Opinion | Wednesday, 16th June 2021

Christian Eriksen: why do cardiac arrests happen in some athletes?

Physiologist Dr Rehan Junejo on what screening can detect and what happens during a cardiac arrest

By Dr Rehan Junejo, lecturer and researcher in physiology, focusing on cerebrovascular and cardiovascular control in health and disease, from Manchester Metropolitan University Institute of Sport

The benefits of regular exercise are well known and the evidence is clear: regular exercise, whether resistance or endurance training is good for you – reducing the risk of strokes, dementia, coronary artery disease, high blood pressure, certain cancers, and countless other health benefits.

However, on extremely rare occasions, the adaptations and strains that the body undergoes with exercise can manifest in harmful ways, often due to some predisposing factors. A sudden cardiac death or cardiac arrest as is suspected in the case of Danish footballer Christian Eriksen, who shockingly collapsed during his country’s game against Finland at the weekend before then receiving emergency treatment on the pitch. Thankfully, it seems that Eriksen is making a good recovery.

Sudden cardiac deaths or arrests are separate from heart attacks as generally understood. Cardiac arrests are when the heart stops beating because its rhythm has changed to something that has become unsustainable or its electrical signals have stopped. Generally speaking, a heart attack or a myocardial infarction is when blood supply to the heart is blocked, often caused by clogged arteries.

But what happens in the case of cardiac arrest during exercise? How and why might someone who is regularly active or an elite athlete experience such a shocking event?

Adaptations

When people exercise, their bodies go through different adaptations. Most of them are beneficial. And that's why, from doctors to GP services to the government, everybody tells you to exercise. When you do exercise your body responds to the demands being placed on it, adapting so that it can cope better next time.

When people do resistance exercises, such as weight training, remodelling of the heart can be slightly different compared to those who do endurance exercises, such as long-distance running or swimming. What the heart, along with other organs, is basically trying to do with the adaptation is to work in a more efficient manner.

When people do endurance exercises, the heart becomes slightly larger and then eventually with each heartbeat, more blood comes out. It becomes more efficient. That's why endurance athletes have a lower resting heart rate – the heart needs to work less in order to do the same amount of work.

In some athletes, particularly those who engage in quick vigorous exercise bouts or sprints every now and then, like for example football players, their hearts may have a slightly different adaptation as well compared to usual endurance athletes. Their heart muscle may become slightly thicker and more efficient at forcefully pumping out blood. These adaptations often come alongside acute release of biomarkers, such as troponin, which are normally associated with pathologies like a heart attack, but here are part of the adaptations of a generally healthy heart to normal exercise. Now, in most circumstances these changes in the heart are no problem and really something that is desired.

However, there is some evidence to show that in elite athletes who are below 35 years of age and who have suffered from a sudden cardiac death that is not due to any physical trauma, the normally beneficial adaptations to the heart muscle have gone to an extreme, often leading to the loss of normal electrical activity of the heart which stops it from beating as normal. So, the heart has lost its normal rhythm which has then become unsustainable. Also depending on which chamber is affected, loss of normal heart rhythm can be slightly different.

Screening

The microscopic scarring or fibrosis which happens in the heart as it is working to its limits, generally doesn't really cause any major pathological problems. However, in extreme cases, this can affect the electrical pathways of the heart. Besides, there is also evidence that when people do intense exercise, the heart muscle can get fatigued.

It is all speculative unless the medical records and data were available, but it is possible something similar, or a combination of factors, may have been the cause of what happened with Christian Eriksen.

I'm sure Eriksen has had regular electrocardiograms and echocardiograms – simple tests to check the heart’s rhythm and electrical activity and image its chambers for size and function – so you may ask why didn't they pick this up before?

Well, you may need to stress test the heart, to make it work harder so that it loses its rhythm or it's not actually functioning as you expect it to function, and is not able to pump as much blood that you expect it to pump out, making pathology screening of these individuals quite tricky. And even then, it can still sometimes be an inconclusive test. However, we are now seeing more work on this and cardiological societies are now producing guidelines to aid in this screening process.

For athletes who are usually above 35 years of age, or retired athletes, there's some evidence to show that coronary artery disease might also be a factor when they have heart problems.

Incredibly rare

It is important to remember that this is an incredibly rare thing and people by no means should just stop exercising. There is very good evidence to show that sedentary inactive lifestyle isn’t good you. But Eriksen is definitely not the first elite athlete who has had cardiac problems: Fabrice Muamba at Bolton Wanderers FC had a similar sudden cardiac event during a football match and there's definitely evidence from other athletes as well, such as Jay Bouwmeester or Rich Peverley from the NHL in America.

If something like this happens, what you need to do is restart the heart as quickly as possible, and that's what they did here with Eriksen. An electric shock to the heart from a defibrator to get it restarted.

There are people who have heart rhythm problems, even without exercise. For example, this might be due to a previous myocardial infarction or a heart attack. In some cases, you can implant a defibrillator inside them so that, if the heart goes out of rhythm or stops completely, it can be automatically shocked back into normal rhythm. You might have heard of Belgian football player Anthony Van Loo who also collapsed during a football match and was revived back with an implanted defibrillator. But it doesn’t have to be an implanted defibrillator: CPR training and public access to external defibrillators does save lives, as we saw in case of Eriksen.

So while these extreme events are not unheard of, they are extremely rare and in some instances might not be detected beforehand. As Eriksen undergoes more tests with doctors, they will start to understand more what caused him to collapse. Until then, we wish him a speedy recovery.