From Forced Rhythm to Autonomous Oscillation: The Threshold of Self-Sustaining Cardiac Loop Re-entry Under V=N/D

CPR delivers external wave injection (N_external). ROSC occurs when internal ionic gradient density (N_internal) crosses critical threshold N_c — the point at which the cardiac KOKU scaffold sustains the three-layer loop autonomously. Three regimes are defined: Forced (V = N_external/D), Transition (V = (N_external + N_internal)/D), Autonomous (V = N_internal/D — ROSC). The transition is a phase transition, not gradual recovery — explaining the clinical suddenness of ROSC. Pre-mature CPR cessation fails because N_internal < N_c despite apparent ROSC from combined driving. Optimal defibrillation timing is defined as the moment N_internal reaches N_c — not a fixed time interval. The cosmological equivalent is identified: cosmic inflation as forced rhythm, autonomous dark-energy expansion as ROSC. The universe's N_internal crossed N_c at 10^-32 seconds post-singularity and has never re-arrested.