Racial disparities in electrical and structural cardiac adaptation among adolescent athletes: A systematic review and meta-analysis

Abstract

BACKGROUND

In pediatric and adolescent athletes, there is a lack of understanding about the impact of factors such as race on the structural or cardiovascular adaptations in response to exercise which may unnecessarily disqualify athletes from the competitive sport. We hypothesized that race has an impact on cardiac adaptions in non-adult athletes.

AIM

To explore the racial disparity in electrocardiographic (ECG) and echocardiographic (ECHO) parameters in healthy adolescent athletes.

METHODS

A comprehensive electronic systematic literature search using MEDLINE database was performed from inception to September 20, 2024. Inclusion criteria included randomized or observational cohort studies that recruited adolescent competitive athletes in any sport discipline and compared between the Black and White races with an age range of 12-18 years.

RESULTS

Of 723 records that were identified by the literature search, seven studies (n = 5036) were included. The mean age was 13.0-18.0 years old with male predominance. Black athletes had significantly longer PR interval [mean difference (MD) = 17.49 millisecond, 95%CI: 11.70-23.29] and shorter QRS complex duration (MD = -7.35 millisecond, 95%CI: -9.17 to -5.53) and corrected QT interval (MD = -4.95 millisecond, 95%CI: -7.69 to -2.22) than the White athletes. Black athletes were approximately four times more likely to have first-degree atrioventricular (AV) block, inverted T wave, ST-segment elevation, and left atrium (LA) enlargement than their White counterparts. In terms of ECHO parameters, Black athletes had significantly greater septal wall thickness (MD = 0.85 mm, 95%CI: 0.62-1.07), posterior wall thickness (MD = 1.07 mm, 95%CI: 0.36-1.78), relative wall thickness (MD = 0.03, 95%CI: 0.001-0.06), maximal wall thickness (MD = 1.05 mm, 95%CI: 0.28-1.83), and LA diameter (MD = 1.64 mm, 95%CI: 0.16-3.12).

CONCLUSION

Race has an impact on the ECG and ECHO parameters that reflect cardiac adaptations in adolescent athletes. Black athletes tend to have an increased prevalence of distinct ECG changes such as first-degree AV block and T-wave inversions compared with their White counterparts. Despite having thicker septal and posterior walls, the overall prevalence of left ventricular hypertrophy did not differ between the races.

Key Words: Adaptation; Athlete’s heart; Atrial dilation; Electrical remodeling; Endurance athletes; Teenage; Ventricular hypertrophy

Core Tip: This systematic review and meta-analysis found that race has an impact on the electrocardiographic and echocardiographic parameters that reflect cardiac adaptations in adolescent athletes. Black athletes tend to have an increased prevalence of distinct changes such as first-degree atrioventricular block, T-wave inversions with thicker septal and posterior walls compared with their White counterparts.

INTRODUCTION

The athlete’s heart which arises from the association between exercise and cardiac remodeling[1,2], differs physiologically and structurally from that of the general population[3]. Physiological adaptations to regular exercise involve complex mechanisms that increase the cardiac output. Prolonged exercise has different effects on the right ventricle (RV) and left ventricle (LV)[4]. However, data suggest there is symmetrical cardiac enlargement in all four chambers which may indicate an increased hemodynamic loading that allows the athletes to maintain an elevated cardiac output status during exercise[5]. Oxygen consumption and cardiac output of both ventricles increase and the vascular resistance decreases with a less pronounced resistance decrease in the pulmonary circulation during exercise. Consequently, vasodilation and increased flow mismatch leads to an increase in RV afterload and pulmonary artery pressure and large increase in RV workload[4]. Exercise type and intensity determine hemodynamic and cardiac adaptations which involve structural, functional, and electrical myocardial remodeling[3].

Structurally, athletes develop concentric (i.e., in strength athletes), eccentric (i.e., in endurance athletes) or most often mixed left ventricular hypertrophy (LVH). Athletes have 15%-20% increase in LV wall thickness and 10%-15% increase in LV size in comparison with the general population[4]. The left atrium (LA) is enlarged in 20% of highly-trained athletes (i.e., ≥ 40 mm) which was associated with LV cavity enlargement and participation in dynamic sports (e.g., rowing, cycling)[6]. Mild enlargement of LA volume index (29-33 mL/m²) in 24.3% of highly-trained athletes was associated with sport type, duration of training, and LV end-diastolic volume (LVEDV)[7]. The physiological enlargement in the RV is common among athletes[8], which was confirmed by cardiac magnetic resonance imaging[9]. Moreover, there are enlarged RV inflow tract and increased right and left atrial measurement in endurance athletes[5].

Functional physiological adaptations to training are not fully understood. Left ventricular ejection fraction is usually normal among athletes, but can also be borderline reduced[4]. However, functional adaptations may be manifested as greater diastolic compliance and decreased left ventricular ejection fraction with functional recovery during exercise and after detraining[3]. Electrical adaptations in athlete’s heart occur due to the conditioning of cardiac autonomic nervous system (i.e., withdrawal of sympathetic impulses and increased vagal tone) and structural remodeling[2,4]. Increased vagal tone commonly leads to sinus arrhythmia and sinus bradycardia. Whereas, junctional or ectopic atrial rhythms, first and second degree atrioventricular (AV) block are considered less common. In highly-trained athletes, heart rates of ≥ 30 beats per minute in the absence of symptoms are considered normal[10]. Approximately 88% of competitive athletes presented normal electrocardiographic (ECG) findings[11], and 10%-12% of them showed uncommon findings[11,12], which suggest a low prevalence of structural heart diseases. The most common abnormalities were prolonged PR interval, early repolarization, and incomplete right bundle branch block (total of 7.0%)[11]. Seven international consensus and guidelines documents on the interpretation of ECG findings in athletes have been published[10,13-18].

Overall, prolonged training is associated with structural, functional, and electrical cardiac adaptations in adult athletes[19,20]. It has been reported that other factors such as age, sex[21], and race[12,22] have significant impact on cardiac adaptions in adult athletes[1,3]. For example, black ethnicity in adult athletes was associated with significantly higher uncommon ECG findings; prevalence of sudden cardiac death; frequency of right atrium (RA) enlargement, first-degree AV block, and early repolarization; and prevalence of LVH in response to the exercise than other races such as West-Asian and Caucasian athletes. This is probably due to a combination of genetic, endocrine, and hemodynamic factors[8]. Other than the Chinese and Japanese athletes, there is limited data about structural or cardiovascular adaptation in the East Asian, South Asian, and Middle Eastern athletes[22]. Moreover, data on pediatric and adolescent athletes is limited to observational original studies of small sample size and considerable heterogeneity. There is a lack of understanding about the potential factors (e.g., sex, race, and physical growth) that may cause a false-positive diagnosis of cardiac conditions which may unnecessarily disqualify athletes from the competitive sport in non-adult athletes[1]. We hypothesized that race has an impact on cardiac adaptions in non-adult athletes. The objective of this systematic review and meta-analysis aims to explore the racial disparity in ECG and echocardiographic (ECHO) parameters in adolescent athletes.

MATERIALS AND METHODS

This systematic review and meta-analysis was conducted according to the Cochrane Handbook for Systematic Reviews[23]. It was reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement[24] and the Meta-analysis Of Observational Studies in Epidemiology checklist[25]. The review protocol was registered in the International Prospective Register of Systematic Reviews (No. CRD42024601542).

Eligibility criteria

Inclusion criteria included randomized or observational cohort studies that recruited healthy adolescent competitive athletes in any sport discipline which investigated electrical and structural cardiac adaptation parameters in Black and White races. Participants age includes 12-18 years. Studies that investigated physical fitness or those focused on physiological adaptation, respiratory, bone, muscular, or performance adaptation were excluded. In addition, studies on paralympic athletes and exercisers or published as abstracts, conference proceedings, study design, case reports or case series were not included. A competitive athlete was defined according to both versions of the Bethesda conference or guidelines: One who participates in an organized team or individual sport that requires regular competition against others as a central component, places a high premium on excellence and achievement, and requires some form of systematic (and usually intense) training[26,27]. Athletes are considered competitive in several sporting disciplines at almost any age or participation level, including those involved in high school, college, professional, and master’s sports[27]. The definition of competitive athletes was adopted by the major societies of cardiology including American Heart Association and the American College of Cardiology that discussed medical issues related to sports and/or athletes[28-30]. The definition seems to be unchanged over the last decades (i.e., since 1985). Similarly, the definition of the competitive athletes according to the European Society of Cardiology is "individuals of young and adult age, either amateur or professional, who are engaged in exercise training on a regular basis and participate in official sports competition. Official sports competition (local, regional, national, or international) is defined as an organized team or individual sports event that, placing a high premium on athletic excellence and achievement, is organized and scheduled in the agenda of a recognized Athletic Association"[31]. A more recent definition for an athlete was proposed by Araújo and Scharhag[32] and necessitated the presence of four criteria, which were updated by MacMahon and Parrington[33] who defined athletes as people who engage in physical activity with the primary goal of improving performance to bolster athletic excellence and/or achievement. An elite athlete is defined as an individual who exercises more than 10 hours per week and whose athletic performance achieves the highest level of competition. A competitive athlete exercises more than six hours per week with improving performance. While a recreational athlete exercises more than four hours per week for unregulated competitions. An exerciser engages in more than 2.5 hours per week of physical activity aiming at maintaining health and fitness status[34].

Search strategy

A comprehensive electronic systematic literature search using MEDLINE database was performed from inception to September 20, 2024. Medical Subject Headings and broad keywords were combined with Boolean term “AND”. The search terms included: (1) Athletes; (2) Adolescent; (3) Cardiomegaly; (4) Exercise-induced; (5) Physiological; (6) Sport; (7) Adaptation; (8) Myocardial adaptation; (9) Cardiac remodeling; (10) Electrocardiography; (11) Echocardiography; and (12) Magnetic resonance imaging. There was no restriction applied to the search strategy. To complement the electronic database searching, manual search of the references’ list of the identified studies and the published systematic and narrative review was performed. The detailed search strategy is presented in Supplementary Table 1.

Study selection and data extraction

The studies were examined at the title and abstract levels. The studies that did not meet the inclusion criteria were excluded. All potential abstracts were retrieved in full text, then the data of included studies were extracted and compiled into prespecified tables. Study selection was done by two independent authors. There were minor disagreements that were solved by discussion. The extracted data included study objectives, study characteristics, eligibility criteria, patient characteristics, sport type, training characteristics, ECG and ECHO parameters. The electrical changes presented by the ECG parameters included PR interval, QRS complex duration, corrected QT (QTc) interval, S1/R5 wave voltages, and number of patients having LVH, RV hypertrophy, LA enlargement, RA enlargement, ST-segment elevation, ST-segment depression, pathologic Q-waves, inverted T-waves, sinus bradycardia, first degree AV block, and incomplete or partial right bundle branch block. The structural changes presented by the ECHO parameters comprised LV end-diastolic dimensions (LVEDD), LV end-systolic dimensions (LVESD), LVEDV, LV end-systolic volume (LVESV), septum thickness, aortic root, A wave, E wave, E/A ratio, LV ejection fraction, LA diameter, LV mass, maximal wall thickness, RV diameter, posterior wall thickness and relative wall thickness.

Risk-of-bias assessment

The methodological quality was evaluated by using the Risk of Bias in Non-randomized Studies of Exposure (ROBINS-E) tool that provides a structured assessment approach. It assesses the risk of bias in a specific result from each included observational cohort study that investigates the effect of the exposure on a prespecified outcome; i.e., the ECG and ECHO parameters in this systematic review and meta-analysis. The ROBINS-E tool includes seven domains of bias (i.e., risk of bias due to confounding, measurement of exposure, selection of the participants into the study, post-exposure interventions, missing data, measurement of the outcome, and selection of the reported result). Each bias domain is assessed using signaling questions and the risk of bias is judged as low risk, has some concerns, high risk, and very high risk of bias. Then, the overall judgement is made based on the risk of bias in each domain, the predicted direction of bias in each domain, and whether the risk of bias in each domain is sufficiently high[35]. Ideally, this process should be done in pairs and disagreements between authors are usually resolved by reaching a consensus or involving a third author.

Statistical analysis

The variables from the included studies were combined in a meta-analysis and the related forest plots using an aggregate approach. Two studies are considered the minimum number to conduct a quantitative synthesis for a pre-specified outcome[36]. For each outcome, the mean difference (MD) or odds ratio (OR) with 95%CI were computed using the random-effects model because of the expected heterogeneity between the included studies. Some studies were not included in computing the pooled MD or OR of an outcome due to the unavailability of the raw data. The statistical heterogeneity was assessed by the Cochran’s Q statistic and quantified, using the inconsistency factor (I²) value for an individual outcome, as high heterogeneity when I² values are greater than 50%[37]. Publication bias was visually inspected by examining the funnel plots (i.e., scatterplots of each study’s effect size plotted against its standard error). Due to the small study numbers (i.e., less than 10 studies) Egger’s test was mathematically invalid. A P value of < 0.05 determined the statistical significance level. The analyses were computed using the statistical program R software.

RESULTS

Search results

Of 723 records that were identified by the literature search, 108 were duplicate records. After screening the search records on the title and abstract levels, 65 articles were obtained in full texts. Of them, seven studies met the inclusion criteria (Supplementary Table 2). The PRISMA flow chart is presented in Supplementary Figure 1[38-44].

Study characteristics

Four studies were conducted in Italy and the remining in the United States, United Kingdom, and France in various sporting disciplines. The details of the included studies are presented in Supplementary Tables 3-5[38-44]. The studies recruited 5036 athletes, out of them 1703 (33.8%) were of Black race (African American and/or Afro-Caribbean) and 2304 (45.8%) were of White race. The remaining 1029 (20.4%) athletes were not included in the analysis for being of other or mixed race (Supplementary Table 3)[38-44].

Participant characteristics

The range of participants’ mean age was 13.0-18.0 years old who were of male majority; all studies recruited male athletes expect one study recruiting almost 80.0% males[44]. The mean body mass index (BMI) ranged between 19.0 kg/m² and 29.0 kg/m², and the body surface area (BSA) ranged from 1.5 m² and 2.0 m² (Supplementary Table 6)[38-44]. There was no difference between Black and White athletes in terms of age, BMI, BSA, systolic blood pressure and heart rate. Diastolic blood pressure at baseline was significantly higher among Black athletes (MD = 2.75, 95%CI: 0.35-5.16) (Table 1 and Supplementary Figure 2)[38-40,42-44].

Table 1 Participant characteristics.

Variable	Number of studies included in analysis	Black vs White athletes (MD, 95%CI)
Age (years)	5	MD = -0.24, 95%CI: -0.69 to 0.21, P = 0.3031, I2 = 92%
Body mass index (kg/m2)	4	MD = -0.22, 95%CI: -0.69 to 0.25, P = 0.3542, I2 = 42%
Body surface area (m2)	5	MD = -0.01, 95%CI: -0.08 to 0.07, P = 0.8754, I2 = 90%
Systolic blood pressure (mmHg)	5	MD = 0.97, 95%CI: -1.20 to 3.04, P = 0.3580, I2 = 78%
Diastolic blood pressure (mmHg)	5	MD = 2.75, 95%CI: 0.35-5.16, P = 0.0248, I2 = 89%
Heart rate (bpm)	5	MD = -1.35, 95%CI: -4.58 to 1.89, P = 0.4141, I2 = 90%

MD: Mean difference.

Impact of race on ECG parameters

Black athletes had significantly longer PR interval (MD = 17.49 millisecond, 95%CI: 11.70-23.29) and higher S1/R5 wave voltage (MD = 11.11 mm, 95%CI: 7.19-15.02), whereas, they had significantly shorter QRS complex duration (MD = -7.35 millisecond, 95%CI: -9.17 to -5.53) and QTc interval (MD = -4.95 millisecond, 95%CI: -7.69 to -2.22) than the White athletes. Black athletes were approximately four times more likely to have first-degree AV block, inverted T wave, ST-segment elevation, and LA enlargement than their White counterparts. Moreover, the prevalence of RA enlargement (OR = 6.15, 95%CI: 3.16-11.95) and RV hypertrophy (OR = 2.08, 95%CI: 1.53-2.81) were significantly higher among Black athletes, but with lower prevalence of the presence of pathological Q wave (OR = 0.40, 95%CI: 0.17-0.96) as presented in Table 2 and Supplementary Figure 3[38,39,41,43,44]. The raw data are presented in Supplementary Tables 7 and 8[38-44].

Table 2 Impact of race on echocardiographic characteristics.

Variable	Number of studies included in analysis	Black vs White athletes (MD, 95%CI)
PR interval (millisecond)	2	MD = 17.49, 95%CI: 11.70-23.29, P < 0.0001, I2 = 3.2%
QRS complex duration (millisecond)	4	MD = -7.35, 95%CI: -9.17 to -5.53, P < 0.0001, I2 = 44%
Corrected QT interval (millisecond)	3	MD = -4.95, 95%CI: -7.69 to -2.22, P = 0.0004, I2 = 0%
S1/R5 wave voltages (mm)	3	MD = 11.11, 95%CI: 7.19-15.02, P < 0.0001, I2 = 71%
First degree atrioventricular block	2	OR = 3.84, 95%CI: 2.27-6.50, P < 0.0001, I2 = 0%
Sinus bradycardia	4	OR = 0.79, 95%CI: 0.52-1.20, P = 0.2692, I2 = 85%
ST-segment elevation	5	OR = 4.31, 95%CI: 2.34-7.97, P < 0.0001, I2 = 89%
Ascending concave STE (domed)	2	OR = 1.39, 95%CI: 1.13-1.72, P = 0.0020, I2 = 0%
Ascending convex STE	2	OR = 5.78, 95%CI: 0.31-109.60, P = 0.2424, I2 = 88%
ST-segment depression	2	OR = 3.69, 95%CI: 0.87-15.63, P = 0.0767, I2 = 0%
Inverted T wave	4	OR = 3.80, 95%CI: 1.48-9.72, P = 0.0054, I2 = 77%
Pathologic Q wave	2	OR = 0.40, 95%CI: 0.17-0.96, P = 0.0392, I2 = 0%
Right bundle branch block	4	OR = 0.53, 95%CI: 0.26-1.08, P = 0.0809, I2 = 77%
Left atrium enlargement	4	OR = 3.53, 95%CI: 1.87-6.68, P = 0.0001, I2 = 49%
Left ventricle hypertrophy	5	OR = 2.12, 95%CI: 0.66-6.80, P = 0.2088, I2 = 96%
Right atrium enlargement	2	OR = 6.15, 95%CI: 3.16-11.95, P < 0.0001, I2 = 0%
Right ventricle hypertrophy	2	OR = 2.08, 95%CI: 1.53-2.81, P < 0.0001, I2 = 0%

MD: Mean difference; OR: Odds ratio; STE: ST-segment elevation.

Impact of race on ECHO parameters

Black athletes had significantly higher septal wall thickness (0.85 mm, 95%CI: 0.62-1.07), posterior wall thickness (1.07 mm, 95%CI: 0.36-1.78), relative wall thickness (0.03, 95%CI: 0.001-0.06), maximal wall thickness (1.05 mm, 95%CI: 0.28-1.83), LV mass indexed (5.02 g/m², 95%CI: 1.79-8.26), LA diameter (1.64 mm, 95%CI: 0.16-3.12), and aortic root (0.30 mm, 95%CI: 0.08-0.53). The following parameters are significantly smaller among the Black athletes: LVEDD (-0.87, 95%CI: -1.58 to -0.17), LVESD (-0.90, 95%CI: -1.26 to -0.53), and (-0.07, 95%CI: -0.11 to -0.03) than the White athletes (Table 3 and Supplementary Figure 4)[38-44]. The raw data are presented in Supplementary Table 9[38-44].

Table 3 Impact of race on echocardiographic characteristics.

Variable	Number of studies included in analysis	Black vs White athletes (MD, 95%CI)
A wave	3	MD = -1.50, 95%CI: -3.84 to 0.85, P = 0.2106, I2 = 89%
E wave	2	MD = -5.71, 95%CI: -19.42 to 8.01, P = 0.4148, I2 = 97%
E/A ratio	4	MD = -0.07, 95%CI: -0.11 to -0.03, P = 0.0011, I2 = 0%
LV ejection fraction (%)	3	MD = -0.08, 95%CI: -0.88 to 0.72, P = 0.8412, I2 = 55%
Left atrial diameter (mm)	3	MD = 1.64, 95%CI: 0.16-3.12, P = 0.0296, I2 = 87%
LVEDD (mm)	6	MD = -0.87, 95%CI: -1.58 to -0.17, P = 0.0153, I2 = 87%
LVEDD indexed (mm/m2)	3	MD = -0.36, 95%CI: -1.36 to 0.63, P = 0.4721; I2 = 95%
LV end-diastolic volume (mL)	3	MD = -4.10, 95%CI: 10.48-2.28, P = 0.2080, I2 = 65%
LV end-systolic dimensions (mm)	4	MD = -0.8979, 95%CI: -1.26 to -0.530, P < 0.0001, I2 = 15.6%
LV end-systolic volume (mL)	3	MD = -0.05, 95%CI: -0.70 to 0.60, P = 0.8789, I2 = 0%
LV mass (g)	3	MD = 17.29, 95%CI: -1.05 to 35.62, P = 0.0646, I2 = 82.7%
LV mass indexed (g/m2)	7	MD = 5.02, 95%CI: 1.79-8.26, P = 0.0023, I2 = 75%
Maximal wall thickness	2	MD = 1.05, 95%CI: 0.28-1.83, P = 0.0080, I2 = 86%
Posterior wall thickness (mm)	4	MD = 1.07, 95%CI: 0.36-1.78, P = 0.0033, I2 = 88%
Right ventricle diameter (mm)	2	MD = -0.60, 95%CI: -1.39 to 0.18, P = 0.1324, I2 = 86%
Relative wall thickness	6	MD = 0.03, 95%CI: 0.001-0.06, P = 0.0126, I2 = 86%
Septal wall thickness (mm)	5	MD = 0.85, 95%CI: 0.62-1.07, P < 0.0001, I2 = 83%
Aortic root (mm)	3	MD = 0.30, 95%CI: 0.08-0.53, P = 0.0087, I2 = 0%

LV: Left ventricle; LVEDD: Left ventricle end-diastolic dimensions; MD: Mean difference.

Risk-of-bias assessment

The overall risk of bias assessment was high-risk of bias for the ECG and ECHO parameters. The bias was mainly due to confounding (Supplementary Tables 10 and 11)[38-44].

Publication bias

For the baseline characteristics variables, most of the respective funnel plots showed asymmetrical patterns that reflect the presence of publication bias and the funnel plots for two variables showed some asymmetry (Supplementary Figure 2)[38-40,42-44]. Most of the funnel plots for the ECG parameters showed some asymmetry and a few showed asymmetry (Supplementary Figure 3)[38,39,41,43,44]. For the ECHO parameters, most of the funnel plots showed asymmetry and a few showed some asymmetry (Supplementary Figure 4)[38-44]. Only two variables showed symmetry on funnel plot inspection (Supplementary Figures 3N and 4O)[38-41,43,44].

DISCUSSION

This systematic review and meta-analysis assessed the impact of race on electrical and structural cardiac adaptations amongst healthy adolescent competitive athletes. The findings of this systematic review and meta-analysis revealed significant differences between Black and White athletes in terms of ECG and ECHO parameters. Black athletes showed significant difference in ECG measurements (e.g., PR interval, QRS complex duration and QTc interval), changes (e.g., ST-segment), and evidence of ECG-detected morphological changes (e.g., ventricles hypertrophy). Similarly, more changes in the ECHO parameters. These findings suggest that consideration should be given to the race of athletes during their cardiovascular evaluation prior to participation in competitive sports.

To the best of our knowledge, this is the first meta-analysis to address the racial differences amongst young athletes. A systematic review and meta-analysis by McClean et al[1] studied the differences in athletes heart compared to non-athletes and in a subgroup, they described the impact of race on electrical and structural changes. The findings from the subgroup were consistent with those in the present systematic review in terms of a greater frequency of first-degree AV block and inverted T-waves on ECG, and a thicker posterior wall in ECHO study. However, McLean et al[1] did not find difference in terms of QTc interval. Moreover, they found that the chance of having LVH was 17 times more likely to occur in the Black athletes than their White counterparts; a finding that may be attributed to possibly increased peripheral vascular resistance and a lesser nocturnal reduction in blood pressure in black athletes. The difference between the studies could possibly be explained by variations in duration and intensity of training between the studies included in both analyses. Finally, McClean et al[1], however, included a broader age range between 6-18 years compared to the age range of 12-18 years in our systematic review. They discussed that the prevalence and extent of changes due to cardiac adaptation are influenced by the chronological age of the young athletes. For example, athletes 14 years or older exhibited a significantly longer QRS duration, significantly more incidence of sinus bradycardia, 1.3 times more likely to have inverted T-waves, and more frequent voltage criteria for LVH than those younger than 14 years[1]. In this systematic review and meta-analysis, we did not find a significant difference in terms of the prevalence of LVH between the groups. Moreover, McClean et al[1], demonstrated sex disparities in pediatric athletes[1]. Although several studies have shown sex disparities in cardiac adaptation to exercise[45-48], it was not possible to assess such disparities in the present systemic review due to the male’s majority of the included studies.

The Black athletes in the included studies of the present systematic review were of African or Afro-Caribbean origins (Supplementary Table 4) with only three studies specified the African countries of origin[38,39,43]. Di Paolo et al[39] found differences in specific ECG and morphological characteristics in African athletes according to the country of origin. Algerian athletes, for example, had larger LV cavity and lower R/S-wave voltage, with less frequent ST-segment elevation or abnormal repolarization patterns than athletes from other African countries[39]. The included studies in the present systematic review mainly recruited endurance athletes (Supplementary Table 4) either in different disciplines[38], soccer/football[39-41,43], or American style football[42]. The type of sport may have an impact on cardiac adaptation to exercise. Endurance athletes usually have greater LV wall thickness and LV mass as well as lower resting heart rate than those practicing strength-oriented sports. In terms of hypertrophy description, endurance athletes usually have eccentric hypertrophy (i.e., increased heart mass and chamber volume, with normal wall thickness), whereas, those practiced strength sports have concentric hypertrophy (i.e., increased heart mass and wall thickness, usually without changes in chamber volume)[2].

The impact of racial differences on electrical and structural cardiac adaptations was studied extensively in adult athletes. Research focused on adult athletes also highlighted the presence of more profound ECG anomalies such as T-wave inversion and repolarization abnormalities. However, a key difference was that adult Black athletes had an increased prevalence of LVH compared to their White counterparts[8,22], a finding that was not seen in the present systematic review. Wilson et al[12] studied differences amongst West Asian, Caucasian, and Black adult athletes and found similar rates of uncommon ECG findings between West Asian and Caucasian athletes. Consistent with the findings of the present meta-analysis, Black athletes had significantly greater frequency of anterior and lateral T-wave inversions, LA enlargement, and first-degree AV block[12]. The discrepancy in findings between the age groups may be attributed to the developmental stage of adolescent athletes, where cardiac remodeling processes might still be in progress which become more pronounced in the adulthood owing to the prolonged exposure to intensive training. However, how cardiac adaptation to exercise occurs before, during, and after puberty is not fully known in comparison to the known musculoskeletal adaptation[1]. Bjerring et al[49] examined the impact of endurance training on the development of the hearts of 12-years-old skiers (n = 48). They reported initial concentric remodeling, then in the athletes who continued training (n = 31) showed eccentric remodeling and chamber dilatation with minor changes in wall thickness at the age of 15. Whereas, those who stopped training (n = 17) did not show chamber dilatation but sustained comparable wall thickness. At follow-up, active athletes showed greater indexed LVEDV (84.0 ± 11.0 mL/m²vs 79.0 ± 10.0 mL/m², P < 0.05) and LVESV (36.0 ± 6.0 mL/m²vs 32.0 ± 3.0 mL/m², P < 0.05). Furthermore, they demonstrated higher indexed maximal oxygen uptake (62.0 ± 8.0 mL/kg/minute vs 57.0 ± 6.0 mL/kg/minute, P < 0.05)[49]. Perkins et al[50] explained that cardiac and hematological measures of adaptations to exercise offer predictive models for maximal oxygen consumption in children that are stronger at puberty. Galanti et al[40] found statistical racial difference between the Afro-Caribbean and Caucasian athletes (mean age: 12.0-13.0 years) in terms of interventricular septum thickness and a trend in increase of posterior wall thickness in the Afro-Caribbean athletes. At four-year follow-up of 57 athletes (i.e., 30 Afro-Caribbean and 27 Caucasian), there were statistically significant differences in both interventricular septum and posterior wall thickness in the Afro-Caribbean group. Other ECHO parameters were comparable between the two groups[40]. It has been reported that African American girls have faster sexual maturation based on earlier pubertal indicators than White girls. There is accumulating epidemiological evidence to suggest that earlier pubertal timing can be an important factor for a poor cardio-metabolic health in adolescence and adulthood[51]. Consequently, race and puberty were significantly associated with fitness. Gammon et al[52] found that fitness decreases during puberty and it was lower among African American than Caucasian girls.

Athlete’s heart usually has normal morphology and function despite the physiological adaptation to exercise which is characterized by hypertrophy without pathological implications. However, a relatively small proportion of sport-associated sudden cardiac arrest or death of the overall burden was reported in middle age (35-65 years) athletes, i.e., incidence rate of 21.7 (95%CI: 8.1-35.4) per 1 million per year[53]. In high school athletes (14-18 years), 104 cases of sudden cardiac arrest (35 cases) and death (69 cases) was reported corresponding to a rate of 1:44832 athlete-years with 88.5% of cases occurred in males (incidence rate ratio = 5.3, 95%CI: 2.9-10.6, P < 0.001). The incidence was highest in men’s basketball, followed by men’s football. The autopsy reports in 50 cases revealed idiopathic LVH or possible cardiomyopathy, hypertrophic cardiomyopathy, and myocarditis in 26.0%, 14.0%, and 14.0% of the cases respectively[54]. In one of the included studies (n = 1232) in the present systematic review, one fatality case was reported for a male Black athlete (15 years old) who experienced exertional chest tightness. Postmortem investigation demonstrated an anomalous origin to the right coronary artery[44].

Our findings underscore the importance of considering the racial differences in preparticipation screening guidelines for adolescent athletes. Understanding how common physiological adaptations appear on the ECG and ECHO studies can aid in preventing unnecessary detailed investigations for these athletes and avoid inappropriate disqualification from competitive sports. It is also important to recognize the overlap between physiological adaptations and the pathological conditions perilous to athletes such as hypertrophic cardiomyopathy or arrhythmogenic right ventricular cardiomyopathy. More attention to the ECG and ECHO characteristics of athlete’s heart in African adolescents is warranted. Ethnic-specific guidelines are lacking due to the inadequate data in the various ethnic groups. Most of the published studies derived imaging or ECG criteria based on investigations conducted on Caucasian athletes. Thus, this raises the question about the applicability of such criteria to other ethnicities[22].

The findings from this review should be interpreted in the context of the following limitations. The studies included in this analysis were primarily observational cohort studies which limits the ability to draw definitive conclusions regarding cardiac adaptations over time. However, in the absence of prospective studies, the epidemiologic observational studies are of considerable importance in the evaluation of the effects of exposures (e.g., the behavioral, environmental, and occupational) on human health. Randomized controlled trials are usually not feasible in this setting and if they are conducted, several limitations may be anticipated. Thus, a systematic review of observational studies can reasonably offer a good level of evidence. Furthermore, the number of studies included in this meta-analysis was limited with considerable statistical heterogeneity (I²) and publication bias in most of the studies. This would indicate differences in terms of patients, interventions, outcome definitions, study design, or risk factor effects. A conservative approach by using a random-effects was adopted in this systematic review to account for the anticipated heterogeneity. A meta-regression analysis was inappropriate to perform given the number of included studies (i.e., < 10). Finally, we must recognize that the interpretation of cardiac parameters mentioned in this study could have been confounded by physiological cardiac changes due to normal growth and maturation occurring during adolescence. Given that over the past decades there has been a noticeable increase in the number of non-Caucasian athletes (e.g., Arab, African, or South American) that participate in an advanced competitive level[22], prospective studies are needed to allow determining the longitudinal cardiac adaptations in athletes and how maturation along with factors such as race and intensity of training may impact such adaptation. Future studies should also address the need for improved standardized measurement techniques and investigate the influence of genetics on cardiovascular adaptations in athletes of different ethnicities.

CONCLUSION

Race has an impact on the ECG and ECHO parameters that reflect cardiac adaptations in adolescent athletes. Black athletes tend to have increased prevalence of distinct ECG changes such as first-degree AV block and T-wave inversions compared to their white counterparts. Despite having thicker septal and posterior walls, the overall prevalence of LVH did not differ between the races. However, the findings should be interpreted with caution due to the detected heterogeneity and publication bias. There is a need to consider racial factors when evaluating athletes during pre-competition screening and to incorporate them into future guidelines on how to stratify these physiological adaptations from common cardiac pathologies.