**7. Causes of SCD**

Elucidation of the etiological causes of SCD in athletes is one of the most controversial issues in this area. Meanwhile, it is one of the key issues for the development of scientifically based methods for SCD prevention, selection of individuals suitable for sports, and primary and secondary prevention of SCD. Due to new technologies in diagnostics and an increasing number of studies in this area, the opinions on the etiology of SCD have changed considerably. In the 1980s, among all SCD cases in young athletes in the USA, HCM was diagnosed in 36% of athletes who died suddenly, with the maximum left ventricular wall thickness from 15 to 40 mm (mean 23 ± 5 mm) and an average weight of the heart of 521 ± 113 g, followed by (in a descending order) coronary artery abnormalities and borderline left ventricular hypertrophy, interpreted as possible HCM [6]. However, we cannot exclude the possibility that it was exercise-induced cardiac hypertrophy (which is a component of the non-pathological athlete's heart), myocarditis, ARVC, and ion-channel cardiac disease or channelopathies (long or short QT syndrome, Brugada syndrome, idiopathic ventricular fibrillation, catecholaminergic ventricular tachycardia), i.e., diseases that can only be determined by an ECG prior to death. The long QT syndrome (LQTS) is the most dangerous ion-channel cardiac disease in young person and sports accordingly. Modern diagnostic of LQTS (in the absence of secondary causes for QT prolongation) is based on the ESC criteria [9]. At the present days, mutation in 16 various genes have been identified (LQTS1–LQTS16). The LQTS1 most dangerous during sports activity because 90% cardiac events (SCD, cardiac arrest, syncope) occur due adrenergic triggers and in water [24]. Other pathologies, such as mitral valve prolapse, aortic rupture, aortic stenosis, dilated cardiomyopathy, Wolff-Parkinson-White syndrome, rare non-specific myocardial damage (sarcoidosis), and other causes, were recorded in 1–2% of cases each.

A smaller (though with a more extended age range (11–65 years) analysis of sports-associated SCD cases in Spain [15] has demonstrated that in most cases

**55**

logical changes.

*Sudden Cardiac Death in Young Athletes DOI: http://dx.doi.org/10.5772/intechopen.90627*

young individuals.

**8. Ethnic differences**

the cause of SCD in all ages was ischemic heart disease (40.9%), arrhythmogenic cardiomyopathy (as in some cases there was not only right ventricular but biventricular dilatation, and this diagnosis was made) in 16.3% of cases, HCM (6.5%), left ventricular hypertrophy (4.9%), myocardial fibrosis (3.2%), nonatherosclerosis coronary artery abnormalities (3.2%), dilated cardiomyopathy (1.6%), etc. In 16.3% of cases, the cause of death remained unknown. When the observation group was divided into SCD cases occurring before and after 30 years of age, it was revealed that the majority of cases of ischemic heart disease were concentrated in the older age group (23 vs. 2 cases younger than 30 years) and that there was an equal number of cases of HCM, while ARVC, coronary artery abnormalities (so as spontaneous dissection), and all cases with uncertain autopsy results were more frequent among

However, in the abovementioned French study [16] of SCD cases in athletes and persons regularly engaged in physical activity aged below 35 years, the percentage of HCM reached 10%, while cases classified as "unexplained death" accounted for 36%; according to the data from the US National Collegiate Athletic Association, published in 2015 [5], the structure of SCD included unexplained death (classified as sudden unexplained death - SUD) in 25% cases, confirmed HCM in 8%, and not otherwise specified HCM in 8%. The most up-to-date information on the subject is probably presented in the 2016 report by the British Registry of SCD in sports [4], where SUD in all age categories constituted 42% and HCM, 6%. Marked changes in the age dynamics of SCD etiology were also noted. In the age group of over 35 years, SUD constituted 28% (idiopathic left ventricular hypertrophy with fibrosis (ILVHF) accounted for the same percentage); at the age of 18–35 years, the proportion of SUD increased to 44% (ILVHF to 14%), and in the youngest group of <18 years, the frequency of SUD was the highest (56%), while ILVHF rates decreased to 10%. Rates of HCM and myocarditis confirmed by autopsy remained virtually unchanged with age at 6–8% for HCM and 1–2% for myocarditis. The frequency of identified ARVC moderately increased with age, from 6% in athletes under 18 years old to 14% at the age of 18–35 and 18% in athletes aged over 35 years.

There are some ethnic differences in SCD rates depending on its cause. In general, for over 27 years of observation in the USA, white males dominated in a large cohort of athletes who died suddenly (46%), followed by African Americans and other minority (43%), and white and black and other minority females (8 and 3%) [6]. However, an analysis of specifically cardiovascular SCD in those who died from HCM and coronary artery abnormalities revealed significantly higher (more than twofold) rates in African Americans, while Caucasians were still at the top of the list for ARVC and primary electrical diseases (channelopathy). In the European study [21], the range of diseases identified in athletes suddenly dying was almost the same, yet there were significant differences in the frequency of the main variants of myocardial damage; ARVC was detected in 24% of cases, HCM in 2%, and myocarditis in 10%. If the proportion of the three major variants of myocardial damage (ARVC, HCM, and myocarditis), detected in suddenly dying young American and Italian athletes, is compared, similar aggregate values are obtained, namely, 38% in Italy and 46% in the USA. Taking into account all potential ethnic differences or autopsy reports, there may be a different interpretation of similar pathomorpho-

Nevertheless, it is obvious that the main risk group for SCD in athletes includes those with life-threatening cardiac arrhythmias and myocardial changes. However,

#### *Sudden Cardiac Death in Young Athletes DOI: http://dx.doi.org/10.5772/intechopen.90627*

*Sudden Cardiac Death*

athletes who had a history of syncope.

**7. Causes of SCD**

specific diseases or conditions or potential symptoms preceding the fatal episode. In 60 squash players who died suddenly, Northcote et al. [20] were performed an analysis of prodromal symptoms before death. In a decreasing order of symptom frequency, athletes with sudden deaths complained of chest pain, increasing fatigue, non-specific gastrointestinal disorders, a burning sensation in the heart area, feeling short of breath, pain in the ears or neck, non-specific malaise, upper respiratory tract infections, dizziness and/or palpitations, and severe headache. Five of the victims (8.3%) had no significant symptoms before death. Prodromal symptoms were more frequent in athletes than in nonathletes of the same age who died suddenly, 32 vs. 23%, respectively, as observed by Corrado et al. [21]. This suggests that even minor, non-specific health complaints in regularly training athletes must be taken seriously by doctors, coaches, and the athletes themselves, as they may herald the onset of a life-threatening event. Some conditions in athletes, often considered to be undoubtedly life-threatening, such as syncope, to the contrary, are not always associated with a risk of sudden death, although that risk should always be ruled out first. For example, cardiac diseases with a high risk of SCD that required a withdrawal from the sports were revealed only in two (0.4%) of 474 young athletes with syncope [22]; these diseases were hypertrophic cardiomyopathy (HCM) in one case and arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVC) in the other. In our study [23], no diseases possessing a risk of SCD and requiring a withdrawal from sports have been identified in any of the 34 high-level

Elucidation of the etiological causes of SCD in athletes is one of the most controversial issues in this area. Meanwhile, it is one of the key issues for the development of scientifically based methods for SCD prevention, selection of individuals suitable for sports, and primary and secondary prevention of SCD. Due to new technologies in diagnostics and an increasing number of studies in this area, the opinions on the etiology of SCD have changed considerably. In the 1980s, among all SCD cases in young athletes in the USA, HCM was diagnosed in 36% of athletes who died suddenly, with the maximum left ventricular wall thickness from 15 to 40 mm (mean 23 ± 5 mm) and an average weight of the heart of 521 ± 113 g, followed by (in a descending order) coronary artery abnormalities and borderline left ventricular hypertrophy, interpreted as possible HCM [6]. However, we cannot exclude the possibility that it was exercise-induced cardiac hypertrophy (which is a component of the non-pathological athlete's heart), myocarditis, ARVC, and ion-channel cardiac disease or channelopathies (long or short QT syndrome, Brugada syndrome, idiopathic ventricular fibrillation, catecholaminergic ventricular tachycardia), i.e., diseases that can only be determined by an ECG prior to death. The long QT syndrome (LQTS) is the most dangerous ion-channel cardiac disease in young person and sports accordingly. Modern diagnostic of LQTS (in the absence of secondary causes for QT prolongation) is based on the ESC criteria [9]. At the present days, mutation in 16 various genes have been identified (LQTS1–LQTS16). The LQTS1 most dangerous during sports activity because 90% cardiac events (SCD, cardiac arrest, syncope) occur due adrenergic triggers and in water [24]. Other pathologies, such as mitral valve prolapse, aortic rupture, aortic stenosis, dilated cardiomyopathy, Wolff-Parkinson-White syndrome, rare non-specific myocardial damage

(sarcoidosis), and other causes, were recorded in 1–2% of cases each.

A smaller (though with a more extended age range (11–65 years) analysis of sports-associated SCD cases in Spain [15] has demonstrated that in most cases

**54**

the cause of SCD in all ages was ischemic heart disease (40.9%), arrhythmogenic cardiomyopathy (as in some cases there was not only right ventricular but biventricular dilatation, and this diagnosis was made) in 16.3% of cases, HCM (6.5%), left ventricular hypertrophy (4.9%), myocardial fibrosis (3.2%), nonatherosclerosis coronary artery abnormalities (3.2%), dilated cardiomyopathy (1.6%), etc. In 16.3% of cases, the cause of death remained unknown. When the observation group was divided into SCD cases occurring before and after 30 years of age, it was revealed that the majority of cases of ischemic heart disease were concentrated in the older age group (23 vs. 2 cases younger than 30 years) and that there was an equal number of cases of HCM, while ARVC, coronary artery abnormalities (so as spontaneous dissection), and all cases with uncertain autopsy results were more frequent among young individuals.

However, in the abovementioned French study [16] of SCD cases in athletes and persons regularly engaged in physical activity aged below 35 years, the percentage of HCM reached 10%, while cases classified as "unexplained death" accounted for 36%; according to the data from the US National Collegiate Athletic Association, published in 2015 [5], the structure of SCD included unexplained death (classified as sudden unexplained death - SUD) in 25% cases, confirmed HCM in 8%, and not otherwise specified HCM in 8%. The most up-to-date information on the subject is probably presented in the 2016 report by the British Registry of SCD in sports [4], where SUD in all age categories constituted 42% and HCM, 6%. Marked changes in the age dynamics of SCD etiology were also noted. In the age group of over 35 years, SUD constituted 28% (idiopathic left ventricular hypertrophy with fibrosis (ILVHF) accounted for the same percentage); at the age of 18–35 years, the proportion of SUD increased to 44% (ILVHF to 14%), and in the youngest group of <18 years, the frequency of SUD was the highest (56%), while ILVHF rates decreased to 10%. Rates of HCM and myocarditis confirmed by autopsy remained virtually unchanged with age at 6–8% for HCM and 1–2% for myocarditis. The frequency of identified ARVC moderately increased with age, from 6% in athletes under 18 years old to 14% at the age of 18–35 and 18% in athletes aged over 35 years.
