Prognostic Impact of Transient Return of Spontaneous Circulation According to Low-Flow Time in Patients with Out-of-Hospital Cardiac Arrest Undergoing Extracorporeal Cardiopulmonary Resuscitation: A Nationwide Cohort Study

Background/Objectives: Low-flow time (LFT) is a major prognostic factor in patients undergoing extracorporeal cardiopulmonary resuscitation (ECPR), but chronological LFT may not fully reflect ischemic burden when transient return of spontaneous circulation (ROSC) occurs. We investigated whether the association between transient ROSC and outcomes varies according to LFT. Methods: This nationwide retrospective cohort study included 810 adults with witnessed out-of-hospital cardiac arrest who underwent ECPR. The primary outcome was survival to hospital discharge, and the secondary outcome was good neurological outcome. A prespecified subgroup analysis compared LFT ≤90 versus >90 min, followed by an exploratory analysis using <60, 60–90, and >90 min categories. Multivariable logistic regression and interaction analyses were performed. Results: Among 810 patients, 450 (55.6%) experienced transient ROSC. In the prespecified analysis, transient ROSC was associated with survival in patients with LFT ≤90 min (adjusted odds ratio [AOR], 2.375; 95% confidence interval [CI], 1.076–5.241; p = 0.032), but not in those with LFT >90 min (AOR, 0.884; 95% CI, 0.595–1.315; p = 0.543), with a significant interaction (p = 0.036). The exploratory three-category analysis showed a significant association in the 60–90-min subgroup (AOR, 3.399; 95% CI, 1.021–11.316; p = 0.046), although the global interaction was not significant (p = 0.126). No significant interaction was observed for good neurological outcome. The prespecified survival interaction remained significant in sensitivity analyses. Conclusions: The association between transient ROSC and survival after ECPR differed according to LFT using the prespecified 90-min cutoff. Transient ROSC may provide prognostic information complementary to chronological LFT, whereas the three-category findings should be considered exploratory.