Characteristics of the study population
The study population included 30
065 participants, with significantly (P<0.001) more men than women (23
570 (78.4%) v
6495 (21.6%)). The mean age was 30.7 (SD 14), with a range of 5-92; 33 were aged over 80. Nearly 40% of the total study population were aged over 30, and 98% were white. Men were significantly older than women (28.4 v
24.6; P<0.001) and included a significantly higher proportion of smokers (13.2% v
10.3%; P<0.001). More than half of the participants were reported to have a sedentary job (56.2%), with no significant difference between men and women. Most people spent an average of four to six hours a week doing sports activities (50.9%), whereas the rest were reported to spend less than four or more than six hours a week (20.7% and 28.4%, respectively) taking part in sports.
Participants took part in over 30 different sporting disciplines, the main ones being football and volleyball (31.3% and 17.7%, respectively). Other leading sports were cycling (6.7%), athletics (5.9%), and basketball (5.8%) among men and swimming (6.5%), athletics (6%), and gymnastics (4.2%) among women.
Personal and family history indicated cardiac abnormalities in less than 0.5%, whereas physical examination reported pathological findings in about 3%.
Resting 12 lead electrocardiography
Abnormalities on resting ECG were present in 1812 (6%) participants, 1570 (6.7%) men and 242 (3.7%) women (P<0.001) (table 1). The most common abnormalities were sinus bradycardia (2.9%) and complete (1.1%) or incomplete (0.7%) right bundle branch blocks, which, together with the type I atrioventricular block and early polarisation pattern, can be considered as innocent modifications that occur in the “athlete’s heart.” These abnormalities accounted for over 80% of the total anomalies (n=1464). A distinctly abnormal pattern was found in the remaining participants (348; 1.2%), the most common being ST-T segment alterations and premature ventricular and supraventricular beats. There was a higher prevalence of innocent ECG changes in men than in women, with the exception of type I atrioventricular block.
Table 1 Results of 12 lead resting and exercise electrocardiography in people screened before taking part in competitive sports. Figures are number (percentage) of participants
With regard to age, participants with reported ECG abnormalities were significantly older than those with a normal ECG pattern (31.1 (SD 13.8) v 29.1 (SD 13.1), P<0.001). Almost half of the population with ECG irregularities comprised participants aged 30-50 (46.9%), with the remaining portion mostly being those aged under 30 (33.6%).
Exercise 21 lead electrocardiography
All participants underwent exercise ECG (table 1), and abnormalities were found in 1459 (4.9%), with a higher prevalence in women than men (521 (8%) v 938 (3.9%)). Those with abnormalities were significantly older than those with normal patterns (30.9 (SD 12.1) v 24.9 (SD 9.9), P<0.001), and an equal proportion (48.9%) were aged over 30. The most prevalent anomalies were premature ventricular and supraventricular beats, accounting for over 65% of the total abnormalities, with a significantly higher prevalence among women than men (P<0.001). The remaining abnormalities comprised non-sustained and sustained ventricular tachycardia, ST-T segment alterations, and cardiac conduction disorders. Notably, only 232 (12.8%) participants with abnormalities on resting ECG also showed these abnormalities on exercise ECG, but exercise ECG showed cardiac anomalies in 1227 participants (939 men; 288 women; mean age 30.7 (SD 11.9)) in whom resting ECG had shown a normal pattern. In particular, the most prevalent cardiac abnormalities found on stress testing comprised findings suggestive of coronary heart disease and arrhythmias.
Eligibility and screening
After screening, 196 (0.6%) people were considered ineligible to take part in competitive sports (182 (0.7%) men and 14 (0.2%) women; mean age 37 (SD 12.3)). In total 159 (81.6%) athletes were disqualified because of cardiac abnormalities, and 37 were disqualified for other reasons (table 2).
Table 2 Causes of disqualification from competitive sports at the end of screening
By analysing disqualifications according to abnormalities found at resting and exercise ECG, we found that, among the 159 participants disqualified because of cardiac abnormalities, personal history or physical examination, or both, had suggested problems in only six (3.7%) and a large proportion (126, 79.2%) had a normal pattern on resting ECG. Conversely, almost all the disqualified participants showed some cardiac abnormalities during the exercise ECG. Indeed, in 56 participants with a normal resting ECG, exercise testing showed some potentially fatal cardiac disorders such as arrhythmias and coronary heart disease that resulted in disqualification from competition.
Finally, we performed a logistic regression analysis to investigate possible predictors of disqualification among the group of participants with a normal resting ECG. After adjustment for possible confounders we found that the risk of being disqualified increased significantly with age. Participants aged over 30 had a significantly increased risk of showing cardiac abnormalities on exercise ECG, thus resulting in disqualification from competition (table 3).
Table 3 Predictors of disqualification among athletes with normal findings on resting ECG