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(Circulation. 2004;109:926-931.)
© 2004 American Heart Association, Inc.

Basic Science Reports

Ventricular Fibrillation Scaling Exponent Can Guide Timing of Defibrillation and Other Therapies

James J. Menegazzi, PhD; Clifton W. Callaway, MD, PhD; Lawrence D. Sherman, MD; David P. Hostler, PhD; Henry E. Wang, MD; Kristofer C. Fertig, BS; Eric S. Logue, BS

From the Department of Emergency Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pa.

Correspondence to James J. Menegazzi, PhD, Department of Emergency Medicine, 230 McKee Place, Suite 500, Pittsburgh, PA 15213. E-mail menegazz+{at}pitt.edu

Received February 27, 2003; de novo received August 4, 2003; revision received October 13, 2003; accepted October 14, 2003.

Background— The scaling exponent (ScE) of the ventricular fibrillation (VF) waveform correlates with duration of VF and predicts defibrillation outcome. We compared 4 therapeutic approaches to the treatment of VF of various durations.

Methods and Results— Seventy-two swine (19.5 to 25.7 kg) were randomly assigned to 1 of 9 groups (n=8 each). VF was induced and left untreated until the ScE reached 1.10, 1.20, 1.30, or 1.40. Animals were treated with either immediate countershock (IC); 3 minutes of CPR before the first countershock (CPR); CPR for 2 minutes, then drugs given with 3 more minutes of CPR before the first shock (CPR-D); or drugs given at the start of CPR with 3 minutes of CPR before the first shock (Drugs+CPR). Return of spontaneous circulation (ROSC) and 1-hour survival were analyzed with ² and Kaplan-Meier survival curves. IC was effective when the ScE was low but had decreasing success as the ScE increased. No animals in the 1.30 or 1.40 groups had ROSC from IC (0 of 16). CPR did not improve first shock outcome in the 1.20 CPR group (3 of 8 ROSC). Kaplan-Meier survival analyses indicated that IC significantly delayed time to ROSC in both the 1.3 (P=0.0006) and the 1.4 (P=0.005) groups.

Conclusions— VF of brief to moderate duration is effectively treated by IC. When VF is prolonged, as indicated by an ScE of 1.3 or greater, IC was not effective and delayed time to ROSC. The ScE can help in choosing the first intervention in the treatment of VF.

Key Words: fibrillation • heart arrest • defibrillation • cardiopulmonary resuscitation

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