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Shocking Research

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Review of: Hallstrom A, Rea TD, Mosesso VN Jr, et al: "The relationship between shocks and survival in out-of-hospital cardiac arrest patients initially found in PEA or asystole." Resuscitation. 74(3):418-426, 2007.

The Science

This study examined the outcomes of 738 cardiac arrest victims who presented with an initial rhythm of pulseless electrical activity (PEA) or asystole. Both are considered "Non-shock" rhythms, and the primary treatment is CPR and medication. If the patients developed V Fib or V Tach "shock" rhythms, then they were defibrillated.

This study comes from data collected during the AutoPulse Assisted Prehospital International Resuscitation (ASPIRE) trial, which was previously published and compared the manual CPR to that of the Zoll AutoPulse cardiac support pump.

The endpoints of the study were survival to four hours and hospital discharge.

Of the 738, 78% (n = 574) subsequently remained in a non-shockable rhythm/state at each evaluation throughout the resuscitation (Non-shock group) while 22% (n = 164) converted to V Fib and were shocked by EMS (shock group). Survival to hospital discharge was significantly greater in the Non-shock group (4.9% versus 0.6%, p = 0.01).

They concluded that, "These results suggest that patients with cardiac arrest who develop [V Fib] during the course of treatment for initially observed pulseless electrical activity or asystole do not benefit from conventional approaches to treatment such as defibrillation. Further study is warranted to define the optimal treatment of this patient cohort."

The Street

I believe in a fundamental difference between PEA and all other forms of cardiac arrest. I suspect many of these patients are in profound shock and should be treated aggressively with vasopressors and other medications targeted at the underlying causes. Asystole probably is a completely different condition, and to lump it together with PEA probably isn't appropriate. Interestingly, about the same percentage of PEA and asystole patients in this study converted to a shockable rhythm, and in doing so they had a significantly worse outcome. Both groups received substantially greater amounts of pre-hospital bi-carb and calcium than did the V Fib/Tach groups. This would seem to support my contention that acidosis and shock are the issues needing to be addressed for PEA and asystole.

However, as much as I'd like to use this study to support my position, we must examine one glaring concern when looking at the data. This study was extracted from the ASPIRE trial. In that study, cardiac arrest patients were randomized to receive CPR either manually or with the AutoPulse. The study was halted prematurely when the survival to emergency department (ED) and hospital discharge was found to be significantly higher for the manual CPR group!

So how does that affect the data presented here? I don't know. The authors state that the patients who didn't get defibrillation because they remained in PEA/asystole did better than those who didn't. But what percentage of these patients were in the manual versus AutoPulse arm of the ASPIRE trial? Without knowing the effects of the CPR variable, it's impossible to draw any conclusions regarding the role of V Fib/Tach that develops following the treatment of PEA/asystole.

I would ask authors to clarify this and present their data again. I suspect the statistical powers of the data would be significantly degraded, but I could be wrong and look forward to hearing from them.

Until then, we simply have to keep treating cardiac arrest the best way we can and hope for better data on what, if any, unique needs exist for PEA and asystole.

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