Why Your Doctor May Think You’ve Had a Heart Attack After a Triathlon (When You Really Haven’t)

After endurance exercise your heart releases a chemical that is always a sign of heart damage — except for athletes.

Craig was ecstatic.

At 43 years old, he had just set a new personal best time in an Ironman triathlon.

As he was getting a massage after the race however, he started to feel light headed and faint.

After spending a few more hours in the sun, Craig collapsed.

He had extremely low blood pressure and small electrical changes in his heart. Blood tests also that showed he may have suffered heart damage.

He was diagnosed with “mild myopericarditis,” which is a kind of inflammation of the heart. Craig was advised to “avoid exercise for 6 weeks.”(1)

What Craig’s doctors didn’t know was that the blood tests they used to make their diagnosis are often misleading for athletes.(2)

Why Your Doctor May Think You’ve Had a Heart Attack after Endurance Exercise

The most accurate blood tests for heart damage are called cardiac troponins.(3-9)

After intense endurance exercise, cardiac troponins often go above levels seen in people who’ve just had a heart attack.(10-44)

After a marathon, 51% of runners have elevated troponins. 23% of these athletes have troponins higher than heart attack patients.(45)

“When we (cardiologists) see a troponin go up, it means one thing — heart muscle has died,” says Dr. James O’keefe,(46) the author of several reviews on this topic.(47-49)

However, cardio appears to be an exception to this rule.

The Best (False) Proof Cardio Damages Your Heart

Cardio can raise your troponins without killing your heart cells.

According to Dr. Robert Shave, one of the leading researchers in this field:

Exercise-induced cardiac damage is the only recognized stimulus of cTn [troponin] release that is not associated with poor clinical outcome, as such we challenge the view-point that “any” release of cTn is indicative of irreversible cardiac damage.”(50)

The reason this kind of heart damage may not always be harmful has to do with how cardio makes your heart “leak.”

How Cardio Makes Your Heart “Leak”

Cardiac troponins can come from two places in your heart cells:

  • The myofibrils (the muscle fibers).
  • The cytosol (the “goo” inside your cells).

About 92-97% of cardiac troponins are attached to the myofibrils — the muscle fibers. The other 3-8% is floating in the cytosol.(51-54)

After a heart attack, heart cells die and fall apart. The cardiac troponins are released from the cytosol and the muscle fibers.(55) This tells doctors that heart cells have died.

In contrast, cardio temporarily weakens the cell membranes in your heart cells.

This causes cardiac troponins to “leak” out of the goo inside your cells — the cytosol — without damaging the actual muscle fibers.(56-61)

“It should not be forgotten that the heart is a muscle and that exercise may… release intra-cellular proteins [troponins], which may not indicate frank myocardial damage,” says Dr. Shave.(62)

It’s possible that in some rare cases, the troponins released after cardio are from permanent heart damage,(63) but this idea is “not presently supported by convincing data.”(64,65)

There’s still some question as to whether or not troponin molecules are small enough to “leak” through healthy cells, and “most experts believe that a rise and fall in troponin is due to true myocardial cell death.”(66)

Yet the same authors concede that, “troponin is often elevated… in conditions other than overt ischemic heart disease.”

Studies using more sensitive tests have found that healthy people can have small amounts of troponins in their bloodstreams with no signs of heart damage.(67-72)

Animal and in vitro studies on human heart cells have also shown that troponins can be released without the cells dying.(73,74)

We’re still not certain why cardiac troponins are released after exercise. It could be from stretching, oxidative stress, or a combination of factors. Nevertheless, most evidence shows it’s probably not from permanent heart damage. In the words of Dr. Shave:

“The data that are available support a mechanism of [troponin] release that is unrelated to frank myocardial injury.”(75)

It’s likely that cardio makes your heart cells “leak” troponins, while permanent heart damage destroys them.

Not All Heart Damage is Permanent or Bad

The rise in troponins after cardio is probably better described as a sign of heart remodeling than heart damage.

Everyone’s heart cells are dying and being replaced at all times.(76,77) This is probably why healthy people have small amounts of cardiac troponins in their blood at rest.(78-81)

Endurance training accelerates this process.(82) 30 minutes of hard running or several hours of moderate walking can increase troponins slightly.(83,84)

A recent study on marathoners put it this way:

“The stress of marathon running seems to be better described as a burden of myocardial overstimulation rather than cardiac injury.”(85)

Overstimulating your muscles, and letting them recover, is how they get stronger and more efficient.(86,87) It makes sense this would also apply to your heart muscle.

This idea was further supported by a 2012 review that concluded “exercise-induced cardiac troponin release is not a marker of exercise-induced pathology but likely a physiologic response to exercise.”(88)

Athletes with the most training also often have the lowest rise in troponins after marathons.(89,90)

The rise in troponins after cardio seems to be part of a natural remodeling process that makes your heart stronger and more efficient — not permanent damage like after a heart attack.(91-95)

The Rise and Fall of Troponins: More Reason for Athletes to Relax

The troponin “leak” theory makes more sense if we look when at troponins are released.

After a heart attack, troponins peak twice.

The immediate, smaller peak in troponins is mostly from heart cells being “leaked.”(96)

The second, much larger peak starts about 12-24 hours after symptoms begin.(97,98) After this point, troponins stay high for about 4-10 days.(99,100)

This second rise in troponins is caused by the heart cells dying, falling apart, and releasing the troponins stored in their myofibrils.(101-106

After a heart attack, troponins (Peak “B”) peak 12-24 hours later, and stay high for about 4-10 days.(107)

After endurance exercise, troponins are released in a completely different pattern. They peak immediately afterwards and tend to decline thereafter. After about 24-36 hours, they’re almost always back to normal.(108-121)

This means the troponins are probably not from permanent heart damage.

After a marathon, troponins peak immediately afterwards, begin to decline, and are almost always back to normal levels 24-36 hours later. This suggests they are released from cells “leaking” troponins, rather than permanent heart damage.(122)

In this study, several runners had troponins that were still rising or didn’t decline the day after a marathon, yet there was no sign of permanent heart damage on an MRI (discussed more below).

If cardio killed even a few heart cells, “a similar sustained release of cTn [troponin] would be anticipated, and there are no data to support this theory,” says Dr. Shave.(123)

Consecutive Workouts Don’t Release More Troponin

If cardio causes permanent heart damage, you would expect multiple consecutive workouts to make troponins keep rising as more heart cells die. 

This is not what happens.

Controlled studies have shown that exhaustive workouts a few hours apart do not cause a cumulative rise in troponins. They go up after the first workout, and stay the same after the second. This suggests that runner’s hearts “cope well with two prolonged runs performed on the same day.”(124)

In one study, during the 3,000 mile long Race Across America bike race, every single rider had high cardiac troponins. However, they tended to peak on the first day, and plateau throughout the race.(125)

This “suggests that the hearts of the cyclists coped well with the extreme cardiac work demanded by this ultra-endurance exercise challenge,” concluded the authors of the study.

There were only four riders in that study, but another study on pro cyclists found the same thing during the 2,000 mile long Giro d’Italia bike race.(126)

Troponins are Not Correlated with Cardiac Fatigue

In most studies, the rise in cardiac troponins is not correlated with the drop in heart function after cardio called cardiac fatigue. They’re considered separate phenomenon.(127-131)

This further supports the idea that troponins are not a sign of permanent heart damage.

A few studies have shown correlations between cardiac troponins and cardiac fatigue,(132-135) but most evidence still indicates this is not a sign of permanent damage.136,137)

Even if cardiac troponins were consistently associated with cardiac fatigue, it wouldn’t prove cardio causes heart damage. Correlation is not causation.

The Best (Good) Proof That Cardio Doesn’t Damage Your Heart

Cardiac magnetic resonance imaging with late gadolinium enhancement (LGE) is the most accurate test for heart damage.(138-141)

Newer studies have used used this technique on athletes after marathons and Ironmans to see if cardio damaged their hearts.

They have all shown that despite extremely high cardiac troponins and other biomarkers after marathons and Ironmans, there is zero evidence of new heart damage.(142-146)

In the first of these studies, the researchers concluded that there was “no evidence” of direct damage to the heart, and that the increases in troponins were due to “cytosolic release [“leak”]… not to the true breakdown of the myocyte [heart cell].”(147)

A later study found similar results, and concluded that “exercise induced cardiac biomarker release is not associated with… myocardial damage (inflammation, oedema, hyperemia, or fibrosis) using current gold standard imaging modalities.”(148)

Studies on heart disease patients have also found that troponin levels are directly proportional to the amount of damage on LGE tests.(149) If the huge rise in troponins after endurance exercise was a sign of true heart damage, there should be at least a small blip of evidence on an LGE. There isn’t.

So far there are only five studies using LGE, which is why they’re good, but not definitive proof that cardio doesn’t damage your heart. Nevertheless, all of them were well designed, covered a variety of different endurance sports and athletic abilities, were extremely comprehensive, and found the same result — no heart damage after cardio.

The best studies to date have found that troponins are probably not a sign that cardio damages your heart.

Troponins are Not Reliable Evidence that Cardio Damages Your Heart

Troponins are one of the most accurate blood tests for detecting heart damage — except for athletes.

Running, cycling, swimming, rowing, and other forms of cardio can make troponins “leak” out of your heart cells, without causing permanent harm. This is considered a natural adaptation to endurance exercise — not a sign of disease.

Troponins are released on a different schedule after cardio than after a heart attack. Most research also indicates they are not related to the drop in heart function that happens after hard cardio workouts.

Every study using the most advanced imaging techniques available has found no evidence of permanent heart damage after endurance exercise, despite high troponins.

This is what confused Craig’s doctors.

Two weeks after being discharged from the hospital, there was no evidence of inflammation or heart damage. Craig “was immediately cleared for training and competition.”(150)

Craig’s doctors thought he had suffered heart damage after an Ironman.

He hadn’t, and the bulk of evidence suggests that most athletes don’t, even when they collapse.(151)

Dr. Barry J. Maron, a researcher who’s been studying this subject longer than almost anyone else, puts it this way:

“At present, there is no evidence that these subclinical findings [cardiac troponins] are associated with permanent clinical consequences [heart damage].”(152)

There are rare times when cardiac troponins might be a sign of permanent heart damage in some athletes. In most cases however, they’re far from convincing evidence that cardio contributes to heart disease.

You’re reading Part 3 of a series on whether or not exercise damages your heart. Click here to read Part 4.

You can read the first post in this series by clicking here.

A special thanks to Drs. Andre La Gerche, Ellen Dawson, Keith George, Rob Shave, Greg WhyteGuenther Neumayr, Jürgen Scharhag, Aaron Baggish, Rory O’Hanlon, and Jessica Scott for their assistance in making this article possible.

 

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