Medicine for the Outdoors
Medicine for the Outdoors

Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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Atrial Fibrillation, Abnormal Heart Rhythms, and Stroke

When the atria (“upper,” smaller chambers of the heart) are fibrillating (quivering) instead of fully contracting in a rhythmic fashion, then these chambers of the heart are not emptying with each heartbeat, and residual swirling blood has a chance to form into clots. This creates a problem when small pieces of the clot break off, travel from the atria into the larger ventricles, and are pumped out into the general circulation. When that happens, the blood vessels into which the clot(s) travel become occluded. If this is a coronary artery, then a heart attack can occur. If this is an artery that supplies the brain, then a stroke may occur. That is the reason that persons with chronic atrial fibrillation are often prescribed anticoagulants (“blood thinners”) to dissolve existing blood clots and prevent the formation of new clots.

People don’t always know that they are suffering from atrial fibrillation. I have a close friend who recently suffered a series of strokes because he had unrecognized atrial fibrillation and the first indication he had was a large stroke. He had not recognized an irregular heartbeat or any change in his health status. Part of his heart was quivering and he just didn’t know. That’s bad luck.

For outdoor travelers, there are lots of other reasons to form blood clots, which occur more commonly in the veins of the lower limb and pelvis. These reasons are dehydration, injuries, prolonged immobilization such as occurs with airplane flight, and certain drugs. We are reminded of the mantras of hydration, stretching, exercise, nutrition and attention to the condition of our bodies. We want to recognize when something is not right.

In an article by Jeff Healey MD and colleagues entitled “Subclinical Atrial Fibrillation and the Risk of Stroke” (New England Journal of Medicine 2012;366:120-129), we are told that a quarter of strokes are of unknown cause, and that perhaps subclinical (unrecognized) atrial fibrillation may be a factor. The authors looked at a group of patients, 65 years of age or older, who had implanted pacemakers. They specifically sought to find subclinical atrial fibrillation and other abnormal heart rhythms, in particular rapid atrial rates. They found that rhythms in which the atria beat faster than normal, which correlated with atrial fibrillation, were associated with an increased risk for strokes or other problems related to blood clots.

So, in an elder population, there can be atrial fibrillation that goes unrecognized and that leads to strokes. The message here is that it would make sense for elder persons contemplating a journey far from home, such as an expedition, particularly to a remote environment, might consider a thorough physical examination, including a heart tracing (electrocardiogram, or “EKG”). The exam and EKG are just a snapshot in time, but they might clue the examiner to an abnormal heart rhythm, which would lead to a more extensive evaluation. The goal would be to identify unrecognized atrial fibrillation, such that it could be managed preemptively before it caused formation of a blood clot in the heart that could shed a piece out into a critical circulation, such as that of the brain.

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Tags: General Interest

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About the Author

Dr. Paul S. Auerbach is the world’s leading authority on wilderness medicine.