A recent study by Québec researchers found that heavy snowfalls are correlated with an increase in hospital admissions for myocardial infarction (MI), or heart attack.

MI occurs due to prolonged cardiac ischemia, the blockage of a coronary artery, which inhibits the flow of oxygenated blood to the heart muscle.

To investigate MI occurrences, the researchers incorporated information from two databases, concerning 128,073 hospital admissions and 68,155 deaths from heart attack between 1981 and 2014 in Québec. They refined their search based on some factors, such as the prominence of snowfall between the months of November and April.

Environment Canada provided the team with weather information about the different regions being evaluated in the study. Dr. Natalie Auger of the University of Montreal Hospital Research Centre then combined this information to provide a detailed and complementary model of the association between time of snowfall and heart attack-associated deaths.

The researchers came to the conclusion that the combination of physical stress exerted on the body and the aerobic demand of shoveling snow was most likely to explain the link between snowfall and higher hospital admission rates due to MI.

The correlation found was directly proportional, meaning that an increase in amount of snow lead to an increased amount of hospital admissions or death caused by MI.

Men were more likely to be subject to heart attack following snowfall, accounting for 60 per cent of hospital admissions and MI-related deaths, as they are “more likely to shovel” snow compared to women, the study found. One of the results of the study indicated that a snowfall of 20 cm was associated to a 34 per cent increased risk of heart attack death in men.

The researchers noted certain factors that could potentially confound aspects of their interpreted results. These factors included the size of areas shoveled, the manner in which snow was shoveled (manually or with a snow blower), and other relevant and underlying symptoms of the patient.

The study recommended that individuals be conscious of the risks involved in the strenuous act of shoveling snow, especially during heavier and longer snowfall. They advise Canadians to shovel as soon as possible, as snow would be lighter. Moreover, shoveling lighter amounts of snow periodically during prolonged snowfall instead of a heavier amount after several hours is a wiser approach and can prevent profound cardiovascular consequences.

“The research is interesting and not at all surprising,” said Dr. Paul Dorian, the Division of Cardiology Department Director at U of T and Staff Cardiac Electrophysiologist at St. Michael’s Hospital, “What is missing is the absolute risk of MI, not the relative risk of MI.”

Dorian that the results merely reveal an association between snowfall and heart attack risk or MI — not causation. An absolute risk of MI is ultimately fixed and nonrelative, that is to say, not related to other factors. On the other hand, a relative risk is viewed as related or associated with other existing factors. Thus, if this independent risk of MI is of small value, Dorian says there is “no need to worry and no need to buy a snowblower.”

He added, “Yes, some people are at risk of MI if they shovel, but they are also at risk if they climb stairs. It is about absolute risk, not relative risk.”

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