Duration of Untreated Cardiac Arrest and Clinical Relevance of Animal Experiments: The Relationship between the "no-Flow" Duration and the Severity of Post-Cardiac Arrest Syndrome in a Porcine Model

INTRODUCTION: The study investigated the effect of untreated cardiac arrest (CA), that is, "no-flow" time, on postresuscitation myocardial and neurological injury, and survival in a pig model to identify an optimal duration that adequately reflects the most frequent clinical scenario. METHODS: An established model of myocardial infarction followed by CA and cardiopulmonary resuscitation was used. Twenty-two pigs were subjected to three no-flow durations: short (8-10 min), intermediate (12-13 min), and long (14-15 min). Left ventricular ejection fraction (LVEF) was assessed together with thermodilution cardiac output (CO) and high sensitivity cardiac troponin T (hs-cTnT). Neurological impairment was evaluated by neurological scores, serum neuron specific enolase (NSE), and histopathology. RESULTS: More than 60% of animals survived when the duration of CA was ≤13 min, compared to only 20% for a duration ≥14 min. Neuronal degeneration and neurological scores showed a trend toward a worse recovery for longer no-flow durations. No animals achieved a good neurological recovery for a no-flow ≥14 min, in comparison to a 56% for a duration ≤13 min (P = 0.043). Serum NSE levels significantly correlated with the no-flow duration (r = 0.892). Longer durations of CA were characterized by lower LVEF and CO compared to shorter durations (P < 0.05). The longer was the no-flow time, the higher was the number of defibrillations delivered (P = 0.043). The defibrillations delivered significantly correlated with LVEF and plasma hs-cTnT. CONCLUSIONS: Longer no-flow durations caused greater postresuscitation myocardial and neurological dysfunction and reduced survival. An untreated CA of 12-13 min may be an optimal choice for a clinically relevant model.