Sudden cardiac death (SCD) among children and young adults is a devastating and tragic event. There is a vast body of literature discussing the importance and the optimal method of performing cardiac screening in this population.^1-3 In this article, we address the question of whether screening should focus only on young individuals playing in organized competitive sports or on a wider population.

Introduction

At present, the American Heart Association/American College of Cardiology and European Society of Cardiology guidelines recommend cardiovascular screening in all young competitive athletes.^2,4,5 There is a general consensus that pre-participation cardiovascular screening in young competitive athletes is "justifiable and compelling on ethical, legal and medical grounds."⁵ The main lines of argument to perform cardiac screens are as follows:

• Non-traumatic sudden death in a young person is almost certainly cardiac in origin, often the result of an underlying cardiac abnormality.^6-8
• If we are able to detect cardiac abnormalities prior to the event, we may be able to reduce the risk of these events from occurring.^1,9
• Cardiac screening provides an opportunity to identify these underlying cardiac conditions and decrease the risk of future cardiac events in asymptomatic, overtly healthy young individuals.

The causes of SCD in the young can be broadly classified into structural heart disease (e.g., hypertrophic cardiomyopathy, dilated cardiomyopathy, anomalous coronary artery, arrhythmogenic right ventricular cardiomyopathy and myocarditis) or primary arrhythmogenic diseases (e.g., Brugada syndrome, Wolff-Parkinson White syndrome, long QT syndrome and catecholaminergic polymorphic ventricular tachycardia). The causes of SCD in athletes and non-athletes are the same. It is, therefore, reasonable to consider whether cardiac screening should focus only on young individuals who participate in organized sports or whether to also include those not competing in organized sport. Young individuals that do not compete in organized sport can be further categorized into recreational athletes and sedentary/non-athletes.

We have historically screened only competitive athletes because most of the data relating to SCD in the young are derived from athletic cohorts. Of these deaths, most occur during exercise. In addition, rigorous exercise may induce myocardial fatigue, scarring and a potential increase in arrhythmogenic risk; however, whether these entities are the direct result of exercise alone and whether they occur in a canonical fashion remain speculative.^10,11 Prima facie, this suggests that screening young competitive athletes is appropriate as they undergo regular, often daily, intense bouts of physical exercise.

However, screening recreational athletes and sedentary young individuals may have merit for three reasons. First, there are a growing number of young individuals participating in regular exercise for recreational purposes, and in this group SCD most commonly occurs during gym workouts.¹² Next, in non-athletes, most cases of SCD do not occur in the setting of exercise.^1,13 Finally, even if most SCD events in athletes are related to exercise, this does not necessarily mean that competitive athletes are at higher risk of SCD than non-competitive athletes or young sedentary individuals.

Therefore, the key issue that needs to be addressed is whether competitive athletes are truly at increased risk of SCD compared to their non-competitive athletic and non-athletic counterparts. The incidence of SCD in young competitive athletes ranges from 0.5 to 13 deaths per 100,000 athletes.^14,15 The incidence of SCD in children and young adults regardless of athletic ability ranges from 1.8 per 100,000 per year to 2.8 per 100,000 person years.^13,16,17 Unfortunately, the discrepancy in the reported incidence rates is largely the result of a difficulty of obtaining this information.

The Difficulty in Reporting True Incidence Rates of SCD in the Young

The calculation of an incidence rate requires a numerator (number of SCD within the chosen population) and a denominator (the total population included in the analysis). The numerator in both the athletic and non-athletic cohorts may be derived from media reports, registries, etc. The denominator is an estimate often derived from the number of institutions (sporting clubs, high schools/colleges) included multiplied by those enrolled in each institution. When expressed as athlete-years there is a further multiplication by the average years an athlete competes during the designated time period. Clearly, both in terms of the numerator and denominator there are assumptions that are made, including whether all sudden deaths have been captured, whether they are secondary to cardiac causes and whether the population at risk has been accurately estimated. These complexities are made even more difficult when conducting studies over a long period of time. Therefore, in many instances the occurrence of SCD remains unknown. While there are ongoing efforts nationwide to reliably capture the true numerator and denominator we must rely on surrogate information to frame our discussion.

Incidence of SCD in Athlete and Non-Athlete Cohorts

Corrado et al. explored trends in SCD in both athletic and non-athletic populations aged 12-35 years in Italy from 1979-2004. The study was not designed to answer the question of whether athletes are at increased risk of SCD than non-athletes; rather, it was to show the effectiveness of cardiovascular screening with ECG to reduce the rates of SCD in young athletes. Yet inferences regarding the rate of SCD in athletic and non-athletic populations may be derived from their data. In the study period, 55 cases of SCD occurred in the screened athletic population during an estimated 2,938,730 person-years of observation, resulting in an overall incidence rate of 1.9 deaths per 100,000 person-years. Notably, the annual incidence of SCD in athletes decreased by 89% (from 3.6/100,000 person-years in 1979-1980 to 0.4/100,000 person-years in 2003-2004; P for trend <.001). In the same period, there were 265 SCD among the unscreened nonathletic population during an estimated 33,205,370 person-years of observation, resulting in an incidence of 0.79 per 100,000 person-years. As expected, the annual incidence rate of SCD among the unscreened nonathletic population did not change significantly over this period. On the face of it, therefore, unscreened athletes have a higher incidence of SCD than their non-athletic counterparts; however, screened athletes have a lower risk of SCD than their non-athletic counterparts. In support of these findings, Corrado et al. subsequently compared the incidence of SCD young competitive athletes and age-matched non-athletes over a 20 year period in a predominantly Caucasian population.¹⁸ They report that the relative risk of SCD among athletes versus non-athletes was 1.95 (CI 1.3 to 2.6; p = 0.0001) for males and 2.00 (CI 0.6 to 4.9; p = 0.15) for females.

However, recent US data on the incidence of SCD in the young provide conflicting results. Maron et al. directly compared the frequency of SCD in young competitive athletes versus non-athletes in Minnesota between 2000 to 2014.¹⁹ Using registry records they reported on 27 cases of SCD in individuals aged between 14-23. Of these, three were competitive athletes. The calculated incidence of SCD was more than three times higher in non-athletes/non-competitive athletes than competitive athletes (1:39,454 person years vs. 1:120,614; p = 0.07). It is important to note, however, that the standard history and physical pre-participation athlete screening may have decreased the incidence of SCD in the athlete population. Data regarding detection of heart conditions associated with SCD or on the number of athletes disqualified were not reported. It is also possible that there may be a geographic difference in the incidence of SCD in Italy and the US.

The Incidence of SCD in Athletes is Sport Specific

We should also acknowledge that the incidence of SCD is sport specific. A retrospective analysis of a database of all NCAA deaths between 2003-2013 showed an incidence of SCD among this athletic cohort of 1:53703 athlete-years (AY) (79 SCD in 4,242,519 AY).²⁰ The rate of sudden cardiac death in NCAA athletes was highest in males and black athletes. While the incidence of SCD varied greatly by sport, male D1 basketball athletes incurred the highest rate of SCD (1:5200 AY). The recent publication by Malhotra et al. on UK adolescent soccer players further highlights the likelihood of a sport-specific incidence of SCD.²¹ This group reported eight deaths over a 20-year follow-up of elite adolescent UK soccer players (incidence of 1 per 14,794 person-years, or 6.8 per 100,000 athlete years). Because the data was derived from a comprehensive Football Association cardiac screening program, there was a clear denominator, the first of its kind, rather than an estimate. Importantly, of the >11,000 athletes screened, 42 were identified during pre-participation screening to have a condition associated with SCD, of which 40 were managed accordingly to reduce their SCD risk (two athletes returned to play against medical advice). Therefore it is plausible, although not certain, to assume that the incidence of SCD in unscreened young soccer players may be higher than that reported in this study.

In sum, variables including type of sport, gender and ethnicity should be acknowledged when discussing the incidence of SCD in competitive athletes, recreational athletes, and non-athletes.

Conclusion

While we have traditionally considered athletes to be at an increased risk of SCD, recent US data challenges this notion.¹⁹ The discrepancy in these findings highlights the difficulty in accurately capturing the number of SCD in a population. The inability to report the true incidence of SCD limits our understanding of the genuine risk of SCD during rigorous training in individuals with underlying cardiomyopathy. Our first insight into the true incidence of SCD in athletes suggest it is markedly higher than previously estimated,²¹ supporting the argument for screening in this group. In reality, however, the risk of SCD likely depends on the ethnicity, type of sport and level of competition played by the athlete. Regardless, there remains considerable uncertainty regarding the risk of SCD in non-competitive athletes and sedentary individuals. If we submit that individuals not competing in organized sport also hold a significant risk of SCD, it is our ethical responsibility to change the current guidelines. If the decision is then made to screen all young individuals regardless of sporting prowess, this will no doubt influence the debate as to how to screen individuals (with particular reference to the use of an ECG) and its attendant cost implications. Indeed, screening athletes using an ECG and the latest international criteria for ECG interpretation would require approximately three percent of individuals to be further evaluated.²² In sum, while the topic of 'how' to perform cardiac screening has dominated the conversation, there are still critical questions to answer regarding whom we should screen.

References

1. Corrado D, Basso C, Pavei A, Michieli P, Schiavon M, Thiene G. Trends in sudden cardiovascular death in young competitive athletes after implementation of a preparticipation screening program. JAMA 2006;296:1593-601.
2. Maron BJ, Friedman RA, Kligfield P, et al. Assessment of the 12-lead echocardiogram as a screening test for detection of cardiovascular disease in healthy general populations of young people (12-25 years of age): a scientific statement from the American Heart Association and the American College of Cardiology. J Am Coll Cardiol 2014;64:1479-514.
3. Maron BJ, Estes NAM, Maron MS. Is it fair to screen only competitive athletes for sudden death risk, or is it time to level the playing field? Am J Cardiol 2018;121:1008-10.
4. Maron BJ, Thompson PD, Ackerman MJ, et al. Recommendations and considerations related to preparticipation screening for cardiovascular abnormalities in competitive athletes: 2007 update: a scientific statement from the American Heart Association Council on Nutrition, Physical Activity, and Metabolism: endorsed by the American College of Cardiology Foundation. Circulation 2007;115:1643-455.
5. Corrado D, Pelliccia A, Bjornstad HH, et al. Cardiovascular pre-participation screening of young competitive athletes for prevention of sudden death: proposal for a common European protocol. Consensus statement of the Study Group of Sport Cardiology of the Working Group of Cardiac Rehabilitation and Exercise Physiology and the Working Group of Myocardial and Pericardial Diseases of the European Society of Cardiology. Eur Heart J 2005;26:516-24.
6. Maron BJ. The paradox of exercise. N Engl J Med 2000;343:1409-11.
7. Maron BJ. Sudden death in young athletes. N Engl J Med 2003;349:1064-75.
8. Corrado D, Thiene G, Nava A, Rossi L, Pennelli N. Sudden death in young competitive athletes: clinicopathologic correlations in 22 cases. Am J Med 1990;89:588-96.
9. Corrado D, Basso C, Schiavon M, Thiene G. Screening for hypertrophic cardiomyopathy in young athletes. N Engl J Med 1998;339:364-9.
10. La Gerche A, Claessen G, Dymarkowski S, et al. Exercise-induced right ventricular dysfunction is associated with ventricular arrhythmias in endurance athletes. Eur Heart J 2015;36:1998-2010.
11. La Gerche A, Rakhit DJ, Claessen G. Exercise and the right ventricle: a potential Achilles' heel. Cardiovasc Res 2017;113:1499-1508.
12. Landry CH, Allan KS, Connelly KA, et al. Sudden cardiac arrest during participation in competitive sports. N Engl J Med 2017;377:1946-53.
13. Bagnall RD, Weintraub RG, Ingles J, et al. A prospective study of sudden cardiac death among children and young adults. N Engl J Med 2016;374:2441-52.
14. Maron BJ, Gohman TE, Aeppli D. Prevalence of sudden cardiac death during competitive sports activities in Minnesota high school athletes. J Am Coll Cardiol 1998;32:1881-4.
15. Eckhart RE, Scoville SL, Campbell CL, et al. Sudden death in young adults: a 25-year review of autopsies in military recruits. Ann Intern Med 2004;141:829-34.
16. Papadakis M, Sharma S, Cox S, Sheppard MN, Panoulas VF, Behr ER. The magnitude of sudden cardiac death in the young: a death certificate-based review in England and Wales. Europace 2009;11:1353-8.
17. Winkel BG, Holst AG, Theilade J, et al. Nationwide study of sudden cardiac death in persons aged 1-35 years. Eur Heart J 2011;32:983-90.
18. Corrado D, Basso C, Rizzoli G, Schiavon M, Thiene G. Does sport activity enhance the risk of sudden death in adolescents and young adults? J Am Coll Cardiol 2003;42:1959-63.
19. Maron BJ, Haas TS, Duncanson ER, Garberich RF, Baker AM, Mackey-Bojack S. Comparison of the frequency of sudden cardiovascular deaths in young competitive athletes versus nonathletes: should we really screen only athletes? Am J Cardiol 2016;117:1339-41.
20. Harmon KG, Asif IM, Maleszewski JJ, et al. Incidence, cause, and comparative frequency of sudden cardiac death in national collegiate athletic association athletes: a decade in review. Circulation 2015;132:10-9.
21. Malhotra A, Dhutia H, Finocchiaro G, et al. Outcomes of cardiac screening in adolescent soccer players. N Engl J Med 2018;379:524-34.
22. Dhutia H, Malhotra A, Finocchiaro G, et al. Impact of the international recommendations for electrocardiographic interpretation on cardiovascular screening in young athletes. J Am Coll Cardiol 2017;70:805-7.

Keywords: Sports, Athletes, Follow-Up Studies, Retrospective Studies, Death, Sudden, Cardiac, Electrocardiography, Risk, Risk Factors, Cicatrix, Cardiomyopathies, Coronary Vessels, Tachycardia, Ventricular, Cardiomyopathy, Hypertrophic, Cardiomyopathy, Dilated, Exercise, Long QT Syndrome, Registries, Myocarditis, American Heart Association, Brugada Syndrome, Wolff-Parkinson-White Syndrome, Arrhythmogenic Right Ventricular Dysplasia

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