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

BMJ 2011; 342 doi: https://doi.org/10.1136/bmj.d3653 (Published 23 June 2011) Cite this as: BMJ 2011;342:d3653
  1. F D R Hobbs, professor and head of department1,
  2. A K Roalfe, senior lecturer in medical statistics2,
  3. G Y H Lip, consultant cardiologist3,
  4. K Fletcher, research fellow2,
  5. D A Fitzmaurice, professor of primary care2,
  6. J Mant, professor of cardiovascular research4
  7. on behalf of the Birmingham Atrial Fibrillation in the Aged (BAFTA) investigators and Midland Research Practices Consortium (MidReC) network
  1. 1Department of Primary Care Health Sciences, University of Oxford, Oxford OX1 2ET, United Kingdom
  2. 2Primary Care Clinical Sciences, Primary Care Clinical Sciences Building, University of Birmingham, Birmingham B15 2TT
  3. 3University of Birmingham Centre for Cardiovascular Sciences, City Hospital, Birmingham B18 7QH
  4. 4Department of General Practice, University of Cambridge, Cambridge
  1. Corresponding to: R D R Hobbs richard.hobbs{at}phc.ox.ac.uk and A K Roalfe roalfeak{at}bham.ac.uk
  • Accepted 24 May 2011

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 CHADS2, 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 CHADS2 (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 CHADS2, Rietbrock modified CHADS2, and CHA2DS2-VASc (CHA2DS2-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 CHADS2) to 0.62 (Rietbrock modified CHADS2), with all except the original CHADS2 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.

Footnotes

  • We are grateful to all the 260 MidReC BAFTA trial investigators listed in the original paper who recruited participants and to the patients who took part.

  • Contributors: RH, JM, GYHL, and DAF conceived the study. RDRH and AKR wrote the first draft, and the paper was edited by all authors. AKR did the statistical analysis. All authors interpreted the data, critically revised the draft, and gave approval for the paper to be published. RDRH is guarantor.

  • Funding: BAFTA was funded by the Medical Research Council, grant G9900264, with additional Service Support funding from the National Institute for Health Research (NIHR). The analyses in this paper were supported by Clinical Trial Unit core funding from the NIHR Health Technology Assessment and by the NIHR National School for Primary Care Research.

  • Competing interests: All authors have completed the Unified Competing Interest form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: no support from any organisation for the submitted work; GL has non-financial interests (author of the CHADS2-VASc score).

  • Ethical approval: Not required.

  • Data sharing: No additional data available.

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