Participation rate in opportunistic screening compared to systematic screening for atrial fibrillation: STROKESTOP III

Background Atrial fibrillation (AF) screening employing a systematic population-based approach can identify previously undiagnosed AF and potentially reduce the risk of stroke. In prior studies, participation rates have been modest, with non-participants often representing individuals at the highest cardiovascular risk. Opportunistic screening during routine primary care visit may increase participation rate. The STROKESTOP III trial aimed to determine whether opportunistic screening increases participation rate for atrial fibrillation screening compared to systematic screening. Methods The STROKESTOP III study is a cluster-randomized trial involving 16 primary care centers. The primary care centers were allocated to either systematic screening (n=8) or opportunistic screening (n=8) using cluster randomization considering size and socioeconomic characteristics. Individuals born 1948/1949 were eligible for inclusion. Exclusion criteria included known AF, contraindications to or ongoing oral anticoagulant (OAC) treatment, and dementia. In the systematic arm, individuals without exclusion criteria received an invitation to participate by post. In the opportunistic arm, individuals were invited during a routine primary care visit. All participants were instructed to perform a single-lead 30 second ECG using handheld ECG device three times daily for a total of two weeks. Results The study was initiated in May 2024 and concluded in October 2025. In total, 2916 patients were registered across the 16 primary care centers. Of the 1479 participants allocated to the opportunistic arm, a total of 730 patients did not visit the clinic or were not assessed for eligibility, leaving 749 individuals who visited their primary care center and were screened for inclusion. Of these, 148 (19.8%) fulfilled exclusion criteria, leaving 601 eligible individuals who were invited to participate. Of those 374 (62.2%) participated. The systematic screening arm consisted of 1437 patients. A total of 119 (8.3%) met exclusion criteria, leaving 1318 eligible individuals, of whom 607 (46.1%) participated, figure 1. Participation among invited individuals was significantly higher in the opportunistic screening arm (62.2%) compared to the systematic screening arm (46.1%), p < 0.005. Overall, participants in the opportunistic screening arm had a higher average CHA2DS2-VASc score (mean 3.99, p<0.005) and a higher prevalence of AF risk factors including hypertension and diabetes compared with participants in the systematic arm (Table 1). AF detection was low in both arms, with 3 cases detected in the opportunistic arm (0.8%), and 8 cases detected in the systematic arm (1.3%), p = 0.54. Conclusion Opportunistic screening yielded higher participation and enrolled participants with a higher cardiovascular risk burden than systematic screening. Contraindications were also more common.