Characteristics and outcomes of younger adults with out-of-hospital cardiac arrest resuscitated with extracorporeal membrane oxygenation: a nationwide study

BACKGROUND: Extracorporeal cardiopulmonary resuscitation has shown promise in out-of-hospital cardiac arrest, but evidence in younger adults remains limited. Younger adults represent a unique subgroup with distinct etiologies and potentially greater physiological reserve. This study aimed to identify clinical characteristics and assess factors associated with outcomes in younger adults receiving extracorporeal cardiopulmonary resuscitation. METHODS: This retrospective observational study analyzed data from the Study of Advanced Life Support for Ventricular Fibrillation with Extracorporeal Circulation in Japan registry, which prospectively collected data on adult out-of-hospital cardiac arrest patients receiving extracorporeal cardiopulmonary resuscitation across 36 Japanese institutions (2013-2018). Patients were stratified by age: younger adults (≤ 40 years) versus older adults (> 40 years). The primary outcome was favorable neurological status at discharge (cerebral performance category 1-2). Multivariable logistic regression and restricted cubic spline analyses were performed to identify factors associated with outcomes. RESULTS: Of 2,129 patients, 212 (10.0%) were younger adults (mean age, 32.2 ± 6.8 years) and 1,917 (90.0%) were older adults (mean age, 62.2 ± 11.1 years). Younger adults showed distinct etiological patterns with fewer acute coronary syndromes (13.7% vs. 53.4%) and more arrhythmias (30.2% vs. 9.8%) and myocarditis/cardiomyopathy (13.7% vs. 4.9%). Notably, the proportion of cases with unknown causes was higher among younger adults (40.6%) compared to older adults (18.3%). Multivariable analysis revealed that shockable rhythm was not associated with neurological outcomes in younger adults, in contrast to older adults where shockable rhythm retained its prognostic significance. Nonlinear spline analysis showed that the odds of favorable neurological outcomes remained relatively stable in younger adults despite prolonged low-flow durations, in contrast to older adults who showed deteriorating outcomes with longer ischemic periods. CONCLUSIONS: Younger adults undergoing extracorporeal cardiopulmonary resuscitation demonstrated distinct etiological patterns and enhanced tolerance to prolonged low-flow time relative to older adults. These findings generate the hypothesis that age-related differences in tolerance to prolonged low-flow time may exist between younger and older adults. However, given the observational and post-hoc nature of this study, prospective validation is needed before age-stratified extracorporeal cardiopulmonary resuscitation protocols can be recommended.