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Review of: Kostera RW, Walker RG, Chapman FW: "Recurrent ventricular fibrillation during advanced life support care of patients with prehospital cardiac arrest." Resuscitation. 78(3):252-257, 2008.
The Science
This study -- which came from the Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands -- examined the rate that cardiac arrest patients found in ventricular fibrillation (V-fib) either remained in V-fib or had recurrent episodes during their resuscitation. They used the 2000 American Heart Association (AHA) guidelines, which called for escalating 200, 200 and 360 joules of stacked shocks followed by 360J. They also used biphasic defibrillators for this study, only examining the shocks delivered by EMS and excluding any provided by public AEDs.
In 465 of the 467 patients enrolled, the initial V-fib episode was terminated within three shocks. Of them, 92%, 61%, and 83% responded to 200 J first, 200 J second and 360 J third shocks, respectively. V-fib recurred in 48% of patients within 2 min of the first episode, and in 74% sometime during prehospital care.
In the 175 patients experiencing five or more V-fib episodes, single-shock V-fib termination dropped from the first to the fifth episode (90-80%, p < 0.001) without change in transthoracic impedance. Yet the proportion returning to organized rhythms increased (11-42%, p < 0.0001).
This means a disproportionate number of their patients represented what they called "frequent refibrillators." It also means that although each time that one of the "refibrillated" the success rate of the shock decreased, those that did actually had a higher rate of return of spontaneous circulation (ROSC).
The authors concluded that repeated refibrillation is common in patients presenting with V-fib cardiac arrest. "The likelihood of countershocks to terminate [ventricular fibrillation] VF declines for repeated episodes of VF, yet shocks that terminate these episodes result increasingly in a sustained organized rhythm," they said.
The Street
This study confirms what several others have already shown. Ventricular fibrillation is recurrent in a large percentage of cardiac arrest patients. This was one of the primary reasons for abandoning the stacked shocks and going to immediate CPR following each defibrillation. All of the study patients received 200J, and 64% received at least one 360J shock. Forty-eight percent refibrillated within two minutes of the first shock, and 74% refibrillated at least once during their resuscitation. Based on this, the authors contend that refibrillators may continue to be in V-fib for a longer period of time with the 2005 guidelines.
Other studies have indicated that all shocks should be delivered at 360J biphasic. These indications are based on data that this level terminates V-fib with one shock very effectively. This would make sense if we were to continue CPR for another two minutes before reanalysis of the rhythm and desire to gain the highest rate of V-fib termination from the first shock.
Whether we will continue to see the same high rates of refibrillators as the authors contend is unknown, but I believe it's unlikely. With the accent on CPR, single-shock delivery and re-evaluation of the role of ventilation, the rates should come down. Another argument against the refibrillators is only a small portion of the victims in this study represented the vast majority of refibrillation events. This may be due to causes other than the energy used and instead due to the underlying cause of their arrest or even the placement of defibrillator pads.
It will be interesting to see what the AHA has in store for us with the 2010 guidelines. Until then, pump hard, pump fast and don't stop.
