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Introduction Following the implementation of the British Cardiovascular Interventional Society (BCIS) algorithm, 1 patients with shockable out-of-hospital cardiac arrest (OHCA) rhythms (ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT)) are preferentially transported to the Essex Cardiothoracic Centre (CTC) for specialist post-arrest care. Concentration of such cases at cardiac arrest centres (CACs) aims to improve survival outcomes. Our analysis aimed to analyse the metabolic phenotype of these patients.Methods We analysed blood gas, low-flow time, MIRACLE-2 score 2 and survival data from OHCA admissions (2019–2020) across the Essex network (within the BCIS OHCA registry). Cardiac arrests were grouped as shockable (VF/VT) or non-shockable (asystole/pulseless electrical activity (PEA)). Metabolic measurements (lactate, pH, bicarbonate, pCO2) were compared between groups using Mann–Whitney tests. Low-flow time (duration of CPR in minutes) was analysed after excluding physiologically implausible outliers. Survival to discharge was stratified by rhythm group. Associations between low-flow time and metabolic markers were explored with correlation and partial-correlation analyses. MIRACLE-2 scores were compared between rhythm groups and categorised as low (0–3), intermediate (4–6) or high (7–10) risk.Results Among 547 patients with blood gas data (290 shockable; 207 non-shockable), shockable arrests presented with significantly lower lactate (median 4.1 vs 8.7 mmol/L), higher pH (7.22 vs 7.00), higher bicarbonate (19.2 vs 14.4 mmol/L), and lower pCO 2 (6.6 vs 8.7 kPa) (all p < 0.001). Survival to hospital discharge was 60.7% in shockable arrests versus 6.2% in non-shockable arrests. Low-flow time remained significantly longer in non-shockable arrests (median 26 vs 20 minutes, p = 0.004), with a small to moderate effect size. Longer low-flow times were strongly associated with higher lactate and more severe acidosis. Among 515 patients with available MIRACLE-2 scores (278 shockable; 237 non-shockable), shockable arrests had substantially lower MIRACLE-2 scores (mean 3.3 ± 2.1 vs 6.1 ± 1.4; p < 0.001), with 50.4% vs 1.7% in the low-risk category and 4.0% vs 34.2% in the high-risk category for shockable and non-shockable rhythms, respectively.Conclusion Patients with shockable cardiac arrest rhythms are inherently more likely to survive, reflecting a more reversible metabolic injury at presentation [3]. Non-shockable arrests experience longer CPR durations and more profound metabolic derangement, which contributes to the observed survival gap [3]. MIRACLE-2 scoring further demonstrates that shockable arrests present with markedly more favourable prognostic profiles. Concentrating shockable arrests at CACs amplifies their intrinsic survival advantage by providing immediate access to interventional cardiology and specialist cardiac intensive care.References To be requested if required.