Effects of Detraining in Endurance Athletes With Atrial Fibrillation

Atrial fibrillation (AF) affects more than 43 million people worldwide, but specific exercise recommendations do not exist for this group of patients. Despite a lack of evidence, athletes are often advised to reduce exercise intensity (detraining) after being diagnosed with AF. This randomized controlled trial will be the first study that investigates effects of detraining in endurance athletes. Participants will be randomized to an intervention group that will be instructed to refrain from high intensity exercise, and a control group. The study aims to clarify whether detraining might reduce the burden of AF and has the potential to guide development of exercise guidelines for AF patients.

Atrial fibrillation (AF) affects more than 43 million people worldwide, but specific exercise recommendations do not exist for this group of patients. Despite a lack of evidence, athletes are often advised to reduce exercise intensity (detraining) after being diagnosed with AF. This randomized controlled trial will be the first study that investigates effects of detraining in endurance athletes. Participants will be included at Bærum Hospital, St.Olavs Hospital, Trondheim, Baker Institute, Melbourne, Leuven University Hospital, Antwerp University Hospital, AZ Jan Palfijn Gent and Jessa Hospital Hasselt, Belgium. In total 120 participants will be monitored with a chest-strap heart rate (HR) monitor and sportswatch (exercise intensity), and an Insertable Cardiac Monitor (ICM, AF burden). Participants will be randomized to an intervention group (n=60) that will be instructed to refrain from high intensity exercise (H) \>75% of maximal HR (HRmax)) for a period of 16 Weeks, or a control group (n=60) that will be instructed to perform at least three weekly sessions of high intensity training (HR ≥85% of HRmax. The primary endpoint will be AF burden, as measured by continuous monitoring with ICMs and calculated as the cumulative duration of all AF episodes lasting ≥30sec divided by total duration of monitoring. The study aims to clarify whether detraining might reduce the burden of AF and has the potential to guide development of exercise guidelines for AF patients. The investigators will also study exercise-induced cardiac remodeling, aiming to improve the understanding of underlying pathophysiological mechanisms for AF.

Eligibility Criteria:
Inclusion Criteria:

* Signed informed consent
* Age ≥ 18 years
* Diagnosed with paroxysmal atrial fibrillation (verified by electrocardiogram)
* Report \>5 (running, rowing) or \>8 (cycling, cross-country skiing), weekly hours, respectively, of endurance sport
* At least two anamnestic (self-reported) episodes of atrial fibrillation, of which one during the last six months
* Use a smartphone and agree to connect their sportswatch with a web-based platform for monitoring of exercise

Exclusion Criteria:

* Permanent atrial fibrillation
* Cardiac conditions (including valvular heart disease of moderate or greater severity, symptomatic ischemic heart disease)
* Left ventricular ejection fraction \<45%
* Hypertension (\>140/90)
* Diabetes mellitus
* Hyperthyroidism
* Smoking during the last 5 years
* Alcohol intake \>20 alcohol units/week
* Use of illegal or performance enhancing drugs
* Body mass index \>30kg/m2
* Injuries preventing physical exercise
* Pregnancy
* Participation in conflicting intervention research studies
* Planned atrial fibrillation ablation within the next six months
* The individual refuses to have an insertable cardiac monitor, blood samples taken or be part of the detraining group