Research in context
Evidence before this study
Stroke constitutes a growing health challenge worldwide. Atrial fibrillation is a well known risk factor for stroke, but the risk can be mitigated by anticoagulation treatment. The LOOP Study was initiated on the basis that individuals with atrial fibrillation are often asymptomatic and thus remain undiagnosed and untreated. Studies of patients with cardiac implantable electronic devices, such as pacemakers, reported a high prevalence of subclinical atrial fibrillation and evidence was growing that this type of atrial fibrillation was associated with increased stroke risk. In 2014, the Cryptogenic Stroke and Underlying Atrial Fibrillation study reported that 30% of patients with cryptogenic stroke had atrial fibrillation detected when continuous heart rhythm monitoring was applied. These findings sparked a growing interest in atrial fibrillation screening, while new technologies emerged to detect the arrhythmia. The effect on hard outcomes, such as incidence of stroke, remains to be determined.
Added value of this study
This study presents outcomes of long-term continuous screening for atrial fibrillation versus usual care in individuals with risk factors for stroke. We found that although atrial fibrillation was detected and treated much more often, systematic, intensive screening did not have a significant effect on stroke risk, and there was no effect on mortality. However, the time-to-event curves for stroke overlapped during the first 2–3 years after which they appeared to diverge due to increasing event rates in the control group, and a sensitivity analysis suggested that screening might prevent strokes if done per protocol—ie, continuous implantable loop recorder monitoring for 3 years. The study also showed high rates of atrial fibrillation diagnosis without active screening, high acceptance of anticoagulation, and modest bleeding rates.
Implications of all the available evidence
In this randomised trial of individuals with stroke risk factors, continuous implantable loop recorder monitoring for atrial fibrillation, and subsequent anticoagulation if atrial fibrillation was detected, did not significantly reduce the risk of stroke or systemic arterial embolism. This result was seen despite a high proportion of atrial fibrillation detection and a high acceptance of anticoagulation therapy and might imply that not all atrial fibrillation is worth screening for, and not all screen-detected atrial fibrillation merits anticoagulation.