Why trends in stroke death in 20th century appeared different to death from heart disease

Authors of a UK study published on THE LANCET's website-www.thelancet.com-report the trends in death due to stroke in England and Wales in the 20th century. Despite an overall decrease in deaths from all types of stroke since the 1930s, the study highlights how this overall reduction masks differences in trends between cerebral haemorrhage and cerebral infarct.

Stroke is usually categorised into two main subtypes-cerebrovascular haemorrhage (bleeding in the brain), and cerebral infarction (blockage of an artery to the brain). Stroke and coronary heart disease have similar risk factors and for a long time doctors have wondered why trends over time in stroke and coronary heart disease have been so different. There was an epidemic of coronary heart disease in the past century but no such epidemic in stroke deaths. As both cerebral infarct and coronary heart disease are caused by atherosclerosis, they should have similar trends in death rates over time; however, researchers have not been able to look at the trends in the two different stroke types.

Debbie Lawlor from the University of Bristol, UK, and colleagues estimated secular trends in cerebral infarct and haemorrhage throughout the 20th century, for England and Wales, with data from autopsy studies. Data were available from 1932 onwards. The ratio of cerebral infarct to cerebral haemorrhage increased fourfold from 0.5 in the 1930s to 2.0 by the 1990s; most of the increase took place between the 1930s and the 1970s. Estimated trends suggested that there was a steady fall in death from cerebral haemorrhage throughout the 20th century, whereas death from cerebral infarct increased to a peak in the 1970s and then fell. Trends in death from cerebral infarction closely matched those for coronary heart disease death over the same timeframe.

Debbie Lawlor comments: "These results resolve the paradoxical discordance between the epidemiology of stroke and that of coronary heart disease. The closely related trends in cerebral infarct and coronary heart disease suggest a common aetiology [cause] for these diseases, but the very different trend in cerebral haemorrhage shows that its aetiology must differ importantly from that of these conditions."

Contact:
Dr Debbie A Lawlor, Department of Social Medicine, University of Bristol, Canynge Hall, Whiteladies Road,
Bristol BS8 2PR, UK;
T) 44-117-928-7267;
F) 44-117-928-7292;
E) D.A.Lawlor@bristol.ac.uk

---

---