Study population:
Cross-country (XC) skiing ranks among the sports with the highest
cardiovascular demands and profound cardiac
remodeling.20 The Norwegian Birkebeiner XC ski race is
one of the world’s most demanding XC ski races, with a course length of
54 km, covering approximately 1000 altitude meters. Previous studies
have demonstrated how participation in the Birkebeiner XC ski race is
associated with athletic cardiac remodeling and an increased risk of
AF.4, 13, 21 To cover the whole range of physical
activity in the population, the Birkebeiner Atrial Fibrillation study
(2012) comprised two independent cohorts; one cohort consisting of
persons who had completed the Birkebeiner XC ski race, and another
cohort of individuals that had participated in a population-based health
survey (The Oslo Health study).4 With the aim to
investigate athletic cardiac remodeling in relation to AF, we invited
520 former participants in the Birkebeiner Atrial Fibrillation study to
participate in a cross-sectional clinical study performed between
January 2019 and October 2020. All veteran skiers with AF living within
a 2-hour perimeter from the study site were invited. Participants with
supraventricular tachycardia other than AF, prior open-heart surgery,
heart failure (EF <35%), or clinically significant valvular
disease were excluded. Veteran skiers without AF, age-matched to the
included skiers with AF, were invited until reaching the same number of
included skiers with and without a history of AF. Age-matched
participants from the non-athletic cohort with and without a history of
AF were consecutively invited until reaching the same number of included
individuals in all four groups. Because the original study cohort lacked
age-matched non-athletic controls, the group of non-athletes with AF was
supplemented by male patients visiting the AF outpatient clinic at
Diakonhjemmet Hospital between May and September 2020. All patients were
screened, and men of the proper age were consecutively invited to
participate. Participants with AF during the examination, paced rhythm,
or left bundle branch block were excluded from the current analysis
(Figure 1). The methods of the study have been described in detail
earlier.10
All participants answered a questionnaire and underwent physical
examination by the main investigator (ES). Data from the questionnaire
(age, sex, history of heart failure, hypertension, stroke, coronary
heart disease, and diabetes mellitus) were used to estimate the
CHA2DS2-VASc score as a marker of
cardiovascular risk.22 Regular endurance exercise was
self-reported in the questionnaire on an eight-level ordinal scale. To
evaluate the dose-response relationship between years of endurance
exercise and LA MD, we condensed this scale into four categories in the
same matter used previously.13
A 12-lead electrocardiogram (ECG) was obtained and exported in digital
format for offline processing using standard Glasgow algorithm with
automatic identification of fiducial points, intervals and amplitudes of
the components of the PQRST-complex.23 We affirmed the
history of AF by review of medical journals, adjudicating AF according
to guidelines.24 In 13 participants (5 athletes and 8
non-athletes), it was challenging to differentiate paroxysmal AF from
persistent AF, these were included as having paroxysmal AF.
The study complies with the Declaration of Helsinki and was approved by
the Regional Committee for Medical and Health Research Ethics (ref.nr:
2016/565). All participants gave written consent.