CHAPTER 64: THE ATHLETE AND THE CARDIOVASCULAR SYSTEM

Evaluation and management of the athlete with cardiovascular disease and arrhythmias represents a unique challenge. Although athletes are symbols of the healthiest segment of our society, they are occasionally affected by cardiovascular conditions that come to the attention of the clinician. The physician can be faced with clinical judgments related to evaluation of symptoms, such as chest discomfort, or signs, such as a murmur, that can be either benign or a manifestation of an underlying cardiac condition. Clinical judgment commonly serves as the basis for recommendations for therapy and athletic participation. In this setting, there is the real risk of failing to detect a cardiac condition that may result in serious or even life-threatening consequences. There is also considerable risk of unnecessarily treating and restricting sports activity in an athlete misdiagnosed as having an underlying cardiac condition. The consequences of missing an important cardiac diagnosis can be life-threatening. The cardiovascular conditions that predispose to life-threatening complications with athletic activity are now known from pathologic studies^1,2 (Table 64–1). Recommendations for clinical evaluation, management, and athletic participation are also available to guide clinicians.³ This chapter will review cardiovascular disease in the athlete from multiple perspectives. These include distinguishing physiologic cardiovascular adaptations to exercise from true cardiac disease, clinical evaluation of the athlete with suspected cardiovascular disease, arrhythmias in athletes, commotio cordis, guidelines for athletic restriction, and performance-enhancing substances.

The athlete’s heart refers to the clinical syndrome of cardiac chamber enlargement, hypertrophy, and normal or augmented ventricular systolic function commonly accompanied by sinus arrhythmia, sinus bradycardia, and a systolic flow murmur.^4,5 The notion that the cardiovascular system differentiates physiologically, structurally, and functionally in response to athletic training was initially advanced more than a century ago.⁵ Using cardiac auscultation and percussion, Henschen described enlargement of the heart caused by athletic activity in cross-country skiers.⁵ He reported that right and left heart physiologic dilation and hypertrophy resulted from cross-country skiing and that these athletic hearts could perform more work than the heart of a nonathlete.⁵

Debate ensued about whether these adaptations to exercise are physiologic and benign or pathologic and the potential harbinger of disease and disability. The heart of the trained athlete was considered by some to be enlarged and weakened because of the strain of endurance training with potential deterioration of cardiac function and a clinical syndrome of heart failure.⁴ However, it is now recognized that the athlete’s heart represents a benign increase in cardiac mass, with specific circulatory and cardiac morphologic alterations, representing a physiologic adaptation to systematic training.⁴ These cardiac changes represent physiologic cardiovascular adaptations to dynamic exercise, also known as isotonic or aerobic training. Thus, the clinical components of the athlete’s heart are most commonly found in athletes participating in endurance or aerobic exercise.

The acute response to training for athletic activities such as cross-country skiing, long-distance running, swimming, or bicycling includes substantial increases in maximum oxygen consumption, cardiac output, stroke volume, and systolic blood pressure, associated with decreased peripheral vascular resistance.⁴ With several weeks of endurance training, the chronic adaptations to training include increased maximal oxygen uptake from augmented stroke volume and cardiac output and increased arteriovenous oxygen difference. The response to endurance exercise predominantly produces a volume load on the left ventricle.

The morphologic adaptations to endurance training have been quantitatively characterized by multiple studies, largely relying on echocardiography.⁴ The cardiac changes of athletes in response to systematic conditioning are variable, with cardiac remodeling in approximately one-half of trained athletes. These changes include alterations in ventricular chamber dimensions, including increased left ventricular (LV), right ventricular (RV) and left atrial cavity size (and volume), associated with normal systolic and diastolic function.⁴ Enlargement of the LV chamber (≥ 60 mm) occurs in approximately 15% of highly trained athletes.^4,6 Occasionally, enlargement of the left ventricle is accompanied by a mild increase in absolute LV wall thickness exceeding upper normal limits (range, 13-15 mm).⁴ Remodeling of LV mass is dynamic and develops after the initiation of vigorous conditioning. Because these changes are reversible with cessation of training, restriction from exercise and reassessment of LV size and wall thickness can be used to distinguish physiologic changes from those associated with hypertrophic cardiomyopathy (HCM).⁴

Differentiating the physiologic changes resulting from habitual exercise in the athletic heart syndrome with HCM or dilated cardiomyopathy represents a challenge to the clinician (Fig. 64–1). Physiologic cardiac adaptation from regular exercise leads to an increase in LV wall thickness. This can be difficult to distinguish from pathologic changes of HCM. Criteria favoring HCM include a high degree of LV hypertrophy (wall thickness, ≥ 16 mm) with an unusual distribution (heterogeneous, asymmetric, or sparing the anterior septum), a small LV cavity (< 45 mm), the presence of striking electrocardiogram (ECG) abnormalities, and the persistence of hypertrophy after physical deconditioning. Although many athletes have increased intracavitary dimensions, LV end-diastolic diameter > 70 mm is distinctly unusual as a manifestation of the athlete’s heart. Additionally, LV wall thickness > 12 mm is unusual even in highly trained athletes, but not uncommon in elite rowers and cyclists. LV wall thickness ≥ 16 mm raises the possibility of HCM. Hypertrophy (> 12 mm) above the normal range is distinctly uncommon in female athletes. Athletes with LV wall hypertrophy may have increased cavity dimensions, which are rarely present in diseases with pathologic wall thickening.⁴

A spectrum of abnormal 12-lead ECG patterns is present in up to one-half of trained athletes, more commonly in men and in endurance athletes (Table 64–2).^{7,8,9,10,11,12} The most commonly observed alterations include early repolarization patterns, increased QRS voltages, diffuse T-wave inversion, and deep Q waves. ECGs in endurance athletes can show mildly increased P-wave amplitude, suggesting atrial enlargement, incomplete right bundle branch block, and increased voltages consistent with RV and LV hypertrophy.^{7,8,9,10,11,12} Among endurance athletes, voltage criteria for RV hypertrophy are present in a substantial proportion. Abnormal and bizarre ECG patterns suggestive of cardiac disease are noted in a minority of elite athletes.^{7,8,9,10,11,12} Most such ECGs represent only extreme manifestations of physiologic athlete’s heart. A significant minority of asymptomatic elite athletes show distinctly abnormal ECG patterns usually associated with precordial T-wave inversions but without evidence of cardiac disease.¹³ Many uncommon ECG findings in athletes are not considered normal variants and require further evaluation (Table 64–3). Arrhythmias commonly noted in athletes include sinus arrhythmia, sinus bradycardia, and junctional rhythm. They are frequently accompanied by other manifestations of enhanced parasympathetic tone. Atrioventricular (AV) conduction delays with first-degree and Wenckebach or Mobitz type I second-degree AV block are common in endurance athletes and attributable to enhanced vagal tone and withdrawal of sympathetic tone at rest.¹³ Ambulatory monitoring of athletes has demonstrated ventricular arrhythmias, including frequent premature beats, couplets, and nonsustained ventricular tachycardia. These arrhythmias can be within the spectrum of physiologic athlete’s heart.¹³ Such arrhythmias are generally not associated with symptoms or an increased risk of sudden cardiac death and are generally reduced with exercise or deconditioning.¹⁴

The underlying cardiovascular conditions that predispose to the rare and tragic sudden deaths in young athletes are known.^{1,2,3,15,16,17,18} Available population-based data show that these events occur with an incidence of 1 to 2 per 100,000 athletes (12-35 years of age) per year with the frequency eightfold lower in female athletes.^{1,2,3,15,16,17,18} In athletes younger than 35 years of age, inherited diseases such as HCM, arrhythmogenic right ventricular cardiomyopathy (ARVC), and congenital coronary artery abnormalities of wrong sinus origin are the most common causes of sudden death. In athletes older than 35 years of age, atherosclerotic coronary artery disease is the most common cause of death.^{1,2,3,15,16,17,18}

HCM is the single most common cause of sudden cardiac arrest in athletes in the United States in which a definitive cardiac diagnosis can be made postmortem. HCM accounts for about one-third of sport-related sudden fatalities (Fig. 64–2).^{1,2,3,15,16,17,18} HCM is a genetically transmitted disease characterized by genotypic and phenotypic heterogeneity. Usually, the characteristic hypertrophied, nondilated left ventricle with increased wall thickness manifests during adolescence.¹ LV hyper­trophy is characteristically asymmetric with a variety of patterns of wall thickening.¹⁹

The characteristic histopathologic marker of HCM is myocardial disarray with disorganized patterns of myocytes associated with increased interstitial fibrosis and often replacement scarring, with fibrosis considered an acquired phenomenon related to microvascular-based myocardial ischemia. The small-vessel disease in HCM involves the intramural coronary arteries, which commonly show dysplasia of the media, and luminal obstruction. Sudden cardiac arrest in athletes with HCM is attributable to ventricular tachyarrhythmias. Myocardial scarring observed in athletes dying suddenly supports the notion that acute episodes of silent myocardial ischemia can trigger the life-threatening cardiac arrhythmias.^{1,2,3,15,16,17,18}

ARVC is an inherited heart muscle disorder characterized pathologically by fibrofatty replacement of RV myocardium.^{20,21,22,23,24} It represents the leading cause of sudden death on the athletic field in the Veneto region of Italy, accounting for approximately 25% of cardiovascular sudden death in young competitive athletes, but is distinctly uncommon in the United States (5% of athlete deaths).^{20,21,22,23,24} Clinical manifestations include ECG depolarization and repolarization abnormalities commonly localized to right precordial leads. These include inverted T waves in V₁-V₃ in most patients with ARVC. Less commonly, distinctive depolarization waves known as epsilon waves are seen after the QRS complex in the ST segment on the ECG. Cardiac imaging techniques demonstrate RV global or regional morphologic and functional abnormalities.^{20,21,22,23,24} Commonly, premature ventricular contractions or sustained monomorphic ventricular tachycardia with left bundle morphology originate from the right ventricle and are associated with exercise.^{19,20,21,22,23,24} Myocardial aneurysms are localized to the posterobasal, apical, and outflow tract regions, resulting in the clinical characterization of these regions as the triangle of dysplasia. Sudden death during physical exercise is likely related to hemodynamic factors, increased RV volume and wall stress, and enhanced sympathetic tone that culminate in ventricular tachycardia.^{20,21,22,23,24,25} Physical exercise can acutely increase RV afterload and cavity enlargement, which in turn can trigger ventricular arrhythmias by stretching the diseased RV musculature.^{20,21,22,23,24,25}

Anomalies of coronary artery origin can precipitate sudden and unexpected cardiac arrest in athletes probably related to acute ischemia.^1,2,3,26 Most commonly, the anatomic finding at autopsy is the left main coronary artery arising from the right coronary sinus. The acute angle relative to the aorta taken by the anomalous artery leaves a narrowed and compromised lumen, frequently characterized as “slit-like,” which limits coronary blood flow and myocardial perfusion with exercise.^1,2,3,26 Evidence of myocardial ischemia caused by anomalous origin of the coronary artery generally is not evident on 12-lead resting ECG and is rarely elicited with stress testing. Therefore, false-negative exercise stress tests are common in athletes who have subsequently died suddenly from coronary anomalies.²⁶ The diagnosis of anomalous origin of the coronary artery requires a high index of suspicion in young people presenting with exertional chest pain and/or syncope.²⁶

Myocarditis, either acute or healed, is also associated with sudden death in the athlete presumptively by resulting in an inflammatory or fibrotic pathologic substrate predisposing to ventricular tachyarrhythmias.^1,2,3 Life-threatening ventricular arrhythmias in athletes can be associated with focal myocarditis that is “silent” and not reliably detected clinically or by endomyocardial biopsy.^1,2,3,26

Approximately 10% of young athletes who die suddenly with exercise have no evidence of structural heart diseases. In many such patients, the cause of sudden death is likely a primary electrical heart disease. These include primary electrical abnormalities such as ventricular pre-excitation (Wolff-Parkinson-White syndrome) and inherited cardiac ion channelopathies including long QT syndrome, short QT syndrome, Brugada syndrome, and catecholaminergic polymorphic ventricular tachycardia.²⁷ These primary electrical abnormalities and other conditions predisposing to athletic sudden death have ECG changes (Table 64–4).^{1,2,3,7,8,9,10,11,12}

In the absence of underlying cardiovascular disease, blunt nonpenetrating chest blows^{28,29,30,31,32,33,34,35} during athletic or recreational activities that cause sudden cardiac death are known as commotio cordis. Although first noted a century ago, it is only in the past 15 to 20 years that commotio cordis has been recognized as a not uncommon occurrence in youth sports and is now regarded as the second leading cause of sudden cardiac death in young athletes, with global recognition.^{28,29,30,31,32,33,34,35} The most common sports associated with commotio cordis deaths in the United States are those in which projectiles are integral to the game (eg, baseball, softball, ice hockey, football, lacrosse).

Ages of victims range from 1 to 50 years, although the mean age of individuals experiencing commotio cordis is 14 years, with 30% of individuals older than 18 years. Collapse is usually instantaneous, although occasionally delayed 10 to 20 seconds after the chest blow. Cardiac arrhythmias documented soon after collapse are generally ventricular fibrillations (VF); however, as the time to first documented arrhythmia increases, asystole is more frequently evident. Early reports of resuscitated commotio cordis showed poor survival, although more recently, survival from these events has increased markedly to more than 50% as a result of more rapid response times and access to external defibrillation as well as greater public awareness of this condition.^{28,29,30,31,32,33,34,35}

The mechanism by which commotio cordis occurs is complex and largely unresolved, and a porcine model was developed for study of this syndrome, which demonstrated that the immediate cause of collapse was VF (Fig. 64–3).^{28,29,30,31,32,33,34,35} Use of this model has allowed definition of several important determinants of VF following a chest blow, including, most importantly, impact delivered directly over the heart and timing within the vulnerable phase of repolarization (a narrow 10- to 30-millisecond window just prior to the T-wave peak, equivalent to only 1%-2% of the cardiac cycle) associated with peak LV pressure caused by the blow, although a wide range of individual vulnerability to VF is evident in the model.^{28,29,30,31,32,33,34,35} Furthermore, impact velocity appears to have a Gaussian distribution with a velocity of 40 mph most likely to trigger VF. In addition, hardness and reduced diameter of the impact object have been correlated directly with the risk of VF.^{28,29,30,31,32,33,34,35}

Sudden cardiac death in commotio cordis appears to be a primary electrical event. The cellular determinants of VF induced by chest wall blows likely include ion channel activation caused by increased LV pressure.^{28,29,30,31,32} The potassium–adenosine triphosphate ion channel mediates the initiation of VF in the swine model and has also been shown to be activated by atrial stretch.^{28,29,30,31,32} It is possible that more stretch-activated ion channels are also involved.

Efforts to minimize the risk of SCD from commotio cordis have centered on the impact object, chest protectors, and changes in the rules of the sport.^{28,29,30,31,32,33,34,35} Balls softer than standard baseballs have been demonstrated to reduce (but not abolish) the risk of commotio cordis.^{28,29,30,31,32,33,34,35} Chest wall protectors intuitively should reduce the risk of commotio cordis. However, in the US Commotion Cords Registry, approximately one-third of the victims experiencing commotio cordis in organized sports were wearing chest protectors, and in the laboratory model, chest protectors did not reduce the risk of VF.^{28,29,30,31,32,33,34,35} Ongoing efforts to develop more effective chest protectors can decrease the risk of sudden cardiac death in vulnerable athletes. American Heart Association (AHA)/American College of Cardiology recommendations promote the use of age-appropriate softballs to reduce the risk of commotio cordis, as well as the timely availability of automated external defibrillators.³⁶

Commonly, athletes are referred to clinicians with symptoms potentially attributable to an arrhythmia. Arrhythmias can be nonsustained or sustained and hemodynamically significant or not significant. Thus, arrhythmia-related symptoms range from brief palpitations to syncope and resuscitated sudden death. The severity of the symptoms, the presence or absence of structural heart disease, and the family medical history determine the extent of the workup. As a general rule, the severity of the symptoms is related to the risk of subsequent sudden death. Thus, palpitations are frequently benign. Presyncope and certainly syncope are more concerning, and resuscitated sudden death is a major concern.

Palpitations can be caused by atrial or ventricular premature depolarizations, nonsustained arrhythmias such as atrial tachycardia or nonsustained ventricular tachycardia, or, even on occasion, sustained arrhythmias such as supraventricular or ventricular tachycardias that do not cause hemodynamic collapse. The critical element in the workup is to record the cardiac rhythm during symptoms. A 24-hour ambulatory Holter monitor or event loop recorder can be used in the athlete with daily or frequent symptoms. Subsequent cardiac workup and treatment depend on the specific arrhythmia found.

Syncope is a common symptom in young people and athletes. Syncope without prodromal symptoms or occurring at peak exercise is more concerning and likely represents underlying cardiac disease (Table 64–5). Injury secondary to syncope is more often seen in arrhythmic disorders and rarely seen in neurocardiogenic syncope. Athletes with syncope should at a minimum be tested with a resting 12-lead ECG and an echocardiogram. In athletes older than 35 years of age and those with syncope during exertion, an exercise tolerance test should be performed to evaluate for cardiac ischemia and exercise-induced arrhythmias.

Unfortunately, complete clinical and pathologic information is available in only a small fraction of athletes with sudden cardiac death, because there is no mandatory reporting.^36,37,38 In those surviving an episode of cardiac arrest, a complete cardiovascular assessment is necessary. Thus, ECGs, long-term telemetry monitoring, echocardiography, and stress tests are generally warranted. These tests will identify most individuals with HCM, exercise-induced polymorphic ventricular tachycardia, long QT syndrome, short QT syndrome, catecholaminergic polymorphic ventricular tachycardia, Brugada syndrome, and possibly ARVC. Cardiac catheterization, cardiac magnetic resonance imaging, and computed tomography should be selectively used if underlying heart disease is not found with this initial workup. Specific electrophysiologic tests for primary electrical diseases (eg, long QT syndrome, Brugada syndrome, Wolff-Parkinson-White syndrome) are often warranted if the diagnosis is not clear.

Because many of the cardiac diseases that predispose to sudden death in athletes are inherited, the family medical history is important. Therefore, the presence of early sudden death or hereditary cardiac abnormality in the family of an athlete should prompt a thorough cardiac workup regardless of the presenting symptoms.²⁶

The competitive athlete is defined as one who participates in an organized team or individual sport that requires regular competition against others as a central component, places a high premium on excellence and achievement, and requires some form of systematic and frequently intense training.^3,39,40 Although not subjected to a randomized trial design, there is nevertheless circumstantial evidence that sudden cardiac death risk can be increased by vigorous training.^1,2,3,39 Furthermore, because of the considerable pressures of competitive sports, athletes are commonly unable to use judgment and control over their level of exertion or reliably discern or respond appropriately to cardiovascular symptoms, thereby increasing their risk.

Consensus recommendations regarding the eligibility of athletes with cardiovascular disease for competition in organized sports are available to guide clinicians both from the United States and Europe.^{38,39,40,41,42,43} These recommendations have been based on the best available data and the consensus of expert panels considering a variety of genetic and/or congenital cardiovascular diseases that may place athletes at increased risk for sudden and unexpected death or disease progression.^42,43 Eligibility and disqualification recommendations are presented according to specific cardiovascular diseases and with respect to a variety of athletic activities.^38,39,40,41

Although the available consensus guidelines are largely focused on the competitive athlete, other recommendations are available for evaluating recreational athletes.^3,39,40,41 The disqualification and eligibility guidelines for competitive athletes with cardiovascular disease from the United States and Europe are similar in many respects, although the European version is restrictive in disqualifying those with long QT syndrome, HCM, and Marfan syndrome, particularly when diagnostic cardiac findings are borderline or when disease-causing mutations are not accompanied by phenotypic expression.^3,39,40,41 Although restricting competitive athletes with certain cardiovascular diseases (eg, HCM) from sports is clinically justified, it should be underscored that these recommendations are not evidence based and are formulated largely based on expert opinion.^39,40,41

The central purpose of preparticipation screening of trained competitive athletes is to identify or raise suspicion of those cardiovascular abnormalities and diseases that are potentially responsible for sudden unexpected death on the athletic field.^{40,41,42,43,44,45,46,47,48,49} When such athletes are recognized, they are exposed to eligibility and disqualification decisions that become the responsibility of the practicing physician and are a subject of this document.^{39,40,41,42,43,44,45,46,47,48,49} There is general (although not universal) agreement with the principle that screening to detect important diseases and potentially prevent sudden death is justified and potentially beneficial.^{13,38,39,40,41,42,43,44,45,46,47,48}

General Considerations

Currently, broad-based cardiovascular screening is practiced systematically in athletes at all levels of performance (not confined to the elite) in only three countries: in the United States with personal or family history and physical examination (but without ECGs) and in both Italy and Israel with 12-lead ECGs in addition to history and physical examination.^{38,39,40,41,42,43,44,45,46,47,48} In many European countries, screening of athletes is limited to those performing at the elite level (eg, in international, Olympic, or professional sports), and there is little information on nonathlete students.^39,40,41,42 The potential benefit of such initiatives is identification of a small number of individuals with potentially lethal genetic and/or congenital cardiovascular diseases (eg, HCM) so that (1) they may be withdrawn from competitive sports to decrease their personal risk and generally make the athletic field a safer environment; and (2) in the process, some high-risk individuals will be identified who may be candidates for disease-modifying medical or surgical intervention or for prevention of sudden death with implantable defibrillators.

Debate and Controversy

Italian investigators have intensely promoted screening with routine 12-lead ECGs (as well as history and physical) based on a unique > 30-year program mandated by Italian law and supported by sports medicine physicians dedicated full time to the program.^{40,41,42,43,44,45,46,47,48,49} Since 1997, Israel has maintained a similar mandatory ECG-based initiative and national sports law.⁵⁰ For > 50 years, it has been customary practice in the United States to routinely screen high school– and college-aged athletes with history and physical examination (but without noninvasive testing).^{39,44,45,46,51,52,53,54,55,56,57} In contrast, Denmark has pointedly rejected systematic screening for cardiovascular disease in both athletes and any other segment of the population as unjustified in consideration of the low event rate.⁵² Other than Japan, no country has systematically attempted broad-based cardiovascular screening in general healthy populations (not limited to athletes), with or without ECGs.^58,59

Universal Screening: Electrocardiogram Versus History and Physical Examination

Preparticipation screening for cardiovascular disease with personal or family history and physical examination has been the customary practice for all high school– and college-aged competitive athletes in the United States for decades, independent of their performance level. This process is guided by the 14-point history and physical examination elements proposed by the AHA.^39,44,45,46 The AHA recommendations acknowledge that athletes and others with underlying (but undiagnosed) cardiovascular abnormalities may well manifest clinical warning signs (eg, chest pain, excessive exertional dyspnea, syncope) identifiable by careful and systematic history. Because most diseases responsible for sudden death in the young are genetic or familial, a thorough family history is likely to raise suspicion of the disorder. An organic heart murmur can alert the examining physician to valvular or other abnormalities, including LV outflow tract obstruction.

A controversy persists as to whether an ECG (in addition to history and physical examination) is superior to history and physical examination alone for detecting potentially lethal cardiovascular disease, particularly when taking into account the important issues of false-negative and false-positive results, as well as cost and resource availability.⁵³ Indeed, studies comparing these two strategies have failed to demonstrate a mortality benefit for ECG screening.⁴⁹

The debate between those strongly promoting routine ECGs and those opposed to ECGs as a routine screening tool is not fully resolved as yet, although a substantial literature consisting largely of editorials and viewpoint commentaries is accumulating rapidly. Nevertheless, several points are indisputable. First, the 12-lead ECG, while a mainstay of hospital-based cardiovascular practice for decades, is an unproven diagnostic tool for reliable detection of cardiovascular disease in generally healthy populations.^59,60,61 Second, outcome data on athlete screening and mortality have been primarily driven by only one database, that of the Veneto region of Italy (9% of the national population) as part of their long-term screening program.^49,51 This ambitious Italian initiative has been shown to be successful in identifying some at-risk athletes with potentially lethal cardiovascular disease (primarily right ventricular cardiomyopathy, which appears to be endemic in this area of Italy), resulting in mandatory withdrawal from sports.⁴² A sharp decrease in mortality over a 30-year period was demonstrated, which these investigators attributed to incorporation of the 12-lead ECG into the screening program in the early 1980s.^43,44

Third, the Italian data showing that ECG screening reduces mortality in athletes have yet to be replicated elsewhere, and evidence from the United States and Israel appears to dispute and/or diminish the value of the ECG in reducing athlete mortality.^50,53 For example, contemporary death rates in US athletes from Minnesota, where screening is limited to history and physical examination, do not differ from those in the Veneto region of Italy where the ECG is routinely employed, and athlete death rates from Israel did not differ before and after legislation for mandatory ECGs.^50,53 The fact that it has been difficult to consistently show a reduction in athlete mortality directly attributable to routine ECGs is an observation that may be in part driven by the generally low event rates in competitive athletes with cardiovascular disease.^50,53

Relevance of Sudden Death Incidence to Screening

Indeed, the low frequency with which sudden deaths occur in the competitive athlete population negatively impacts the justification for broad-based screening in large populations of young people, as well as the weight that can be afforded to this issue as a public health problem. In this regard, there is now overwhelming evidence that these events are relatively uncommon, albeit exceedingly tragic in each case. Most data place these cardiovascular sudden deaths in the range of about 1 per 80,000 to 1 per 200,000 participants per year, much less common in relative terms than motor vehicle accidents (5000-fold), suicide, drugs, homicide, or cancer in the same age group, and similar in frequency to that of fatal lightning strikes.^44,62,63 In a college (National Collegiate Athletic Association [NCAA]) athlete population, drugs and suicide combined accounted for a similar number of deaths as did confirmed cardiac disease, although a non–forensic-based analysis reported a higher incidence for sudden death.⁶⁴

Furthermore, the absolute number of sudden deaths as a result of documented cardiovascular disease in competitive athletes is small in populations for which forensic data are reported. For example, the 33-year US Sudden Death in Athletes Registry has reported a maximum of 75 such deaths in any given year nationally, and the Veneto database has reported 55 sudden deaths in 26 years, or only about two deaths per year.⁴⁴ In other populations, the average number of confirmed cardiovascular deaths annually is much less (ie, less than one death in Minnesota high school athletes or about four deaths in college [NCAA] athletes).^36,46 Notably, of major concern are false-negative screening results in which the system fails to identify cardiac disease that is in fact established. Indeed, a substantial proportion of athletes (about 30%-40%) may die suddenly of cardiovascular abnormalities that would not necessarily be reliably detected by screening, even with ECGs.⁶⁴

Universal Electrocardiogram Screening

On multiple occasions, AHA consensus expert panels have evaluated and decided not to support mandatory national athlete screening in the United States with routine use of ECGs.^43,44,45,46 Indeed, sudden cardiovascular deaths in athletes are rare (albeit tragic) events insufficient in number to be judged as a major public health problem or justify a change in national health care policy. The most frequently cited obstacles to mandatory national screening of trained athletes are as follows: (1) the large number of athletes to be screened nationally on an annual basis (ie, about 10-12 million); (2) low incidence of events; (3) substantial number of expected false-negative and false-positive results in the wide range of 5% to 20% depending on the specific ECG criteria used; (4) cost-effectiveness considerations (ie, extensive resources and expenses required vs few events in absolute numbers); (5) liability issues unavoidably impacting physicians (ie, charged with both enforcement and the sole responsibility to disqualify athletes from competition); (6) lack of resources or physicians dedicated to performing examinations and interpreting ECGs, in contrast to the long-standing sports medicine program in Italy; (7) influence of observer variability, technical considerations, and the impact of ethnicity/race on the interpretation of ECGs, particularly important for multicultural athlete populations such as in the United States; (8) need for repetitive (ie, annual) ECG screening during adolescence, given the possibility of developing phenotypic evidence of cardiomyopathies during this time period or later; (9) logistical challenges and cost related to second-tier confirmatory screening with imaging and other testing, should primary evaluations raise the suspicion of cardiac disease; and (10) recognition that even with testing, screening cannot be expected to identify all athletes with important cardiovascular abnormalities and that a significant false-negative rate can be expected.^{39,40,41,42,43,44,45,46,47,48,49,65,66,67,68,69}

Nonuniversal Screening for Athletes

Screening programs on a smaller regional and non-national basis have been implemented in some high schools, colleges, and local communities using ECGs (or echocardiograms) with varying expertise, quality control, and results for identifying important cardiac disease. Consistently, the AHA has not opposed ECG-based screening initiatives (often performed by volunteers) in smaller venues. However, for such screening initiatives, the AHA has prudently advised adequate quality control with due consideration for the prominent limitations of the process (including false-negative and false-positive test results) so that the risks as well as benefits can be understood and are acceptable to all participants, communities, and organizations.^44,45,46 Sudden deaths caused by genetic or congenital heart disease are more common in nonathletes than athletes. This brings to the forefront an ethical issue regarding systematic screening of athletes exclusively.

There are certain known and anticipated limitations in using ECGs in population screening, including (but not limited to) false-positive and false-negative test results, technical and interpretation issues, “gray zone” ambiguous diagnoses, and cost and logistics involved in arranging second-tier diagnostic testing, all of which promote anxiety, uncertainty, and legal considerations.^44,45

The use of performance-enhancing drugs and substances remains one of the most important and challenging issues in contemporary athletics. By definition, sports-related doping occurs when a prohibited substance or its metabolite is proven by testing or when an unapproved method is used to increase athletic performance.⁷⁰ Doping substances include stimulants, anabolic steroids, and peptide hormones.⁷¹ Generally, the scientific evidence is insufficient to assess any desired performance-enhancing effect or toxicity. These substances have undergone formal evaluation for therapeutic use. Clinical observations indicate that some have serious side effects.⁷² Appropriately designed clinical trials for toxicity and efficacy have not been performed. Randomized clinical trials are considered unethical because they involve the assessment of banned substances.⁷²

The abuse of drugs or substances that are not approved is a threat to the athlete’s health.⁷² Doping also threatens the integrity of athletics. The use of performance-enhancing drugs or techniques to gain an advantage over others in competition is fundamentally unfair to athletes who train and compete legally. All participating in athletics should be educated with guidance from physicians and relevant athletic organizations regarding the risks of illicit drugs.⁷² The use of performance-enhancing drugs and substances such as anabolic-androgenic steroids, growth hormone, and red cell–boosting agents, as well as medications such as diuretic agents, β₂-adrenergic agonists, and glucocorticoids, jeopardizes athletic eligibility. These drugs and substances, including some commercially available nutritional supplements, can be harmful and result in athletic disqualification. Athletes should disclose all prescription medication and supplement use to health care providers and governing organizations. A therapeutic use exemption can be obtained as an official authorization from a governing agency indicating that an athlete may take a medication that is otherwise considered a banned substance without jeopardizing athletic eligibility.⁷⁰

Recently, multiple specific recommendations related to drugs and performance-enhancing substances have been updated.⁷² These include the recommendation that all athletes should have their nutritional needs met through a healthy, balanced diet without dietary supplements. Additionally, governing bodies should develop policies and educate all athletics that performance-enhancing drugs and supplements should be prohibited by sponsoring or participating organizations as a condition for continued participation in athletic activities. Importantly, it is now explicitly stated that the principle of “unreasonable risk” (ie, the potential for risk in the absence of defined benefit) should be the standard for banning or recommending avoidance of substances being evaluated for permission to use by athletes. Finally, athletes should receive formal education and counseling by physicians and athletic department staff on the potential dangers of recreational drugs and performance-enhancing substances, including the risk of sudden death and myocardial infarction.

Cardiovascular disease potentially contributing to cardiovascular death in athletes presents several challenges to the medical professional and health care system, including diagnosis of cardiac abnormalities associated with sudden cardiac death, management of these cardiac disorders, and the evolution of universally applicable screening protocols aimed at reducing exposure of susceptible individuals to risk of death. The current clinical focus is on identification of underlying cardiac disease by screening strategies, appropriate treatment, and selective restriction from athletic participation. At the same time, it is important to recognize the limitations of this approach and also focus on preparation for cardiovascular emergencies caused by undetected cardiac disease that may manifest on the athletic field. Although significant advances have been made regarding identification, treatment, athletic restrictions, and emergency preparation regarding cardiovascular disease in the athlete over the past several years, it is evident that much remains unknown.