No-Flow Duration and Outcomes After Cardiogenic Out-of-Hospital Cardiac Arrest in Older Adults.

Importance: The burden of cardiogenic out-of-hospital cardiac arrest (OHCA) among older adults is increasing. No-flow time is a key determinant of prognosis, and the aging brain may be increasingly vulnerable to ischemic injury during this interval. Objective: To delineate the association between no-flow duration and outcomes in older adults with cardiogenic OHCA using dynamic probability curves. Design, Setting, and Participants: This nationwide, population-based, multicenter retrospective observational cohort study used data from the All-Japan Utstein Registry from January 1, 2010, through December 31, 2023. Participants included adults 65 years or older with witnessed cardiogenic OHCAs treated within Japan's nationwide emergency medical service (EMS) system. Data were analyzed from December 1, 2025, to July 7, 2026. Exposure: No-flow time, defined as the interval from witnessed arrest to initiation of cardiopulmonary resuscitation by EMS clinicians. Main Outcomes and Measures: The primary outcome was 30-day favorable neurologic outcome, defined as cerebral performance category of 1 or 2. Age-stratified dynamic probability curves were constructed for patients aged 65 to 74 years, 75 to 84 years, 85 to 94 years, and 95 years or older to describe the time-dependent likelihood of outcome according to no-flow duration. For each age group, the no-flow time at which the estimated probability fell below 1% with 95% CIs was identified. Results: Among 1 795 502 registry cases, 259 851 patients met the inclusion criteria. The median patient age was 82 (IQR, 75-88) years, 148 018 (57.0%) were male, and the median no-flow time was 11 (IQR, 8-15) minutes. Overall, 8711 patients (3.4%) achieved a 30-day favorable neurologic outcome. In all patients 65 years or older, the no-flow times at which the estimated probability of favorable neurologic outcome fell below 1% was 11 (95% CI, 11-11) minutes. Corresponding thresholds for favorable neurologic outcome was 14 (95% CI, 14-14) minutes for those aged 65 to 74 years, 11 (95% CI, 10-11) minutes for those aged 75 to 84 years, 2 (IQR, 0-4) minutes for those aged 85 to 94 years, and 0 (95% CI, 0-0) minutes for those 95 years or older. Conclusions and Relevance: In this cohort study of older adults with cardiogenic OHCA, the no-flow time window compatible with an estimated probability of at least 1% for favorable neurologic outcome became progressively shorter with advancing age. These findings may inform resuscitation decision-making in aging populations.