (17% vs. 13%), and correction for this difference at baseline would further reduce the apparent risks associated with asymptomatic AF.” To propose that the higher incidence of TIA and stroke in the asymptomatic group can be used to demonstrate that they have a lower risk of stroke is not logical. Indeed the authors of this paper concluded that “The absence of symptoms and the differences in treatment does not confer a more favourable prognosis when differences in baseline clinical parameters are considered. Anticoagulation should be considered in these patients.” Most doctors would manage patients with AF similarly, whether they were identified because of symptoms (such as palpitations) or were asymptomatic and would not withhold anticoagulation because AF had been detected incidentally. The NSC has said that the screening test for AF needs to be improved. However, there are now a number of widely available technologies that allow simple and automated recording of an ECG (such as a hand-held mobile phone attachment that automatically transmits an ECG to a secure site for interpretation) that could, and have been used as screening methods. [9] They also raise concerns that screening might miss atrial flutter but this does not justify a policy of not screening for AF. Moreover, it is rare for a patient with atrial flutter to present without symptoms and even if they did, an ECG would detect atrial flutter as well as AF. The NSC points out that many patients with a known diagnosis of AF are poorly managed. While it is true that anticoagulation rates for those at highest risk are inadequate, this is improving and is not a reason to rule against screening. Education and publicity campaigns have improved AF management as has the introduction of novel oral anticoagulants. Any screening programme would need to be coupled with an effective and safe anticoagulation service. Conclusion The risk of stroke is about 1 in 20 per year among people with AF aged 65 and this risk increases with age. Anticoagulation reduces the risk of stroke by about two thirds. There is no evidence to suggest a material difference in the risk of stroke or in the protective effects of anticoagulation between people who would be detected through screening and people who are diagnosed because of symptoms. For this reason we believe that it is now time to offer all people with AF the opportunity to reduce their stroke risk, and a national screening policy should be specified. References
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