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Cold fronts trigger heart attacks, study finds
Scripps Howard News Service


July 04, 2005

While you're enjoying not having to shovel snow this month, consider this: It may be dramatic changes in air pressure that accompany winter storms rather than the cold or snow that trigger more heart attacks during the winter.

"It's not shoveling snow. It's the snowstorm,'' said Dr. Philip Houck, co-chairman of the cardiology division at Scott and White Hospital and the Texas A&M College of Medicine and lead author of a new study on the phenomenon.

Writing in the July issue of the American Journal of Cardiology, Houck and colleagues showed a time-delayed relationship between drops in barometric pressure and the occurrence of heart attacks.

"My experience taking care of patients over the years told me that the day after a major weather event, like a thunderstorm, we would see a cluster of heart attacks. Our study now shows that a relationship does exist,'' Houck said.

Looking at records of patients in central Texas spanning three years, and comparing them against weather records, Houck found that the number of heart attacks increased within 24 hours of an atmospheric pressure drop.

"The more the pressure falls, the greater the chance someone has of having a heart attack the next day,'' Houck said. "If the pressure drops one unit (on the barometer), the risk of heart attacks is 10 percent greater the next day; with two units, there is a 20 percent greater chance."

Other studies have shown seasonal variations in heart attacks, with increased numbers during the winter months.

One French study published last year showed an increase in heart attacks among people with high blood pressure both from a drop in temperature or a shift of air pressure, but noted the peak in heart attacks came from passage of a cold front, or high-pressure system, rather than low-pressure warm fronts.

Houck suggests that the winter months may be harder on the heart because there's a greater variation in atmospheric pressure during the winter than in other seasons of year.

Houck said there have been various suggestions that the cold affects blood cell counts, blood pressure or blood-clotting chemicals to increase incidence of heart attacks in the winter, but he said those factors were unlikely to explain what he found among people living with the relatively mild winter temperatures of central Texas.

The study also looked at stroke patients, but found no relationship with atmospheric pressure changes.

"This makes sense,'' Houck said. "The coronary artery in the chest is exposed to atmospheric pressure through breathing. But the carotid artery in the neck, which is involved with stroke, is more sheltered."


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