Sudden Cardiac Death in the Young Athlete

A. E. Housman’s celebrated literary work, “To an Athlete Dying Young,” romanticizes the premature death of a young athlete. The poem reveals the concept that those dying at the peak of one’s glory or youth are actually quite lucky. This horrifying and ill-fated phenomenon in apparently healthy, young athletes is often the result of sudden cardiac death (SCD). The sobering reality, however, is that young athletes are dying from SCD with a frequency that is much higher than originally thought.^1-6 Regrettably, there is obviously nothing “lucky” about dying at the peak of one’s youth. This past fall, Detroit, Michigan, was witness to SCD in two young athletes during the city’s annual marathon. These occurred just months after the Baltimore marathon claimed the life of a 23-year-old runner. The surrounding community was shocked and devastated with the news that the two young, well-conditioned runners, both under the age of 36, had collapsed within a couple miles of one another. The Wayne County medical examiner's office listed cardiac dysrhythmia as the cause of death. The concept that young, healthy individuals who epitomize invulnerability could be subject to potential lethal cardiovascular disease and subsequent sudden death is not only counterintuitive, but quite disturbing. Accordingly, we need to increase awareness within the community to the causes of SCD, provide comprehensive and cost-effective screening strategies to the population at risk, and provide easier access to resuscitation equipment at all athletic venues.^7-9

Incidence, Prevalence, and Distribution of SCD

SCD is defined as death due to any cardiac disease within 1 hour after the onset of symptoms.¹⁰ SCD may be due to arrhythmic causes (e.g., ventricular fibrillation [VF], ventricular tachycardia [VT], or asystole) or non-arrhythmic causes (e.g., pulmonary embolus or rupture of the sinus of Valsalva). The true prevalence of SCD is difficult to determine, as a significant percentage of cases are underreported.^1-9 Relying on media reporting may also grossly underestimate the true incidence, since lower profile, non-elite athlete cases are more likely to be overlooked or unrecognized by the public and press. Estimates for runners range from 1 in 15,000 joggers and 1 in 50,000 marathon runners, representing 1 death per 50,000 to 375,000 man-hours of exercise.¹¹ Sudden death is more common in male athletes, approximately 9 to 1, probably because young women have lower rates of participation in certain sports.^1,12 This also may be explained by the disproportionate rate of recognition of hypertrophic cardiomyopathy (HCM) in women.¹³ One of the largest demographic studies of SCD in athletes demonstrated an equal distribution among different ethnic groups.¹⁴ When SCD in athletes is categorized according to etiology, HCM occurs more commonly in males than females and in African-American athletes than in Caucasian athletes, whereas aortic valve stenosis and arrhythmogenic right ventricular cardiomyopathy (ARVC) occurs with more prevalence in Caucasian athletes.^1,14-15 In the United States, SCD most commonly occurs with football or basketball, while in Europe, particularly northern Italy, soccer is most common. However, any sport with vigorous physical exertion may trigger SCD.^14-15 The majority of athletes who die suddenly of heart disease collapse during or immediately after a training session.^2-6,9,14 Only a minority of athletes experience cardiovascular symptoms prior to collapsing, making prevention and screening more difficult, perplexing and ultimately tragic.

Causes of SCD in Young Athletes

Hypertrophic cardiomyopathy. In the United States, the most common cardiovascular cause of SCD is HCM. It accounts for approximately 30% of all SCD events.¹ HCM is an autosomal dominant genetic disorder that results in asymmetric hypertrophy, most commonly the interventricular septum, due to disorganization of cardiac myocytes and myocardial fibrosis.^16-17 Genetic linkage studies have demonstrated multiple chromosome-encoding abnormalities and a variety of different genes that result in a phenotypically similar clinical event.¹⁸ SCD is probably a consequence of an electrically unstable and unpredictable myocardial substrate with reentrant ventricular tachyarrhythmias. This is evidenced histologically by the presence of disorganized myocardial architecture and scarring, leading to microvascular abnormalities and myocardial ischemia.^1,16-17 The annual incidence of SCD in patients with HCM is approximately 1%. Advanced cases are easily diagnosed with echocardiography, and prognosis is confidently determined.¹ However, early presentation or low penetrance cases of HCM may be confused with the benign hypertrophic changes of a normal athlete’s heart. In order to distinguish between these two entities, it would require the athlete to become sedentary for 3-6 months to allow for benign changes to reverse.^19-20 Unfortunately, this process of waiting is inherently problematic to athletes, as most are unable and unwilling to devote that amount of time away from training, which can inevitably have significant emotional and financial implications.

Congenital coronary artery anomalies. The second most frequent cardiovascular cause of SCD in a young athlete is congenital coronary artery anomalies.¹⁴ The most common anomaly presenting with SCD is the left main coronary artery arising from the right sinus of Valsalva or the right coronary artery itself. The proposed mechanisms of sudden death in coronary anomalies relates to the expansion of the aorta and pulmonary arteries from the increased stroke volume, causing changes in the take-off angle of the artery.^14,21-22 The artery, as a consequence, may become compressed, leading to ischemia and polymorphic VT. The compression of the arterial lumen may only be present at vigorous exercise. The possibility of a coronary anomaly should always be considered in a young athlete with a history of chest pain or syncope, particularly if the episodes are triggered by exercise.²³ Transthoracic or transesophageal echocardiography and magnetic resonance imaging (MRI) can be used to diagnose the coronary anomaly.^24,27 Definitive diagnosis by coronary angiography is an indication for surgical repair.

Arrhythmogenic right ventricular cardiomyopathy. ARVC is a disorder more prevalent in Europe than in North America, and is characterized by a thin-walled right ventricle with fibrofatty infiltration.^28-29 These patients suffer from VT with left bundle branch morphology, right ventricular failure, syncope and SCD.^28-29 ARVC is an autosomal dominant disorder with multiple genetic loci.^28-29 Often, ECG abnormalities precede abnormalities identified with common imaging modalities, such as echocardiography and MRI.

Other causes. Other causes of SCD from cardiovascular etiology among young athletes include conditions such as valvular heart disease (aortic stenosis or myxomatous mitral valve prolapse), dilated cardiomyopathy, Marfan syndrome, and myocarditis.^{1-5,9,12,24-25,29-30} A small percentage of young athletes who experience SCD have normal cardiac structure at autopsy and no definitive cause of death can be established. Such deaths are probably due to conditions that are not associated with gross cardiac abnormalities but rather ion channel defects (channelopathies) leading to abnormalities in the electrical circuitry of the heart, including: long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, conduction system abnormalities causing bradycardia, and asystole.^31-36 Another such electrical disorder that may be identified by histology or with screening ECGs is Wolff–Parkinson–White syndrome. Each of these entities is responsible for a small percentage of SCD in athletes and poses a serious dilemma to the physician in the absence of symptoms.

Commotio cordis. Sudden death may also occur among athletes without underlying cardiovascular disease.¹⁴ The most notable is commotio cordis, Latin for “commotion of the heart,” which may present with a wide array of circumstances. A modest, non-penetrating trauma to the chest directly over the heart, without causing damage to the chest wall, may result in SCD in the absence of heart disease.^37-38 This is most commonly seen when a baseball player is hit in the chest with a pitch; however, it may occur in any sport with collisions, including hockey and martial arts. Animal studies revealed that the mechanism relates to the timing of the impact with the cardiac cycle.³⁹ Blunt trauma to the heart within a precise 15-30 millisecond window, just prior to the peaking of the T-wave, may result in VF.³⁹ The exact frequency with which commotio cordis occurs in athletic competition is unknown; however, it appears that it may be more common than many of the other causes of SCD associated with antecedent heart disease.¹⁴ When commotio cordis does occur, only 10% survive the event, largely due to prompt cardiopulmonary resuscitation and defibrillation from an on-site automatic external defibrillator.^37,40 Prevention of commotio cordis entails wearing protective equipment, specifically to the chest wall.^37,40

Guidelines and Management

The objective of systematic pre-participation screening before athletic competition is to detect "silent" cardiovascular abnormalities that, under physical exertion, predispose the athlete to sudden death. However, the standard pre-participation screening process appears to be limited in its ability to identify those cardiovascular abnormalities. In one study evaluating athletes who experienced SCD, 115 were exposed to a standard screening examination, and The American Way Guidelines from the American Heart Association (AHA) and the 26th Bethesda Conference on athletic eligibility and disqualification are based on the premise that intense training increases the risk of sudden death in susceptible athletes with heart disease, and that this risk is likely to be reduced by temporary or permanent withdrawal from sports.^7,8,41 The AHA’s focus is on the systematic exclusion of structural heart diseases known to cause sudden death in young people, beginning with a standardized, complete history taking and physical examination. Only if a high suspicion for cardiovascular disease is evident based on symptoms or findings during screening, then a 12-lead ECG is recommended, and if necessary, referral to a cardiovascular specialist.⁷ The 26th Bethesda Conference was established with the goal of developing consensus recommendations to provide guidance to physicians, athletes, and team officials as well as to the courts regarding the acceptable risk of athletic participation with known cardiovascular abnormalities.⁸ An example of permanent proscription under the current Bethesda guidelines: young athletes with a definitive diagnosis of HCM are discouraged from participating in competitive sports, with the exception of low-intensity sports such as golf and bowling.⁸ An example of temporary exclusion would be acquired diseases that may be reversible, such as myocarditis, justifying temporary withdrawal of an athlete from competition, followed by resumption of organized sports if resolution is documented.⁸

The European Way

Since 1971, Italian law has required that every athlete undergo an annual clinical evaluation to obtain approval to participate in competitive sports.^7-8,15 The annual evaluations routinely include history taking, physical examination, and a 12-lead ECG.¹⁵ An ECG may be abnormal in up to 90% of patients with HCM and ARVC, which can increase the diagnostic screening utility in this population and may, in the long run, confer considerable cost savings.^17,42 The results of the Italian initiative suggest that the identification and disqualification of affected athletes at screening before participation in competitive sports may have prevented sudden death; however, the cost effectiveness of this strategy is still controversial.^7,8,15,43

Lack of Consensus

Although formally controlled studies are lacking, indirect evidence and clinical intuition suggest that screening and disqualification strategies are justified and probably reduce the number of sudden deaths in young athletes.^7,15 However, currently there is no universally accepted policy for screening non-professional athletes. Moreover, the inability to effectively implement recommended guidelines is a glaring problem. For example, in a minority of states,¹¹ non-physician healthcare workers are actually allowed to perform the pre-participation screening, whereas in other states,⁵ legislature does not even require pre-athletic screening.⁷

The Psychosocial Effect

Ultimately, the most challenging aspect to pre-participation screening is not in the screening itself, but rather in the course of action to follow once a decision has been made to disqualify an athlete from participation. There exists tremendous social, psychological, emotional, and financial concerns that are coupled with the recommendation and decision to disqualify an athlete from athletic competition. When a recommendation to forego athletics is made, the pressure that an athlete experiences is intense and can alter an athlete’s ability to choose what is in their best interest. Some may even be willing to accept the risk despite compelling advice.^6,44 The intoxicating effect of sports in some ways nurtures a risk-taking behavior in some individuals, as the potential for financial reward and personal recognition is too overwhelming to walk away from. After all, for a significant percentage of athletes, a disqualification from sports is to deny a person a part of their livelihood, a potential career, and at the very least, an avenue toward achieving personal fulfillment.