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Dr. Paul D. Thompson, MD, describes how thinking about marathon running and heart protection has changed, the heart findings reported in lifelong high-level endurance athletes, and his own theory that a big heart may explain them.
Lifelong Endurance Exercise and the Heart: Unexpected Changes in Veteran Athletes
Jump To Section
- From the marathon protection theory to known risk
- Atrial fibrillation in lifelong athletes
- Fibrosis at the hinge points
- Coronary plaque and a larger aorta
- Slow heart rates and pacemakers
- Heart size as a possible explanation
- Benefits and realistic expectations
- Full Transcript
From the marathon protection theory to known risk
Ideas about endurance exercise and the heart have changed over the career of Dr. Paul D. Thompson, MD. Asked by Dr. Anton Titov, MD, how lifelong endurance exercise changes the heart, he recalls that when he finished training, a theory held that marathon runners never got a heart problem.
It was called the Bassler theory, after Thomas Bassler, a pathologist in California. Dr. Thompson says Bassler wrote letters to the editor that constantly quoted his own earlier letters, which made the idea look authoritative. Dr. Thompson then wrote a research article in the Journal of the American Medical Association reporting 18 deaths among runners.
Thinking has since moved, he says, from seeing marathon running as totally protective to knowing that risk increases during exercise, even though there are benefits.
Atrial fibrillation in lifelong athletes
Atrial fibrillation is one change Dr. Thompson describes in lifelong high-level endurance athletes. The atrium, the top part of the heart, squeezes to fill the ventricles below. If the atrium gets too big, he explains, it can quiver instead of squeeze.
Without that squeeze, less blood gets into the big chamber. Blood clots can also form inside the atrium and come out to cause a stroke. He says it has been shown that men who are lifelong athletes have more atrial fibrillation.
Fibrosis at the hinge points
Fibrosis in the heart has also been shown in lifelong endurance athletes. Dr. Thompson points to the interventricular septum, which separates the right part of the heart from the left. The places where the right part of the heart inserts into it are called hinge points, and he says these hinge points have more fibrosis, a big surprise.
Coronary plaque and a larger aorta
Coronary artery changes were also unexpected. Exercise was expected to prevent atherosclerosis, Dr. Thompson notes, yet lifelong endurance athletes appear to have more cholesterol deposits in their arteries. Their aorta, the big blood vessel that comes out of the heart, also tends to be bigger.
Slow heart rates and pacemakers
A slower heart rate is a known effect of exercise. Dr. Thompson says lifelong endurance athletes get more pacemakers as they get older because the heart gets so slow. He stresses that these findings come from very heavy endurance athletes who train this way for most of their lives.
Heart size as a possible explanation
Why these changes happen is not really known, Dr. Thompson says. His own theory is heart size: a good endurance athlete needs a big heart, a big pump for exercise.
He links each finding to that idea. A big atrium is more likely to fibrillate. A bigger right ventricle may put extra strain where it inserts into the septum. In a bigger heart, the coronary arteries have to twist and turn more with each beat, and he suggests this may lead to more atherosclerosis.
A big squeeze needs a bigger tube, so the aorta gets bigger, and a heart with a big squeeze does not need to beat as often, so the rate slows. He adds that changes in the genes in the beating part of the heart are now known.
Benefits and realistic expectations
The overall benefits seem to outweigh the risk, Dr. Thompson says. His message for clinicians, patients and lifelong endurance athletes is not to treat a lifetime of endurance exercise as a panacea that protects them totally from any event, as the Bassler hypothesis proposed 50 years ago.
Full Transcript
Dr. Anton Titov, MD: The athlete's heart, how lifelong endurance exercise changes the heart. You were first author of a review asking whether the heart can get an overuse sports injury. Lifelong endurance exercise may increase heart muscle scarring, coronary plaque, atrial fibrillation and aortic enlargement. On your blog you wrote that the benefits of exercise still outweigh these risks. Professor Thompson, how does lifelong endurance exercise change the heart? Which findings in a long-time athlete need follow-up?
Dr. Paul D. Thompson, MD: This is really an amazing thing, because when I finished training in the late 1970s, there was a person who said that if you ran a marathon, you never got a heart problem. It was a very interesting sort of theory. What this person did is they wrote letters to the editor, and he would constantly quote his prior letters.
Dr. Paul D. Thompson, MD: So it looked like it was very authoritative, and so people really believed that if you ran a marathon, you would not get a heart attack. It was called the Bassler theory, and this guy, Thomas Bassler, was a wonderful pathologist in California, and he went around the country proposing that. Then I wrote a paper in 1979 that was published in the Journal of the American Medical Association reporting 18 deaths among runners. So over my lifetime, this has really changed.
Dr. Paul D. Thompson, MD: It has gone from thinking that exercise like running a marathon was totally protective to the point where we know that there is an increased risk during exercise, even though there are benefits. And now we have also gone on to show that people who are lifelong high-level endurance athletes have some changes in their heart. One thing they have is they get more atrial fibrillation.
Dr. Paul D. Thompson, MD: What is that? The top part of the heart is called the atrium. It squeezes and it fills the bottom part of the heart, the ventricles. Squeeze, squeeze.
Dr. Paul D. Thompson, MD: The atrium, if it gets too big, can go into this quivering. So rather than squeeze, squeeze, it quivers, quivers, quivers. That atrial fibrillation, because the blood is not moving around, decreases the amount of blood that gets into the big chamber, because there is no squeeze.
Dr. Paul D. Thompson, MD: But also, because it is not squeezing effectively, you can form blood clots inside the atrium, and those blood clots can come out and give a stroke. It has been shown that men, lifelong athletes, have higher atrial fibrillation. We will come back to why.
Dr. Paul D. Thompson, MD: It has also been shown now that the heart can develop fibrosis in lifelong endurance athletes. Where? So here is what we call the interventricular septum.
Dr. Paul D. Thompson, MD: It separates the right part of the heart from the left part of the heart. And what we found is that here is the right part of the heart, where the right part of the heart inserts down here and inserts up here. Those are called hinge points, and it has been shown that these hinge points have more fibrosis.
Dr. Paul D. Thompson, MD: A big surprise. It has also been shown that the heart arteries can actually get more atherosclerosis than expected. We expected exercise to prevent the development of atherosclerosis, but over time it has now been shown that lifelong endurance athletes may have more cholesterol.
Dr. Paul D. Thompson, MD: They appear to have more cholesterol deposits in their arteries. Their aorta, the big blood vessel that comes out of the heart, tends to be bigger. The athletes get more pacemakers as they get older.
Dr. Paul D. Thompson, MD: We know exercise slows the heart, slows the heart rate. And now it has been shown that the lifelong endurance athletes wind up with more pacemakers because the heart gets so slow. So these things are all very surprising.
Dr. Paul D. Thompson, MD: They have been shown to happen in very heavy-level endurance athletes who do this most of their lifetime. Now, why does it happen? We really do not know.
Dr. Paul D. Thompson, MD: My theory is it is heart size. To be a good endurance athlete, you have to have a big heart. Why?
Dr. Paul D. Thompson, MD: Because you need a big pump to use during exercise. So if the atrium gets big, we know that a big atrium is more likely to fibrillate. So I wonder if the big heart does not lead to more atrial fibrillation.
Dr. Paul D. Thompson, MD: If the heart gets big, the right ventricle has to get big. Where the right ventricle inserts into the septum, maybe that puts a little extra strain on it. If you have coronary arteries, every time the heart beats, they have to go around for the ride.
Dr. Paul D. Thompson, MD: So if the heart gets big, those coronary arteries have to twist more and turn when the heart beats. Maybe that twisting and turning leads to more atherosclerosis. If you have a big heart with a big squeeze, it needs a bigger tube, so the aorta gets bigger.
Dr. Paul D. Thompson, MD: And if you have a big squeeze, you do not need to squeeze as often. So your heart rate goes slow. We actually now know that there are changes in the genes in the beating part of the heart.
Dr. Paul D. Thompson, MD: Now remember, the overall benefits seem to outweigh the risk. But it is important for clinicians and for patients and for lifelong endurance athletes not to think that being a lifelong endurance athlete is a panacea and protects them totally from any event, like the Bassler hypothesis of 50 years ago proposed.