Clinical paperAmplitude spectrum area to guide resuscitation—A retrospective analysis during out-of-hospital cardiopulmonary resuscitation in 609 patients with ventricular fibrillation cardiac arrest☆
Introduction
Cardiopulmonary resuscitation (CPR) in conjunction with electrical defibrillation (DF) can re-establish spontaneous circulation (ROSC) after cardiac arrest from ventricular fibrillation (VF) and pulseless ventricular tachycardia (VT).1, 2 However, despite major efforts to improve outcomes from cardiac arrest, survival rates remains dismal.3, 4, 5 Major factors contributing to poor outcomes include delays in CPR, ineffective and frequently interrupted chest compressions (CC), and limited access to, or delayed DF.2, 6, 7
Timing of DF in relationship to CC has been a subject of major interest. Based on available evidence, the 2005 guidelines recommended an initial interval of CC prior to DF, especially when the duration of untreated cardiac arrest exceeded 4 mins.1, 8 Nevertheless, the recent 2010 guidelines highlighted the insufficient evidence to support or refute CPR before DF and called again for early DF.9, 10, 11 Subsequent DF has been recommended to be attempted on a time based protocol, i.e. after every 2 min cycle of CC,9 which may lead to futile DF attempts and unnecessary CC interruptions, potentially creating worse outcome.12, 13, 14, 15, 16 The timing of DF is even more difficult in the instance of recurrence of VF.17
The onset time of VF is rarely known, especially in the out-of-hospital setting, making it difficult to determine the priority of CPR intervention based on the duration of the untreated cardiac arrest. There is also insufficient knowledge about the optimal duration of the CC interval prior to DF. The decision whether to interrupt CC to deliver a DF is therefore difficult. Electrocardiographic (ECG) analysis of the VF waveform might represent the best non-invasive decision guide.
The “Amplitude Spectrum Area” (AMSA) has been demonstrated to be one of the most accurate predictors for successful DF, in both animal and small retrospective clinical studies.18, 19, 20, 21, 22 In the present study, we retrospectively evaluated the ability of AMSA to predict DF success in a large database of out-of-hospital VFs. We hypothesized that AMSA, derived from conventional AED pads, would be an useful indicator to predict DF success and guide CPR interventions. We further hypothesized that AMSA could serve as a monitor of CC quality.
Section snippets
Methods
A database of ECG traces recorded during pre-hospital CPR, including 1410 DFs, obtained from 748 patients between 2005 and 2007, was available through the courtesy of ZOLL Medical Corporation (Chelmsford, MA, USA). ECGs were recorded from defibrillation pads using ZOLL AED PLUS and ZOLL AED PRO in multiple emergency medical systems in the United States through a regular field case submission program. The electronic data did not contain any patient identifiable information, accordingly to Health
Results
A total of 1260 DFs, including 578 first attempts and 682 subsequent ones from 609 patients, were included in the analyses.
Discussion
Current DF algorithms are static in the sense that they do not consider the passage of time and the pathophysiology of the arrested myocardium.9, 24 In our data, the standard DF approach led to a successful DF in only 25% of attempts. The ability of AMSA to predict DF success is therefore of great importance, since this may allow to optimize timing of DF delivery. There is also a potential to reduce CC interruptions and minimize myocardial damage by limiting repetitive and unnecessary DFs.12, 13
Conclusions
In this retrospective study, AMSA was capable to predict DF outcome with high accuracy. A specific AMSA threshold could be identified in order to predict DF outcome for both initial and subsequent attempts. AMSA showed also additional promise for monitoring the effectiveness of CC.
Conflict of interest statement
Author W.Q. is employee of ZOLL Medical Corp. The other authors have no conflicts.
Acknowledgements
The authors thank Gary Freeman and Ulrich Herken from ZOLL Medical Corp. for their scientific interest that allowed to perform the present study.
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A Spanish translated version of the abstract of this article appears as Appendix in the final online version at http://dx.doi.org/10.1016/j.resuscitation.2013.08.017.