BACKGROUND Due to limited data on athletic QRS duration, this cross-sectional study aims to establish normative digital reference values in asymptomatic, apparently healthy athletes ages 12 to 35 undergoing pre-participation examinations. OBJECTIVES We hypothesized that QRS duration of athletes would be longer in males, increase with age, and rarely exceed 120 ms in the absence of a bundle branch block. METHODS We analyzed QRS duration from standardized digital ECG recordings in 9,084 athletes (58% male, age 12-35 years, mean age 18) obtained during pre-participation examinations. Sex-stratified 99th-percentile quantile-regression equations were developed and applied in an APP to demonstrate that QRS duration outliers could be easily identified. RESULTS Females had shorter QRS durations than males (88.5 +/- 8.3 ms vs. 97.3 +/- 9.1 ms; mean difference 8.9 ms, 95% CI: 8.5-9.2 ms). QRS duration demonstrated a positive cross-sectional association with age and was greater in men than women. Female 97.5th and 99th percentile QRS duration were 106.0 ms and 108.0 ms, respectively, with range 62-130 ms. Male 97.5th and 99th percentile QRS duration were 116.0 ms and 118.3 ms, respectively, with range 70-132 ms. 7(0.2%) females and 55 (1.0%) males had QRS duration >120 ms. 99th percentile quantile regression equations were derived (Female: QRS=99.6 + 0.56 x age; Male: QRS = 104.7 + 0.74 x age). CONCLUSIONS Our results indicate that defining prolonged QRS criteria necessitates adjustments according to age and sex. To facilitate future prospective research, we offer specific regression models to detect outliers.
