We’re Not Invincible: More Heart Arrhythmias in Endurance Athletes (Book Review)

When I heard that there was a new book coming out about heart arrhythmias in endurance athletes, I was interested.

Several years ago, I read some of the research papers that the book’s authors refer to. One was a cohort study on participants in the Vasaloppet, the 90-kilometer ski marathon in Sweden. Those researchers found that skiers who competed in more Vasaloppets had more heart arrhythmias – as did those who finished the race the fastest.

I wrote a piece about the findings at the time. The FasterSkier commenting system has changed, so original comments no longer appear at the bottom of the article, but I remember them clearly. Multiple commenters found the study hard to believe. One commenter was so sure that the findings were impossible that he wrote multiple angry comments arguing that exercise is good for you, so it couldn’t possibly cause heart problems.

As a scientist, I was flabbergasted.

There are a lot of crappy studies out there in sports science — and science in general, but I’m used to reading sports science papers with sample sizes of eight athletes. It’s hard to defend a lot of conclusions made from such studies. But this one? The researchers had following thousands and thousands of individuals and, well, numbers are numbers. An individual is either diagnosed with an arrhythmia or they aren’t. This was pretty straightforward.

Scientists go out and measure a phenomenon, and then we present numbers as an estimation of the world. There are many legitimate reasons to question the data or interpretation, and this is actually built into the scientific process. Before publication, other scientists will rip a a study apart as part of “peer review”, suggesting ways to make it better or even recommending it not be published.

That doesn’t mean that all published research is perfect. After publication, scientists continue to raise important points about whether the data collected represents reality (due to potential flaws like bias or study design), whether the statistical techniques are appropriate and correctly performed, whether alternative mechanisms could explain the patterns shown, and more. The public should absolutely engage in this process — and scientists should do better about engaging with the public. Anyone outside the study itself can ask questions that the researchers might not have seen, illuminating important aspects and leading to new research questions or repeating the study in a different way. In the end, this leads to gradually more and more accuracy in that estimation of the world.

Asking good questions is different than arguing that data is wrong simply because of a gut feeling or belief. The reaction to the Vasaloppet article was a frustrating moment for me but, I would come to realize, not an unusual one. When presented with facts that do not support our worldview, we tend to just discount them. It’s human nature.

All of which is to say that I was very interested to read The Haywire Heart by Chris Case, John Mandrola and Lennard Zinn.

First, I wanted to get more background on the topic, and I wanted it to be explained to me in clear, straightforward language instead of the scientific jargon of research papers.

Second, I wondered if the book would get the same reaction as my old writeup of the Vasaloppet study.

And third, I was interested to see whether, when presented with some scary narratives, I had the same reaction as those few FasterSkier commenters. After all, as much as I tout that I’m a scientist, I, too, have knee-jerk reactions — and I spend a lot of time exercising. I guessed that I might find the conclusions of the book plenty threatening.

The book opens with the story of Zinn, who is a former national team cyclist and a staff writer for VeloNews. Zinn is riding his bike outside of Boulder, Colo. He feels his heart skip a beat, and his heart rate “had jumped from 155 to 218 beats per minute (bpm), and stayed elevated.”

Zinn initially takes some rest and dials his training back, but ultimately he tries to keep riding and training. The incidents become more and more frequent until his heart actually stops at one point.

After that, Zinn radically changes his lifestyle. He does no hard efforts and much less training volume, period. Because of that, he’s still around to write the book today. His life is richer now, he writes (although it sometimes sounds like he is trying to convince himself as much as the reader). He has developed more different hobbies and can spend more time with his family. But it took him a long time to come to that understanding.

It’s a transfixing story about what can happen to a seemingly fit, healthy person. Because Zinn is an author on the book, you know that he will make it out alive. But how far will he go before he stops training? What will happen to him? Could that happen to me?

As we say in research, the plural of anecdote is not data.

While the authors include “case studies” at the end of every chapter (several of which feature cross-country skiers who nearly died on the side of Colorado ski trails), they also bring the data.

The book presents a compelling argument that we should be thinking more about our hearts – and particularly, the heart’s “electrical system,” as the authors call it. Endurance exercise doesn’t seem to increase the prevalence of problems with the “plumbing system,” or how the blood is pumped.

That’s not to say that athletes don’t have heart attacks (or, more accurately, myocardial infarctions). Risk factors are risk factors, and don’t completely disappear with exercise. High blood pressure, high cholesterol, a family history of heart disease, being male rather than female – these increase the risk of a myocardial infarction. In particular, athletes who came to endurance sports later in life and previously smoked or were overweight still carry those risks with them.

But the unique risk associated with long and intense bouts of exercise seems to be in the electrical system. Studies across multiple sports and countries, as well as in animal models like mice, rats and goats, have shown that the electrical impulses that keep the heart in rhythm can be made, well, haywire, by a lifetime of endurance training.

There’s a wealth of observational, epidemiological data suggesting that a long-term habit of endurance exercise can cause atrial fibrilliation, a rapid and irregular heartbeat originating in the atria. (Atrial fibrillation was the type of arrhythmia mentioned in the Vasaloppet study.)

Other arrhythmias seem to occur more frequently in athletes, too, like ventricular fibrillation. Premature ventricular contractions are common in trained athletes and don’t necessarily lead to bad outcomes; complex ventricular arrhythmias are also common, and can lead to cardiac arrest.

Exercise can also make genetic diseases like arrhythmogenic right ventricular cardiomyopathy (ARVC) more dangerous, and can lead to the disease even in the absence of genetic markers.

Some causes are straightforward. One symptom of “athlete’s heart,” as it is called, is enlarged chambers in the heart. And this is associated with atrial fibrillation: patients with atrial fibrillation tend to have larger left atria than those without.

Exercise also leads to inflammation of muscles. The heart is a muscle; inflammation can lead to scarring, which can then disrupt the transmission of electrical signals across cells.

The logic and evidence go on and on. The authors explain all of this much better than I can, even when paraphrasing. I’ll let you read the book and just say: it’s convincing. And if you haven’t studied human anatomy since high school, don’t worry. It’s clear and well-explained.

As to the second question, the authors tackle that, too. Mandrola, a doctor, notes that when many athletes receive a diagnosis of a heart problem, they go into denial. Many decide not to change their behavior. There’s a sort of cognitive dissonance to being told that something you have always believed is healthy is actually putting you at eventual risk of death.

“It is completely natural to go into denial for a while,” Zinn writes. “I don’t know of any masters athletes diagnosed with non-life-threatening arrhythmias who didn’t go back to pushing it hard in training or racing in hopes that the incident that sent them to a cardiologist was just a fluke.”

If you do have a problem with heart rhythm, the authors provide several chapters as a guide for when to go to the doctor, what to ask and tell them, and what treatment options might be available. Getting a correct diagnosis is key, and as cross-country skiers, that is not a trivial ask.

“Even doctors who run marathons don’t quite get the intensity thing,” Mandrola writes. “Marathons are a different sort of affair. There is no question that they are hard, but they generally have an even pace and don’t involve the competitive crises that flare up repeatedly in a bicycle race or a cross-country ski race or triathlon.”

Women, too, are often misdiagnosed. The authors explain that women are more likely to be assessed as having an anxiety disorder than men, even when suffering from the same underlying heart problems: “Women younger than 55 were seven times more likely to be misdiagnosed and turned away from the ER than their male counterparts.”

But the main advice, when confronted with a heart arrhythmia, is first to go to the doctor, and second to back off of training. It might save your life – and it might also make the problem disappear. That doesn’t necessarily mean stopping completely, but it might mean going slower and for shorter sessions. “Detraining” is a good therapy for several diagnoses.

“In the end, I believe that all that denial and continued racing and training hard with the hopes of retaining some portion of my former life either damaged my heart or trained it so that it now goes into arrhythmia more easily,” Zinn writes of his own situation.

Detraining might seem horrible, like an unacceptable lifestyle adjustment. But as the authors point out, once you know the other options – medications with scary side effects, procedures with non-trivial rates of complications, death – training a bit less might seem like a much better option.

As for me? I definitely reacted to the book, but not by going into denial. Instead, I was scared.

“The day before he died, he had gone for a six-hour run,” the authors wrote of Micah True, a barefoot- and distance-running legend.

I read that the day after I had done a four-hour overdistance running workout. It hit home: none of us are invincible.

That said, the one thing I found missing from the book was a real estimate of the prevalence of these heart problems. I could easily follow why they would develop, based on the physiology of the heart and what we do to it. And I found the research cited credible. But how many people does this happen to? Just what is the risk, statistically?

One reason the answer might be lacking is simply that it’s hard to do comprehensive research on such a topic. As the authors point out, you can’t really do a randomized, controlled, double-blind trial – the gold standard for scientific studies – about the effects of lifelong exercise.

Nevertheless, it’s clear that such health issues are common enough to give one pause.

I’m just 30 years old, and I am probably not going to change my exercise habits after having read this book. But it reinforced a lot of peripheral behaviors that I should know are important anyway.

For instance, in some patients, arrhythmias pop up only when they are stressed. Leading a high-stress life and sleeping too little are major risk factors. Burning the wick at both ends: that’s the sort of life I lead – and the sort of thing I always know I should work to address, but here’s another good reason to do so.

Likewise, making sure to get enough electrolytes when training, to avoid dehydration, to get good rest and recovery, and to listen to your body – these are important.

“You have probably been training for many years, if not most of your life,” Mandrola writes in one chapter. “Those years of training have given you a good sense of what ‘normal’ feels like. What you are looking for is anything that falls outside the boundaries of normal.”

If I do ever feel a flutter in my chest, I’ll now know not to ignore it.