SCD, mainly caused by malignant ventricular arrhythmias,6 is one of the leading causes (>50%) of cardiovascular death worldwide. It is defined as unexpected natural death from a cardiac cause within a short time period, generally ≤1 hour from the onset of symptoms, in a person without any prior condition that would appear fatal.7 Although rare in the young, participation in competitive sports increases the risk of SCD7; the annual incidence of SCD in athletes aged <35 years is reported as 1:100000–300000,8 although recent studies have suggested that this is an underestimate and that 1:50000 is more realistic.9 It is more common in males.10

The fatal event is usually caused by rhythm disturbances, particularly tachyarrhythmias such as ventricular fibrillation. The arrhythmia may have various causes (ischemia, primary arrhythmia, rapid atrioventricular conduction), but the common denominator is electrical instability7 (Table 2).

The most common cause of SCD in young athletes is hypertrophic cardiomyopathy (HCM),11 although in a study in the region of Veneto, Italy, the leading cause was arrhythmogenic right ventricular dysplasia (ARVD).12 This may be explained by regional differences between Europe and the USA and by the different screening methods used in Italy, where all competitive athletes aged under 35 undergo testing consisting of a thorough clinical and family history, physical examination and 12-lead ECG. Such screening is more likely to detect HCM (in which over 95% of cases present a pathological ECG) than ARVD, most cases of which are only diagnosed on autopsy and which contribute significantly to mortality in young athletes.14 In athletes aged over 35, the leading cause of SCD is atherosclerotic coronary disease.3

According to the BC#36, a competitive athlete is defined as one who participates in a team or individual sport, competes regularly, and undergoes systematic training (usually intense) to achieve excellence.2 A sport is an organized, competitive, entertaining, and skillful activity requiring commitment, strategy, and fair play, in which a winner can be defined by objective means. It is governed by a set of rules or customs.15 This definition does not include recreational or leisure activities, since they are not competitive,15 and according to the BC#36 and ESC guidelines, sport is considered more demanding than other recreational activities, placing the individual at higher risk of a fatal arrhythmia. However, it should be borne in mind that some competitive sports may incur less risk than certain leisure activities; for example, competitive shooting is less likely to lead to SCD than amateur weightlifting.2 The BC#36 recommendations accordingly classify sports by the intensity of their static and dynamic components (low, moderate or high) (Table 1). On this basis, weightlifting has a large static component and running has a large dynamic component.16

The sooner defibrillation is performed, the more effectively ventricular fibrillation can be terminated. If the shock is delivered within 30 s, there is a 90% probability that it will be successful, but this falls by 7%–10% for every minute that passes, and if defibrillation is begun 10 min after the event the likelihood of resuscitation is only 10%.17,18

The location of an ICD means that it can interpret the cardiac rhythm and apply a shock almost immediately, which leads to success rates of 95%–99%. As a result, in the last 20 years ICDs have become the gold standard treatment for ventricular arrhythmias.4

The indications for ICD implantation in athletes in the ESC6,20 and American College of Cardiology/American Heart Association (ACC/AHA)6 guidelines are similar to those for the general population. The main complications are lead dislodgment or fracture, inappropriate shocks, and generator migration or pocket erosion.3

The number of individuals with ICDs for primary prevention has risen sharply in recent years, due to more widespread screening of families with a history of inherited arrhythmia syndromes, channelopathies and cardiomyopathies, as well as improved identification of silent mutation carriers. As a consequence, there are increasing numbers of apparently healthy and highly active individuals who, due to their increased risk of suffering an arrhythmic event (or to prevent recurrence), have an ICD to prevent SCD, which can be the first manifestation of disease.

There are various considerations specific to athletes that can affect the safety and efficacy of ICDs in this population and thus influence the decision whether they can resume their sporting activity after implantation (Table 3).3 A major concern is that the ICD may not reliably defibrillate under athletic conditions, because of physiological alterations such as increased circulating catecholamine levels, leading to dehydration, acidosis, electrolyte disturbances and volume depletion, which in turn make the occurrence and perpetuation of arrhythmias more likely.22 There is little evidence on the efficacy of ICD shocks under the metabolic conditions of intense exercise.21

Furthermore, strenuous exercise worsens certain conditions such as ARVD and dilated cardiomyopathy.23,24

Another potential problem is that inappropriate shocks may be more frequent during exercise, due to sinus or supraventricular tachycardia or atrial fibrillation. Moreover, an athlete (and, in the case of motor sports, spectators) may be injured as a result of transient loss of consciousness and/or control due to arrhythmia or ICD shock. In addition, the ICD or leads may be damaged, particularly due to repeated energetic arm movements, as found in sports such as golf and boxing, or to direct impacts on the ICD itself or the subclavian region (“subclavian crush”), as may occur in any contact sport.3 Finally, those who argue that athletes with ICDs should be excluded from competition point out that inappropriate shocks can have a negative psychological effect on these individuals.

In light of the above, current guidelines recommend that athletes with ICDs should be disqualified from all competitive sports except those with low static and dynamic components, such as golf, billiards or bowling (category IA of the BC#36 classification) (Table 1).

Table 4 summarizes the main results of studies assessing the use of ICDs in athletes.

A 2006 survey5 of physician members of the Heart Rhythm Society designed to assess the decisions being made regarding sports participation in patients with ICDs painted a very different picture from that to be expected from the guidelines: of the 614 physicians who responded, only 62 (10%) followed the BC#36 and ESC guidelines strictly by excluding patients from all sports except those in category IA, while most (n=464; 76%) only recommended avoidance of contact, 273 (45%) recommended avoidance of competitive sports, and 71% reported caring for patients who participated in sports, including vigorous, competitive sports. More than two-thirds based restrictions on patients’ underlying heart disease and not solely on the guidelines. It is worth noting that 40% of responders had over 10 years’ experience with ICD patients. Although a high proportion of patients participated in sports, and shocks were common, adverse events were rare. Most complications were due to device failure such as lead fracture or migration attributed to repetitive arm movements (n=28), most commonly weightlifting (n=16), tennis (n=2) and golf (n=5). Interestingly, the latter is classified as IA and thus not excluded by the guidelines. While there was agreement that heart failure and ischemic heart disease should limit sports participation, physicians disagree concerning long QT syndrome and Brugada syndrome.5

In view of the observation that despite the guidelines, ICD patients continue to take part in competitive sports, Lampert et al. established a multicenter international registry.26 Participants were recruited via mailings to physicians and by direct communication with patients via patient group Internet sites and mailing lists. Data were collected through telephone contact every six months and medical records were obtained from 41 sites in North America and 18 in Europe. Patients were queried about shocks received, sequelae, preshock activity and any change in sports participation, health or ICD status. Of the 372 participants, 328 were participating in organized sports and 44 were participating in high-risk sports. Median age was 33 years and 33% were female. The most frequent diagnoses were long QT syndrome (n=73), HCM (n=63), and ARVD (n=55); the most common sports were running (n=106), soccer (n=69) and basketball (n=56), while the most common high-risk sport was skiing.

During a median follow-up of 31 months, there were no tachyarrhythmic deaths, resuscitated cardiac arrests, or injuries related to arrhythmias or shocks during sports participation. There were 49 shocks in 37 participants (10% of the study population) during competition/practice, 39 shocks in 29 participants (8%) during other physical activity, and 33 shocks in 24 participants (6%) at rest. More individuals received shocks during either competition/practice or physical activity than during rest (16% vs. 6%; p<0.0001), but there was no significant difference between the proportion receiving a shock during competition/practice and those receiving a shock during other physical activity (10% vs. 8%; p=0.34). Similarly, the proportion receiving appropriate shocks during either competition/practice or other physical activity was greater than the proportion receiving appropriate shocks during rest (8% vs. 3%; p=0.006), but there was no difference between competition/practice and other physical activity (6% vs. 4%; p=0.18). Of a subgroup of 60 highly competitive athletes, all ≤21 years of age, 17 (28%) experienced a total of 25 shocks. In this subgroup there was no significant difference between the number of shocks in this subgroup during competition/practice (1%) and at rest (4%).

There were no reported ICD malfunctions in 97% of the participants at five years and in 90% at 10 years. Most (70%) of athletes who received shocks during sports chose to continue playing.

These findings suggest that many athletes can safely participate in various contact or high-intensity sports without risk of injury, device damage, or ineffective defibrillation. Shock rates in the study population were generally similar to those in ICD patients who do not play sports or are less active.27,28 The rate of lead failure or fracture was also similar to five-year rates seen in other populations (85%–98%).29

Disqualifying athletes with ICDs from sports can significantly affect their quality of life,30 particularly younger individuals, who describe feelings of exclusion and being considered ‘not normal’ as the main problem with having an ICD. The fact that most athletes in the study continued to play even after receiving shocks suggests that the benefits of sport outweigh the negative impact that shocks may have.

Following publication of the above studies, other researchers have set out to investigate further. Saarel et al.31 recently presented preliminary results of a registry of 21 young patients with ICDs who choose to play competitive or dangerous sports greater than IA in both static and dynamic components. Ten had congenital heart disease, six had inherited arrhythmia syndromes and five had cardiomyopathy. Mean follow-up was five years; the most common sports were basketball and baseball. There were no cardiac deaths and no increase in morbidity after four years. One participant received two appropriate shocks for supraventricular tachycardia during a basketball game and subsequently retired from competitive sports; no other participant suffered more frequent shocks, appropriate or inappropriate, during sports, and no increase in device malfunction was reported. All participants were under beta-blocker therapy to prevent inappropriate shocks due to sinus or ventricular tachycardia.

The authors declare that the procedures followed were in accordance with the regulations of the relevant clinical research ethics committee and with those of the Code of Ethics of the World Medical Association (Declaration of Helsinki).

The authors declare that no patient data appear in this article.

The authors declare that no patient data appear in this article.