Abstract 98: Spontaneous Refibrillation Following External Defibrillation of Long Duration Ventricular Fibrillation in Swine

Abstract

Background: Following successful defibrillation of the long duration ventricular fibrillation (LDVF) associated with sudden cardiac arrest (SCA), refibrillation occurs in over half of resuscitation attempts. In experimental animals with normal hearts, refibrillation almost never occurs following short duration VF lasting < 1 min (SDVF). It is not known if refibrillation following LDVF is due to the cardiac disease that caused the initial LDVF of SCA or if the LDVF itself causes abnormalities that can initiate VF. Further, the mechanism of refibrillation initiation is unknown. We tested the hypothesis that refibrillation occurs frequently following LDVF in previously normal hearts and propagates from a common area within the heart. Methods : In 6 pigs, 115–120 plunge needles containing 3– 6 electrodes each were inserted throughout the heart. With the chest closed, external defibrillation pads were placed in a left lateral to right lateral configuration. Following successful defibrillation of 20 s of SDVF, the animal was observed for spontaneous VF for at least 4 min. After termination of 7 min of LDVF, the animal was placed on cardiopulmonary bypass and observed for 15 min for spontaneous VF. Results: Following LDVF, 1.33 ±0.8 episodes of spontaneous VF occurred in each animal. The mean time to VF was 71 s (range 5 – 139 s) following defibrillation of LDVF. Three animals had a second episode of VF within 3 min of termination of LDVF. Earliest sites of origin of spontaneous VF occurred equally in the LV (3), RV (3), and septum (2) and arose equally from the endocardium (3), epicardium (2), and myocardium (3). Refibrillation originated in the posterior half of the ventricles 75% of the time. The first refibrillation cycle appeared focal in 75% of cases and reentrant in 25%. Premature ventricular beats arising out of the posterior RV base immediately preceded 75% of VF episodes. Conclusions: Spontaneous VF is common after defibrillation of LDVF but not SDVF in previously health swine, indicating that refibrillation does not require preexisting cardiac disease but can be caused by the detrimental effects of LDVF. Most episodes of refibrillation begin as focal activity within the posterior half of the ventricles.