IMPORTANCE: Subclinical atrial fibrillation (AF) is associated with an increased risk for stroke. OBSERVATIONS: Subclinical AF is asymptomatic, short in duration, and usually detected with long-term, continuous monitoring. Most prior studies have explored its consequences using cardiovascular implantable electronic devices (CIEDs). Although current prevalence estimates are derived from study populations with prior CIEDs, 3 trials will assess the time to a first AF diagnosis among patients receiving a CIED for purposes of AF detection. Stroke risk estimates are currently limited to patients with a prior CIED and vary widely, ranging from a hazard ratio of 0.87 (95% CI, 0.58-1.31) to 9.40 (95% CI, 1.80-47.00). Stroke risk pathogenesis may include factors that are proximately causal, upstream risk activators, and risk markers. The treatment of subclinical AF may be a useful stroke prevention strategy; however, no direct evidence of benefit from oral anticoagulation exists in this population. Two ongoing trials will assess the risk and benefit of non–vitamin K oral anticoagulants among patients at high risk for stroke with a previously placed implantable CIED, but without a prior diagnosis of clinical AF. If clinical benefit is proven, then the cost-effectiveness of screening for and the treatment of subclinical AF will require additional study. CONCLUSIONS AND RELEVANCE: At present, no evidence suggests that implanting a CIED to detect AF or initiating oral anticoagulation therapy among those in whom AF is detected is beneficial. Ongoing and future studies will identify people at high risk for developing subclinical AF and will evaluate the efficacy, safety, and economic value of oral anticoagulation therapy in this population.