Atrial fibrillation (AF) is the most common type of cardiac arrhythmia, affecting up to 6.1 million individuals in the United States (US) and an estimated 50 million globally as of 2020.^1,2 As a major contributor to stroke risk, AF is responsible for one in every seven strokes and is often more severe compared to other etiologies.^1,3 Early detection of AF is crucial for stroke prevention, yet despite its impact, widespread screening is not yet universally recommended.^1,4 Researchers are exploring various approaches, including the Heartline Study, which seeks to investigate the role of wearable technology in identifying AF early and preventing stroke.⁴

The prevalence of AF continues to rise with the aging population, leading to significant morbidity and mortality.¹ Beyond stroke, AF is associated with an increased risk of other serious conditions, such as heart failure (5-fold), sudden cardiac death (2-fold), and chronic kidney disease (1.6-fold).² The irregular heart rhythm in AF increases the risk of blood clot formation, which travels to the brain, potentially resulting in a stroke.3 Anticoagulation therapy, the main treatment to reduce this risk, carries potential risks of bleeding, particularly in elderly or frail patients.^1,2 These challenges underscore the need for effective early detection strategies.4 However, despite its importance, the optimal approach to screening and early intervention remains unclear, with significant debate among healthcare professionals about the risks and benefits of universal screening.^1,4

The Heartline Study is a pragmatic, prospective, randomized, controlled trial conducted entirely through a study application, without clinical sites or in-person visits.⁴ With a target enrolment of 28,000 subjects, it recruited participants aged 65 and older in the US, who must have an iPhone and no prior ownership of an Apple Watch.⁴ The study includes four cohorts, with participants randomized into two groups: one with access to both an Apple Watch (with irregular rhythm notifications and electrocardiography [ECG] functionality) and an iPhone application, and the other with only the iPhone application.⁴ The primary endpoint is the time from randomization to clinical diagnosis of AF, confirmed via healthcare claims data.⁴ Secondary endpoints include the incidence of composite cardiovascular events, health resource utilization, medication adherence, and the time to hospitalizations for bleeding events.⁴ Although the results have not yet been published, the study is expected to provide critical insights into whether this wearable technology can reliably detect AF in real-world settings, facilitate treatment adherence, and improve overall clinical outcomes.⁴

A recent trial involving patients with subclinical AF found that early treatment with apixaban reduced the risk of stroke or systemic embolism compared to aspirin (0.78% vs. 1.24% per patient-year; HR=0.63; 95% CI: 0.45-0.88; p=0.007), though it was associated with a higher risk of major bleeding (1.71% vs. 0.94% per patient-year; HR=1.80; 95% CI: 1.26-2.57; p=0.001).5 This suggests that early intervention may help prevent poorer outcomes like stroke, although the risk of bleeding must be carefully considered.⁵

In the meantime, clinical guidelines from leading health organizations continue to highlight the uncertainty surrounding universal screening for AF.^1,2 The 2022 guidelines from the United States Preventive Services Task Force (USPSTF) concluded that there is insufficient evidence to recommend screening for asymptomatic adults aged 50 or older.¹ Similarly, a 2023 joint guideline from the American Heart Association (AHA) and American College of Cardiology (ACC) emphasized that screening programs must improve both health outcomes and cost-effectiveness.² While screening may be beneficial for high-risk individuals, the current lack of consensus on detection methods, and the question of when to initiate treatment, means that broad-scale AF screening is not yet supported.² Wearables show promise in detecting AF, but more evidence is needed to prove their effectiveness in reducing stroke rates across the population.^2,4

In conclusion, while the question of universal AF screening remains unresolved, ongoing research—including the Heartline Study—holds promise for advancing our understanding of how early detection and intervention can reduce stroke risk in individuals with AF.^1,4 Until more data are available, healthcare professionals are encouraged to follow current guidelines, focusing on high-risk patients for AF and tailoring screening and treatment to individual needs.^1,2 The results of the Heartline Study, once published, will likely shape the future of AF management and help clarify the role of screening in preventing stroke.⁴