Many of us will be able to recall the horrifying scenes at Euro 2020 of Christian Eriksen collapsing from a cardiac arrest during a football match. It seems counterintuitive that an activity like exercise, which is universally accepted as being beneficial for general health and longevity, can have such potentially fatal consequences. The population benefits of exercise could not be clearer.¹ Regular physical activity has a wide array of benefits from reducing the risk of cardiovascular disease, diabetes and even some cancers to improving mental health and wellbeing. So, what causes sudden cardiac death (SCD) in otherwise apparently healthy athletes who perform at the highest level?

What is sudden cardiac death?

SCD is defined as an unexpected death from cardiac causes that occurs within one hour (or within 24 hours in unwitnessed cases) from the onset of an acute change in cardiovascular status in the absence of external causal factors.² The reported incidence of SCD in athletes is quite variable due to heterogeneity of reporting and definitions of what constitutes being ‘an athlete’, although the true incidence is likely to be between 1 in 40 000 and 1 in 80 000 of all high-level sporting individuals.³

When exercising, our bodies are exposed to increased physiological stress. Dehydration, increased sympathetic drive and electrolyte imbalances all put pressure on our heart muscle. In elite athletes, due to the sheer intensity at which they perform, this effect is naturally far higher. While these stressors may be tolerated by an athlete with a healthy heart, those with structural or electrical abnormalities are the individuals where problems arise and the risk of fatal arrythmia can occur.

Causes of sudden cardiac death

When asked which condition most likely predisposes an athlete to SCD, most would answer ‘hypertrophic cardiomyopathy' (HCM). HCM, a condition where there is an unexplained increased myocardial wall thickness, often due to sarcomeric protein mutations, has been shown in some studies in the USA to be the most common cause of SCD in athletes.⁴ However, Italian researchers found arrthymogenic right ventricular cardiomyopathy (ARVC), a condition where the right ventricular myocytes are replaced by fatty tissue, to be the most common (23%) cause of SCD in young athletes, with HCM accounting for only 2% of deaths.⁵ This contrasts with a study in the UK, where postmortem confirmation showed hearts were structurally normal in the majority (42%) of cases.⁶

In individuals with structurally normal hearts, channelopathies or primary arrhythmogenic states such as Brugada or polymorphic ventricular tachycardia syndrome are more likely to be the cause. As these conditions result in electrical disturbances that require an ECG diagnosis, they cannot be diagnosed postmortem. Accordingly, establishing the true aetiology of SCD in athletes is highly variable.

What is generally agreed though is that these causes of SCD to some extent have a predictable incidence based on athletic population demographics. For instance, older athletes have a higher risk of SCD than younger ones.⁷ In this group atherosclerotic coronary artery disease contributes to the majority of cases of SCD, whereas younger athletes (usually considered as those under 35 years old) are more likely to have suffered SCD from an underlying congenital abnormality (eg anomalous coronary artery origin), primary arrythmia, channelopathy or cardiomyopathy like HCM/AVRC. Similarly, males carry a higher risk than their female counterparts^{8, 9} (the mechanism for this is highly disputed although possibility related to the higher known incidence of premature coronary disease in males/’protective oestrogen’) while those of African descent carry the highest risk over others due to higher incidence of aforementioned conditions such as HCM.¹⁰

Screening and management of athletes

The detection of underlying cardiac conditions that may pose a risk of SCD in athletes is crucial, with the European Society of Cardiology recommending pre-participation screening.¹ While there is no consensus of what this constitutes (with variability between country, sports and level), generally individuals will have a medical history taken, physical examination, 12-lead electrocardiogram and cardiac imaging (nowadays either an echocardiogram or cardiac magnetic resonance imaging). Further emphasis is also put on having individuals nearby at sporting events who can perform high-quality cardiopulmonary resuscitation (CPR) and the presence of automated external defibrillators (AEDs) (Figure 1). The most crucial parameter for survival is the time from collapse to defibrillation, with chances of survival reducing by up to 10% for every minute defibrillation is delayed.¹¹

The effect of screening is highly variable. Some studies have shown it can reduce SCD by nearly 80% whereas others have shown a far smaller benefit.^{12, 13} Furthermore there are cardiac perturbations that occur naturally with athletes as part of their conditioning. Athletes’ hearts pump larger volumes of blood per beat and hence can have larger cardiac chambers, thicker heart muscle, mild valvular regurgitation and some conduction abnormalities. This further muddies the ability to discern natural adaptive changes with overlapping pathologies, which could lead to false positive results.

Then there is the impact disqualification can have on athletes. The inability to play desired sports coupled with loss of income and status has huge ramifications (even if this may seem trivial against the backdrop of possible SCD). It is clear that the decision to stop an athlete playing their desired sport is extremely difficult and often involves a multidisciplinary approach – balancing objective evidence from diagnostic assessments with risk factors such as a family history of cardiac arrest, collapse or confirmed diagnosis of a particular condition.

Rapid response saves lives

Christian Eriksen's story is a testimony to the huge advances in the management of SCD in athletes where others previously have not been so lucky, such as Antonio Puerta and Pier Mario Morosini to name but two.

Prior to his incident, Eriksen underwent regular cardiac screening with all previous tests reportedly being normal. During the match he collapsed and arrested due to a fatal arrythmia causing a disruption of cerebral blood flow. It was because of the rapid recognition and response from officials and then bystanders who performed CPR that he was promptly resuscitated with an early electric shock delivered via AED, achieving rapid spontaneous return of circulation. Eighteen months later he now has an implantable defibrillator in situ and is successfully playing at an elite level without any further incidents. His case epitomises many of the points made in this article and the knowledge gap that exists on sports science and cardiovascular medicine. Although Christian Eriksen's screening was not preventative, his treatment was lifesaving by receiving rapid gold-standard, high-quality CPR and AED shocks. In other cases, the opposite may be true.

Conclusion

Although complex in its aetiology, early identification of insidious cardiac diseases in athletes through screening may help prevent these tragedies while global implementation and widespread use of early CPR and AEDs at every level remain of paramount importance.

Declaration of interests

None declared.