Myocardial infarction, commonly known as a heart attack, occurs when blood flow stops to a part of the heart causing damage to the heart muscle. ST-elevation myocardial infarctions are the most severe types of heart attacks. They are usually due to an acute plaque rupture within the coronary arteries and the chance of dying from this type of heart attack is the highest. The most common symptom of myocardial infarction is chest pain or discomfort which may travel into the shoulder, arm, back, neck, or jaw. About 30% of people have symptoms, with women more likely than men to present. Among those over 75 years old, about 5% have had an myocardial infarction with little or no history of symptoms.
Now, a study from researchers at the University of Manitoba has shown that cold weather is associated with a higher risk of severe heart attack. The team state that their six year study found that each 10°C drop in temperature was associated with a 7% increased risk of ST-elevation myocardial infarction (STEMI), the most severe form of heart attack. The group presented their findings at the ESC Congress 2015.
Previous studies have looked at the effects of climate on total heart attack admissions and cardiac death. However, it is unclear which class of heart attacks were included, with the diagnostic criteria for STEMI unchanged in the last 20 years. The lab state that they are the first to look specifically at STEMI, which is known to be the most dangerous type of heart attack. They go on to add that this also allowed them to be consistent with case definition over the course of the study.
The current study investigated the effects of temperature on the risk of heart attacks in Winnipeg, Canada, one of the coldest large cities in the world. The results show that there is a clear relationship between daily temperature and the risk of STEMI, with the risk predicted up to two days before the actual heart attack. Increased public awareness and reallocation of resources may help us to respond to this predictable seasonal risk of heart attacks in the future.
The lab explain that Winnipeg, a city of approximately 700 000 inhabitants in Manitoba, is in the geographic centre of Canada. They go on to add that it is known for its very cold winters and hot and dry summers, which allows the perfect opportunity to study the effect of temperature and the environment on cardiac events. The group performed a retrospective review of all ST-elevation myocardial infarctions in Winnipeg over the last six years. Data was collected from Environment Canada on daily high, low and average temperature of the day, previous day and two days before each heart attack. Information was also obtained on daily snowfall. Wind direction and humidity were not assessed. Some 32% of the days had a daily high temperature under 0oC, 38% were between 0-20oC and 31% were above 20oC.
Results show that during the six year period there were 1,817 ST-elevation myocardial infarctions, with the daily high the strongest predictor of STEMI. Data findings show that on days with a daily high less than 0oC, STEMI event rates were 0.94/day, compared to 0.78/day when the daily high was greater than zero degrees centigrade. In contrast, the group observed that warmer temperature ranges were not associated with higher STEMI rates and with every drop of 10oC in the daily high, the risk of STEMI increased by seven percent.
The team surmise that their study highlights the potential influence of the environment on occurrence of STEMI, with daily temperatures predicting STEMI risk one or two days before it happens. For the future, the researchers state that these findings create an opportunity for studies to examine whether there are treatment strategies that can temper the effects of climate on the risk of heart attacks.
Source: University of Manitoba
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