A randomised controlled trial and cost-effectiveness study of systematic screening (targeted and total population screening) versus routine practice for the detection of atrial fibrillation in people aged 65 and over. The SAFE study

Citation

(2006), "A randomised controlled trial and cost-effectiveness study of systematic screening (targeted and total population screening) versus routine practice for the detection of atrial fibrillation in people aged 65 and over. The SAFE study", Clinical Governance: An International Journal, Vol. 11 No. 2. https://doi.org/10.1108/cgij.2006.24811baf.002

A randomised controlled trial and cost-effectiveness study of systematic screening (targeted and total population screening) versus routine practice for the detection of atrial fibrillation in people aged 65 and over. The SAFE study

A randomised controlled trial and cost-effectiveness study of systematic screening (targeted and total population screening) versus routine practice for the detection of atrial fibrillation in people aged 65 and over. The SAFE studyF.D.R. Hobbs, D.A. Fitzmaurice, J. Mant, E. Murray, S. Jowett, S. Bryan, J. Raftery, M. Davies and G. Lip

Background

Atrial fibrillation (AF) is a major risk factor for stroke. This risk can be reduced through treatment with antithrombotic therapy, with a risk reduction of up to 68 per cent observed with warfarin therapy. Guidelines for treatment of AF recommend ages 65 years and over as an indication for treatment with antithrombotic therapy in the presence of AF. This raises the question of whether screening for AF would be a useful policy, and if so what would be the best method for screening. There are no good data on the prevalence of AF in the UK. One small UK study (four practices, n=3,001) demonstrated that systematic nurse-led screening detected more cases than opportunistic case finding; however, most of those cases detected were already diagnosed. Two further single practice-based studies investigated the role of practice nurses in the screening process and whole population screening, but were too small to be meaningful.

Objectives

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  To evaluate the incremental cost-effectiveness of targeted, population and opportunistic screening with prompts compared with routine clinical practice.

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  To evaluate the relative cost-effectiveness of different methods of recording and interpreting the ECG within a screening programme.

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  To identify the prevalence and incidence of AF in patients aged 65 years and over.

Methods

This multicentred randomised controlled trial involved patients aged 65 years and over from 50 primary care centres across the West Midlands. These purposefully selected general practices were randomly allocated to 25 intervention practices and 25 control practices. GPs and practice nurses in the intervention practices received education on the importance of AF detection and ECG interpretation. Patients in the intervention practices were randomly allocated to systematic (n=5,000) or opportunistic screening (n=5,000). Prospective identification of pre-existing risk factors for AF within the screened population enabled comparison between targeted screening of people at higher risk of AF and total population screening. AF detection rates in systematically screened and opportunistically screened populations in the intervention practices were compared with AF detection rate in 5,000 patients in the control practices. The screening period was 12 months.

Results

The total number of patients included in each arm was:

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  control 4,936;

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  opportunistic screening 4,933; and

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  systematic screening, 4,933.

Baseline prevalence of AF was 7.2 per cent, with a higher prevalence in males (7.8 per cent) and patients aged 75 years and over (10.3 per cent). The control population demonstrated higher baseline prevalence (7.9 per cent) than either the systematic (6.9 per cent) or opportunistic (6.9 per cent) intervention population. In the control population, 47 new cases were detected (incidence 1.04 per cent per year). In the opportunistic arm, 243 patients without a baseline diagnosis of AF were found to have an irregular pulse, with 177 having an ECG, yielding 31 new cases (incidence 0.69 per cent per year). A further 44 cases were detected outside the screening programme (overall incidence 1.64 per cent per year). In the systematic arm, 2,357 patients had an ECG, yielding 52 new cases (incidence 1.1 per cent per year). Of these, 31 were detected by targeted screening and a further 21 by total population screening. A further 22 cases were detected outside the screening programme (overall incidence 1.62 per cent per year).

In terms of ECG interpretation, computerised decision support software (CDSS) gave a sensitivity of 87.3 per cent, a specificity of 99.1 per cent and a positive predictive value (PPV) of 89.5 per cent compared with the gold standard (cardiologist reporting). GPs and practice nurses performed less well. The only difference in performance between intervention populations and controls was that practice nurses from the control arm performed less well than intervention practice nurses on interpretation of limb-lead (PPV 38.8 per cent versus 20.8 per cent) and single-lead (PPV 37.7 per cent versus 24.0 per cent) ECGs.

The within-trial economic evaluation results showed the lowest incremental cost to be for the opportunistic arm, with an incremental cost-effectiveness ratio of £337 for each additional case detected compared to the control arm. Opportunistic screening dominated both more intensive screening strategies. Model-based analyses showed small differences in cost and quality-adjusted life-years for different methods and intensities of screening, but annual opportunistic screening resulted in the lowest number of ischaemic strokes and greatest proportion of cases of AF diagnosed. Probabilistic sensitivity results indicated that there was a probability of approximately 60 per cent that screening from the age of 65 was cost-effective in both men and women.

Conclusions

The prevalence of AF in this population was found to be 7.2 per cent. The incidence ranged from 1.04 to 1.64 per cent per annum. Within the trial, in terms of a screening programme, the only strategy that improved on routine practice was opportunistic screening, at a cost of £337 per additional case detected. Model-based analyses indicated that there was a probability of approximately 60 per cent of annual opportunistic screening being cost effective. Use of CDSS may be considered for analysis of ECGs for detection of AF.

Recommendations for research

It is suggested that the following topics are worthy of further investigation:

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  How does the implementation of a screening programme for AF influence the uptake and maintenance of anticoagulation in patients aged 65 years and over?

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  An evaluation of the role of CDSS in the diagnosis of cardiac arrythmias.

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  What is the best method for routinely detecting paroxysmal AF?

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  How can healthcare professionals’ performance in ECG interpretation be best improved?

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  The development of a robust economic model to incorporate data on new therapeutic agents for use as thromboprophylactic agents for patients with AF.

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  An evaluation of the relative risk of stroke for patients with incident as opposed to prevalent AF.

©2005 Crown Copyright

(F.D.R. Hobbs, D.A. Fitzmaurice, J. Mant, E. Murray and S. Jowett are all based at the Department of Primary Care and General Practice, University of Birmingham, Birmingham, UK. S. Bryan and J. Raftery are based at the Health Economics Facility, University of Birmingham, Birmingham, UK. M. Davies is based at Selly Oak Hospital, Birmingham, Birmingham, UK. G. Lip is based at City Hospital, Birmingham, UK.)