A cross-sectional analytical study with prospective data collection was conducted from April 1 to August 31, 2019, at the Brazzaville sports medical center, located within the Alphonse Massamba Débat stadium. This center, placed under the coordination of the sports and anti-doping directorate, provides medical follow-up for all high-level athletes in Brazzaville and is equipped with an ECG-AM-3303G® electrocardiograph (Shanghai, China).

The study included a thorough, exhaustive sampling of high-level athletes (≥6 hours training/week) who were seen for non-contraindication visits for the 2019 season. Inclusion criteria were age 12 to 35 years, sports practice for at least one year in a club affiliated with a recognized federation, and written consent. Symptomatic athletes and those who had ceased activity for more than six months were excluded.

Sports disciplines classification: for the purpose of this analysis, sports were classified into endurance and non-endurance categories based on their primary physiological demands. Endurance sports were defined as those requiring sustained cardiovascular effort with predominant aerobic metabolism for extended periods (>30 minutes). In our cohort, the following were classified as endurance sports: football, marathon, and volleyball. Non-endurance sports included handball, taekwondo, and basketball, which are characterized by intermittent high-intensity efforts with shorter duration and greater reliance on anaerobic metabolism.

A standardized interview collected sociodemographic, sports-related data and medical history. Physical examination included blood pressure measurement (OMRON M3®), anthropometric parameters, and cardiovascular auscultation.

A 12-lead resting ECG was recorded after 15 minutes of rest in supine position, at 25 mm/second with standard calibration. Interpretation was performed according to ESC 2018 recommendations for classification into physiological, borderline, and pathological abnormalities.

Study variables included sociodemographic data (age, sex), sports-related factors (discipline, experience, weekly training duration), clinical parameters (history, physical examination), and electrocardiographic findings (rhythm, frequency, morphological abnormalities). ECG abnormalities were classified according to ESC 2018 criteria: physiological (athlete’s heart), borderline (debated link with sports), and pathological (requiring thorough investigation) .

Analysis was performed using EpiInfo 7.2®. Quantitative variables are expressed as mean ± standard deviation, qualitative variables as frequencies and percentages. Proportion comparisons used chi-square or Fisher tests. Multiple logistic regression identified factors associated with ECG abnormalities, including age, sex, sport type, and training duration. For the sport type variable in the multiple logistic regression analysis, handball was used as the reference category due to its largest representation in the cohort (31.4%). Variables with p ≤ 0.20 in univariate analysis were included in the multivariate model. The significance threshold was set at p < 0.05.

A total of 436 high-level athletes were included in the study. Men represented 76.6% of the sample (n = 334) with a sex ratio of 3.3:1. Mean age was 21.6 ± 5.1 years (range: 12 - 35 years), with a predominance of 12 - 19 years age group (43.1%).

Six sports disciplines were represented: handball (31.4%), football (21.6%), taekwondo (13.1%), basketball (12.4%), volleyball (11.7%), and marathon (9.8%). Mean weekly training duration was 8.6 ± 2.6 hours (range: 6 - 24 h), with 95.4% of athletes training 6 - 12 hours/week. Mean practice experience was 5.5 ± 4.5 years (range: 1 - 20 years).

Physical examination was normal in all athletes. Medical history revealed alcohol consumption in 13.5% of athletes (regular in 3.4%), current smoking in 2.7%, and family cardiovascular history in 11.5%. Mean body mass index was 20.6 ± 2.8 kg/m² with 8.3% overweight and 0.9% obesity. Blood pressure was normal in 81.4% of cases for systolic and 83.9% for diastolic.

Rhythm was sinus in 94% of athletes and regular in 75%. Mean heart rate was 64.3 ± 12.1 bpm with bradycardia in 37.6% of athletes. Mean cardiac axis was 59.1 ± 22.5˚, normal in 93.6% of cases.

ECG abnormalities were detected in 87.6% of the athletes (n = 382). Among these, physiological abnormalities accounted for 56.2% (n = 245). Specifically, sinus bradycardia was observed in 37.6% of athletes (n = 164), early repolarization in 37.6% (n = 164), left ventricular hypertrophy in 43.3% (n = 189), right ventricular hypertrophy in 10.8% (n = 47), first-degree atrioventricular block in 5.7% (n = 25), Afro-Caribbean repolarization in 5.0% (n = 22), and sinus arrhythmia in 22.9% (n = 100).

Borderline abnormalities were present in 7.8% of athletes (n = 34). These included right axis deviation in 5.7% (n = 25), right atrial hypertrophy in 3.2% (n = 14), and both left axis deviation and left atrial hypertrophy in 0.7% each (n = 3).

Pathological abnormalities (23.6%, n = 103) are summarized in .

Multivariate analysis identified several factors significantly associated with ECG abnormalities.

Overall, male sex was associated with a higher risk of ECG abnormalities, with an adjusted Odds Ratio (ORa) of 4.4 (95% CI: 2.3 - 8.6; p < 0.001). Endurance sports were also linked to these abnormalities: football (ORa 2.4; 95% CI: 1.2 - 11.7; p = 0.03), marathon (ORa 2.5; 95% CI: 1.4 - 14.7; p = 0.02), and volleyball (ORa 4.2; 95% CI: 1.7 - 3.3; p = 0.04).

Regarding physiological abnormalities, sinus bradycardia was associated with male sex (ORa 3.8), age over 19 years (ORa 2.7), and training more than 13 hours per week (ORa 2.6). Early repolarization was strongly associated with male sex (ORa 17.4) as well as endurance sports. Finally, left ventricular hypertrophy was associated with male sex (ORa 4.5).

Overall factors associated with ECG abnormalities are presented in .

. Representative 12-lead electrocardiogram demonstrating borderline abnormalities in a 17-year-old male handball player with 4 years of training experience. The ECG shows: (1) right axis deviation with QRS axis of 120˚; (2) right ventricular hypertrophy with RV₁ + SV₅ = 16 mm; and (3) early repolarization pattern with J-point elevation and upward concave ST segments (indicated by arrows) in the inferior and lateral leads.

ORa: Adjusted Odds Ratio; Bold values indicate statistical significance (p < 0.05).

The high prevalence of electrocardiographic abnormalities observed in our study (87.6%) reflects a fundamental duality between physiological adaptations of the athlete’s heart and the potential presence of underlying pathologies. This distinction is of paramount importance for cardiovascular risk stratification in high-level athletes.

Typical abnormalities of physiological adaptations include sinus bradycardia (37.6%), early repolarization (37.6%), left ventricular hypertrophy (43.3%), and first-degree atrioventricular blocks (5.7%) . These modifications reflect cardiac adaptation to intensive training through harmonious electrical and morphological remodeling.

The exceptionally high prevalence of pathological abnormalities (23.6%) observed in our cohort represents a significant clinical concern and warrants detailed analysis. The most frequent pathological finding was inverted or flat T waves, observed in 19.3% of athletes. These repolarization abnormalities can indicate underlying cardiomyopathies, including hypertrophic cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, or dilated cardiomyopathy—all conditions associated with increased risk of sudden cardiac death during exercise. Prolonged QTc intervals (1.6%) suggest channelopathies such as long QT syndrome, which can predispose to potentially fatal ventricular arrhythmias. Complex conduction disorders (1.1%) may indicate structural heart disease or infiltrative processes, while pathological Q waves (0.9%) could suggest previous myocardial infarction or cardiomyopathy. The presence of ventricular arrhythmias (0.7%) is particularly concerning, as these can be harbingers of more serious arrhythmic events during physical exertion. These findings collectively indicate that nearly one in four athletes in our study population requires a comprehensive cardiological evaluation to exclude life-threatening cardiac conditions.

Our results fall within the variability observed internationally but reveal a higher prevalence than European and North American studies. This difference is explained by several contextual factors: limited accessibility to preventive cardiovascular care in our context, socioeconomic conditions influencing medical management, and genetic specificities of African populations [10] - [12] .

Regarding genetic specificities in African populations, previous research has demonstrated distinct electrocardiographic patterns in athletes of African descent. Studies by Rawlins et al. have shown that athletes of African/Afro-Caribbean origin exhibit higher rates of early repolarization patterns, T-wave inversions in the right precordial leads, and voltage criteria for left ventricular hypertrophy compared to Caucasian athletes. These findings are consistent with the “benign” repolarization variants described in up to 25% of young black athletes [18] . The Afro-Caribbean repolarization pattern observed in 5% of our cohort aligns with these ethnic-specific ECG characteristics. Research has also indicated that black athletes demonstrate greater cardiac chamber dimensions and wall thickness, which may explain the higher prevalence of voltage criteria for ventricular hypertrophy observed in our population. These genetic and ethnic influences on cardiac adaptation necessitate population-specific interpretation criteria for ECG screening in African athletes.

Male predominance (sex ratio 3.3:1) reflects local sociocultural realities where female access to high-level sports remains restricted [13] . The mean age of our athletes (21.6 ± 5.1 years) corresponds to international standards [14] - [16] , confirming the representativeness of our cohort.

The significant association between male sex and ECG abnormality prevalence (ORa 4.4; 95% CI 2.3 - 8.6) is explained by fundamental physiopathological differences. Men present superior myocardial mass, a more pronounced hypertrophic response to training, and hormonal influence (testosterone) favoring certain cardiovascular adaptations [12] [17] .

Endurance sports (football ORa 2.4, marathon ORa 2.5, volleyball ORa 4.2) impose specific cardiovascular stress characterized by chronic volume overload. This overload leads to cardiac cavity dilatation, intraventricular conduction modifications, and vagal hypertonia explaining the increased prevalence of ECG abnormalities [18] [19] . Sinus bradycardia, multifactorial in nature, results from cardiac hypertrophy, decreased intrinsic sinus node frequency, and autonomic balance modifications [18] .

The use of ESC 2018 criteria allows precise classification into three categories:

Physiological abnormalities (56.2%): sinus bradycardia, early repolarization, ventricular hypertrophies, and first-degree AV blocks, reflecting the adapted athlete’s heart.

Borderline abnormalities (7.8%): axial deviations, atrial hypertrophies, whose link with sports activity remains debated but is more frequent in black athletes [15] [17] .

Pathological abnormalities (23.6%): inverted/flat T waves, prolonged QTc, requiring temporary cessation and thorough cardiological evaluation [9] [20] [21] .

The strategic choice of Brazzaville sports medical center ensures optimal centralization of high-level athlete follow-up. Exhaustive sampling during major competition periods ensures maximum and diversified recruitment. The calculated sample size (n = 436) limits selection bias, and application of ESC 2018 criteria ensures standardized interpretation [9] .

The monocentric nature limits generalization to the entire Congolese territory. Modest training duration (8.6 ± 2.6 h/week) compared to international standards [22] [23] could influence adaptation prevalence. The absence of complementary explorations (echocardiography, exercise testing) constitutes a limitation for complete cardiovascular phenotype characterization.

The observed electrocardiographic parameters (mean heart rate 64.3 ± 12.1 bpm, cardiac axis 59.1 ± 22.5˚) correspond to expected athlete’s heart adaptations [24] [25] . Repolarization disorders, particularly frequent in African athletes [18] , include Afro-Caribbean repolarization (5%), specific to the black athlete’s heart and reflecting racial influences on cardiovascular adaptation [17] .

The absence of symptoms in all athletes confirms the often asymptomatic nature of cardiac adaptations and certain potentially lethal pathologies, emphasizing the importance of electrocardiographic screening [26] - [28] .

This study establishes the foundation for a cardiovascular screening protocol adapted to the African context. The high prevalence of pathological abnormalities (23.6%) justifies reinforced surveillance and integration of complementary explorations into management algorithms. Development of a national multicentric network would improve data representativeness and validation of norms specific to African populations.

The identification of 23.6% of abnormalities requiring thorough evaluation underscores the public health challenge represented by sudden cardiac death prevention in Sub-Saharan African athletes.