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Introduction The electrocardiogram (ECG) is the most effective screening tool in athletes for conditions associated with sudden cardiac death. Adolescent athletes are a high-risk group but data on age-related ECG changes are sparse. This study reports the distribution of ECG characteristics in elite adolescent athletes and to assess how these differ according to age.Methods We evaluated 24,995 consecutive elite football players, including 22,429 males and 2,566 females, who underwent pre-participation cardiovascular screening between March 2017–24. The screening included a health questionnaire, physical examination, 12-lead ECG, and echocardiogram. The ECG measurements included PR, QRS, and QTc intervals, abnormalities of which can indicate cardiac pathology. A short PR was defined as <120ms and may be associated with Wolff-Parkinson-White syndrome, a prolonged PR interval was defined as >200ms, indicating 1st degree atrioventricular (AV) block, and an abnormal QTc interval considered at >470ms.Results The mean age of the 24,995 players was 17.3 ± 3.9 years. Most were of white ethnicity (60.0%), followed by black ethnicity (19.2%), mixed-race ethnicity (10.7%), and Asian ethnicity (1.0%). A short PR interval was more common in younger athletes (5.89% in those =16 years vs 2.05% in those =17 years, p<0.0001) and in females compared to males (6.2% vs 4.2%, p<0.0001). On the other hand, the proportion of players with a longer PR interval increased with age. 1st degree AV block was over eight times more likely in athletes aged =21 years compared to those aged =14 years (12.6% vs 1.65, p<0.0001). Younger athletes demonstrated a shorter QRS interval compared with older counterparts. Age was not a factor among athletes with a prolonged QTc interval.Conclusion Key ECG parameters (PR and QRS duration) increase with age. Age-specific reference values could improve ECG accuracy and identification of cardiovascular conditions, which is essential to correctly identify athletes at risk of sudden death and conversely, help allay anxiety by reducing false-positive results.Abstract 7-042 Table 1Subjects with PR interval <120 ms and ≥200 ms in each age category Age Group Subjects with PR interval <120 ms n (%) Subjects with PR interval ≥200 ms n (%) ≤14 years 412 (7.27%) 88 (1.55%) 15 – 16 years 441 (4.96%) 275 (3.09%) 17 – 18 years 93 (2.54%) 185 (5.06%) 19 – 20 years 55 (2.39%) 166 (7.20%) ≥21 years 38 (1.21%) 395 (12.55%) p<0.0001 p<0.0001 Abstract 7-042 Table 2Subjects with QRS duration <80 ms and ≥120 ms and corrected QT interval ≥470 ms in each age category Age Group Subjects with QRS duration <80 ms n (%) Subjects with QRS duration ≥120 ms n (%) Subjects with corrected QT interval ≥470 ms n (%) ≤14 years 387 (6.81%) 59 (1.04%) 19 (0.33%) 15 – 16 years 354 (3.96%) 133 (1.49%) 38 (0.43%) 17 – 18 years 98 (2.68%) 69 (1.88%) 17 (0.46%) 19 – 20 years 53 (2.29%) 54 (2.33%) 9 (0.39%) ≥21 years 66 (2.10%) 89 (2.83%) 12 (0.38%) p<0.0001 p<0.0001 p=0.6171 Abstract 7-042 Figure 1Distribution of the PR interval in each age category