Sudden death (athletes)

The prevention of sudden death by athletes, defined as natural, unexpected, death within one hour of the onset of symptoms and subsequent cardiac arrest, remains a challenge. The prevalence of any single, associated condition is very low, probably less than 0.3% and the sensitivity and specificity of tests commonly used to screen leaves much to be desired.

Wider definitions of sudden death are also in use but not usually applied to the athletic situation.

The single most important predictor is exercise fainting or near fainting, which should require explanation and investigation.

While most causes relate to congenital or acquired cardiovascular disease, an exception is commotio cordis, in which the heart is structurally normal but a potentially fatal loss of rhythm occurs because of the accident of timing of a blow to the chest. Survival is about 15% and time to CPR and defibrillation may determine this.

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Defibrillator

Incidence

Sudden death occurs in approximately one in 200,000 athletes annually. The victim is usually male and, in the US, two-thirds occur in football and basketball. This reflects the popularity of these sports and the number of athletes involved in them and elsewhere in the world, soccer is most commonly associated. From statistics derived from NCAA data, one death per 25,000 collegiate athletes over a five-year period was attributable to medical causes.

A series of observational studies have reported on death rates in athletes for causes other than trauma. Van Camp reported rates of approximately 7:1,000,000 and 1:1,000,000 for male and female high school and colleges students respectively, during organized athletic activity. Philips reported rates of 1:735,000 US Air Force recruits aged 17 to 28 during training. The sudden death rate amongst Rhode Island joggers was reported as 1:280,000 for those under 30 years of age, by Ragosta, and 1:7,260 for those 30–65 years according to Thompson. Finally, Maron reported rates of 1:50,000 race finishers in marathons, where the mean age was 37.

To place in context, sudden cardiac death in the US (population 300 million), is estimated to occur 180,000 – 250,000 times per year. While the predominant cause is coronary artery and other vascular disease, about 20% of cases show no obvious structural cardiovascular abnormality and remain undiagnosed after autopsy. Interest in these 'autopsy-negative' deaths in the past ten years has centered around the 'ion channelopathies'. These channels are pores controlling the movement of sodium, potassium and calcium ions into cardiac cells, cumulatively responsible for creating and controlling the electrical signals which control the heart's rhythm. Abnormalities in this system are known to cause relatively rare genetic diseases such as 'Long QT syndrome', 'Brugada syndrome' and 'Catecholaminergic polymorphic ventricular tachycardia', all associated with sudden death. Consequently, more patients with autopsy-negative sudden cardiac death (no genetic abnormalities identified) may comprise a larger part of the 'channelopathies' than previously anticipated and it has been estimated that their incidence may be as high as 11/100,000, in a survey of unexpected sudden cardiac death in England, involving presumed healthy individuals aged 16–64 years.

Age

Age 35 serves as a watershed as to the likely cause of sudden death. Before age 35, congenital abnormalities of the heart and blood vessels predominate. These are usually asymptomatic prior to the fatal event although not invariably so. Congenital cardiovascular problems are reported to occur disproportionately in African-American athletes.

After age 35, acquired coronary artery disease predominates (80%), and this is true regardless of the athlete's former level of fitness.

Causes

Cause	Incidence
Hypertrophic cardiomyopathy	26.4%	Genetically determined
Commotio cordis	19.9%	Structurally normal heart
Coronary artery anomalies	13.7%	Exact mechanisms unknown - some association with other congenital cvs abnormalities
Left ventricular hypertrophy of undetermined origin	7.5%	Probable variant of hypertrophic cardiomyopathy
Myocarditis	5.2%
Ruptured aortic aneurysm (Marfan syndrome)	3.2%	Genetically determined
Arrhythmogenic right ventricular cardiomyopathy	2.8%	Genetically determined
Tunneled coronary artery	2.8%
Aortic valve stenosis	2.6%
Atherosclerotic coronary artery disease	2.6%	Mainly acquired

Screening

Screening is problematic because of low prevalence and indifferent performance of various tests that have been used. Nevertheless, sudden death attracts much public and legislator attention because of its visible and tragic nature. As an example, the Texas Legislature appropriated funds for a pilot study of statewide screening in 2007.

Echocardiogram showing left ventricle

The study employed a combination of questionnaire, examination, and electrocardiography, in all students and echocardiography in a majority selected because of abnormal findings in the preceding three. 35% of the student population studied were flagged as potentially at risk but there were many false positive results with actual disease being confirmed in only 1.23%. Further, a substantial number of that 1.23% declined follow-up evaluation. It should be stressed that this is a single pilot program and original research, but it is indicative of the problems associated with screening and concordant with other experience.

Genetics

Cardiomyopathy

Arrhythmogenic right ventricular dysplasia showing fatty infiltration of right and left ventricle, and poor contraction of right ventricle

Cardiomyopathies are generally inherited as autosomal dominants although recessive forms have been described, and dilated cardiomyopathy can also be inherited in an X linked pattern. Consequently, in addition to tragedy involving an athlete who succumbs, there are wider implications. Within many families of index cases, more than 300 causative mutations have been identified although there is no clear understanding of how these mutations (which affect the same myosin molecule) can lead to the dramatically different clinical characteristics and outcomes associated with hypertrophic cardiomyopathy(HCM) and dilated cardiomyopathy(DCM).

Since HCM, as an example, is typically an autosomal dominant trait, children of an HCM parent have a 50% chance of inheriting the mutation. In individuals without a family history, the most common cause of the disease is a 'de novo' mutation of the gene that produces the β-myosin heavy chain. Not all mutations, it should be noted, have the same potential for a disastrous outcome. For example, troponin T mutations are associated with a 50% mortality before the age of 40, while β-myosin mutations are less threatening.

The role of 'channelopathies' leading to 'Brugada syndrome', 'long QT syndrome' and 'Catecholaminergic polymorphic ventricular tachycardia' has been referred to in 'incidence'.

Heritable connective tissue disease. Heritable connective tissue diseases are rare, each disorder estimated at one to ten per 100,000 of which 'Marfan syndrome' is the most common.

'Myxomatous' degeneration of the aortic valve, common in Marfan Syndrome

It is carried by the FBN1 gene on chromosome 15, which encodes the connective protein fibrillin-1, inherited as a dominant trait. This protein is essential for synthesis and maintenance of elastic fibers. Since these fibers are particularly abundant in the aorta, ligaments and the ciliary zonules of the eye, these areas are among the worst affected. Everyone has a pair of FBN1 genes and because transmission is dominant, those who have inherited one affected FBN1 gene from either parent will have Marfan syndrome. Although it is most frequently inherited as an 'autosomal dominant', there is no family history in 25% of cases.

Recruiting practices aimed at attracting athletes who are unusually tall or who have an unusually wide arm span (phenotypic characteristics of Marfan Syndrome) have the potential to alter the expected prevalence of the syndrome within certain sports.

Testing

Once a disease causing mutation has been identified in an index case, the main task is genetic identification of carriers within a pedigree, a process known as “cascade testing.” Family members with the same mutation may show different severities of disease, a phenomenon known as variable penetrance. As a result, some may remain asymptomatic, with little lifelong evidence of disease. Nevertheless, their children remain at risk of inheriting the disorder and potentially being more severely affected.

Notable athletes who have succumbed

• Pheidippides
• Hank Gathers
• Reggie Lewis
• Marc-Vivien Foé
• Pete Maravich
• Flo Hyman
• Jim Fixx
• Sergei Grinkov
• Darryl Kile
• Miklós Fehér
• Alexander Dale Oen
• Eddie Guerrero