The influence of aerobic fitness on electrocardiographic and heart rate variability parameters in young and older adults.

Long-term endurance training is associated with an increased risk of atrial arrhythmia in older adults (OA). We tested the hypothesis that Aerobically-Fit OA would have prolonged indices related to atrial arrhythmias (e.g. PR-intervals and P durations) compared to younger adults (YA) and Aerobically-Unfit OA. 10-minute stable supine electrocardiogram (ECG) recordings were collected at 1000 Hz in 15 YA (4F, 22 ± 2 years, 50.7 ± 8.5 ml/kg/min), 11 Aerobically-Unfit OA (6♀, 63 ± 7 years, 25.2 ± 2.3 ml/kg/min) and 10 Aerobically-Fit OA (4F, 64 ± 3 years, 45.5 ± 7.0 ml/kg/min) to assess ECG morphology and spectral indices of heart rate variability. In the pooled sample, age was a predictor of PR-interval (r = 0.75) and P wave duration (r = 0.80) (both, p < 0.01). Regardless of age, aerobic fitness was positively associated with PR interval duration (r = 0.81; p < 0.01). Aerobically-Fit OA had prolonged PR-intervals (187 ± 17 vs 161 ± 14 vs. 168 ± 20 ms) and P-wave durations (123 ± 9 vs. 97 ± 9 vs. 96 ± 9 ms) compared to YA and Aerobically-Unfit OA, respectively (all, p < 0.05). In addition, Aerobically-Fit OA had greater normalized high-frequency (HF) power compared to Aerobically-Unfit OA (40.7 ± 4.5nu vs. 30.1 ± 14.2 ± nu; p = 0.03) suggestive of enhance parasympathetic tone. These data highlight that the combination of age-related electrical remodeling and enhanced vagal tone in OA with higher aerobic fitness may contribute to prolongation of atrial-related ECG indices. This is further supported by the correlation between HF power and PR-interval duration (r = 0.45; p = 0.02). These findings may help identify older individuals at risk for atrial arrhythmias who are otherwise free of cardiovascular disease.