Transthoracic defibrillation potential gradients in a closed chest porcine model of prolonged spontaneous and electrically induced ventricular fibrillation☆
Received 3 October 2009; received in revised form 8 December 2009; accepted 23 December 2009. published online 01 February 2010.
Abstract
Objective
The purpose of this study was to measure the local electrical field or potential gradient, measured with a catheter-based system, required to terminate long duration electrically or ischaemically induced ventricular fibrillation (VF). We hypothesized that prolonged ischaemic VF would be more difficult to terminate when compared to electrically induced VF of similar duration.
Methods
Thirty anesthetized and instrumented swine were randomized to electrically induced VF or spontaneous, ischaemically induced VF, produced by balloon occlusion of the left anterior descending coronary artery. After 7min of VF, chest compressions were initiated and rescue shocks were attempted 1min later. The potential gradient for each shock was measured and the mean values required for defibrillation compared for the VF groups.
Results
The number of shocks and the shock strength required for termination of VF were not significantly different for the groups. The potential gradient of the first successful defibrillating shock was significantly greater in the spontaneous, occlusion-induced VF group (12.80±2.82V/cm vs 9.60±2.48V/cm, p=0.002). The number of refibrillations was greater in the ischaemic group than in the non-ischaemic electrical group (6±4 vs 1±1, p<0.001). The number of animals requiring a shock at 360J was 2.5 times greater for the ischaemic group.
Conclusions
Defibrillation of prolonged VF produced by acute myocardial ischaemia requires a significantly greater potential gradient to terminate than prolonged VF induced by electrical stimulation of the right ventricular endocardium. The VF duration used in this study approximates that occurring in victims of out-of-hospital cardiac arrest. Our findings may be of clinical importance in the management of such patients.
aThe David Geffen School of Medicine at UCLA, Los Angeles, CA, United States
bDepartment of Emergency Medicine, Harbor-UCLA Medical Center, Torrance, CA, United States
cThe Department of Surgery, Division of Emergency Medicine, University of Utah, Salt Lake City, UT, United States
dThe Department of Medicine, Division of Cardiology, University of Chicago, Chicago, IL, United States
Corresponding author at: Harbor-UCLA Medical Center, Department of Emergency Medicine, 1000 West Carson Street, Box 21, Torrance, CA 90509, United States. Tel.: +1 310 222 3503; fax: +1 310 782 1763.
ABSTRACT