ABSTRACT
Regular physical activity is important for cardiovascular health. However, high-volume endurance exercise has been associated with increased number of electrocardiogram (ECG) abnormalities, including disturbances in cardiac rhythm (arrhythmias) and abnormalities in ECG pattern. The aim of this study was to assess if heart rate variability (HRV) is associated with ECG abnormalities. Fifteen participants with previous cycling experience completed a 21-day high-volume endurance exercise cycle over 3,515 km. Participants wore a 5-lead Holter monitor for 24 h pre- and post-exercise, which was used to quantify ECG abnormalities and export sinus R-to-R intervals (NN) used to calculate HRV characteristics. As noise is prevalent in 24-h HRV recordings, both 24-h and heart rate collected during stable periods of time (i.e., deep sleep) were examined. Participants experienced significantly more arrhythmias post high-volume endurance exercise (median = 35) compared to pre (median = 12; p = 0.041). All 24-h and deep sleep HRV outcomes were not different pre-to-post high-volume endurance exercise (p > 0.05). Strong and significant associations with arrhythmia number post-exercise were found for total arrhythmia (total arrhythmia number pre-exercise, ρ = 0.79; age, ρ = 0.73), supraventricular arrhythmia (supraventricular arrhythmia number pre-exercise: ρ = 0.74; age: ρ = 0.66), and ventricular arrhythmia (age: ρ = 0.54). As a result, age and arrhythmia number pre-exercise were controlled for in hierarchical regression, which revealed that only deep sleep derived low frequency to high frequency (LF/HF) ratio post high-volume endurance exercise predicted post total arrhythmia number (B = 0.63, R 2Δ = 34%, p = 0.013) and supraventricular arrhythmia number (B = 0.77, R 2Δ = 69%, p < 0.001). In this study of recreationally active people, only deep sleep derived LF/HF ratio was associated with more total and supraventricular arrhythmias after high-volume endurance exercise. This finding suggests that measurement of sympathovagal balance during deep sleep might be useful to monitor arrhythmia risk after prolonged high-volume endurance exercise performance.
ABSTRACT
BACKGROUND: This study assessed the acute effect of 21â¯days of challenging exercise on heart structure and function in recreationally active people across a range of age categories. METHODS: 15 recreationally active people completed a 21-day fundraising cycling ride (MADRIDE) over a distance of 3515â¯km. Twenty-four hour Holter electrocardiography and blood biochemistry analyses were performed before and after the MADRIDE. RESULTS: Incidence of cardiac arrhythmia was higher after MADRIDE (OR: 5.93; 95% CI: 5.68-6.19), with increases in both ventricular arrhythmias (OR: 9.90; 95% CI: 9.27-10.57) and supraventricular arrhythmias (OR: 3.09; 95% CI: 2.91-3.29). Adults (OR: 11.45; 95% CI: 7.41-17.69) and older adults (OR: 10.42 95% CI 9.83-11.05) were approximately 10 times more likely to experience arrhythmias after the MADRIDE. Whereas, young participants experienced 18% less cardiac arrhythmias after MADRIDE (OR: 0.82; 95% CI: 0.75-0.90). Aortic valve max velocity was reduced (MD: -0.12â¯m/s; 95% CI: -0.19-0.05â¯m/s) and mitral valve deceleration time was slower (MD: -28.91â¯m/s; 95% CI: -50.97-6.84â¯m/s) after MADRIDE. Other structural and functional characteristics along with heart rate variability were not different after MADRIDE. CONCLUSIONS: Multi-day challenging exercise increased the incidence of both supraventricular and ventricular arrhythmias in active adults and older adults. Increases in arrhythmia rates after MADRIDE occurred without changes in cardiac structure and autonomic control. Further exploration is necessary to identify the causes of exercise-induced cardiac arrhythmia in adult and older adults.
