Long-term trends in incidence and risk factors for ischaemic stroke subtypes: Prospective population study of the South London Stroke Register

Abstract

Background: As the average life expectancy increases, more people are predicted to have strokes. Recent studies have shown an increasing incidence in certain types of cerebral infarction. We aimed to estimate time trends in incidence, prior risk factors, and use of preventive treatments for ischaemic stroke (IS) aetiological subtypes and to ascertain any demographic disparities.

Methods and findings: Population-based data from the South London Stroke Register (SLSR) between 2000 and 2015 were studied. IS was classified, based on the underlying mechanism, into large-artery atherosclerosis (LAA), cardio-embolism (CE), small-vessel occlusion (SVO), other determined aetiologies (OTH), and undetermined aetiologies (UND). After calculation of age-, sex-, and ethnicity-specific incidence rates by subtype for the 16-year period, we analysed trends using Cochran-Armitage tests, Poisson regression models, and locally estimated scatterplot smoothers (loess). A total of 3,088 patients with first IS were registered. Between 2000-2003 and 2012-2015, the age-adjusted incidence of IS decreased by 43% from 137.3 to 78.4/100,000/year (incidence rate ratio [IRR] 0.57, 95% CI 0.5-0.64). Significant declines were observed in all subtypes, particularly in SVO (37.4-18; p < 0.0001) and less in CE (39.3-25; p < 0.0001). Reductions were recorded in males and females, younger (<55 years old) and older (≥55 years old) individuals, and white and black ethnic groups, though not significantly in the latter (144.6-116.2; p = 0.31 for IS). A 4-fold increase in prior-to-stroke use of statins was found (adjusted odds ratio [OR] 4.39, 95% CI 3.29-5.86), and despite the increasing prevalence of hypertension (OR 1.54, 95% CI 1.21-1.96) and atrial fibrillation (OR 1.7, 95% CI 1.22-2.36), preventive use of antihypertensive and antiplatelet drugs was declining. A smaller number of participants in certain subgroup-specific analyses (e.g., black ethnicity and LAA subtype) could have limited the power to identify significant trends.

Conclusions: The incidence of ISs has been declining since 2000 in all age groups but to a lesser extent in the black population. The reported changes in medication use are unlikely to fully explain the reduction in stroke incidence; however, innovative prevention strategies and better management of risk factors may contribute further reduction.

Fig 1. Standardised† annual incidences per 100,000 per year (95% CI) of first ISs over time, stratified by sex, ethnicity, and age groups.

† To the 2011 census population of England and Wales. Complete information for other periods is available in Table C in S1 Appendix. IRR, incidence rate ratio; IS, ischaemic stroke.

Fig 2. Trends in the age-standardised† annual incidence per 100,000 per year for first-ever ISs by sex, ethnicity, and age.

† To the 2011 population of England and Wales. p-Values were obtained from the Cochran-Armitage tests for trend. * denotes significant trends (p < 0.05). CE, cardio-embolism; IS, ischaemic stroke; LAA, large-artery atherosclerosis; OC, other causes; SVO, small-vessel occlusion.

Fig 3

Trends in standardised† incidences per 100,000 per calendar year for IS aetiological subtypes; (A) overall, (B) by sex, (C) by ethnicity, and (D) by age groups. † To the 2011 census population of England and Wales. Data are the observed values with regression fitted lines (loess). p-Values were obtained from the Cochran-Armitage tests for trend. * denotes significant trends (p < 0.05). CE, cardio-embolism; IS, ischaemic stroke; LAA, large-artery atherosclerosis; loess, locally estimated scatterplot smoothers; SVO, small-vessel occlusion; UND, undetermined aetiologies.

Fig 4. Prior risk factors and medication use over time in patients with incident first-ever IS.

p-Values were obtained by the Cochran-Armitage tests for trend and are presented for the unadjusted rates. * denotes significant trends (p < 0.05). † adjusted for age, sex, and ethnicity, allowing for interaction between time and ethnicity as appropriate. IS, ischaemic stroke.

Fig 5. Multiply adjusted† changes in risk factor profile in first-ever IS patients (with reference to 2000–2003 index cases).

Data are OR (95% CI). † for age, sex, ethnicity, and possible interaction between time and ethnicity as appropriate, after multiple imputation of missing values. IS, ischaemic stroke; OR, odds ratio; TIA, transient ischaemic attack.