Cold weather may increase stroke risk

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Cold weather is associated with an increased risk of stroke in patients with cardiac arrhythmia, according to a new large-scale study.
The study in nearly 290,000 patients suggests that cool climate may be an underrated issue for health that deserves more attention.
"Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and it increases the risk of ischaemic stroke by four- to five-fold," said Dr Tze-Fan Chao, cardiologist at Taipei Veterans General Hospital and the National Yang-Ming University in Taiwan.
"During AF, the electrical activity of the left atrium is disordered and the contraction is ineffective which results in stasis of blood in the atrium.

"The blood pools and becomes sluggish and can result in the formation of blood clots. If a clot leaves the heart and travels to the brain, it can cause a stroke by blocking the flow of blood through cerebral arteries," said Chao.
The autumn/winter season has been associated with a higher incidence and mortality rate of myocardial infarction, stroke and congestive heart failure, researchers said.

A greater plasma fibrinogen level and factor VII clotting activity in the winter have been reported as possible mechanisms, they said.
"The elevation and activation of these coagulation factors may lead to a pro-coagulant status in cool climates which may promote the formation of blood clots within the left atrium and increase the risk of stroke for AF patients," said Chao.

The study investigated this issue in 289,559 new-onset AF patients from the "National Health Insurance Research Database" in Taiwan during 2000 to 2011.
Among the Taiwan AF cohort, 34,991 patients suffered from an ischaemic stroke during the mean follow up of three years. The risk of ischaemic stroke was higher among the months with a lower average temperature.
In addition, the incidence of ischaemic stroke was highest in winter and lowest in summer. Compared to summer, the risk of ischaemic stroke increased by 10 per cent in spring and 19 per cent in winter. Stroke risk did not differ significantly between summer and autumn.

"Our study shows a clear association between temperature and risk of ischaemic stroke in patients with AF. Risk may increase in cold weather because of the pro-coagulant status," said Chao.
"This suggests that there may be an opportunity to predict strokes in AF patients before they happen and put preventative measures in place such as adequate anticoagulants and reducing cold exposure through protective clothing and heating homes in winter," Chao said.
When the average temperature was below 20 degrees Celsius the risk of ischaemic stroke significantly increased compared to days with an average temperature of 30 degrees Celsius.
"This may be because of the increased coagulability and plasma viscosity," said Chao.