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.