Reproducibility:
For SD-TPS intra-observer intraclass correlation coefficient (ICC) was 0.935 (0.812-0.978), and the inter-observer ICC was 0.932 (0.803-0.977). LAVImax intra-observer ICC was 0.985 (0.957-0.995) and inter-observer ICC 0.984 (0.954-0.995). For LAVImin, the corresponding numbers were 0.980 (0.922-0.994) and 0.959 (0.881-0.986). For LASr, intra-observer ICC was 0.846 (0.543-0.948) and inter-observer ICC 0.893 (0.676-0.964). LAScd intra-observer ICC was 0.872 (0.614-0.956), inter-observer ICC 0.854 (0.557-0.951), and for LASct the intra-observer ICC was 0.869(0.614-0.956) and the inter-observer ICC 0.820 (0.452-0.940).
Discussion: The main finding of this study is that LA MD was associated with paroxysmal AF regardless of athletic status and not associated with years of performing endurance exercise, despite extensive cardiac remodeling among those reporting the longest history of endurance exercise. However, LA MD had no independent incremental value in identifying veteran athletes with a history of AF on top of clinical markers, other relevant echocardiographic variables, and LASr.
Due to promising results in its ability to identify patients with paroxysmal AF when in sinus rhythm, association with atrial fibrosis on MRI, and ability to identify electrical remodeling regardless of LA size, LA MD has emerged as an interesting marker when evaluating LA remodeling in athletes.18, 28, 29 The present study is the first to investigate the associations between LA MD, prolonged endurance and AF in a large group of veteran endurance athletes.
Most studies of LA MD have defined the parameter as SD-TPS corrected by the R-R interval (%) instead of the crude SD-TPS value in ms.14, 17, 28, 30 Endurance athletes experience exercise-induced bradycardia and as expected, the athletes in the present study had a lower resting heart rate than the non-athletic group.31 Hence, we introduced an association between athletic status and LA MD when correcting SD-TPS by the R-R interval. Consequently, we chose to focus on SD-TPS in ms in this study and suggest stating the crude SD-TPS values in ms as well as SD-TPS (%) when investigating LA MD in endurance athletes.
An MRI study by Peritz et al. suggested an association between long-term endurance exercise and atrial fibrosis among a small group of healthy athletes, and LA MD has been demonstrated to associate with LA fibrosis on MRI.19, 29 We found no association between years of reported endurance exercise and LA MD in this study, despite increasing atrial volumes by years of exercise, indicating that athletic remodeling per se has little effect on LA MD measured by echocardiography.
We found a highly significant association between paroxysmal AF and LA MD irrespective of athletic status, suggesting LA MD assessed by SD-TPS could be a promising marker of pathological atrial remodeling in endurance athletes, less affected by physiological exercise-induced cardiac remodeling than absolute volumetric measurements. However, SD-TPS did not add an independent incremental value in identifying veteran athletes with AF when including LASr in the model. This questions the clinical utility of LA MD in veteran athletes, especially considering novel software with automated function imaging of the LA, making LA strain measurements more feasible without including LA MD measurements as an option. Several studies in non-athletic cohorts have demonstrated LA MD to have an independent incremental value at identifying individuals with AF on top of LASr and to predict the recurrence of AF post ablation.14, 16 Current knowledge indicates that LA MD increases with increasing age in healthy individuals.32 As the mean age in this study is 70 years, we must assume age-induced alterations in electromechanical function are present and affect LA MD. As LA MD is perceived to increase as associated with the pathophysiology of healthy aging, prospective studies and studies in younger endurance athletes will have to answer whether LA MD is an independent predictor of AF in endurance athletes and if it adds incremental value to LASr when trying to identify younger athletes with AF.
Strengths and limitations: This is the first study to explore the relationship between endurance exercise, AF, and LA MD, and it comprises a unique cohort of veteran XC skiers with an average of 40-50 years of performing endurance exercise.
The study may have seemed more appealing to individuals interested in endurance exercise, attracting the fittest members of the non-athletic control cohort, and possibly diluting the effect of training in the athletic group. Finally, this is a single-center study, and due to the low number of female participants in the Birkebeiner study with exercise-related AF, men only were included.
Conclusion: LA MD was associated with paroxysmal AF regardless of athletic status but not associated with years of performing endurance exercise despite considerable atrial remodeling in those reporting the longest history of endurance exercise. These results suggest LA MD could be a relevant marker of pathological atrial remodeling in endurance athletes. However, LA MD did not add incremental value to LASr identifying veteran athletes with AF, questioning its clinical utility in this group.