Resuscitation 80 (2009) 24���29 Contents lists available at ScienceDirect Resuscitation j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / r e s u s c i t a t i o n Clinical paper Progressing from initial non-shockable rhythms to a shockable rhythm is associated with improved outcome after out-of-hospital cardiac arrest Theresa M. Olasveengen a,b,���, Martin Samdal c, Petter Andreas Steen d, Lars Wik e, Kjetil Sunde a,b a Institute for Experimental Medical Research, Ulleval University Hospital, N-0407 Oslo, Norway b Department of Anaesthesiology, Ulleval University Hospital, N-0407 Oslo, Norway c Medical Faculty, University of Oslo, N-0316 Oslo, Norway d Division of Prehospital Medicine and University of Oslo, Faculty Division UUH, Ulleval University Hospital, N-0407 Oslo, Norway e The National Competence Centre for Emergency Medicine, Ulleval University Hospital, N-0407 Oslo, Norway a r t i c l e i n f o Article history: Received 19 July 2008 Received in revised form 18 August 2008 Accepted 3 September 2008 Keywords: Heart arrest Out-of-hospital CPR Advanced life support (ALS) Outcome Pulseless electrical activity (PEA) Return of spontaneous circulation Asystole a b s t r a c t Background: Cardiac arrest patients with initial non-shockable rhythm progressing to shockable rhythm have been reported to have inferior outcome to those remaining non-shockable. We wanted to confirm this observation in our prospectively collected database, and assess whether differences in cardiopulmonary resuscitation (CPR) quality could help to explain any such difference in outcome. Materials and methods: All out-of-hospital cardiac arrest (OHCA) cases in the Oslo EMS between May 2003 and April 2008 were retrospectively studied, and cases with initial asystole or pulseless electrical activity (PEA) were selected. Pre-hospital and hospital records, Utstein forms, and continuous ECGs were reviewed. Quality of CPR and outcome were compared for patients who progressed to a shockable rhythm and patients who remained in non-shockable rhythms. Results: Of 753 cases with initial non-shockable rhythms 517 (69%) had asystole and 236 (31%) PEA. Ninety- eight (13%) patients progressed to a shockable rhythm, while 653 (87%) remained non-shockable during the entire resuscitation effort (two unknown). Hands-off ratio was higher in the shockable than the non- shockable group, 0.21 �� 0.12 vs. 0.16 �� 0.10 (p = 0.000) with no significant difference in compression and ventilation rates. Overall survival to hospital discharge was 3% 7% in the shockable and 2% in the non- shockable group (p = 0.014). Based on a multivariate logistic analysis young age, initial PEA, and progressing to a shockable rhythm were associated with better outcome. Conclusion: Progressing from initial non-shockable rhythms to a shockable rhythm was associated with improved outcome after OHCA. This occurred despite more pauses in chest compressions in the shockable group, probably related to defibrillation attempts. �� 2008 Elsevier Ireland Ltd. All rights reserved. Introduction The relative frequency of asystole and pulseless electrical activ- ity (PEA) as the first recorded rhythm in out-of-hospital cardiac arrest (OHCA) has increased gradually over the last decades. In recent population-based studies 60���80% of the patients now present with these initial non-shockable rhythms.1���4 This is partly due to reduced absolute incidence of ventricular fibrillation (VF) as the first recorded rhythm,1,3 and a relative or absolute increase in cardiac arrest of non-cardiac origin.1,2 A Spanish translated version of the summary of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2008.09.003. ��� Corresponding author at: Institute for Experimental Medical Research, Ullev��l University Hospital, University of Oslo, Division Ullev��l University Hospital, N-0407 Oslo, Norway. Tel.: +47 23016837 fax: +47 23016799. E-mail address: t.m.olasveengen@medisin.uio.no (T.M. Olasveengen). Survival rates for patients initially presenting with asystole or PEA is much lower than for patients presenting with initial shock- able rhythms and usually reported in the range 2���3%.4,5 The current treatment strategies for OHCA are largely based on research from patients with cardiac aetiologies and initial shockable rhythms, and a better understanding of patients presenting with asystole or PEA is necessary to further improve survival rates in this group. A small proportion of patients with initial non-shockable rhythms progress to shockable rhythms during the resuscita- tion efforts.6,7 In the recent ASPIRE trial, comparing manual and mechanical cardiopulmonary resuscitation (CPR), this occurred in 22% of the patients, and Hallstrom et al. reported that survival was superior if the patients stayed in a non-shockable rhythm 5% vs. 1% for those converting.7 They presented one possible expla- nation for their findings as less than optimal attention to good quality CPR in the converting group due to the treatment protocols themselves.7 0300-9572/$ ��� see front matter �� 2008 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.resuscitation.2008.09.003

T.M. Olasveengen et al. / Resuscitation 80 (2009) 24���29 25 We wanted to confirm the earlier finding7 that patients pro- gressing from non-shockable to shockable rhythms during the resuscitation efforts actually have inferior outcome from our prospectively collected database, and assess whether differences in CPR quality could help to explain any such difference in outcome. Material and methods Description of EMS and in-hospital treatment The city of Oslo has a one-tiered centralised community run EMS system for a population of 540,000. On weekdays between 7:30 and 22:00, a physician-manned ambulance staffed by two paramedics and an anaesthesiologist functions on the same level as the regular paramedic staffed ambulances. The Norwegian version of the 2005 ERC guidelines8 were implemented January 2006, prior to this a modified version of the 2000 ERC guidelines was followed. In both versions the modification consisted of three instead of 1 min (2000) or 2 min (2005) of CPR before and in between defibrillation. Stacked shocks were used prior to 2006. All paramedics are trained to use the defibrillators in manual mode. Endotracheal intubation was the standard method for securing the airways, followed by uninter- rupted chest compressions with 10���12 interposed ventilations per minute. Nurses and paramedics staff the dispatch centre. Due to an ongoing randomized study of the effect of intravenous access and drugs (the IV study) in the Oslo Emergency Medical Service (EMS), some of our included patients are also included in this study reg- istered at www.clinicaltrials.gov (NCT00121524). Less than half of the patients will therefore be expected to have received intravenous drugs during resuscitation. All hospitals in Oslo have standardised goal directed post- resuscitation protocols including therapeutic hypothermia. The post-resuscitation protocols are applied to all patients regardless of initial rhythm or aetiology if active treatment is desired.9 Study design and recruitment All patients older than 18 years suffering from non-traumatic out-of-hospital cardiac arrests of all causes from May 2003 to 28 April 2008 were retrospectively studied. Locally adapted Utstein style forms10 (with information on type of bystander CPR upon arrival of first ambulance), dispatcher recordings, and ambulance and hospital records are routinely collected and reviewed at The National Competence Centre for Emergency Medicine (Ulleval Uni- versity Hospital, Oslo, Norway). Data collection Utstein forms are routinely filled out by ambulance personnel after every cardiac arrest and submitted to the study supervi- sor along with a copy of the ambulance run sheet. Automated, computer-based time records from the dispatch centre supple- ment ambulance run sheets with regards to response times. For all admitted patients, additional hospital records were obtained from the respective receiving hospitals. Information from Utstein forms, ambulance run sheets, dispatch and hospital records are linked together with continuous ECG tracings as described below. Based on these records the patients with initial non-schockable rhythms (PEA or asystole) were divided into two groups the shock- able group (patients progressing to a shockable rhythm during the resuscitation effort) or the non-shockable group (patients remain- ing in a non-shockable rhythm). Equipment and data processing Standard LIFEPAK 12 defibrillators (Physio-Control, a Division of Medtronic, Redmond, WA, USA) were used, which routinely measure transthoracic impedance by applying a near constant sinu- soidal current across the standard defibrillation pads. After a CPR effort the ECGs with transthoracic impedance signals were nor- mally transferred to a local server at The National Competence Centre for Emergency Medicine (Ulleval University Hospital, Oslo, Norway), and data from each case were viewed and annotated using a CODE-STATTM 7.0 (Physio-Control, Redmond, WA, USA) for detec- tion of chest compressions and ventilations from transthoracic impedance changes. Annotations were made while reviewing avail- able clinical information from the Utstein forms and ambulance records. Total time without spontaneous circulation (CPR time), time without chest compressions divided by CPR time (hands-off ratio), compression rate and the actual number of compressions and ventilations per minute were calculated for each episode. All available continuous ECGs were also reviewed to assess whether the shocks delivered were appropriate, and only patients receiving shocks for a shockable rhythms (ventricular fibrillation, VF and pulseless ventricular tachycardia, VT) were included in the shockable group. Patients receiving shocks for non-shockable rhythms (asystole or PEA), were included in the non-shockable group. In cases where ECGs were not available for analysis, the information from pre-hospital and hospital records were used to classifying patients according to initial and pre-shock rhythms. Statistical analysis Statistical calculations were performed using a spreadsheet pro- gram (Excel 2002, Microsoft Corp., Redmond, WA, USA) and a statistical software package (SPSS 14.0, SPSS Inc., Chicago, IL, USA). Values are given as means with standard deviations (S.D.), except for response times given as medians with 25th and 75th percentiles. Differences between the two groups were analysed using Student���s t-tests for continuous data and chi-squared with continuity correc- tion for categorical data. p-values less than 0.05 were considered significant. Prognostic factors found to be significant in preliminary univariate and bivariate analyses were included in a multivariate logistic regression analysis together with progression to shock- able rhythm (dependent variable: discharged from hospital alive). The results from the multivariate logistic regression analysis were reported as adjusted odds ratios with 95% confidence intervals (95% CI) and p-values. Results Between 1 May 2003 and 28 April 2008 the Oslo EMS responded to 1133 cardiac arrests where resuscitation was attempted. There were 753 cases with initial non-shockable rhythms 517 (69%) with asystole and 236 (31%) with PEA. Ninety-eight (13%) patients progressed to a shockable rhythm, while 653 (87%) remained in a non-shockable rhythm during the entire resuscitation effort (two unknown). Sixteen patients in the non-shockable group received shocks for non-shockable rhythms (none of whom sur- vived) (Figure 1). There was a non-significant trend towards a slightly shorter response time (p = 0.061) and more bystander and ambulance wit- nessed arrests in the shockable group. Endotracheal intubation was performed more often in the shockable than the non-shockable group (92% vs. 82%, respectively, p = 0.018) No other significant demographic differences were found between the two groups (Table 1).