Clinical paperShock outcome is related to prior rhythm and duration of ventricular fibrillation☆
Introduction
Although early defibrillation is the most important single intervention during advanced life support (ALS),1 the majority of the shocks do not lead to direct restoration of spontaneous circulation (ROSC).2, 3, 4, 5 Optimal timing of the defibrillation, i.e. to give the shock when the myocardium is in optimal condition to regain organised electrical activity with adequate contractility, has been discussed.6, 7, 1 It is difficult to measure the condition of the myocardium during out-of-hospital resuscitation. Various ventricular fibrillation (VF) analysis shock outcome predictors have been researched recently,8, 9, 10, 11, 12 and “median slope” has been found to be a good predictor.13 With a sensitivity of 95% and a specificity of around 50–60% we may have reached the limit of information we can get from the ECG VF waveform.1 Time to defibrillation and bystander cardiopulmonary resuscitation (CPR) influences overall survival in out-of-hospital cardiac arrest,1 and a longer chest compression pause before shock is associated with worse outcome.14, 15, 16 However, there is lack of information about the relation between shock efficacy and the duration of onset of VF until shock and the rhythm before VF for reoccurring VF. The VF duration is influenced by time to detection, treatment given before shock, and time for rhythm analysis and charging. We hypothesised that VF duration would influence the probability of achieving ROSC, and that the extent of myocardial perfusion before onset of VF would affect both VF characteristics and the probability of ROSC following a shock.
We performed an analysis on ECG registrations of victims of both in- and out-of-hospital arrests used in a previous study of CPR quality,17, 18, 5 to investigate the impact of VF duration, rhythm before onset of VF, and also pre-shock pause on shock outcome. We also analysed how these variables relate to the median VF analysis feature.
Section snippets
Data collection
The data were extracted from a subset of patients from a prospective study of quality of CPR during in-18 and out-of-hospital cardiac arrest.17, 5 The inclusion criterion was at least one shock for VF/VT. The subset includes 72 patients from Akershus, 59 from Stockholm, 50 from London and 40 from Vienna, all recorded between April 2002 and August 2005.
The data were recorded by standard HeartStart 4000 (Philips Medical Systems, Andover, MA, USA) biphasic defibrillators modified to collect the
Data summary
From the 221 patients, 231 cardiac arrest episodes were identified, and 1223 shocks were recorded. Inappropriate shocks accounted for 161/1223 (13%), and after applying the other exclusion criteria, median slope were analysed for 735 shocks. Of these, 105 (14%) produced ROSC and 137 (19%) were performed on initial VF. For 22 of the shocks included only 2.73 to 5 s of noise-free ECG were available and block lengths were correspondingly shortened. Prolonged pulseless ventricular tachycardia was
Discussion
In this retrospective study, VF duration and pre-shock pause were both inversely correlated to probability of ROSC. We found both features to have poor correlation with the ECG derived VF waveform feature median slope, but median slope was well correlated with rhythm before onset of VF and probability of ROSC.
Animal and clinical studies have shown that longer pauses before defibrillation reduce the probability of ROSC.14, 15 Most recently, the pre-shock pause was also found to be associated
Conclusion
In conclusion, our findings suggest that reoccurring VF should be shocked as soon as possible, and that median slope might be a usable tool for prediction of shock outcome. The prior rhythm influenced shock outcome as did the pre-shock pause. Further research is needed to combine several measures for an improved shock predictor that can be tested and used clinically.
Conflict of interest statements
Joar Eilevstjønn is employed by Laerdal Medical AS. Jo Kramer-Johansen has received research support for CPR quality research from Laerdal Medical AS. Kjetil Sunde has received unrestricted grants from the Laerdal Foundation for Acute Medicine.
Acknowledgments
The authors would like to thank Dr. Fritz Sterz and his colleagues for their contribution in collecting the data from Vienna, and Prof. Petter Andreas Steen (principal investigator), all involved paramedics and local coordinators at the out-of-hospital research sites.
Funding: This research was funded by Laerdal Medical AS (JE fixed salary), Norwegian Air Ambulance Foundation (JKJ PhD scholarship), and unrestricted grants from the Anders Jahre Foundation for Sciences and Regional Health
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A Spanish translated version of the summary of this article appears as Appendix in the final online version at 10.1016/j.resuscitation.2007.02.014.