Exercise-induced electrocardiographic changes after treadmill exercise testing in healthy children: A comprehensive study

Abstract

Background: Treadmill exercise testing is a crucial diagnostic tool for evaluating congenital and acquired heart disease in the pediatric population. This study aimed to perform a comprehensive evaluation of exercise-induced electrocardiographic (ECG) changes in children. Although there are numerous studies on exercise testing in various cardiac pathologies, studies on exercise-induced ECG changes in normal children with coverage of all ECG parameters of atrial and ventricular depolarization and repolarization are very scant, if any.

Aims and objectives: This study aimed to investigate the exercise-induced ECG changes in healthy children and evaluate the effects of gender and four different formulas of heart rate correction of Bazett, Fridericia, Framingham and Hodges on ventricular repolarization parameters pre-and post-exercise.

Materials and methods: Between April 2019 and April 2020, all children with normal electrocardiogram, echocardiogram and exercise test, high-quality ECG tracings and consent for participation were enrolled in this prospective study. Twenty electrocardiographic parameters were measured and 25 indices were calculated. P-value < 0.05 was considered significant.

Results: Seventy-four healthy children were studied. Amplitudes of P, S, and T waves increased significantly after the exercise. All durations, except P wave time to peak and T peak -T end /QT (Tp-e/QT) interval decreased significantly with exercise. Generally, the parameters of ventricular repolarization were not statistically significant between males and females. There were significant differences among the heart-rate corrected values of intervals of QTc, QoTc, JTc, J point to peak T and Tp-e/QTc by various formulas. There was no U wave either at pre-exercise or post-exercise. QT interval was shortened by 24.6 % ± 12.1 % with exercise. The ECG-derived estimated duration of mechanical systole and diastole decreased with exercise. The percentage of decrease in diastole was more than systole (43.79 %± 13.31% versus 33.74% ±15.79 %, respectively, P-value < 0.001).

Conclusion: Diastolic time decreased more than systolic time with exercise and systolic time to diastolic time increased with exercise. Hodges' and Fridericia's formulas resulted in the longest and shortest QT and QoT, JT, and JTP, respectively. Thus, using a single value as the cut-off for long QT syndrome can lead to under or over-diagnosis. Nomograms incorporating data on age, heart rate, and heart rate correction formula are indispensable for accurate long QT diagnosis. Furthermore, gender differences in ventricular repolarization parameters are not generally present in 5 to 14-year-old healthy children. The lack of U wave in this study may implicate the need for more careful investigation in the presence of U wave in the treadmill exercise testing of healthy children.

Keywords: Electrocardiogram; J point to end of T wave interval; J to peak T interval; Onset of Q wave to the end of T wave interval; T peak to T end interval; exercise test.

Figure 1

Simplified Wiggers diagram of the cardiac cycle for electrocardiographic-derived estimation of duration of systole and diastole

Figure 2

J point to end of T wave interval (from J point to the end of T wave), J to peak T and T peak to T end intervals

Figure 3

Box-and-whisker plot of Tp-e interval at preexercise in milliseconds, showing the median and lower and upper quartiles