-induced atrial fibrillation: mechanisms and management

The relationship between physical activity and heart rhythm is complex, with decades of evidence showing that regular exercise reduces cardiovascular morbidity and mortality. Yet within sports cardiology, a paradoxical observation has emerged: prolonged, high-volume endurance training appears to predispose some athletes to atrial fibrillation, the most common sustained arrhythmia encountered in clinical practice. First described in middle-aged male endurance athletes in the late 1990s, the condition is now recognised across a wider demographic, including women, masters competitors, and elite performers, and warrants tailored diagnostic and therapeutic strategies.

Australia's outdoor lifestyle and deep-rooted endurance culture make this issue particularly relevant. Each year, tens of thousands of Australians participate in events such as the Sydney Marathon, the Gold Coast Marathon, and the Melbourne Marathon, while Ironman Australia in Port Macquarie draws triathletes from across the region. Ocean swimming clubs from Bondi to Brighton, races through the Adelaide Hills during the Tour Down Under, and ultramarathons in the Flinders Ranges reflect a national appetite for sustained physical exertion. Within this active population, a small but important subgroup develops atrial fibrillation linked directly to training load.

Clinicians in cardiac electrophysiology, sports medicine, and general practice increasingly encounter symptomatic athletes presenting with palpitations, reduced exercise tolerance, or fatigue. Distinguishing benign training-related cardiac adaptations from pathological arrhythmia is critical, as is providing evidence-based guidance on training modification, anticoagulation, and rhythm management. This article reviews the current understanding of exercise-induced atrial fibrillation in endurance athletes, with practical guidance for clinicians managing affected patients in Australian settings.

The discussion that follows synthesises mechanistic insights, risk stratification approaches, and contemporary management recommendations. It also highlights emerging research directions and areas of ongoing debate, including the dose-response relationship between cumulative endurance exposure and arrhythmia risk, and the safety of continued high-intensity training after ablation.

Mechanisms and pathophysiology

The precise mechanisms by which sustained endurance exercise promotes atrial fibrillation remain incompletely understood, but several overlapping processes are implicated. Atrial remodelling, both structural and electrical, is the most consistently reported finding. Chronic volume overload during prolonged exercise produces atrial dilatation, while repetitive surges in sympathetic activity and inflammatory cascades promote fibrosis and altered conduction. These changes lower the threshold for re-entrant circuits and shorten the effective refractory period, creating a substrate conducive to fibrillation.

Autonomic dysfunction plays a complementary role. Long-term endurance training induces high vagal tone, and episodes of atrial fibrillation in athletes frequently occur at rest, during sleep, or immediately after exercise, when parasympathetic predominance is greatest. Genetic predisposition, including variants associated with familial AFib, may interact with these acquired changes to determine individual susceptibility.

Subclinical myocardial injury is another consideration. Elevated cardiac troponin levels and transient right ventricular dysfunction following ultra-endurance events have raised questions about repetitive microtrauma, particularly in athletes with inadequate recovery. Australian researchers at the Baker Heart and Diabetes Institute in Melbourne have contributed to this field, using cardiac MRI and biomarker analysis to characterise the short- and long-term effects of prolonged exercise. The emerging view is that atrial fibrillation in athletes rarely reflects a single mechanism, but rather a convergence of structural, electrical, autonomic, and inflammatory factors.

Identifying at-risk athletes

Not every endurance athlete develops atrial fibrillation, and recognising those most likely to do so informs screening and counselling. Cumulative lifetime training hours appear to be the strongest modifiable risk factor, with risk rising notably beyond approximately 1500 to 2000 hours of sustained activity. Men carry a higher baseline risk than women, although female endurance athletes are not immune, and risk increases with age, particularly after the fifth decade.

Cardiovascular risk factors that influence atrial fibrillation in the general population also apply to athletes, with hypertension, obstructive sleep apnoea, and elevated body mass index all contributing. Athletes often exhibit low traditional risk profiles, so clinicians must actively seek these contributors rather than rely on routine screening. A personal or family history of arrhythmia, including conditions such as long QT syndrome, warrants careful evaluation, and resources discussing long QT syndrome and epilepsy highlight the diagnostic complexity that arises when channelopathies present with overlapping symptoms.

In Australia, where masters-level competition is common well into the sixth and seventh decades, the interaction between age and training volume is especially relevant. Triathlon Australia maintains rigorous pre-participation screening for elite competitors, but recreational athletes engaged in high-volume training often undergo no formal cardiac review. The Heart Foundation's community-based screening clinics in Sydney, Brisbane, and Perth are valuable entry points for identifying previously unrecognised arrhythmias.

Diagnostic workup

A thorough evaluation begins with a detailed training history, capturing lifetime cumulative exposure across running, cycling, swimming, and multisport disciplines. Symptoms should be characterised with attention to triggers, timing relative to exercise, and associated features such as chest discomfort or syncope. Twelve-lead electrocardiography is essential and may reveal left atrial enlargement, premature atrial complexes, or signs of underlying channelopathy.

Ambulatory monitoring is the cornerstone of arrhythmia documentation. For infrequent symptoms, implantable loop recorders offer a higher diagnostic yield than external Holter or patch monitors, and their use is increasingly accepted in symptomatic athletes. Echocardiography assesses atrial size, ventricular function, and structural disease. In selected cases, cardiac MRI provides additional information about atrial fibrosis, right ventricular morphology, and prior myocardial injury, particularly when an underlying cardiomyopathy is suspected.

Exercise stress testing serves a dual purpose, reproducing symptoms under controlled conditions and evaluating rate control adequacy. Athletes with documented atrial fibrillation warrant routine blood testing including thyroid function, electrolytes, and inflammatory markers, and clinicians should consider sleep studies where obstructive sleep apnoea is suspected. Coronary imaging is reserved for those with exertional symptoms suggestive of ischaemia or with elevated cardiovascular risk.

Acute and long-term management

Management of atrial fibrillation in endurance athletes follows the same overarching principles as in non-athletic populations: rhythm control, rate control, and stroke prevention tailored to individual circumstances, with sport-specific considerations modifying these decisions. Many athletes are highly symptomatic and prefer a rhythm control strategy to preserve performance, with antiarrhythmic medications such as flecainide or sotalol commonly used, often in a pill-in-the-pocket approach for paroxysmal episodes.

Catheter ablation has emerged as an effective option for athletes with symptomatic, drug-refractory atrial fibrillation. Pulmonary vein isolation remains the procedural cornerstone, with success rates comparable to or slightly better than in non-athletic cohorts, possibly because of less comorbidity. Recovery typically permits a graduated return to training within two to four weeks, and most athletes achieve comparable or improved performance. In Australia, ablation is performed in major tertiary centres across Sydney, Melbourne, Brisbane, Perth, and Adelaide, with waiting times varying between public and private systems.

Anticoagulation decisions are guided by stroke risk stratification, recognising that athletes often score low despite arrhythmia recurrence. Bleeding risks associated with contact sports, cycling crashes, and swimming in remote locations should be discussed openly, and individualised decisions are essential. Rate control with beta-blockers may limit performance, and non-dihydropyridine calcium channel blockers are often preferred where rate control alone is the chosen strategy.

Training modifications and return to sport

There is no universal threshold for safe training, and guidance must balance the well-established cardiovascular benefits of exercise against the arrhythmia-promoting effects of excessive volume. A pragmatic approach involves reducing weekly endurance hours, incorporating more low-intensity sessions, and avoiding very prolonged events during periods of arrhythmia instability. Heart rate monitoring during training can help athletes identify sessions that consistently provoke symptoms.

Detraining entirely is rarely necessary. Evidence suggests that reducing cumulative training volume by 20 to 40 percent lowers atrial fibrillation recurrence without compromising general cardiovascular fitness. Athletes should be counselled that symptoms often recur if they return rapidly to previous loads, and a phased return with structured monitoring is advisable. Open communication between the treating electrophysiologist, sports physician, and coach supports realistic goal-setting, particularly for masters athletes preparing for events such as the Ultra-Trail Kosciuszko by UTMB or the Sydney to Melbourne ultra-cycling challenge.

Psychological factors deserve attention. Many athletes equate training volume with identity, and a diagnosis of atrial fibrillation can provoke anxiety and reluctance to modify routines. Cardiac rehabilitation programmes with sports cardiology experience, including those offered through the Australian Sports Commission network and selected private providers, offer valuable multidisciplinary support.

Future research and knowledge gaps

Several important questions remain unanswered. The dose-response relationship between cumulative endurance exposure and atrial fibrillation risk requires clearer quantification, ideally through large prospective cohorts with detailed activity tracking. Biomarkers predicting susceptibility before arrhythmia develops would transform prevention, and work on circulating microRNAs and inflammatory profiles is advancing rapidly.

The role of atrial fibrosis, as assessed by late gadolinium enhancement on cardiac MRI, in stratifying long-term risk after ablation is another active area of investigation. Australian-led multicentre studies, including collaborations between the Victor Chang Cardiac Research Institute and the University of Sydney, are contributing to global efforts to refine ablation indications and predict outcomes. The long-term safety of very high-volume training, including ultra-endurance and multiday events, also warrants further study.

Continued dialogue between clinicians, researchers, and athletes will refine understanding and improve care. Readers interested in contributing to this evolving field can consult the manuscript submission guidelines for the Journal of Arrhythmia, where original research, reviews, and case reports on cardiac electrophysiology are welcomed.