Sudden death in an athlete inevitably stirs public concern as front-page headlines question what more could have been done to identify the risk. Parents may wonder—if this could happen to a young star athlete, could it also strike their child, who participates in recreational athletics? It might also be natural to ask whether the benefits of sports and exercise are worth the apparent risk.

A sudden death is at least as devastating to the primary care/sports medicine community. Physicians are humbled when an asymptomatic athlete with an apparently normal clinical examination dies suddenly. In 1992, the then president of the American College of Sports Medicine directed a “call to action” to the sports medicine community.¹ He noted the decrease in the number of sports-related fatalities achieved by modifying rules and equipment, and by encouraging such simple interventions as including more water intake in daily football practices. The “bad news,” however, was that as other deaths were diminishing, congenital cardiovascular disease was emerging as the major cause of sudden death in high school and college athletes. This article updates the incidence and etiology of sudden death in young athletes and outlines current recommendations for preparticipation screening.

Incidence

Fortunately, sudden death in an athlete, especially a young athlete, is a rare event. Estimates vary greatly depending on the age of the athlete, the source of the sampling population, the sports activity and the definition of sudden death. Sudden cardiac death has usually been defined as one that is unexpected and nontraumatic and that occurs instantaneously or within a few minutes of an abrupt change in the person's previous clinical state.²

Several incidence studies of large population groups have been performed (Table 1).^3–7 One study estimated the incidence of sudden death during exercise in unscreened Rhode Island men less than 30 years of age between 1975 and 1982 as one death per 280,000 men per year.⁵ Another study estimated the incidence of sudden death as one per 735,000 per year among screened, exercising, U.S. Air Force recruits between 17 and 28 years of age in the years 1965 to 1985.⁴

Researchers³ from the National Center for Catastrophic Sports Injury Research identified 160 nontraumatic athlete deaths in high school and college organized sports between July 1983 and June 1993. In addition to the estimated rates of nontraumatic sports deaths in male and female high school and college athletes (Table 1), they noted the following:

1. Estimated death rates were fivefold higher in male athletes than in female athletes (7.47 versus 1.33 per million athletes per year).

2. Estimated death rates were twofold higher in male college athletes than in male high school athletes (14.5 versus 6.6 per million athletes per year).

3. Noncardiac causes of death accounted for 22 percent of the cases.

4. Most deaths occurred in male football and basketball athletes (104 and 160, respectively).

In older athletes, incidence estimates increase somewhat, but the event remains rare. It has been estimated that one exercise-related death per year occurred per 18,000 previously healthy men between the ages of 25 and 75 living in Seattle.⁸ In another study,⁶ the incidence of death during jogging was estimated as one death per year for every 7,620 male Rhode Island residents 30 to 64 years of age between 1975 and 1980, with one death for every 15,240 persons without known disease.

Etiology

Several series of case studies in the past 20 years have reviewed death certificates or used clinical autopsy findings to illustrate the conditions associated with sudden death. A fairly consistent theme has evolved: Sudden deaths in younger athletes were more often associated with congenital cardiovascular structural abnormalities, while sudden cardiac deaths in older athletes were more often associated with acquired atherosclerotic cardiovascular disease. The simple epidemiologic observation that the prevalence of atherosclerosis increases with age appears to begin to have its impact on sudden death etiologies around age 30 to 35.While atherosclerosis has some role before age 35, it is clearly the predominant cause after that age.

In 1980, one of the earliest clinicopathologic studies⁹ in young competitive athletes identified structural cardiovascular abnormalities in 28 of 29 athletes, with hypertrophic cardiomyopathy as the most likely etiology of sudden death in 14 of the 29 cases. In 1991, another researcher¹⁰ reviewed seven etiologic studies and found that hypertrophic cardiomyopathy led the list at 24 percent, with coronary anomalies next at 18 percent and myocarditis at 12 percent.

In 1990, an interesting autopsy study¹¹ identified right ventricular dysplasia as a likely etiology in six of 22 cases of sudden death in competitive young athletes in Northern Italy (ages 11 to 35). This condition was much less prevalent in other studies. Next in frequency in this study was coronary artery atherosclerotic disease; it was found in four of the 22 cases. Finally, a detailed retrospective case control review¹² of exercise-related sudden cardiac deaths in Maryland between 1981 and 1988 demonstrated a statistically strong association between hypertrophic cardiomyopathy and sudden cardiac death in exercising young adults. Table 2 lists the possible causes of sudden, exercise-related cardiac death in young athletes (under age 30) in the estimated descending order of frequency.

Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy is an autosomal-dominant congenital disorder characterized by left ventricular outflow obstruction with asymmetric septal hypertrophy and marked disarray of ventricular muscle fibers. In a recent review¹³ of 4,111 subjects in the Coronary Artery Risk Development in (Young) Adults (CARDIA) Study, the prevalence of echocardiographically defined hypertrophic cardiomyopathy was estimated at two per 1,000 young adults. It is thought that this condition could predispose persons to malignant ventricular arrhythmias leading to syncope or sudden death.

Hypertrophic cardiomyopathy is often clinically silent, but a personal or family history of unexplained syncope, especially effort syncope or sudden-death events, is an important clinical clue. Chest radiography may show cardiomegaly, and electrocardiography may show left ventricular hypertrophy or other changes, but results of these tests may also be normal. The diagnosis is best confirmed with two-dimensional and M-mode echocardiography.

Congenital and Acquired Coronary Disease

Congenital coronary anomalies are multiple, the most common being misplaced aortic ostium, in which the left main and right coronary artery arise from the right sinus of Valsalva. These conditions are difficult to identify unless complaints of early fatigue, angina or exercise-induced syncope lead to a directed evaluation. In one review¹⁴ of 78 cases of sudden death thought to be secondary to autopsyproven coronary anomalies, 62 percent occurred in asymptomatic persons.

Tragically, acquired premature coronary artery disease can appear in the athlete under age 30. Genetic predisposition plus other risk-factor prevalence can sometimes lead to coronary events resulting from typical atherosclerosis. Attention to risk factors and to the early symptoms of ischemia, angina and other effort-related symptoms should be just as aggressively pursued in younger athletes as in older athletes.

Myocarditis

Acute myocarditis is a rare but potentially devastating condition that is most commonly caused by viruses. Coxsackie B virus has been implicated in 50 percent of cases.¹⁵ Early symptoms, if present, may include exercise intolerance and congestive heart failure symptoms with dyspnea, cough and orthopnea. Subtle clinical signs include tachycardia in the absence of fever, pulsus alternans and other clinical signs of heart failure (e.g., S₃ gallop, soft apical murmur, distended neck veins, peripheral edema). Most patients with myocarditis present with sudden death secondary to a ventricular arrhythmia and had few, if any, prodromal signs or symptoms. In addition, inflammatory coronary artery aneurysms associated with Kawasaki's disease have also been reported as a cause of sudden death.¹⁶

Other Conditions

Finally, many other conditions have much less frequently been associated with sudden cardiac death in the young athlete. Marfan's syndrome, with its lethal association with ruptured aortic aneurysms, deserves particular note because of helpful clinical clues¹⁷ that make it a screenable condition. In addition, other preventable conditions should be noted, such as cocaine use (associated with coronary artery spasm) and anabolic steroid use (potential association with hypertrophic cardiomyopathy).^18,19 Other such conditions include conduction abnormalities, aortic stenosis, idiopathic concentric left ventricular hypertrophy and, possibly, mitral valve prolapse.

Screening Strategies and Dilemmas

The impact of sudden death in a young athlete during competition always drives the question as to what more could have been done to identify this person who, apparently, was at higher risk. The use of screening tests, however, should be evaluated by epidemiologic criteria for determining effectiveness, not merely by media and/or public consensus.

Attempts have been made²⁰ to put screening strategies for the prevention of sudden death into perspective by estimating disease prevalence. It has been estimated that 200,000 competitive asymptomatic athletes would need to be screened to potentially identify one athlete who would die as a result of competition. [ corrected] If we had a tool to screen for sudden death with a sensitivity and specificity of 99 percent, the low prevalence of disease would yield a positive predictive value of only 0.05 percent. In other words, only one positive test out of every 2,000 would be correctly positive, and 1,999 would be falsely positive.

One of the problems with screening athletes is that “abnormalities” detected during examinations may merely be normal variants. The changes that occur in the heart in response to athletic training are known as “the athletic heart syndrome.”²¹ The well-trained athlete often demonstrates electrocardiographic, radiographic and echocardiographic changes of cardiac enlargement and enhanced vagal tone. In addition, the clinical examination may demonstrate bradycardia, S₃ and S₄ heart sounds, and innocent flow murmurs. While clinical criteria have been developed to assist in distinguishing athletic heart syndrome from pathologic conditions, differentiation of normal from abnormal changes may be extremely difficult.

Use of Echocardiography

Because hypertrophic cardiomyopathy is the most common cause of sudden death in the young competitive athlete, health care strategy should focus on detection of this disease. A good history and physical examination are accepted as the minimal standard for preparticipation assessment. Since electrocardiography and treadmill stress testing are plagued by a high degree of false-positive results (primarily because of athletic heart syndrome),²² most attention in the literature has focused on the use of echocardiography for diagnosis. The echocardiogram is considered to be sensitive and specific in detecting hypertrophic cardiomyopathy. The principal concerns with echocardiography are the cost and the risk of misdiagnosing a healthy athletic heart and, therefore, restricting an otherwise-healthy athlete.²³

Several studies have applied echocardiography to screening large athletic populations. In one study,²⁴ two-dimensional echocardiography was performed on 265 college athletes of predominately African-American descent. The interventricular septum was 13 mm or greater in 29 men (13 percent), but none had abnormal septal-to-posterior wall-thickness ratios (normal: less than 1.3). None of the athletes who had echocardiography as the initial screening test were thought to have an increased risk for sudden death.

In another study,²⁵ 501 college athletes were screened with both a personal and family medical history and 12-lead electrocardiography. Subsequently, 90 athletes were triaged to undergo echocardiography. While three athletes were identified as having interventricular septal thickening, no athlete was restricted from participation. At the then cost of $280 to $500 for echocardiography alone, the cost to that athletic program would have been $25,000 to $45,000.²³

In an attempt to evaluate the economic feasibility of a limited screening echocardiogram, another group of researchers²⁶ performed 2,997 echocardiograms during annual athletic preparticipation examinations. The estimated total cost per athlete was $13.81 (the tests were provided nearly free). Each test took approximately two minutes to complete. The estimated interpretation cost was $60.00 per hour (reading 35 echocardiograms per hour). No abnormalities were uncovered that precluded athletic participation. While the authors concluded that screening echocardiograms can be cost-effectively incorporated into the preparticipation examination, they noted that validation of the screening echocardiogram requires further work.

While the role of echocardiography in routine screening in the asymptomatic athletic population is limited by cost and the low prevalence of the disease, recent evidence suggests that even echocardiography may not always demonstrate hypertrophic cardiomyopathy. Recent molecular genetic studies²⁷ have demonstrated that clinical features such as arrhythmias, myocardial ischemia and/or diastolic dysfunction may be present in patients in the absence of left ventricular hypertrophy as determined by echocardiography. While the reports of these studies clearly state that current practice is far from incorporating genetic testing into routine clinical practice and screening, they concluded that relying solely on echocardiography provides a restricted view of the prevalence and clinical spectrum of hypertrophic cardiomyopathy.

In a recently published detailed study,²⁸ the demographics of sudden death in young competitive athletes was profiled. A review of the records of victims of sudden death revealed that a standard history and physical examination had been completed in 115 of the athletes (158 cases were reviewed). In only four (3 percent) of these athletes was there any suspicion of a cardiovascular problem. In only one athlete was the correct diagnosis, Marfan's syndrome, made—and that athlete did not withdraw from athletic participation.

In 15 of the 158 athletes, symptoms provoked individualized work-ups. These evaluations led to seven correct diagnoses and two disqualifications from competitive athletics. In reviewing cases retrospectively, 31 percent of the athletes with anomalous coronary arteries had symptoms (syncope or dizziness) and just 21 percent of the athletes with hypertrophic cardiomyopathy had symptoms. These medical evaluations failed to identify 47 of 48 cases of hypertrophic cardiomyopathy.

Current Recommendations

The Science Advisory and Coordinating Committee of the American Heart Association (AHA) appointed a panel to develop a consensus recommendation that was recently published.²⁹ Their recommendations are consistent with the newly published Preparticipation Physical Evaluation Monograph endorsed by the American Academy of Family Physicians.³⁰ The AHA concluded that some form of preparticipation cardiovascular screening for high school and collegiate athletes is justifiable and compelling, based on ethical, legal and medical grounds. The AHA resolved that a complete and careful personal and family history and physical examination designed to identify (or raise suspicion of) cardiovascular lesions known to cause sudden death or disease progression in young athletes is the best available and most practical approach to screening populations of competitive athletes, regardless of age. The AHA additionally recommends that an examination be performed before participation in organized high school and collegiate sports. Screening should then be repeated every two years; in intervening years, an interim history should be obtained.

In addition, the AHA made specific recommendations about the content and performance of the preparticipation cardiovascular examination. The history should include the following: previous occurrence of chest pain; discomfort or syncope; near syncope; excessive, unexpected and unexplained shortness of breath or fatigue associated with exercise; past detection of a heart murmur or increased systemic blood pressure; family history of premature death or significant disability from cardiovascular disease in close relatives younger than 50 years of age; and specific knowledge of the occurrence of certain conditions (e.g., hypertrophic cardiomyopathy, dilated cardiomyopathy, Marfan's syndrome, long QT syndrome or clinically important arrhythmias).

The cardiovascular examination should include the following: precordial auscultation in both the supine and standing positions to identify, in particular, heart murmurs consistent with dynamic left ventricular outflow obstruction; assessment of the femoral arteries to exclude coarctation of the aorta; recognition of the physical stigmata of Marfan's syndrome and brachial blood pressure measurement in the seated position (Table 3).

The “focused” examination should seek to rule out historical or physical examination features that have been associated with common causes of sudden death in young athletes (Table 4). Athletes who demonstrate abnormalities on either the history or the physical examination warrant a more detailed examination. This evaluation may include electrocardiography, echocardiography, exercise stress testing and/or cardiac catheterization. In addition, the athlete may require temporary disqualification from athletic participation pending further evaluation. Because further testing has certain limitations, it is the authors' opinion that cardiac consultation is warranted in an athlete suspicious for cardiac disease.

Cardiovascular abnormalities should be judged with respect to the 26th Bethesda Conference³¹ consensus panel recommendations for the final determination of eligibility for future athletic competition. The Bethesda report classifies individual sports according to the type and intensity of exercise and the danger of bodily injury from collision, or the consequences of syncope. This detailed, comprehensive report, which is available through the American College of Cardiology (Heart House, 9111 Old Georgetown Rd., Bethesda, MD 20814-1699), provides useful guidance to physicians with regard to the acceptable medical risks of athletic participation in patients with known cardiovascular abnormalities.