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Prevalence of AF in the UK

 

Clinical bottom line

About 1 in 20 people aged 65 years or older have AF (4.7%). Anticoagulants were least used among elderly women, who may be the most likely to benefit.


Reference

M Sudlow et al. Prevalence of atrial fibrillation and eligibility for anticoagulants in the community. Lancet 1998 352: 1167-1171.

Study

The study was carried out in 26 practices in Northumberland. 4,800 patient aged 65 years or older were invited to a centre for screening electrocardiograms to identify patients with AF. Blood pressure was also measured and a questionnaire on stroke risk factors and contraindications for anticoagulant therapy completed. Patients with AF were invited for a second visit for echocardiography. Home visits were offered for those unable to come to a centre.

Results

AF was found in 228 patients, a prevalence of 4.7%. It was 10% in men aged 75 and older, and 5.6% in women aged 75 and older.

Who was on warfarin?

One in four of these patients (23%) were on warfarin. What proportion should have been on warfarin was calculate from risk factors and contraindications. The estimates from three different calculations ranged from 41% to 61%. Women aged 75 years or more were most likely to be untreated. Only 12% were on warfarin, yet the three estimates were 50% to 68%.

How many had contraindications?

Contraindications to warfarin treatment are shown in Table 1. History of bleeding was uncommon, and at the expected level of about 1%. More frequently represented were uncontrolled hypertension, a history of falling, being unable to comply with treatment and daily use of NSAIDs.

Table 1: Contraindications to warfarin treatment in patients with AF

Contraindication

Percent affected

Uncontrolled hypertension (>180/100 mmHg)

14.0

Frequent falls or blackouts

13.2

Inability to comply with treatment

9.8

Daily use of NSAIDs

9.2

GI or urinary bleeding in last six months

1.0

How many had risk factors?

The proportions who had risk factors are shown in Table 2. Hypertension history, current systolic hypertension and a history of stroke or TIA were the major clinical risk factors represented. Increased left atrial size was the largest found on echocardiography.

Table 2: Risk factors for stroke in patients with AF

Criterion

Percent positive

Clinical

Hypertension current or previous

57

Current systolic hypertension

30

Previous stroke or TIA

20

Diabetes

10

History of uncontrolled heart failure

8

Echocardiogram

Increased left atrial size

61

Global left ventricular dysfunction

28

Functional shortening <25%

4

Rheumatic mitral stenosis

2

Comment

This large study had high response rates, and there was no apparent non-response bias, where patients responding are different from those not responding to questionnaires. It showed that fewer patients were being treated than was justified on the clinical evidence, and that this was particularly true for older women.

The authors calculated that of the 21,000 strokes annually in patients with AF, 3,000 are probably prevented by anticoagulation, but that another 3,000-5,000 could be prevented if there was wider use of anticoagulant therapy.