Exercise & the heart

Update on Swimming Induced Pulmonary Edema (SIPE)

May 26, 2015 By Larry Creswell, MD 6 Comments

I saw this week that there was an important new paper on swimming induced pulmonary edema (SIPE). Richard Moon, MD, and his colleagues at Duke University published a report entitled, “Immersion Pulmonary Edema and Comorbidities: Case Series and Updated Review” in a recent edition of the sports medicine journal, Medicine & Science in Sports & Exercise (1).

SIPE is known to occur not only in recreational or competitive swimmers, but also in divers. In fact, the condition was first recognized because of breathing difficulties encountered by military divers. As triathlete and swimmer readers here will know, there are many reasons why an athlete might develop shortness of breath during an open water swim. Water conditions, water and air temperature, exertion, and anxiety all play a role. SIPE is something different, altogether, though. This is a condition that develops because of immersion in the water, in which fluid builds up in the lungs and makes breathing difficult. The condition is believed to be self-limiting; if a swimmer gets out of the water, the condition will resolve. The underlying mechanisms and risk factors are not completely understood.

I’ve written about this condition in 2 previous blog posts….SIPE and More on SIPE. These posts might be a good starting point.

The newly published report is important because it reviews the medical literature and gathers all of the pertinent information about pre-existing medical conditions, or so-called comorbidities, in victims of SIPE. Dr. Moon is probably the world’s foremost authority on the topic of SIPE, so this new report deserves our attention.

The Study

There are 2 parts to the study: 1) a look at the Duke University experience with recreational swimmers who’ve had a SIPE episode and 2) a review of the medical literature on SIPE cases, both in military and recreational divers and swimmers.

In the first part, the investigators collated information on 41 swimmers who, over the past several years, had been studied at Duke University after reporting a SIPE episode. The mean age was 50.1 +/- 10.8 years (range, 25-71 years). Complete medical history data was available for 36 of the 41 swimmers.

In the second part, the investigators collected 45 previously published articles in the medical literature that reported on 292 cases of SIPE. There were 156 recreational swimmers or divers (89 men and 67 women), with a mean age of approximately 47.8 +/- 11.3 years. There were also 136 military swimmers or divers (135 men and 1 woman), with a mean age of approximately 23.3 years (range, 18-47 years).

For each of these groups, the investigators gathered information about pre-existing medical conditions in order to determine potential risk factors for the development of SIPE, focusing on: hypertension (high blood pressure), lung disease, overweight/obesity, sleep apnea, hypothyroidism, and cardiac abnormalities).

The Results

Among the Duke University group, 9 (25%) of the 36 swimmers with available health history were completely healthy. The remaining 27 (75%) had 1 or more medical/health conditions, including:

overweight/obesity in 12
hypertension in 7
cardiac arrhythmias in 4
heart valve problem (mitral valve prolapse) in 1
reduced heart function in 2
repaired congenital heart conditions in 2
asthma in 3
COPD in 1
reactive airways disease in 1
hypothyroidism in 3
diabetes in 2
polycystic ovary syndrome in 1
obstructive sleep apnea in 2

Twelve subjects had more than one of these conditions.

In the literature review, all of the 136 military swimmers and divers were healthy; they had none of the pre-existing medical/health conditions that were surveyed. In contrast, 70 (45%) of the 156 recreational swimmers or divers had one or more significant pre-existing risk factors:

asthma in 4
enlarged heart in 2
arrhythmias in 2
coronary artery disease in 3
diabetes in 4
exercise-induced cough in 1
Elevated serum lipids in 22
hypertension (high blood pressure) in 25
thickening of the left ventricle in 9
peripheral vascular disease in 1
sleep apnea in 6

As a side note, approximately 17% of cases in the literature review reported similar previous episodes or follow-up episodes that were suggestive of SIPE, giving an important look at the potential recurrence rate. And in total, 6 fatal cases of SIPE were identified in the literature review.

My Thoughts

How can all of this collated information be useful to us?

First, it’s important to note that all of the military swimmers and divers included in the literature review were healthy. We shouldn’t overlook the possibility that even completely healthy swimmers may experience SIPE.

Second, the recurrence rate of ~17% in the literature review is probably an underestimate. No doubt, some swimmers who experienced a worrisome episode of SIPE might avoid future swimming altogether. It’s very important to remember that this condition may recur.

Third, it’s very apparent that, among recreational swimmers who experience SIPE, the prevalence of important pre-existing medical conditions is rather high, at 75% in the Duke group and 45% in the recreational swimmers in the literature review. I suspect that the Duke investigators were more thorough in their history-taking and the 75% is probably more reflective of the reality.

The investigators’ aim was to identify risk factors for SIPE. Sadly, there’s obviously no single, unifying thread here. Hypertension (high blood pressure) was the most commonly identified condition among the cases, but this accounted for only ~15% of the cases. As I mentioned at the top, the physiologic underpinnings of SIPE are not completely understood and indeed there may be more than one responsible mechanism leading to some common final pathway by which fluid accumulates in the lungs. All of the various cardiovascular abnormalities identified in the cases might conceivably play a role. There’s more to learn.

It’s worth noting that the long list of medical conditions that were identified deserve careful medical attention before participating in recreational swimming events.

Advice

I’ll reprint here my best advice to athletes and event organizers regarding SIPE. I originally included this in another blog post, but this is still my best advice!

Triathletes and open water swimmers should be aware of SIPE and the possibility that this condition can be lethal.
Symptoms of SIPE can manifest for the first time even in experienced swimmers. Symptoms may develop rapidly, be unexpected, and confuse the athlete about the cause.
The development of SIPE does not appear to be confined to cold water swims or only to victims who are wearing a wetsuit at the time.
SIPE appears to be self-limiting–that is, the symptoms will subside if the victim stops exercising and gets out of the water.
Because of #2, #3, and #4, athletes who experience breathing difficulties in the open water should treat the problem like a medical emergency and STOP swimming and SEEK immediate assistance. Because of the challenges of rescue in the open water, your life could depend on recognizing a problem early and getting out of the water. I would encourage affected athletes to get complete medical evaluation as soon as possible after an episode.
There appear to be no effects on lung function after an episode of SIPE, but repeat episodes of SIPE may occur.
Affected athletes have described a variety of strategies for preventing repeat episodes of SIPE. From athlete accounts, no single strategy appears to be universally successful.
Affected athletes should use EXTREME CAUTION in subsequent open water training and races, being hypervigilant for warning signs.
Event organizers and on-water rescue personnel should be familiar with SIPE. The safety plan should allow for athletes with breathing difficulties to be removed from the water as quickly as possible.

Reference

1. Peacher DF, Martina S, Otteni C, et al. Immersion pulmonary edema and comorbidities: Case series and updated review. Med Sci Sports Exerc 2015;47(6):1128-1134.

2. More on Swimming Induced Pulmonary Edema (SIPE)

Triathlon, Open Water Swimming, and the Heart: What Can We Learn From Dolphins and Seals?

March 16, 2015 By Larry Creswell, MD Leave a Comment

A recent study about marine mammals caught my eye. I don’t know much about non-human biology and physiology, but this study on dolphins and seals may shed some light on the problem of fatalities during open water swimming or triathlon events.

The Study

A group of investigators headed by Terrie Williams from the University of California at Santa Cruz shared their report, “Exercise at depth alters bradycardia and incidence of cardiac anomalies in deep-diving marine mammals” in the January 16th edition of Nature Communications (1).

This group of investigators has been interested in the physiology of the so-called “dive response” in marine mammals. This is a response that is governed by the involuntary, or autonomic, nervous system, which has two antagonistic components: the parasympathetic nervous system and the sympathetic nervous system. As a group, the marine mammals depend on feeding by chasing pray to depths that can range up to 3,000 m. Even at lesser depths, these mammals must maintain a breath-hold under large hydrostatic pressures while they undergo extreme exertion to catch their pray. During a dive, breath-holding stimulates the parasympathetic nervous system to slow the heart rate (producing bradycardia). At the same time, the exertion required to chase pray stimulates the sympathetic nervous system, producing an increase in the heart rate. The current study offers the first detailed study of the interplay between the components of the autonomic nervous system during routine diving and feeding activity in these animals.

The investigators created an electrocardiograph-accelerometer depth monitor that was deployed on 10 Atlantic bottle-nosed dolphins and 3 Weddell seals. This device allowed high-fidelity recording of the heart rate, ECG, water depth, and swimming stroke frequency (a measure of exertion) during dives. For the dolphins, measurements were made for 74 dives to depths of up to 210 m. For the seals, measurements were made for 91 dives to depths of up to 390 m.

The Results

As expected, there was a strong relationship between diving depth and heart rate for both species, with heart rates falling during descent and reaching a minimum at the lowest depth of the dive. Superimposed on this effect was an additional effect of exertion. For the dolphins, the maximum heart rate was 1.7 to 3.7 times greater during periods of extreme exercise compared to gliding alone. For the seals, the maximum heart rate was 1.5 to 1.8 times greater during periods of extreme exercise compared to gliding alone.

The surprising finding was that cardiac arrhythmias occurred in more than 73% of the dives. The investigators defined arrhythmias to include ectopic beats or significantly increased variability in the interbeat interval (IBI). There were apparently no sustained or fatal arrhythmias., but there were discrete examples of “wandering pacemaker” and ventricular premature beats. In the Weddell seals, there were often patterns of alternating periods of tachycardia (fast heart rate) and bradycardia (low heart rate) during periods of constant, intense exertion.

The presence of cardiac arrhythmias was strongly correlated with increased depth of dive (parasympathetic activation) and increased exertion (sympathetic activation). As an example, cardiac arrhythmias occurred in 81% of the dolphin dives to >210 m but in only 26% of dives to <100 m.

The authors concluded that our previous understanding of the dive reflex in marine mammals was not totally correct. Given that these animals depend on diving for their food sources, the development of cardiac arrhythmias during feeding appears to be mal-adaptive. In fact, feeding might actually be dangerous.

My Thoughts

At first glance, the physiology of the diving response of dolphins and seals during feeding seems far afield from open water swimming and triathlon. And moreover, we already know about the development of cardiac arrhythmias during submersion in breath-holding humans as well as other marine species. The important observation here, though, is what I might call “irritability” or “instability” in the heart rhythm during periods of intense parasympathetic and intense sympathetic activation….and that’s the possible link to human fatalities during open water swimming or triathlon.

We know from autopsy reports of triathletes who’ve died during the swim portion of an event that there are sometimes only subtle abnormalities of the heart, and often nothing that seems explanatory. That leaves us in a difficult position to explain such deaths. In a previous blog post, I wrote about one very plausible hypothesis. Two UK physiologist,s X and X, proposed the concept of “autonomic conflict,” where a surge in both the parasympathetic and sympathetic stimulation of the heart might lead to a fatal arrhythmia. I’ve been intrigued with this hypothesis because it seems to fit many of the observations made about the swim victims. It is easy to see where exertion, cold water, anxiety, etc. might lead to strong sympathetic activation. And it’s equally easy to see where facial wetting, water entering the mouth/hypopharynx/nasopharynx, and breath-holding, even without diving, might lead to strong parasympathetic activation. In that instant, in an athlete with some sort of susceptible heart, a fatal arrhythmia might occur.

The new observations about the dolphins and seals seem to play into this hypothesis.

2. Triathlon Fatalities: 2013 in Review

Reference:

1. Williams TM, Fuirman LA, Kendall T, et al. Exercise at depth alters bradycardia and incidence of cardiac anomalies in deep-diving marine mammals. Nature Communications 2015;6:6055.

Book Review: Heart to Start

March 13, 2015 By Larry Creswell, MD 1 Comment

Check out the newly published “Heart to Start: The Eight Week Exercise Prescription to Live Longer, Beat Heart Disease, and Run Your Best Race,” by cardiologist, James Beckerman, M.D. The book is available at Amazon and other outlets.

This is a terrific book!

First, let me share a little bit about the author. Dr. Beckerman is the Medical Director of the Center for Prevention and Wellness at the Providence Heart and Vascular Institute in Portland, Oregon. He is also the team cardiologist for the Portland Timbers Major League Soccer team and the founder and medical director for Portland’s Play Smart Youth Heart Screenings. He is passionate about wellness, exercise, and preventive cardiology. Follow him on Twitter at @jamesbeckerman.

Perhaps you’ve had a heart attack and your doctor has recommended exercise.

Perhaps you’ve discovered that your blood pressure or cholesterol is elevated and your doctor has suggested exercise as a treatment.

Perhaps you’ve just decided to get up off the couch and be more active.

The inevitable question is, “How do I get started?” This book is for you! In Dr. Beckerman’s words, “This is a book about exercise and I guarantee that it will move you….”. More coach than doctor, he will guide you every step of the way as you get going. Take him up on the offer.

This book starts with a very personal and riveting Foreword by Dave Watkins. He asks, “What is your legacy?” He shares his near-death experience with urgent heart surgery for a diseased heart valve and aortic aneurysm on the verge of rupture. There were certainly ups and downs during Dave’s recovery, but he survived and then some! Read about Dave’s return to exercise, his successes in triathlon, and the founding of his Ironheart Foundation. Dave’s story will provide ample motivation.

The book is divided into 3 sections….

Warm Up. In the first section, Dr. Beckerman helps you to take stock of your health in general and your heart in particular. He introduces the concept of preventive cardiology and illustrates this with real-world examples where “an ounce of prevention is worth a pound of cure.” Dr. Beckerman shows you how to use the Sit Rise Test and the 6-minute walk test to size up your fitness level. This section concludes with a discussion of how traditional cardiac rehab and structured exercise can be so valuable.

Workout. In the second section, Dr. Beckerman lays out what he calls your “Heart to Start Exercise Prescription.” You’ll start with an assessment of your VO2max, an index of your aerobic capacity or fitness, and then embark on an 8-week exercise program that is tailored to your fitness level. There are both HEART (aerobic exercise) and START (strength exercise) components. The program is structured but simple.

Cool Down. In the final section, Dr. Beckerman sums things up. He recognizes that there are always choices and asks you to remember to consider, “What would a healthy person do?” For those wishing to continue on, he leaves you with a 12-week exercise program that will get you to the start line of a 5K running race. It’s a program that he uses in Portland with his popular Heart to Start group (see the photo). You can be sure that the program works.

This book is for….

If you’re ready to get going, take a copy of “Heart to Start” to your next doctor’s visit and talk about getting started. Team up with your doctor to put Dr. Beckerman’s exercise prescription to work for you.

For many readers here at the blog, exercise may already be an important part of your routine. But I bet you know others, perhaps in your own family, who haven’t yet embraced exercise. Get them a copy of the book and help them get started.

Perhaps you’re in a position to organize a group exercise program like Dr. Beckerman’s Heart to Start program. I bet he’d be happy to hear from you and help you get things organized.

Related Posts (Other Book Reviews):

1. Cardiac Athletes, by Lars Andrews

2. The Exercise Cure, by Jordan Metzl, MD

The Medical Toll at Endurance Events

June 16, 2014 By Larry Creswell, MD 2 Comments

Have you wondered about the “medical toll” at endurance sports events? By that, I mean the sum of all the medical problems that occur to atletes during their participation (and perhaps shortly afterwards as well).

It’s an interesting issue, with many practical implications. If you’re organizing a swim meet, you’d be interested in the likelihood of drowning. If you’re participating in a bicycle race, you’d be interested in the frequency of crash-related traumatic injuries. If you’re the spouse of a long-distance runner, you’d be interested in the likelihood of heart-problems for the participants of a marathon. Should your event have a “medical tent” to handle anticipated injuries or medical problems? Where should the medical tent be located and how should it be staffed? How should your local EMS system or hospital prepare to handle athlete-patients? You get the idea.

Yet surprisingly little has been written in the medical and scientific literature about the medical toll of endurance events. There’s probably a bunch of reasons, including the fact that nobody in particular’s keeping track.

This past week there was an interesting report in the British Medical Journal from a group of investigators in Cape Town, South Africa, and headed by Martin Schwellnus. The report, “Medical complications and deaths in 21 and 56 km road race runners: a 4-year prospective study in 65,865 runners–SAFER study I,” describes the “medical toll” at recent editions of the Two Oceans Marathon races. The report and the findings caught my eye.

The Study

The participants in the study were the 65,865 runners who took part in either the 21 km half marathon or 56 km ultra marathon, the premier events at the Two Oceans Marathon races that are held each year in Cape Town, South Africa. They focused on the 2008 through 2011 editions. The weather conditions for these races was generally favorable, with temperatures ranging from 11.5 to 18.2 degress C and relative humidity ranging from 77% to 93%.

Like many long distance running events, these races had an elaborate set-up for provision of medical care on race day, including on-route medical stations, a dedicated medical facility at the finish, and designated hospitals where athlete-patients would be transferred should they need emergency care. Because the system for medical care was so well proscribed, the investigators were able to compile a list of all “medical complications” that occured in the race participants.

The investigators did not consider the most minor of medical complications, such as seeking medical attention at various first-aid stations for minor injuries or requiring physical therapy attention at the finish line. For simplicity, “medical complication” was defined as an episode that required the attention of a doctor. Exercise-associated muscle cramps alone were not considered a “medical complication” unless there were additional symptoms such as confusion, dizziness, nausea, or vomiting. A serious medical complication was defined as a “medical complication that could result in death unless urgently diagnoses and treated.” And finally, deaths were recorded as well.

The Results

Of the 65,865 participants, 64,420 (97.8%) finished their race(s). The finishing rate was 99% for the 21 km races and 97% for the 56 km races.

Two deaths were documented, each in a 21 km race. The fatality rate, then, was approximately 1 per 20,000 participants in the 21 km races. There were no deaths in the 56 km races.

Overall, there were 545 medical complications among the 65,865 participants, a rate of approximately 0.8% (8.27 per 1000 participants). The rate was approximately 0.5% for participants in the 21 km races and 1.3% for participants in the 56 km races.

Included in the 545 total medical complications were 37 that were designated as serious medical complications. This is a rate of approximately 0.06% (0.56 per 1000 participants). There was no significant difference in the overall rate of serious medical complications based on the distance of the race. The serious life-threatening medical complications included:

Ischemic heart disease (including successful resuscitation from cardiac arrest), in 3 runners
Myocarditis, in 2 runners
Serious cardiac arrhythmias, in 2 runners
Symptomatic hyponatremia (low sodium), in 9 runners
Serious metabolic complications, in 5 runners
Serious heat-related disorders in 7 runners (1 with hypothermia, 6 with hyperthermia)
Pulmonary edema, in 2 runners
Serious fluid, electrolyte, or acid-base abnormalities, in 4 runners
Bronchospasm, in 2 runners
Convulsions, in 1 runner

Further statistical analysis was used to evaluate groups of medical complications, depending upon the body’s organ system that was involved. In this analysis, the frequency of complications involving the cardiovascular, musculoskeletal, metabolic, gastrointestinal, and respiratory systems was greater among the 56 km runners than for the 21 km runners.

The Takehome Messages

The chances of a medical complication or serious medical complication were small, for both of the race distances. Athletes should know, then, that these risks are small as they consider participation in an event.

Information like this should inform safety planning on the part of event directors, event medical directors, and events’ local medical communities.

I suspect that the results are generalizable to races outside of South Africa and also to the real-world question of half marathon vs. marathon races which would be typical distances in the United States.

It is a somewhat surprising finding that the only 2 deaths occurred in the shorter, 21 km races. We know from recent detailed studies involving millions of runners that the risk of sudden cardiac arrest at long-distance running events is almost 3 times higher for marathon runners than for half marathon runners. In this study, it’s a statistical oddity–that not enough years were considered to evaluate such a rare end point.

Intuitively, it is not surprising that there would be more medical complications in the longer events. If nothing else, there is more “time exposure”–more athlete-hours spent in strenuous exercise.

I am surprised, though, that the frequency of serious, life-threatening, medical complications was similar for the 2 race distances, I would have guessed that these, too, would be more common in the longer distance races. Perhaps the take home message is the converse–that a shorter race is not necessarily safer when it comes to life-threatening medical complications. And the real world consequence would be that half marathoners not give short shrift to their health before participating.

Lastly, I’ll continue to hope that national governing bodies and large event organizers (eg, World Triathlon Corporation [WTC[) might collect and disseminate information about the “medical toll” at their races. As a sporting community, we would all benefit.

Physical Activity Levels and Atrial Fibrillation

May 23, 2014 By Larry Creswell, MD 1 Comment

In the medical news last week came another interesting report on the relationship between physical activity and atrial fibrillation (AF). Reported in the medical journal, Heart, a team of investigators led by Nikola Drca from the Karolinska Institute in Stockholm gave us a study entitled “Atrial fibrillation is associated with different levels of physical activity levels at different ages in men.” This is the largest-ever study of the relationship between physical activity and AF, so the findings and conclusions deserve our attention here in the athlete community.

To set the stage for our discussion, recall that AF is a fairly common arrhythmia that is generated in the upper chambers of the heart–the left and right atrium. I’e written about AF here at the blog previously, in general terms for athletes. We’ve known for a long time that AF is associated with some other types of heart disease, particularly heart valve disease, and increases in prevalence as we age. The problem of AF is not benign. For athletes, the arrhythmia disrupts training or competition, but over the long term there is a small but real risk of stroke and also the chance of harm to the heart itself. Moreover, the available treatments–medications or ablation procedures–carry risk as well.

We also know that AF is associated with exercise. We know from prospective, longitudinal population studies that long-time, regular exercisers are more likely to develop AF over the years. And we know from targeted studies that athletes in the endurance sports are particularly at risk for developing AF.

Healthy endurance athletes should be asking the questions like:

What are my chances of developing AF?
How can I exercise safely and avoid developing AF?

Questions like these motivated the current study. Let’s take a look….

The Study

The purpose of the study was to determine if there was an association between physical activity level and the development of new AF in middle-aged men.

Back in 1997-1998, the investigators contacted all of the men aged 45-70 years who were residing in 2 counties in central Sweden and asked them to participate. About half (48,850 men, or 49%) responded by completing a questionnaire. From these, several thousand were excluded from further study because of: missing data on the questionnaire, death before the study’s follow-up period began, a current diagnosis of AF (1,496 men, or about 3% of the entire group), and the current diagnosis of some forms of cancer. This left 44,410 men to be part of the study. The average age of the participants at the time of enrollment was 60 years.

The questionnaire asked 2 questions about the amount of physical activity that the men engaged in. They were asked to think back and to recall their activity levels at age 15, at age 30, at age 50, and at the current (“baseline”) time. The participants younger than 50 years only answered for age 15 and for age 30 and “baseline.” The questions were:

“How many hours per week do you engage in leisure-time exercise (such as running, soccer, bicycling, swimming, floorball, gymnastics, cross-country skiing, etc.)?”

The respondents had to choose between:

<1 hour
1 hour
2-3 hours
4-5 hours
>5 hours.

“How much time each day do you spend walking or bicycling for everyday transportation purposes?”

The respondents had to choose between:

<20 min per day
20-40 min per day
40-60 min per day
>1 hour per day

In addition to the questions about physical activity, the respondents provided information about their medical history, smoking history, family medical history, medications, alcohol consumption, and level of education.

The respondents were then followed for 12 years to see what happened to them….and, in particular, to see if they developed AF.

The Results

At the end of the 12 years, there was an accumulated experience of 476,112 person-years! And during that time, there were 4,568 new cases of AF. Doing the math, that works out to 9.6 cases of AF per 1,000 person-years. Put another way, of the 44,410 participants, about 10.3% developed AF.

But the goal of the study was to determine if the individuals’ activity level was related to their chance of developing AF.

The primary finding of the study was that the self-reported leisure-time exercise at age 30 was indeed associated with the risk of developing AF. The investigators performed a statistical analysis designed to isolate the effect of the number of hours of exercise per week (and eliminating, as best possible, the effects of other influences on the risk of AF). They showed that the risk of developing AF was 19% greater among the individual who exercised >5 hours per week (at age 30) compared to those who exercised <1 hour per week. Remember that overall, 10.3% developed AF….so in terms of absolute risk difference between the extremes of exercise level reported at age 30, we’re talking about a couple percentage points different in the chances of developing AF. It’s because of such a large number of participants that differences this small can be detected.

Another important finding of the study was that the self-reported leisure-time exercise at baseline (when participants enrolled in the study, at mean age 60 years) was not related to the development of AF. And furthermore, the investigators found no relationship between the amount of self-reported leisure-time exercise at age 15 or at age 50 and the development of AF. The only such relationship was for the activity level at age 30.

The last important finding of the study came from a subgroup analysis. The participants who were at greatest risk of developing AF were those who reported >5 hours per week of leisure-time exercise at age 30….and <1 hour per week of leisure-time exercise at the time of enrollment in the study. These individuals were 49% more likely to develop AF during the 12-year follow-up period than individuals who exercised <1 hour per week at both age 30 and at the time of enrollment in the study.

There was no relationship between the amount of walking/cycling for transportation purposes at any age and the development of AF.

The Take-home Messages

The current study adds to our knowledge about exercise and AF. I hope that more studies are to come.
The relationship between exercise and AF is not completely understood and, indeed, the relationship may not be straightforward. Studies like this one ask participants to recall and note their activity levels at just a few moments during their lifetime. That can be hard to do, memory being what it is. Undoubtedly, the risk for developing AF must be related to some sort of dose of exercise over time. In retrospect, that’s hard to quantify. People exercise more some years than others. Some start exercising and some stop. They start and stop different types of exercise. I’ll bet that the intensity is important, too, yet how do we quantify this (in some straightforward way) so that analyses can be performed?
Previous studies, both in large longitudinal cohorts as well smaller invetigations of particular endurance athletes, have shown an increased risk of AF over the long term among individuals who exercised a lot. This phenomenon has been shown best for individuals in young to middle age, and for men more so than women. This relationship has been shown in enough different populations that we should accept it as fact. The current study points out that the increased relative risk compared to non-exercisers may reflect a rather modest increase in absolute risk. But that’s at odds with previous studies that have shown as much as a several-fold increased risk for AF among heavy exercisers. But whatever the magnitude, that risk must be considered together with the other, well-established benefits of exercise over the long term when athletes are making decisions about their activity level. Don’t forget that exercisers live longer. That’s an important endpoint to keep in mind.
The current study is curious in at least one respect. At first glance, it seems a bit odd that a relationship between exercise and development of AF could only be established for the amount of exercise reported at age 30…..and not at age 15, 50, or at the time of enrollment. Why is that? Could it be possible that we should exercise freely, with no worry about AF, while we’re young….and then again when we’re old? Maybe the 30-year-olds exercise with greater intensity. Maybe they accumulate more hours of exercise over more years. Maybe they engage in different forms of exercise that carry more risk. Perhaps “>5 hours” for the 30-year-olds was actually much more than 5 hours. The current study doesn’t provide answers. This needs to get sorted out with future studies. We need to better define the safe dose of exercise with respect to AF.
Finally, why is exercise associated with AF? In truth, we don’t know in any detail. It seems that it must have something to do with the structure of the atrium that changes over years’ time with exercise. The investigators note several of the potential reasons: enlargement of the atrium, inflammatory changes in the atrium, and overdevelopment of the parasympathetic portion of the autonomic nervous system. Perhaps all of these play a role. I like Dr. John Mandrola’s blog post this week about this issue. I like his take.

2. In the News: Atrial Fibrillation in Cross Country Skiers

3. Atrial Fibrillation in Athletes (In a Nutshell)