Sudden cardiac death (SCD) related to exercise or sports is generally defined as unexpected death due to loss of heart function occurring during or within one hour of exercise or participation in athletic activity. The event is also referred to as sudden cardiac arrest and death (SCA/D).
SCD related to sport or exercise means that the exerciser suffered a cardiac arrest during exercise/sport or within one hour of stopping the activity. While sometimes the SCD is due to a known cause or trauma, the cardiac arrest is often completely unexpected in an athlete who was presumably healthy and fit. Sometimes there are warning signs and symptoms leading up to the cardiac arrest, such as syncope during or after exertion, but in many cases, the athlete was performing the athletic activity without any apparent symptom or issue.
Sudden cardiac death during exercise or sports is uncommon. In high school and college athletes in the United States (age 12–24 years), the incidence of SCD has been found to be 0.5/100,000 participants per year. However, because there was no mandated national registry as of 2016 for recording all deaths related to sport and exercise, this number may be underestimated.
Statistics concerning sudden death related to exercise and sport vary with the subgroup studied. Among athletes who suffer sudden cardiac death in the United States, one in 15,000 occurs in recreational runners; one in 50,000 occurs in marathon runners; and one in 100,000 occurs in high school athletes. One study of NCAA college athletes suggested that the highest rates of SCD in the United States occur in basketball and football players; this figure is partly due to the popularity of these sports in North America and the large number of players who participate in them. In Europe, soccer players are the group of athletes at highest risk of SCD; in Japan, practitioners of kendo (Japanese swordsmanship) have a higher than average rate of SCD. According to the Canadian Cardiovascular Society, the rates of SCDs among Canadian athletes are comparable to those reported in the United States.
At the high school level, there appears to be a higher rate of SCD in football, basketball, baseball, lacrosse, and soccer than in such activities as swimming or tennis. For athletes older than 35 years, sudden death is most commonly related to running, particularly marathon running, rather than other sports.
Sports-related SCD is more common in men than women, which partially reflects the greater rate of sport participation in men; the sex ratio in the United States as of 2016 was 9 males to 1 female. Sportsrelated SCD is also more common in African Americans than in Asians, Hispanics, or Caucasians.
The most common underlying causes of sport/exercise-related sudden cardiac death vary by age. Older athletes (typically defined as older than 35 years) are more likely to suffer cardiac arrest as a result of unsuspected coronary artery atherosclerosis. In this case, the athlete may have a positive family history of premature heart disease or such other cardiac risk factors as high cholesterol, high blood pressure, diabetes, obesity, or a history of smoking. Older individuals with known or unknown atherosclerosis performing an unaccustomed level of higher-intensity exercise, particularly in extreme environments, such as snow shoveling, may be at particularly high risk. The older athlete/exerciser may have warning signs and symptoms, such as chest tightness with exertion, feeling out of breath, or feeling faint; or the person may be asymptomatic leading up to the cardiac arrest.
For athletes younger than 35 years, nontraumatic sudden cardiac death is usually a result of congenital malformations of the heart or acquired cardiac disturbances. The most common causes of nontraumatic sudden cardiac death in the United States are:
Regardless of underlying pathology, the cause of SCD is typically a sudden lethal arrhythmia, though in the case of Marfan syndrome, the cause of death may be sudden dissection of the aorta.
Sudden cardiac arrest in younger athletes can also be caused by commotio cordis, which occurs when blunt trauma to the chest, such as a blow caused by a pitched baseball, hockey puck, or lacrosse ball, strikes the chest in a specific phase of the cardiac cycle, causing sudden ventricular fibrillation or another dangerous arrhythmia. The tragedy in commotion cordis is that these athletes have anatomically normal hearts and are simply in the wrong place at the wrong time. Commotio cordis is the cause of 19.9% of cases of SCD in the United States.
In the early 2000s, another subgroup of exerciserelated deaths was making headlines. Anecdotally, it appeared that there was an increase in sudden cardiac death related to running, particularly races of a 10k distance or greater. It was unclear whether there was an actual increase in deaths or whether the increase reflected better tracking. Assuming the death rate had indeed risen, one likely explanation is the mainstreaming of marathons and other races, meaning that a higher number of less fit, older, and potentially less healthy individuals are participating.
There remained a possibility that even healthy runners are at greater risk during or immediately following a challenging race. The prevailing theory as of 2016 was that the musculoskeletal trauma of running and other types of endurance exercise release muscle enzymes, which may activate platelets and produce a thrombus (blood clot), inducing cardiac ischemia (lack of oxygen) and an arrhythmia. Thus the guidelines issued by the International Marathon Medical Directors Association suggest taking a baby aspirin the morning of a training run or race of 10k distance or greater. The association's full recommendations for runners of 10k distances or greater are:
Finally, though not all athletes will suffer warning signs and symptoms, it is important to realize that many do. Athletes, coaches, trainers, and physicians should be aware of warning signs that could indicate an underlying cardiac problem: chest pain or tightness during or after exertion; unusual shortness of breath during or after exertion; presyncope or syncope during or after exercise; and palpitations or an irregular heartbeat during or after exercise. In addition, a family history of sudden cardiac death, particularly at a young age, should be considered a risk factor and may necessitate further testing.
An athlete who is seen to fall suddenly unconscious and lack a pulse during or after exercise or sport is diagnosed as having suffered a SCD.
An athlete who has suffered a SCD needs immediate cardiopulmonary resuscitation and defibrillation. This event requires prompt response by trained personnel and transport to a medical center for more advanced testing and treatment. The use of automated external defibrillators (AEDs) at sports arenas, gyms, health clubs, and finish lines has increased the survival rate of athletes who suffer sudden cardiac death.
The prognosis depends on the speed of CPR administration, defibrillation, and the EMS response, as well as the underlying cause of the SCD. Experiencing an SCD with an AED and a trained person nearby dramatically increases the odds of survival.
The fact that a number of cardiomyopathies and such disorders as Marfan syndrome are genetically determined has led to the suggestion of using genetic screening to identify athletes at increased risk of SCD. Unfortunately, the low predictive value of such testing combined with the difficulty of interpreting uncertain findings made this approach to preventive care unfeasible as of 2016.
See also Cardiovascular disease ; Cardiovascular system .
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American College of Cardiology, Heart House, 2400 N St. NW, Washington, DC, 20037, (202) 375-6000, (800) 253-4636, Fax: (202) 375-7000, email@example.com, http://www.acc.org .
American Heart Association, 7272 Greenville Ave., Dallas, TX, 75231, (800) 242-8721, http://www.heart.org .
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International Marathon Medical Directors Association, 24 W. 57th St., Ste. 605, New York, NY, 10019, (212) 765-5763, IMMDANYC@aol.com, http://immda.org .
Lisa Womack, PhD
Revised by Rebecca J. Frey, PhD