An estimated 1 to 3 per 100,000 apparently healthy young athletes develop an abrupt-onset heart rhythm abnormality Overview of Abnormal Heart Rhythms Abnormal heart rhythms (arrhythmias) are sequences of heartbeats that are irregular, too fast, too slow, or conducted via an abnormal electrical pathway through the heart. Heart disorders are... read more 
and die suddenly during exercise. Males are affected up to 10 times more often than females. Basketball and football players in the United States and soccer players in Europe may be at highest risk.
Causes of Sudden Cardiac Death in Athletes
Generally, the causes of sudden death during exercise are very different in young athletes than in older athletes. However, in all athletes, asthma Asthma Asthma is a condition in which the airways narrow—usually reversibly—in response to certain stimuli. Coughing, wheezing, and shortness of breath that occur in response to specific triggers are... read more 
, heatstroke Heatstroke Heatstroke is a life-threatening condition that results in very high body temperature and malfunction of many organ systems. (See also Overview of Heat Disorders.) Heatstroke can develop after... read more , and the use of performance-enhancing or recreational drugs may cause death due to sudden abnormal heart rhythms.
Young athletes
In young athletes, the most common cause of sudden cardiac death is
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Undetected, abnormal thickening of the heart muscle (hypertrophic cardiomyopathy Hypertrophic Cardiomyopathy Hypertrophic cardiomyopathy includes a group of heart disorders in which the walls of the ventricles (the two lower chambers of the heart) thicken (hypertrophy) and become stiff. Most cases... read more
)
Other heart disorders, such as long QT syndrome Long QT Syndrome and Torsades de Pointes Ventricular Tachycardia Torsades de pointes ventricular tachycardia is a specific type of ventricular tachycardia that occurs in people who have a particular disorder of the heart's electrical activity called long... read more or Brugada syndrome Cardiac Channelopathies Cardiac channelopathies are genetic abnormalities in heart cell proteins that control heart electrical activity and thus can cause heart rhythm disturbances. (See also Overview of Abnormal Heart... read more that cause abnormal heart rhythms, and aortic aneurysms Overview of Aortic Aneurysms and Aortic Dissection The aorta, which is about 1 inch (2.5 centimeters) in diameter, is the largest artery of the body. It receives oxygen-rich blood from the left ventricle and distributes it to all of the body... read more may also cause sudden death in young athletes.
Less commonly, undetected heart enlargement (dilated cardiomyopathy Dilated Cardiomyopathy Dilated cardiomyopathy is a group of heart muscle disorders in which the ventricles (the two lower chambers of the heart) enlarge (dilate) but are not able to pump enough blood for the body’s... read more 
) may be present in a young person who has no symptoms, and the person may die suddenly during or after vigorous exercise.
Abnormalities of the coronary arteries (coronary artery disease Overview of Coronary Artery Disease (CAD) Coronary artery disease is a condition in which the blood supply to the heart muscle is partially or completely blocked. The heart muscle needs a constant supply of oxygen-rich blood. The coronary... read more 
), especially when one of the arteries takes an abnormal path through, rather than on top of, the heart muscle, may also cause sudden death in athletes when the compression cuts off blood flow to the heart during exercise.
Rarely, young, thin athletes may also have sudden heart rhythm disturbances if they experience a strong blow to the area directly over the heart (commotio cordis Commotio cordis Blunt injury to the heart is a blow to the chest that bruises the heart muscle, tears (ruptures) the heart's walls, or damages a heart valve. People may feel that their heart is pounding or... read more ) even when they have no heart disorder. The blow often involves a fast-moving projectile such as a baseball, hockey puck, or lacrosse ball or impact with another player.
Older athletes
In older athletes, the most common cause is
Occasionally, hypertrophic cardiomyopathy Hypertrophic Cardiomyopathy Hypertrophic cardiomyopathy includes a group of heart disorders in which the walls of the ventricles (the two lower chambers of the heart) thicken (hypertrophy) and become stiff. Most cases... read more or heart valve disease Overview of Heart Valve Disorders Heart valves regulate the flow of blood through the heart's four chambers—two small, round upper chambers (atria) and two larger, cone-shaped lower chambers (ventricles). Each ventricle has... read more 
is a cause.
Symptoms of Sudden Cardiac Death in Athletes
Diagnosis of Sudden Cardiac Death in Athletes
Screening
People are commonly screened by their doctor before starting an exercise program Starting an Exercise Program People should consult their doctor before beginning competitive sports or an exercise program. Doctors ask about known medical disorders in the person and family members and about symptoms the... read more 
. Doctors screen people who have medical disorders and also those who do not think they have any medical disorders. People without known medical disorders should typically be checked because some serious disorders do not cause problems until people exercise. People in the United States are reevaluated every 2 years (if high school age) or every 4 years (if college age or older). In Europe, screening is repeated every 2 years no matter what the athlete's age.
Doctors always ask people questions and do a physical examination, but they do testing only when the person's age and reported symptoms are cause for concern. Questions focus on three areas:
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Symptoms such as chest pain or discomfort, fainting or near-fainting, fatigue, and difficulty breathing, particularly when these symptoms occur during vigorous exercise
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Family history, particularly any history of family members who fainted or died during exercise, or who died suddenly before about age 50
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Use of drugs
The physical examination focuses on listening to the heart with a stethoscope for heart murmurs that indicate a possible heart disorder and measuring blood pressure with the person lying down and again while the person is standing.
For younger people, doctors typically do not do any tests unless something abnormal is identified in the person's history or is found during the physical examination. Routine use of electrocardiography (ECG) screening of young athletes is not considered practical in the United States. However, if findings suggest a heart problem, doctors typically do ECG Electrocardiography Electrocardiography (ECG) is a quick, simple, painless procedure in which the heart’s electrical impulses are amplified and recorded. This record, the electrocardiogram (also known as an ECG)... read more 
, echocardiography Echocardiography and Other Ultrasound Procedures Ultrasonography uses high-frequency (ultrasound) waves bounced off internal structures to produce a moving image. It uses no x-rays. Ultrasonography of the heart (echocardiography) is one of... read more 
, or both.
For people over age 35, doctors may also do ECG and exercise stress testing Stress Testing Stressing the heart (by exercise or by use of stimulant drugs to make the heart beat faster and more forcibly) can help identify coronary artery disease. In coronary artery disease, blood flow... read more 
before approving vigorous exercise.
If a heart disorder is found, the person may need to stop participating in competitive sports and undergo further testing. Some people with severe heart disease, such as hypertrophic cardiomyopathy Hypertrophic Cardiomyopathy Hypertrophic cardiomyopathy includes a group of heart disorders in which the walls of the ventricles (the two lower chambers of the heart) thicken (hypertrophy) and become stiff. Most cases... read more , should not participate in competitive sports. However, most people with heart disease may participate in noncompetitive sports. Increased activity is directly related to better health outcomes such as a decrease in "bad" cholesterol levels (low-density lipoproteins), prevention of high blood pressure, and reduction of body fat. Regular exercise is routinely included in care plans for people with most forms of heart disease (cardiac rehabilitation Rehabilitation for Heart Disorders Cardiac rehabilitation is useful for some people who have had a recent heart attack, have heart failure or coronary artery disease that has recently developed or suddenly worsened, or had heart... read more ).
Treatment of Sudden Cardiac Death in Athletes
If people stop breathing and collapse, immediate treatment is with
Resuscitation is continued in the emergency department. If the person survives, doctors treat the condition that caused the abnormal rhythm. Sometimes doctors place an implantable cardioverter-defibrillator Abnormal heart rhythms (arrhythmias) are sequences of heartbeats that are irregular, too fast, too slow, or conducted via an abnormal electrical pathway through the heart. Heart disorders are... read more , which continually monitors the person's heart rhythm and delivers a shock to return the rhythm to normal if needed.
Automated External Defibrillator: Jump-Starting the Heart
More Information
The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
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Nick of Time Foundation: This organization works to increase survival of sudden cardiac arrest with awareness, "hands-only" CPR training, advocacy for having defibrillators in all public places, and access to screening for young athetes.
