Excessive exercise in endurance athletes: Is atrial fibrillation a possible consequence?

The effect of chronic exercise training and acute exercise on power spectral analysis of heart rate variability

Moderate to vigorous physical activity performed regularly is cardioprotective and reduces all-cause mortality, concomitant with increased resting heart rate variability (HRV). However, there are contradictory reports regarding the effects of chronic and acute exercise on nocturnal HRV in those performing exercise well-beyond physical activity guidelines. Therefore, the purpose of this study was to compare the power spectral analysis components of HRV in middle-aged endurance athletes (EA) and recreationally active individuals (REC) and explore acute exercise effects in EA. A total of 119 EA (52, 49-57 years) and 32 REC (56, 52-60 years) were recruited to complete 24 h Holter monitoring (GE SEER 1000) in the absence of exercise. Fifty one EA (52, 49-57 years) then underwent 24 h Holter monitoring following an intense bout of endurance exercise. Power spectral HRV analysis was completed hourly and averaged to quantify morning (1000-1200 h), evening (1900-2100 h), and nocturnal (0200-0400 h) HRV. EA had greater very low frequency (VLF) and low frequency (LF) (both p < 0.001) compared to REC. LF/high frequency (HF) was greater in EA at 0200-0400 h (p = 0.04). Among all participants, the change in HR and HF from 1000-1200 to 0200-0400 h was negatively correlated (r = -0.47, p < 0.001). Following acute exercise in EA, only nocturnal HRV was assessed. VLF (p < 0.001) and HF (p = 0.008) decreased, while LF/HF increased (p = 0.02). These results suggest that in EA, both long-term and acute exercises increase nocturnal sympathovagal activity through an increase in LF and decrease in HF, respectively. Further work is required to understand the mechanism underlying reduced nocturnal HRV in middle-aged EA and the long-term health implications.

Heart Rate Variability-Based Subjective Physical Fatigue Assessment

Accurate assessment of physical fatigue is crucial to preventing physical injury caused by excessive exercise, overtraining during daily exercise and professional sports training. However, as a subjective feeling of an individual, physical fatigue is difficult for others to objectively evaluate. Heart rate variability (HRV), which is derived from electrocardiograms (ECG) and controlled by the autonomic nervous system, has been demonstrated to be a promising indicator for physical fatigue estimation. In this paper, we propose a novel method for the automatic and objective classification of physical fatigue based on HRV. First, a total of 24 HRV features were calculated. Then, a feature selection method was proposed to remove useless features that have a low correlation with physical fatigue and redundant features that have a high correlation with the selected features. After feature selection, the best 11 features were selected and were finally used for physical fatigue classifying. Four machine learning algorithms were trained to classify fatigue using the selected features. The experimental results indicate that the model trained using the selected 11 features could classify physical fatigue with high accuracy. More importantly, these selected features could provide important information regarding the identification of physical fatigue.

Atrial structure and function in middle-aged, physically-active males and females: A cardiac magnetic resonance study

Recent studies have reported on an association between endurance sport, atrial enlargement and the development of lone atrial fibrillation in younger, male cohorts. The atrial morphology and function of middle‐aged, physically‐active males and females have not been well studied. We hypothesized that middle‐aged males would demonstrate larger left atrium (LA) and right atrium (RA) volumes compared to females, but atrial function would not differ. LA and RA volume and function were evaluated at rest in healthy adults, using a standardized 3.0Tesla cardiac magnetic resonance protocol. Physical activity, medical history, and maximal oxygen consumption (V˙O2peak) were also assessed. Physically‐active, middle‐aged men (n = 60; 54 ± 5 years old) and women (n = 30; 54 ± 5 years old) completed this study. Males had a higher body mass index, systolic blood pressure, and V˙O2peak than females (p < .05 for all), despite similar reported physical activity levels. Absolute and BSA and height‐indexed LA and RA maximum volumes were higher in males relative to females, despite no differences in ejection fractions (p < .05 for all). In multivariable regression, male sex p < .001) and V˙O2peak (p = .004) were predictors of LA volume (model R² = 0.252), whereas V˙O2peak (p < .001), male sex (p = .03), and RV EF (p < .05) were predictors of RA volume (model R² = 0.377). While middle‐aged males exhibited larger atrial volumes relative to females, larger, prospective studies are needed to explore the magnitude of physiologic atrial remodeling and functional adaptations in relation to phenotypic factors.

Exercise characteristics and incidence of abnormal electrocardiogram response in long-distance runners with exercise-induced hypertension

While long‐distance running has important health benefits, chronic elevation of blood pressure during exercise might induce cardiac events and sudden death. This study aimed to investigate characteristics of exercise and incidence of abnormal exercise electrocardiography findings in long‐distance runners with exercise‐induced hypertension. Long‐distance runners (n = 606) underwent a questionnaire survey, history taking, and exercise stress testing, and they were classified into the non‐exercise‐induced (n = 268) and exercise‐induced (n = 338) hypertension groups. Exercise‐induced hypertension was defined as systolic blood pressure ≥210 mm Hg during maximal exercise. Abnormal electrocardiogram response (AER) were defined as abnormal electrocardiography findings, such as arrhythmias or ST‐segment changes, during exercise stress testing. There were no differences in general and exercise‐related characteristics between the non‐exercise‐induced and exercise‐induced hypertension groups. The AER group (AERg, n = 37) had a significantly longer training history and total exercise time than the non‐AER group (non‐AERg, n = 569) (p < .05). Atrial arrhythmias and ST‐segment depression were more prevalent in the exercise‐induced hypertension group than in the non‐exercise‐induced hypertension group (atrial arrhythmias: 5% [17/338] vs. 1.9% [5/268]; ST‐segment depression: 2.7% [9/338] vs. .4% [1/268]; p < .05). The incidence of AER was significantly higher in the exercise‐induced hypertension group (n = 30, 8.8%) than in the non‐exercise‐induced hypertension group (n = 7, 2.6%) (p < .05). This study showed that long‐distance runners with AER had a longer training history and total exercise time than those without AER, and the exercise‐induced hypertension group had a higher rate of AER.

Left Ventricular Fibrosis in Middle-Age Athletes and Physically Active Adults

INTRODUCTION

Cardiac magnetic resonance (CMR) late gadolinium enhancement (LGE) and T1 mapping techniques enable the quantification of focal and diffuse myocardial LGE, respectively. Studies have shown evidence of fibrosis in middle-age athletes, but not relative to physically active (PA) adults who perform recommended physical activity levels. Therefore, we examined cardiac remodeling and presence of left ventricular (LV) LGE and T1 values in both recreational middle-age endurance athletes (EA) and PA adults.

METHODS

Healthy EA and PA adults (45-65 yr) completed a standardized 3-T CMR protocol with ventricular volumetry, LV LGE, and T1 mapping.

RESULTS

Seventy-two EA and 20 PA participants (mean age, 53 ± 5 vs 56 ± 4 yr; P < 0.01; V˙O2peak = 50 ± 7 vs 37 ± 9 mL·kg·min, P < 0.0001) were examined, with CMR data available in 89/92 participants. Focal LV LGE was observed in 30% of participants (n = 27/89): 33% of EA (n = 23/69; 33%) and 20% of PA (n = 4/20; 20%). LGE was present at the right ventricular hinge point (n = 21/89; 23.5%) or identified as ischemic (n = 2/89; 2%) or nonischemic (n = 4/89; 4%). Focal LV LGE was observed similarly in both EA and PA (P = 0.25). EA had larger LV chamber sizes and T1 native values (1169 ± 35 vs 1190 ± 26, P = 0.02) compared with PA, with similar LV ejection fraction. Global extracellular volume (ECV) was similar in both EA and PA (22.6% ± 3.5% vs 21.5% ± 2.6%, P = 0.26), with no relationship between global ECV and LV mass (r = -0.16, P = 0.19).

CONCLUSIONS

Focal LGE at the right ventricular hinge point was detected at the same frequency in both groups, was unrelated to demographic or clinical indices, and was found without evidence of global ECV expansion in EA, suggesting a physiologic remodeling response. The long-term clinical implications of hinge-point LGE require clarification using prospective, long-term follow-up studies.

Transcriptomic Bioinformatic Analyses of Atria Uncover Involvement of Pathways Related to Strain and Post-translational Modification of Collagen in Increased Atrial Fibrillation Vulnerability in Intensely Exercised Mice

Atrial Fibrillation (AF) is the most common supraventricular tachyarrhythmia that is typically associated with cardiovascular disease (CVD) and poor cardiovascular health. Paradoxically, endurance athletes are also at risk for AF. While it is well-established that persistent AF is associated with atrial fibrosis, hypertrophy and inflammation, intensely exercised mice showed similar adverse atrial changes and increased AF vulnerability, which required tumor necrosis factor (TNF) signaling, even though ventricular structure and function improved. To identify some of the molecular factors underlying the chamber-specific and TNF-dependent atrial changes induced by exercise, we performed transcriptome analyses of hearts from wild-type and TNF-knockout mice following exercise for 2 days, 2 or 6 weeks of exercise. Consistent with the central role of atrial stretch arising from elevated venous pressure in AF promotion, all 3 time points were associated with differential regulation of genes in atria linked to mechanosensing (focal adhesion kinase, integrins and cell-cell communications), extracellular matrix (ECM) and TNF pathways, with TNF appearing to play a permissive, rather than causal, role in gene changes. Importantly, mechanosensing/ECM genes were only enriched, along with tubulin- and hypertrophy-related genes after 2 days of exercise while being downregulated at 2 and 6 weeks, suggesting that early reactive strain-dependent remodeling with exercise yields to compensatory adjustments. Moreover, at the later time points, there was also downregulation of both collagen genes and genes involved in collagen turnover, a pattern mirroring aging-related fibrosis. By comparison, twofold fewer genes were differentially regulated in ventricles vs. atria, independently of TNF. Our findings reveal that exercise promotes TNF-dependent atrial transcriptome remodeling of ECM/mechanosensing pathways, consistent with increased preload and atrial stretch seen with exercise. We propose that similar preload-dependent mechanisms are responsible for atrial changes and AF in both CVD patients and athletes.

Can strenuous exercise harm the heart? Insights from a study of cardiovascular neural regulation in amateur triathletes

Regular exercise is recommended to improve the cardiovascular risk profile. However, there is growing evidence that extreme volumes and intensity of long-term exertion may increase the risk of acute cardiac events. The aim of this study is to investigate the after-effects of regular, strenuous physical training on the cardiovascular neural regulation in a group of amateur triathletes compared to age-matched sedentary controls. We enrolled 11 non-elite triathletes (4 women, age 24±4 years), who had refrained from exercise for 72 hours, and 11 age-matched healthy non-athletes (3 women, age 25±2 years). Comprehensive echocardiographic and cardiopulmonary exercise tests were performed at baseline. Electrocardiogram, non-invasive blood pressure, respiratory activity, and muscle sympathetic nerve activity (MSNA) were continuously recorded in a supine position (REST) and during an incremental 15° step-wise head-up tilt test up to 75° (TILT). Blood samples were collected for determination of stress mediators. Autoregressive spectral analysis provided the indices of the cardiac sympathetic (LF_RR) and vagal (HF_RR) activity, the vascular sympathetic control (LF_SAP), and the cardiac sympatho-vagal modulation (LF/HF). Compared to controls, triathletes were characterized by greater LF_RR, LF/HF ratio, LF_SAP, MSNA, and lower HF_RR at REST and during TILT, i.e. greater overall cardiovascular sympathetic modulation together with lower cardiac vagal activity. Cortisol and adrenocorticotropic hormone concentrations were also higher in triathletes. In conclusion, triathletes were characterized by signs of sustained cardiovascular sympathetic overactivity. This might represent a risk factor for future cardiovascular events, given the known association between chronic excessive sympathetic activity and increased cardiovascular risk.

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.