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      Performance of stroke risk scores in older people with atrial fibrillation not taking warfarin: comparative cohort study from BAFTA trial

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          Abstract

          Objective To compare the predictive power of the main existing and recently proposed schemes for stratification of risk of stroke in older patients with atrial fibrillation.

          Design Comparative cohort study of eight risk stratification scores.

          Setting Trial of thromboprophylaxis in stroke, the Birmingham Atrial Fibrillation in the Aged (BAFTA) trial.

          Participants 665 patients aged 75 or over with atrial fibrillation based in the community who were randomised to the BAFTA trial and were not taking warfarin throughout or for part of the study period.

          Main outcome measures Events rates of stroke and thromboembolism .

          Results 54 (8%) patients had an ischaemic stroke, four (0.6%) had a systemic embolism, and 13 (2%) had a transient ischaemic attack. The distribution of patients classified into the three risk categories (low, moderate, high) was similar across three of the risk stratification scores (revised CHADS 2, NICE, ACC/AHA/ESC), with most patients categorised as high risk (65-69%, n=460-457) and the remaining classified as moderate risk. The original CHADS 2 (Congestive heart failure, Hypertension, Age ≥75 years, Diabetes, previous Stroke) score identified the lowest number as high risk (27%, n=180). The incremental risk scores of CHADS 2, Rietbrock modified CHADS 2, and CHA 2DS 2-VASc (CHA 2DS 2-Vascular disease, Age 65-74 years, Sex) failed to show an increase in risk at the upper range of scores. The predictive accuracy was similar across the tested schemes with C statistic ranging from 0.55 (original CHADS 2) to 0.62 (Rietbrock modified CHADS 2), with all except the original CHADS 2 predicting better than chance. Bootstrapped paired comparisons provided no evidence of significant differences between the discriminatory ability of the schemes.

          Conclusions Based on this single trial population, current risk stratification schemes in older people with atrial fibrillation have only limited ability to predict the risk of stroke. Given the systematic undertreatment 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 “high risk” until better tools are available.

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          Most cited references26

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          CIRCULATION

          K Nielsen (1972)
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            A risk score for predicting stroke or death in individuals with new-onset atrial fibrillation in the community: the Framingham Heart Study.

            Prior risk stratification schemes for atrial fibrillation (AF) have been based on randomized trial cohorts or Medicare administrative databases, have included patients with established AF, and have focused on stroke as the principal outcome. To derive risk scores for stroke alone and stroke or death in community-based individuals with new-onset AF. Prospective, community-based, observational cohort in Framingham, Mass. We identified 868 participants with new-onset AF, 705 of whom were not treated with warfarin at baseline. Risk scores for stroke (ischemic or hemorrhagic) and stroke or death were developed with censoring when warfarin initiation occurred during follow-up. Event rates were examined in low-risk individuals, as defined by the risk score and 4 previously published risk schemes. Stroke and the combination of stroke or death. During a mean follow-up of 4.0 years free of warfarin use, stroke alone occurred in 83 participants and stroke or death occurred in 382 participants. A risk score for stroke was derived that included the following risk predictors: advancing age, female sex, increasing systolic blood pressure, prior stroke or transient ischemic attack, and diabetes. With the risk score, 14.3% of the cohort had a predicted 5-year stroke rate < or =7.5% (average annual rate < or =1.5%), and 30.6% of the cohort had a predicted 5-year stroke rate < or =10% (average annual rate < or =2%). Actual stroke rates in these low-risk groups were 1.1 and 1.5 per 100 person-years, respectively. Previous risk schemes classified 6.4% to 17.3% of subjects as low risk, with actual stroke rates of 0.9 to 2.3 per 100 person-years. A risk score for stroke or death is also presented. These risk scores can be used to estimate the absolute risk of an adverse event in individuals with AF, which may be helpful in counseling patients and making treatment decisions.
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              Mortality trends in patients diagnosed with first atrial fibrillation: a 21-year community-based study.

              The purpose of this study was to assess the mortality trends of atrial fibrillation (AF) in a community. Limited data exist regarding the mortality trends of patients diagnosed with first AF. A community-based cohort of adult residents of Olmsted County, Minnesota, who had electrocardiogram-confirmed first-documented AF in the years 1980 to 2000 were identified and followed to 2004 or death. The primary outcome was all-cause mortality. Of a total of 4,618 residents (mean age 73 +/- 14 years) diagnosed with first AF, 3,085 died during a mean follow-up of 5.3 +/- 5.0 years. Relative to the age- and gender-matched general Minnesota population, the mortality risk was increased (p < 0.0001) with a hazard ratio (HR) of 9.62 (95% confidence interval [CI] 8.93 to 10.32) within the first 4 months and 1.66 (95% CI 1.59 to 1.73) thereafter. Cox proportional hazards modeling showed no change in overall age- and gender-adjusted mortality (HR for the year 2000 vs. 1980: 0.99; 95% CI 0.86 to 1.13; p = 0.84), even after adjustment for comorbidities. In secondary analyses, no changes in mortality were seen for early (within first 4 months) or late (after 4 months) mortality for the entire group or within the subgroup of patients who did not have cardiovascular disease at baseline. In this cohort of patients newly diagnosed with AF, mortality risk was high, especially within the first 4 months. There was no evidence for any significant changes over the 21 years in terms of overall mortality, early or late mortality, or mortality among patients without pre-existing cardiovascular disease.
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                Author and article information

                Contributors
                Role: professor and head of department
                Role: senior lecturer in medical statistics
                Role: consultant cardiologist
                Role: research fellow
                Role: professor of primary care
                Role: professor of cardiovascular research
                Journal
                BMJ
                bmj
                BMJ : British Medical Journal
                BMJ Publishing Group Ltd.
                0959-8138
                1468-5833
                2011
                2011
                23 June 2011
                : 342
                : d3653
                Affiliations
                [1 ]Department of Primary Care Health Sciences, University of Oxford, Oxford OX1 2ET, United Kingdom
                [2 ]Primary Care Clinical Sciences, Primary Care Clinical Sciences Building, University of Birmingham, Birmingham B15 2TT
                [3 ]University of Birmingham Centre for Cardiovascular Sciences, City Hospital, Birmingham B18 7QH
                [4 ]Department of General Practice, University of Cambridge, Cambridge
                Author notes
                Corresponding to: R D R Hobbs richard.hobbs@ 123456phc.ox.ac.uk and A K Roalfe roalfeak@ 123456bham.ac.uk
                Article
                hobf840322
                10.1136/bmj.d3653
                3121229
                21700651
                b9515824-6643-494e-98ed-02d08cdf2d29
                © Hobbs et al 2011

                This is an open-access article distributed under the terms of the Creative Commons Attribution Non-commercial License, which permits use, distribution, and reproduction in any medium, provided the original work is properly cited, the use is non commercial and is otherwise in compliance with the license. See: http://creativecommons.org/licenses/by-nc/2.0/ and http://creativecommons.org/licenses/by-nc/2.0/legalcode.

                History
                : 24 May 2011
                Categories
                Research
                Epidemiologic Studies
                Drugs: Cardiovascular System
                Heart Failure
                Stroke
                Hypertension
                Venous Thromboembolism

                Medicine
                Medicine

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