The prevalence of cardiovascular disease in young athletes is low, as is the risk of sudden cardiac death in athletes with underlying disease. Of the 10 to 15 million athletes of all ages who participate in organized sports each year in the United States, fewer than 300 die of cardiovascular-related causes. However, sudden cardiac deaths in competitive athletes are highly visible events that have significant liability considerations. Sudden deaths have occurred in athletes of both sexes, in minorities, and in a wide range of ages and sports (most commonly basketball and football in the United States).
The American College of Cardiology (ACC) has released new eligibility guidelines for competitive athletes with cardiovascular abnormalities and clinical guidelines for preparticipation screening. The recommendations were published in the April 19, 2005, issue of the Journal of the American College of Cardiology and are available online at http://content.onlinejacc.org/content/vol45/issue8/index.dtl#_th_bethesda_conference.
The ACC recommendations for eligibility and disqualification of competitive athletes assume a prior diagnosis of cardiovascular abnormalities. The diagnosis of these diseases and reasons that athletes present for evaluation of eligibility may involve several scenarios. Athletes may be referred for assessment of clinical symptoms of cardiovascular disease, or physicians may recognize symptoms during routine history-taking or physical examination. Young athletes also may be suspected of having cardiovascular disease by customary screening examinations before participation in competitive sports.
The objective of preparticipation screening is to recognize “silent” cardiovascular abnormalities that can progress or cause sudden cardiac death. Customary screening strategies for high school and college athletes include history-taking and physical examination. However, these methods have limited power to consistently identify significant cardiac abnormalities. Furthermore, the quality of cardiovascular screening for high school and college athletes, particularly the design of approved questionnaires, is inadequate when measured against screening recommendations from the American Heart Association. Legislation in several states allows health care workers with different levels of training to conduct preparticipation examinations. Improvements in the screening process would result in a greater number of athletes identified with previously unsuspected but clinically relevant cardiovascular abnormalities.
The ACC guidelines are meant to identify the cardiovascular abnormalities and degrees of severity that place the competitive athlete at increased risk for sudden death or disease progression. Physicians should use clinical judgment in defining competitive forms of physical activity for participants in many youth sports activities, particularly for children younger than 12 years.
When a cardiovascular abnormality is suspected, diagnosis should focus on the systematic exclusion of conditions known to cause sudden death in young athletes. Approaches include echocardiography, electrocardiography (ECG), history, and physical examination. In selected patients, additional testing with cardiac magnetic resonance imaging (MRI), exercise testing, ambulatory Holter ECG, implanted loop recording, tilt table examination, or electrophysiologic testing with programmed stimulation can be considered. Diagnostic myocardial biopsies are used only selectively in athletes with clinically suspected myocarditis.
Despite considerable evidence for the effectiveness of DNA-based diagnosis of genetic cardiovascular diseases such as arrhythmogenic right ventricular cardiomyopathy (ARVC), Marfan syndrome, hypertrophic cardiomyopathy (HCM), long QT syndrome, and other ion-channel disorders, diagnosis of these diseases continues to be made through clinical testing in the majority of patients. Genetic testing for heart disease is not readily available on a routine clinical basis for application to large athletic populations.
Echocardiography. Two-dimensional echocardiography is the principal diagnostic imaging modality for clinical identification of HCM by demonstrating otherwise unexplained and usually asymmetric left ventricular (LV) wall thickening. A maximal LV end-diastolic wall thickness of at least 15 mm generally is accepted for the clinical diagnosis of HCM in an adult athlete (in children, two or more standard deviations from the mean relative to body surface area). Echocardiography also would be expected to detect other relevant congenital structural abnormalities associated with sudden death or disease progression in young athletes (e.g., mitral valve prolapse, aortic valve stenosis, aortic root dilation, LV dysfunction). Such testing requires interpretation by a physician trained in echocardiography but cannot guarantee full recognition of all relevant lesions, and some important diseases may escape detection. Annual serial echocardiography is recommended throughout adolescence in athletes with a family history of HCM.
Electrocardiography. The 12-lead ECG may be of use in the diagnosis of cardiovascular disease in young athletes and is a practical and cost-effective alternative to routine echocardiography for population-based pre-participation screening. ECG results are abnormal in up to 95 percent of patients with HCM, often before the appearance of hypertrophy. ECG also will identify many patients with long QT, Brugada, and other inherited syndromes associated with ventricular arrhythmias. It raises suspicion for myocarditis by premature ventricular complexes and ST-T abnormalities, and for ARVC by T-wave inversion in leads V1through V3 and low amplitude potentials. However, some patients with inherited long QT syndrome may not have QT interval prolongation, and ECG abnormalities usually are absent in random recordings from patients with congenital coronary artery abnormalities.
Other Tests. For patients in whom echocardiography results are normal or borderline for LV hypertrophy, but suspicion for HCM persists, cardiac MRI may be useful to clarify wall thickness or detect segmental areas of hypertrophy in selected regions of the LV chamber. Definitive diagnosis of congenital coronary artery anomalies of wrong sinus origin usually requires sophisticated laboratory imaging, including multislice computed tomography or coronary arteriography. In young athletes, however, transthoracic or transesophageal echocardiography or cardiac MRI may be used to raise suspicion of these malformations. ARVC often cannot be diagnosed reliably with echocardiography, and cardiac MRI probably is the most useful noninvasive test for identifying structural abnormalities in patients with this condition (i.e., right ventricular enlargement, wall motion abnormalities, adipose tissue replacement within the wall, and aneurysm formation). However, cardiac MRI is not an entirely sensitive or specific diagnostic test for ARVC.
ATHLETE’S HEART AND CARDIOVASCULAR DISEASE
Systematic training in endurance or isometric sports may trigger physiologic adaptations and structural cardiac remodeling, including increased LV wall thickness, enlarged ventricular and atrial cavity dimensions, and calculated cardiac mass, in the presence of normal systolic and diastolic function (i.e., “athlete’s heart”). The magnitude of physiologic hypertrophy may vary according to the type of athletic training. Other potential adaptations include a variety of abnormal 12-lead ECG patterns, which can mimic those of cardiac disease (i.e., increased R- or S-wave voltages, Q waves, and repolarization abnormalities); these adaptations are seen in approximately 40 percent of elite athletes. Frequent or complex ventricular tachyarrhythmias on Holter ECG are not uncommon in athletes and also are similar to symptoms of cardiac disease, including myocarditis.
Morphologic adaptations of athlete’s heart can lead to a differential diagnosis of HCM, dilated cardiomyopathy, and ARVC. Such dilemmas may arise when cardiac dimensions fall outside clinically accepted partition values. The most common clinical scenarios that result in ambiguous diagnoses for athletes are differentiating HCM from athlete’s heart in athletes with an LV wall thickness of 13 to 15 mm, nondilated and normally contractile LV, and absence of mitral valve systolic anterior motion; and differentiating early presentation of dilated cardiomyopathy from athlete’s heart with an LV end-diastolic cavity dimension of at least 60 mm with low-normal LV function. Diagnostic uncertainty in such cases is common and may be resolved with independent noninvasive clinical parameters, including the response of cardiac mass to short periods of deconditioning, or assessment of diastolic filling. Cardiac MRI, genotyping, and serial acquisition of clinical and morphologic evidence over time also may clarify the diagnosis.
Clinical distinctions between physiologic athlete’s heart and pathologic conditions have critical implications for trained athletes because cardiovascular abnormalities may result in disqualification from competitive sports. Overdiagnosis may lead to unnecessary restrictions, depriving athletes of the social, psychologic, and possible economic benefits of sports.
Medications such as beta blockers, which are commonly used to treat systemic hypertension, HCM, long QT syndrome, and Marfan syndrome, probably will inhibit performance in trained athletes. The use of such drugs should not be considered a means of protection against arrhythmias or a primary means for retaining eligibility in vigorous competitive sports. The use of beta blockers is specifically contraindicated in some sports.
The availability of freestanding automatic external defibrillators (AEDs) at sporting events should not be considered absolute protection against sudden cardiac death nor a treatment strategy for athletes with known cardiovascular disease. In addition, AEDs should not be used as justification for participation in competitive sports that otherwise would be restricted because of underlying cardiac abnormalities and the risk of life-threatening ventricular tachyarrhythmias.
With the increased use of implantable cardioverter-defibrillators (ICDs), more high-risk athletes will become involved in competitive sports. Although little direct evidence is available, the ACC panel concluded that the use of an ICD should disqualify athletes from most competitive sports (with the exception of low-intensity, class IA sports), including those that potentially involve bodily trauma. The presence of an ICD in high-risk patients should not be considered protective therapy or a justification for permitting participation in competitive sports that otherwise would be restricted. Athletes with pacemakers also should not participate in most competitive sports that potentially involve bodily trauma.