Age-Related Electrocardiographic Characteristics of Male Junior Soccer Athletes

Abstract

Introduction: Very limited data exist on normal age-related ECG variations in adolescents and no data have been published regarding the ECG anomalies induced by intensive training, which are relevant in pre-participation screening for sudden cardiac death prevention in the adolescent athletic population. The purpose of this study was to establish normal age-related electrocardiographic measurements (P wave duration, PR interval, QRS duration, QT, and QTc interval) grouped according to 2-year age intervals.

Methods: A total of 2,151 consecutive healthy adolescent Soccer athletes (trained for a mean of 7.2 ± 1.1 h per week, 100% male Caucasians, mean age 12.4 ± 1.4 years, range 7-18) underwent pre-participation screening, which included ECG and transthoracic echocardiography in a single referral center.

Results: Their heart rate progressively slowed as age increased (p < 0.001, ranging from 80.8 ± 13.2 to 59.5 ± 10.2 bpm), as expected. The P wave, PR interval, and QRS duration significantly increased in older age classes (p = 0.019, p = 0.001, and p < 0.001, respectively), and after Bonferroni's correction, the difference remained significant in all age classes for QRS duration. The QTc interval diminished progressively with increasing age (p = 0.003) while the QT interval increased progressively (p < 0.001).

Conclusions: Significant variations in the normal ECG characteristics of young athletes exist between different age groups related to increasing age and training burden, thus, age-specific reference values could be adopted, as already done for echocardiographic measurements, and may help to further discriminate potentially pathologic conditions.

Keywords: adolescent; athlete's heart; electrocardiogram; exercise; nomograms; normal values; reference values.

Figure 1

Centile rainbow plots for heart rate (top left panel), P wave duration (right panel), PR (mid-left panel), QRS (mid-right panel), QT (bottom left panel), and QTc (bottom right panel), expressed as median and quartile and age ranges. (A) Heart rate. (B) P wave duration. (C) PR duration. (D) QRS duration. (E) QT duration. (F) QTc duration.

Figure 2

Heatmap correlation between individual features and ECG variables. Each square of the heatmap represents the correlation between the x-axis and the y-axis variables, which ranges between −1 and +1. The closer to +1 the stronger the correlation is (red in the legend, high correlation). The closer to −1 there is an inverse correlation (blue in the legend). White color represents no correlation. The diagonals are all dark red because the heatmap plot is symmetrical about the diagonal and those squares represent the same variable paired together on both axes. The dendrogram highlights the different clusters in which the study population has been divided based on the different variables analyzed.

Figure 3

Graphical representation of why reference values are important in clinical practice. Values <2nd or >98th percentiles correspond to Z−scores of < -2 or > 2, respectively, and they may imply the presence of a specific pathology or disease that should be ruled out because that value is outside the normal values, present in the 96% of the study population.