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Stroke down

Study
Results
Treatments and risk factors
Comment

Bandolier 125 examined the evidence that changes in both medical treatments and lifestyles had contributed to the reduction in coronary heart disease in industrialised countries over recent decades. A new study in Oxfordshire [1] paints a similar picture for stroke.

Study

What we have is two studies. In 1981-84 the Oxford Community Stroke Project examined stroke in people registered with family doctors in Oxfordshire. The Oxford Vascular Study repeated the exercise for 2003-4, using similar methods. Both studies went to enormous lengths to identify strokes through collaboration with family doctors, computerised codes in the hospital serving the population, visits to neurology wards, vascular imaging lists, eye hospital referrals, coroner's office registers, and others.

Patients were assessed as soon after the event as possible, with a standard clinical history and examination, with scanning in every case. Diagnosis and clinical subtyping in the more recent study were as close as possible to those in the earlier study.

The most recent measurement of blood pressure was recorded, and total cholesterol measured at assessment of event. Surviving patients were followed up for 12 months and a disability score calculated (Bandolier 124).

Results

Both studies involved populations of about 90,000 under the care of about 65 family doctors, and each study had several hundred strokes or transient ischaemic attacks. The population was stable over the period of the two studies, with little difference in racial mix. Organisation of health care was similar in practice, even if labels kept changing.

Over the 20 years between the studies there was a significant ageing of the population. The proportion aged less than 35 years fell by nearly 8%, with increases in all older age groups for 2004 over 1984 (Figure 1). The incidence of first stroke fell in almost all of these age groups (Figure 2), particularly in the age range of 55 to 85 years.



Figure 1: Changes in age-structure of population between 1984 and 2004







Figure 2: Changes in crude stroke incidence between 1984 and 2004





Significant reductions in stroke incidence for 2004 compared with 1981-4 occurred overall, in men and women, and in all patients aged less than 85 years. Significant reductions occurred in ischaemic and haemorrhagic stroke, but not subarachnoid haemorrhage. Strokes in 2004 were significantly less severe than those occurring in 1981-4.

Overall stroke incidence fell by about 30% between 1981-4 and 2004. On the basis of the demographic changes with an older population, extrapolating 1981-4 stroke incidence to 2004 would have predicted an increase in stroke incidence of about 30%.

Treatments and risk factors

There were large changes in both pre-morbid treatments and risk factors for people with an incident stroke and those with incident transient ischaemic attack (Table 1). Compared with 1981-4, in 2004 many more patients were receiving anti-hypertensives, antiplatelets, and lipid lowering agents.



Table 1: Percentage of pre-morbid treatments and risk factors in persons with incident stroke or TIA in 1984 or 2004



Treatment/risk factor
Incident stroke
Incident TIA
1981-84
2004
1981-84
2004
Anti-hypertensive
20
47
no data
46
Antiplatelet
3
34
5
38
Lipid lowering agent
0
11
0
22
Mean cholesterol over 6.0 mmol/L
58
30
67
36
Systolic BP over 150 mmHg
61
46
67
45
Diastolic BP over 85 mmHg
59
40
56
35
Current smoker
33
18
31
15


Risk factors were also lower. Fewer people had high cholesterol or blood pressure, or were current smokers. Compared with 1981-4, average cholesterol levels in those with a first event were lower by about 1 mmol/L, mean systolic blood pressure by about 10 mmHg, and mean diastolic blood pressure by about 6 mmHg.

Comment

This detailed study took an in-depth look at stroke incidence in Oxfordshire. Because of an ageing population, more strokes would have been expected. Fewer occurred. Both treatment of pre-morbid conditions, and improved risk factors contributed, but how much by each is not clear. Oxfordshire probably does as well as most places in implementation of preventative medicine, and many people have taken on board healthy living advice. Together these have resulted in reducing the number of strokes in the population of 2004 by about 55 per 100,000 people over what would have been expected without them. This is beginning to look like good value.

Reference:

  1. PM Rothwell et al. Change in stroke incidence, case fatality, severity, and risk factors in Oxfordshire, UK from 1981 to 2004 (Oxford Vascular Study). Lancet 2004 363: 1925-1933.

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