The early defibrillation gap: a time-dependent systems model of survival loss in out-of-hospital cardiac arrest

Background Survival after out-of-hospital cardiac arrest (OHCA) declines steeply with increasing time to defibrillation, yet the temporal mismatch between physiological shockability and delivered shock timing is not explicitly represented in resuscitation system metrics. Purpose To formalize the early defibrillation gap (EDG) as a time-dependent systems construct linking physiological rhythm evolution with operational defibrillation timing in OHCA. Methods A conceptual systems model was developed using targeted evidence synthesis across five domains: OHCA epidemiology, time-to-defibrillation survival relationships, temporal evolution of ventricular fibrillation, rhythm distribution over time, and emergency response intervals. Extracted temporal constructs were mapped to a unified collapse-to-shock axis to derive operational metrics describing defibrillation timing relative to biological shockability. Results The EDG was defined as the interval between circulatory collapse and first defibrillation delivery (T_shock − T_collapse). The model delineates temporal domains of arrest and introduces three operational metrics: Electrical Salvage Window (duration of preserved shockability), Survival–Defibrillability Product (time-dependent salvageable survival), and EDG Burden (survival loss attributable to defibrillation delay). The framework integrates physiological deterioration of ventricular fibrillation with cumulative response latency, enabling quantification of survival potential not realized due to delayed shock delivery. Conclusion The Early Defibrillation Gap model formalizes the time-dependent disconnect between biological defibrillation opportunity and operational shock delivery in OHCA. By providing measurable metrics of survival loss attributable to delay, the EDG framework enables benchmarking of resuscitation systems and evaluation of strategies aimed at reducing collapse-to-shock intervals.