How Common Are Heart Attacks From Shoveling Snow?

Safety Tips to Reduce Your Risk

shoveling snow
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Anyone working in an emergency department in a northern climate knows that on days when it snows heavily, they will not be seeing any down time—they will be running non-stop during their entire shifts. It’s pretty likely they will see at least a few people injured in snow-related car crashes, or in sledding or skiing accidents. 

But it’s virtually certain they will be inundated with people who have developed sudden medical problems caused by shoveling snow.

And to deal with these shoveling-related medical problems they will have at least two kinds of medical specialists on speed dial. The first, of course, is the orthopedic surgeon, who will find him/herself booked for several days treating back injuries, hip injuries, twisted ankles, torn rotator cuffs, and ruptured biceps.

The second specialist on speed dial is the cardiologist. In fact, any cardiology department worth its salt will have already fully staffed and fired up the catheterization laboratory. Because as it turns out, shoveling snow is an extremely efficient way to precipitate a heart attack in people who have any degree of coronary artery disease (CAD).

How Often Do Shoveling-Related Heart Attacks Occur?

Heart attacks that occur while shoveling snow are distressingly common. 

In a study published in 2012, investigators looked at 500 patients who were treated for acute coronary syndrome (ACS) over two consecutive winters.

They found that 7 percent of these cardiac emergencies were directly related to snow-shoveling. Further, they found that being male and having a family history of premature heart disease were each strongly associated with ACS caused by shoveling snow.

In a study from Canada published in 2017, researchers compared hospital admission records and death certificates for residents of Quebec with an extensive weather database, for the years 1981 through 2013.

During this period, over 128,000 heart attacks and 68,000 deaths due to heart attack occurred. Remarkably, fully one-third of the heart attacks occurred the day after a substantial snowfall. Furthermore, they found a “dose-response trend”—that is, the more it snowed (the deeper the snow, or the more consecutive days it snowed) the higher the incidence of heart attacks. In this study, outdoor temperatures were not associated with an increased incidence of heart attacks, but the level of snowfall was strongly correlated. 

As with virtually every other study looking at snow-shoveling and heart attacks, the 2017 Canadian study also found an association only with men, and not with women. 

Why Does Shoveling Snow Precipitate Heart Attacks?

Shoveling snow places unusual stress on the cardiovascular system. This cardiac stress can trigger a heart attack in a person with underlying CAD. When shoveling snow, several factors work together to produce greatly increased cardiovascular stress. 

For one thing, shoveling itself involves strenuous arm exercise. Arm exercise notoriously places more stress on the cardiovascular system than leg exercise. In fact, studies in healthy young men show that when they shovel snow, they reach heart rates and blood pressure levels that are substantially higher than when they perform treadmill exercise.

And when the snow is deep or heavy, the work of shoveling becomes proportionally greater.

When people lift a heavy shovelful of snow, most will naturally hold their breaths, producing a Valsalva effect. This Valsalva effect acutely increases the blood pressure even higher during moments of maximum work. 

Shoveling snow, by definition, is a cold weather exercise. And in cold weather, vasoconstriction (narrowing of the blood vessels) occurs in the small blood vessels, which also increases blood pressure and produces significant cardiac stress. Furthermore, breathing in cold air can constrict the airways and make it more difficult to deliver the extra oxygen the heart needs during periods of excessive stress.

Cold temperatures themselves can provoke spasm of certain arteries—even coronary artery spasm—in some people. 

To make matters worse, most people shovel snow in the morning, when they are concerned with getting out of the house and going about their daily business. This means two things. First, snow-shovelers tend to be in a hurry, so in their rush to get out of the driveway they exert themselves more than they might otherwise do. Second, they are trying to do all this extra work during a time when their circadian rhythms make them more prone to cardiovascular catastrophes. Adding a bout of vigorous snow-shoveling at this particular time of day can turn out to be a very bad thing.

Who Is Prone to Heart Attacks While Shoveling Snow?

Anyone with any degree of CAD is at higher risk of an acute cardiac event while shoveling snow. This risk goes up substantially in people who are generally sedentary and deconditioned.

We should note explicitly that most people who have CAD don’t know it. People who know they have CAD, in general, have already had symptoms of one kind or another (most often angina), that has led to a diagnostic evaluation. In general, these people already know that shoveling snow places them at risk, and they are reasonably likely to avoid doing so. 

The majority of people who have heart attacks while shoveling snow don’t know that they have CAD. What they do know (or ought to) is that they have risk factors for CAD, such as diabeteshypertension, smoking, elevated cholesterol, or being overweight, sedentary, or over 55 or 60 years of age. Cardiologists have come to believe that the large majority of people over 55 or so, who also have a couple of these other risk factors, do indeed have at least a little CAD.

If you know you have CAD, or you have one or two of these risk factors, and especially if you are a man, you need to be extremely careful about shoveling snow. At the very least, snow shoveling constitutes an episode of significant stress for your cardiovascular system. The deeper and/or heavier the snow, and the larger the area you have to shovel, the higher your risk.

What About Women?

As noted, studies that have looked at the relationship of snow shoveling and heart attacks have found the risk to be elevated in men, but not in women. While it is certainly possible that snow shoveling actually may be less dangerous for women, it seems more likely that the studies have turned out this way simply because men are far more likely to go out to do the shoveling. However, possibly because it has become politically incorrect to even speculate about such things as sex-related snow-shoveling habits, researchers as yet have not attempted to collect this kind of data. Shoveling snow is probably just as dangerous in women, but we can’t say so with any confidence.

So until the appropriate data is collected, the most conservative advice for women would be to consider snow shoveling to be just as serious a risk as it is in men. 

Reducing Your Snow-Shoveling Risk

There is no way around the fact that shoveling snow produces tremendous stress on the cardiovascular system. The very best advice for reducing your risk is simply to avoid shoveling snow if you have CAD, or one or two risk factors for CAD—especially if you are a man over 55 years of age or so. If this is you, the best course would be to hire a service to clean your driveway and your walk. It may be expensive, but it’s cheaper than a heart attack.

If you are going to shovel snow despite this excellent advice, you should do everything you can to reduce the acute cardiovascular stress you are creating for yourself. 

The best thing you can do is to exercise regularly in order to build up your exercise tolerance. Maintaining good cardiovascular fitness will allow you to shovel snow while producing less (though still substantial) cardiac stress. But if you’re looking at a foot of snow on your driveway right now, this advice may not apply. So pay the neighbor kid $25 to do the job today, then get into shape for next winter.

If you still insist on shoveling yourself, try to wait until later in the day when your circadian rhythms are in a less malignant phase and the temperatures outside are likely to moderate a bit. Cover your mouth with a scarf to warm the air you breathe. Pace yourself. Do the job in two, three, or four separate outings instead of all at once, and warm up and hydrate (and reconsider your plans) in between.

And if shoveling produces any symptoms at all—especially chest discomfort, lightheadedness, or shortness of breath—just stop what you’re doing. Your concern is not the snow anymore, it’s that you need to see a doctor. Let’s stop shoveling right now and have you see a doctor before (and not after) you’ve done permanent damage to your heart—or worse.

Sources:

Alter DA. The Eco-Biological-Behavioural Perfect Storm that Follows Heavy Snowfall. CMAJ 2017; 189:E22522-6.

Auger N, Potter BJ, Smargiassi A, et al. Association Between Quantity and Duration of Snowfall and Risk of Myocardial Infarction. CMAJ 2017; 189:E235-242. Abstract

Nichols RB, McIntyre WF, Chan S. et al. Snow-shoveling and the Risk of Acute Coronary Syndrome. Clinical Research in Cardiology 2012;101:11-15.

 

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