Background: It is hypothesized that degree of left atrial (LA) fibrosis detected by late gadolinium-enhancement (LGE) MRI correlates with risk of developing atrial arrhythmias. Endurance athletes (EAs) have been noted to have a high incidence of AF and while myocardial fibrosis has been documented in this population, techniques to quantify LA fibrosis is lacking.

Purpose: Using LGE-MRI, we sought to quantify the degree of LA fibrosis in healthy EAs compared to healthy controls.

Methods: We recruited sixteen endurance athletes >35 yrs old who have participated in ≥10 yrs of competitive endurance sports and actively train for ≥10 hrs/wk. Endurance activities included: running, cycling, rowing, and nordic skiing. Questionnaires regarding medical history and training exposure were performed. Twenty healthy control subjects were recruited during screening colonoscopies. All participants underwent cardiac MRI with 3D visualization using processing software.

Results: Overall athletes were younger, had a lower BMI and fewer comorbidities. Mean LA fibrosis score, reported as a percentage, was 13.7% ± 5.4 in EAs compared to 11.8% ± 7.3 in the controls. When controlling for both age and BMI, both known to affect LA fibrosis, being an EA was associated with 6% more LA fibrosis compared to controls (p=0.05). Endurance athlete exposure (R2 = 0.16) had a greater impact on degree of fibrosis than any comorbidity including diabetes, hypertension and tobacco use.

Conclusion: We report a significant correlation between endurance training and LA fibrosis detected on cardiac MRI. In our cohort, despite being younger and with fewer comorbidities, athletes showed significantly more LA fibrosis. While the clinical significance is unclear, it is possible that increased LA fibrosis may explain the increased prevalence of atrial arrhythmia including AF observed in EAs.