Secular trends in mortality by stroke subtype in the 20th century: a retrospective analysis

Since both cerebral infarction and coronary heart disease are caused by atherosclerosis, they would be expected to have similar secular trends in mortality. Because differential diagnosis of stroke subtype on routine death certificates is inaccurate, we aimed to estimate secular trends in cerebral infarct and haemorrhage throughout the 20th century, for England and Wales, with data from autopsy studies.

We calculated the ratio of cerebral infarct to cerebral haemorrhage from all available sources of autopsy data from the 20th century. These data were used to estimate the ratio of cerebral infarct to haemorrhage for every year, and hence to estimate rates of cerebral infarct and cerebral haemorrhage from the total stroke mortality rate, obtained from the UK Office for National Statistics.

Data about stroke subtypes from autopsies were available from 1932 to 1999. 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 secular trends suggested that there was a steady fall in mortality from cerebral haemorrhage throughout the 20th century, whereas mortality from cerebral infarct increased to a peak in the 1970s and then fell. Trends in estimated cerebral infarct mortality closely matched those for coronary heart disease mortality.

The closely related trends in cerebral infarct and coronary heart disease suggest common causes, but the very different trend in cerebral haemorrhage shows that its cause probably differs importantly from these conditions.