Abstract 103: Is All Ventricular Fibrillation the Same? A Comparison of Ischemically Induced and Electrically Induced Ventricular Fibrillation in a Porcine Cardiac Arrest and Resuscitation Model
Background: The standard porcine model for the study of cardiac arrest and resuscitation utilizes electrical induction of VF. Reported restoration of spontaneous circulation (ROSC) and survival rates, in this model, are as high as 90% for VF durations of 7 to 10 min, values substantially greater than in the clinical population, i.e., 20–30%. A high first shock success rate, infrequent refibrillation, short ROSC times, and minimal need for vasopressor support during CPR are typical of the standard VF model. The purpose of this study was to determine if ischemic induction of VF in swine followed by standard ACLS would result in short-term outcomes approximating those observed in human victims of out-of-hospital VF.
Methods: Swine were randomized to either electrically induced VF (EVF) or ischemic VF (IVF) produced by balloon occlusion of the mid-LAD (n = 20 per group). Transthoracic impedance was measured and 30 ohms added in series for all animals. The balloon remained inflated during resuscitation efforts in IVF animals. After 7 min of VF, CPR was initiated and defibrillation was attempted 1 min later. Epinephrine (epi) and antiarrhythmics were administered as per guidelines. Resuscitation was terminated if ROSC had not occurred after 15 min of ACLS.
Results: Findings are summarized in the table⇓. Values are mean ± SD. Mean impedance for each group was 71 ohms. CPR coronary perfusion pressure was not different between groups. Cardiac dysfunction was greater in the IVF group (LV stroke work 30 ± 7 vs 15 ± 9 gm-m, p<0.001) at 6 hours.
Conclusions: Resuscitation from IVF is more difficult that EVF and characterized by greater time to ROSC, frequent refibrillation, greater number of countershocks and higher epi dose during resuscitation efforts, profound cardiac dysfunction, and a short-term survival rate approaching clinical experience. Ischemically induced VF is a more clinically relevant model for the evaluation of resuscitation interventions.