Prearrest hypothermia improved defibrillation and cardiac function in a rabbit ventricular fibrillation model

Abstract

BackgroundHypothermia when cardiopulmonary resuscitation begins may help achieve defibrillation and return of spontaneous circulation (ROSC), but few data are available. ObjectiveThe objective of this study was to determine whether prearrest hypothermia improved defibrillation and cardiac function in a rabbit ventricular fibrillation (VF) model. ResultsThirty-six New Zealand rabbits were randomized equally to receive normothermia (Norm) (~39°C), post-ROSC hypothermia (~33°C), or prearrest hypothermia (~33°C). Ventricular fibrillation was induced by alternating current. After 4 minutes of VF, rabbits were defibrillated and given cardiopulmonary resuscitation until ROSC or no response (≥30 minutes). Hemodynamics and electrocardiogram were monitored; N-terminal pro–brain natriuretic peptideand troponin I were determined by enzyme-linked immunosorbent assay. Myocardial histology and echocardiographic data were evaluated. First-shock achievement of perfusion rhythm was more frequent in prearrest than normothermic animals (7/12 vs 1/12; P = .027). After ROSC, dp/dtmax was higher in prearrest than normothermic animals (P < .001). Left ventricular end-systolic pressure was higher in prearrest than normothermic animals (P = .001). At 240 minutes after ROSC, troponin I and N-terminal pro–brain natriuretic peptide were lower in prearrest than normothermic animals (15.74 ± 2.26 vs 25.09 ± 1.85 ng/mL and 426 ± 23 vs 284 ± 45 pg/mL, respectively), the left ventricular ejection fraction and cardiac output were lower in the Norm group than other 2 groups (P < .01). Myocardial histology was more disturbed in normothermic than post-ROSC and prearrest animals, but was not different in the latter 2 groups. ConclusionsInduction of hypothermia before VF led to improved cardiac function in a rabbit VF model through improving achievement of perfusing rhythm by first-shock defibrillation and facilitating resuscitation.