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Wednesday, May 12, 2010

Is heavy physical activity a major trigger of death by sudden cardiac arrest? Not in Oregon

The idea that heavy physical activity is a main trigger of heart attacks is widespread. Often endurance running and cardio-type activities are singled out. Some people refer to this as “death by running”.

Good cardiology textbooks, such as the Mayo Clinic Cardiology, tend to give us a more complex and complete picture. So do medical research articles that report on studies of heart attacks based on comprehensive surveys.

Reddy and colleagues (2009) studied sudden cardiac arrest events followed by death from 2002 to 2005 in Multnomah County in Oregon. This study was part of the ongoing Oregon Sudden Unexpected Death Study. Multnomah County has an area of 435 square miles, and had a population of over 677 thousand at the time of the study. The full reference to the article and a link to a full-text version are at the end of this post.

The researchers grouped deaths by sudden cardiac arrests (SCAs) according to the main type of activity being performed before the event. Below is how the authors defined the activities, quoted verbatim from the article. MET is a measure of the amount of energy spent in the activity; one MET is the amount of energy spent by a person sitting quietly.

- Sleep (MET 0.9): subjects who were sleeping when they sustained SCA.
- Light activity (MET 1.0–3.4): included bathing, dressing, cooking, cleaning, feeding, household walking and driving.
- Moderate activity (MET 3.5–5.9): included walking for exercise, mowing lawn, gardening, working in the yard, dancing.
- Heavy activity (MET score ≥6): included sports such as tennis, running, jogging, treadmill, skiing, biking.
- Sexual activity (MET score 1.3): included acts of sexual intercourse.

What did they find? Not what many people would expect.

The vast majority of the people dying of sudden cardiac arrest were doing things that fit the “light activity” group above prior to their death. This applies to both genders. The figure below (click to enlarge) shows the percentages of men and women who died from sudden cardiac arrest, grouped by activity type.


Sudden cardiac arrests were also categorized as witnessed or un-witnessed. For witnessed, someone saw them happening. For un-witnessed, the person was seen alive, and within 24 hours had died. So the data for witnessed sudden cardiac arrests is a bit more reliable. The table below displays the distribution of mean age, gender and known coronary artery disease (CAD) in those with witnessed sudden cardiac arrest.


Look at the bottom row, showing those with known coronary artery disease. Again, light activity is the main trigger. Sleep comes second. The numbers within parentheses refer to percentages within each activity group. Those percentages are not very helpful in the identification of the most important triggers, although they do suggest that coronary artery disease is a major risk factor. For example, among those who died from sudden cardiac arrest while having sex, 57 percent had known coronary artery disease. For light activity, 36 percent had known coronary artery disease.

As a caveat, it is worth noting that heavy activity appears to be more of a trigger in younger individuals than in older ones. This may simply reflect the patterns of activities at different ages. However, this does not seem to properly account for the large differences observed in triggers; the standard deviation for age in the heavy activity group was large enough to include plenty of seniors. Still, it would have been nice to see a multivariate analysis controlling for various effects, including age.

So what is going on here?

The authors give us a hint. The real culprit may be bottled up emotional stress and sleep disorders; the latter may be caused by stress, as well as by obesity and other related problems. They have some data that points in those directions. That makes some sense.

We humans have evolved “fight-or-flight” mechanisms that involve large hormonal discharges in response to stressors. Our ancestors needed those. For example, they needed those to either fight or run for their lives in response to animal attacks.

Modern humans experience too many stressors while sitting down, as in stressful car commutes and nasty online interactions. The stresses cause “fight-or-flight” hormonal discharges, but are followed by neither “fight” nor “flight” in most cases. This cannot be very good for us.

Death by running!? More like death by not running!

Reference:

Reddy, P.R., Reinier, K., Singh, T., Mariani, R., Gunson, K., Jui, J., & Chugh, S.S. (2009). Physical activity as a trigger of sudden cardiac arrest: The Oregon Sudden Unexpected Death Study. International Journal of Cardiology, 131(3), 345–349.

6 comments:

Drs. Cynthia and David said...

I was reading once about "broken heart" syndrome, which is a real syndrome, despite the sappy name. It has to do with overstimulation of the heart with stress hormones from a severely stressful event, and has nothing to do with blockage of the artery from atherosclerosis or from physical activity per se. It looks like a heart attack though. If you don't actually do an autopsy, you might assume there was a blockage when in fact the loss of function was due to some other cause. Of course, excess physical activity might lead to excess stress hormones too, but the degree of increase is much less.

I thought your previous post about the J-curve relationship with running was pretty interesting too.

Thanks.

Cynthia

Ned Kock said...

Thank you. You have a great blog.

Coincidentally, I was reading the other day about this syndrome, a.k.a. takotsubo cardiomyopathy.

Anonymous said...

Good post. This relates to the comment that I made on the blood sugar post. I would love to know what happens (physiologically) to an individual when they are playing video games. I think this would be analogous to the road rage situation. Do you know of any studies where they looked at the physiological responses of individuals in these low energy expenditure states where catecholamines are elevated? It makes me think of the days when I was a teenager drinking soda, eating chips and playing first person shooters for hours on end.

Thanks
JC

Ned Kock said...

Hi JC.

I recalled our comment exchanges on the other post when I was writing this one, particularly the last part of the post.

Right now I don't recall any such study. But I am pretty sure that there is at least one out there.

What is difficult is to find the time to do the search ...

Justin Cain said...

Ned,

I know what you mean about the time thing. If I was independently wealthy I would be perfectly content spending most of my time reading scientific literature and blogs like this one. Oh well :) Thanks again for the thought provoking blog.

JC

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Indeed heavy physical activity may harm your heart seriously sir...