Sudden Cardiac Death in Young Athletes: A Brief Review

By Christopher M. Rausch, MD
Director, Cardiopulmonary Exercise Laboratory, Children's Hospital Colorado
Instructor of Pediatrics, University of Colorado School of Medicine

Sudden cardiac death in young athletes continues to be a topic of much concern and debate in both the lay and medical communities. Athletes are often regarded as the healthiest segment of the community, and sudden death events can lead to fear and confusion regarding the safety of sports participation. These deaths are often highly publicized in the media resulting in ramifications beyond the individual's family or local community. Cardiac sudden death itself is an uncommon entity with an estimated incidence of 1 in 100,000 - 200,000 participants. However, given that these estimates are likely under-representative, coupled with up to 12 million young people who participate in competitive and high school athletics in the United States, sudden cardiac death results in the tragic loss of many young athletes each year.

Causes of sudden cardiac death in young athletes

One of the many factors complicating the sudden cardiac death discussion is the number of different cardiovascular conditions which may predispose an athlete to sudden death (Figure 1). Causes including structural cardiac anomalies, coronary artery anomalies, infectious and toxic cardiac disease, inherited connective tissue disorders, trauma, and arrhythmia syndromes have all been shown to play a role in sudden cardiac death.

Hypertrophic cardiomyopathy (HCM) is recognized as by far the most common cause of sudden cardiac death in young athletes in the United States, responsible for at least one-third of cases. This diagnosis may be suspected by physical examination (harsh midsystolic murmur which accentuates with standing or the Valsalva maneuver); however, the murmur may be inaudible or difficult to distinguish from an innocent murmur in some cases. A relatively common genetic cardiac disease, HCM is present in the general population at a rate of 1 in 500 (0.2 percent). Inherited as an autosomal dominant trait, HCM shows a highly variable clinical and morphological expression which may complicate accurate diagnosis. Mutation may occur in any one of at least 11 identified genes encoding cardiac sarcomere proteins. These genetic changes can result in asymmetric hypertrophy of the left ventricle secondary to chaotic hypertrophy and abnormal intracellular connection of cardiac myocytes. The resultant disordered myocardium is prone to microvascular ischemia and scarring leading to a predisposition to reentrant ventricular tachyarrhythmias.

Another common cause of sudden death in young athletes is aberrant coronary circulation. Rarely caused by atherosclerotic disease in young athletes, these deaths are more typically secondary to anatomic coronary artery anomalies (particularly the left main coronary originating from the right sinus of valsalva). In these cases, the mechanism of sudden death is felt to be secondary to insufficient coronary flow due to an acute take-off angle of the coronary from the aorta as well as possible compression of the coronary between the great vessels during strenuous exercise. The vast majority of deaths in these patients occur during exercise and, unfortunately, many have no preceding symptoms.

Less common, with estimates of prevalence in the range of one in 5,000, arrhythmogenic right ventricular cardiomyopathy (ARVC) is another important cause of sudden death in young athletes representing up to 10 percent of cases. These patients rarely have significant physical findings but may present with a personal history of syncope or arrhythmia, or a family history of sudden death. At least 12 different genetic variants have been identified, which are inherited as both autosomal dominant and recessive forms showing incomplete penetrance and variable expression of the ARVC phenotype. While the exact mechanism remains unclear, it is felt that abnormalities of the desmosomes (an important component in mechanical coupling between myocytes) may lead to the progressive death of right ventricular myocardial cells. The loss of myocytes leads to a resultant fibro-fatty replacement. As in HCM, this abnormal ventricular architecture causes a predisposition to reentrant ventricular tachyarrhythmias.

The group of inherited ion channelopathies including Long QT syndrome, Brugada syndrome, and catacholaminergic polymorphic ventricular tachycardia (CPVT), is another cause of arrhythmia which may lead to sudden death in young athletes. Autosomal dominant and recessive inheritance of myocardial ion channel mutations result in abnormalities of cardiac depolarization/repolarization which in turn predisposes these individuals to ventricular dysrhythmias. While the reported prevalence of these diseases is low in athletes who have died suddenly, the true prevalence is likely much higher given that the lack of structural or pathological evidence may preclude accurate diagnosis at autopsy.
A variety of other less common causes have been implicated as well in sudden cardiac death in young athletes. Arrhythmia syndromes such as Wolff-Parkinson-White Syndrome, myocarditis, Marfan Syndrome, aortic stenosis, and mitral valve prolapse have all been shown to be present in a small percentage of cases.

Screening for cardiovascular abnormalities

There has been a great deal of discussion recently regarding how best to identify athletes with clinically significant cardiovascular abnormalities prior to sports participation. This preparticipation screening has been recommended in the hope that athletes at risk could be limited from participation in competitive sports, thereby reducing their risk for sudden cardiac death. While it has been widely agreed upon that athletes should undergo some form of preparticipation screening, the tools that should be used to perform this screening have been highly debated.

The use of non-invasive studies such as electrocardiograms and echocardiograms to screen for many predisposing diseases has been suggested. In Italy, Corrado et al. have demonstrated good success in reducing the numbers of sudden cardiac death through the routine use of screening ECG to identify and exclude from participation athletes at risk, especially those with cardiomyopathy. Based to a large extent on these findings, preparticipation screening electrocardiograms have been recommended by the European Society of Cardiology for all young athletes across Europe. With a reported sensitivity of >90 percent for hypertrophic cardiomyopathy, the ECG may be a useful screening tool. Unfortunately, a wide variety of changes are commonly seen on electrocardiograms of highly trained athletes that are not seen in the general population thereby significantly decreasing the specificity of ECG screening in this population. Additionally, while some cardiac abnormalities such as hypertrophic cardiomyopathy, arrhythmogenic right ventricular dysplasia, Wolff-Parkinson-White syndrome, and long QT syndrome can frequently be readily diagnosed by electrocardiogram, many causes of SCD may have very subtle or no changes by ECG. Given the number of student athletes actively participating in sports in the United States, and with predictions of a cost of hundreds of millions of dollars, the feasibility of implementing a similar ECG screening program in the United States has understandably come under some scrutiny.

In the setting of cardiovascular screening for sudden cardiac death, the role of echocardiography is primarily in identification of well established structural lesions, left ventricular dysfunction/hypertrophy/dilation, or possibly significant right ventricular dysfunction/dilation. Many of the potential causes for sudden death will have only limited or nonexistent findings by standard transthoracic echocardiography. Also, similar to electrocardiography, changes seen in echocardiograms of highly trained athletic individuals often blur the lines between normal and abnormal. As a result, several studies of screening echocardiograms in young athletes were unable to produce a single definitive diagnosis associated with sudden death in athletes.

Due to the cost ineffectiveness of these other tools for screening purposes, many still feel that the sports preparticipation history and physical examination (preparticipation physical evaluation or PPE) remains the most practical method for identification of athletes who may be at risk for sudden cardiac death. While it must be recognized that sudden death may be the first clinical manifestation, many of the disease entities that predispose individuals to sudden cardiac death have a genetic origin and/or may cause clinical symptoms lending them to identification by a routine history. For example, 30 percent of patients with catecholaminergic polymorphic ventricular tachycardia have a family history of unexplained sudden death, and up to one fourth of young individuals suffering from sudden death had previously reported syncope. As such, the American Heart Association has recommended that all young athletes undergo screening with eight elements of personal and family history, and four elements of physical examination prior to sports participation (Figure 2). Unfortunately, the vast majority of high school preparticipation forms in use are grossly incomplete compared with these current consensus guidelines.

Discussion

Sudden cardiac death in young athletes is an uncommon but highly visible event. While many valid arguments exist for the inclusion of other screening tools such as the electrocardiogram and possibly the echocardiogram, their routine use in the current United States healthcare system is currently impractical. Based upon the large population of young athletes, a screening program similar to that recommended by the European Society of Cardiology would be cost prohibitive in the United States. As such, efforts must continue to be made to maximize the impact and effectiveness of the preparticipation screening history and physical examination. Ensuring that screening examinations are performed by adequately trained practitioners using currently recommended guidelines is an important first step in identifying individuals at risk and preventing sudden cardiac death.

Useful references

^{Maron B, Thompson P, Ackerman M, Balady G, Berger S, Cohen D, et al. Recommendations and considerations related to preparticipation screening for cardiovascular abnormalities in competitive athletes: 2007 update. Circulation 2007; 115:1643-1655.}

^{Corrado D, Basso C, Schiavon M, Pelliccia A, Thiene G. Pre-Participation screening of young competitive athletes for prevention of sudden cardiac death. J Am Coll Cardiol 2008; 52:1981-9.}

^{Rausch CM and Phillips G. Adherence to guidelines for cardiovascular screening in current high school preparticipation evaluation forms. J Pediatr 2009; 155:584-6.}

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