Clinical paperDouble sequential defibrillation therapy for out-of-hospital cardiac arrests: The London experience☆
Introduction
Mortality following out-of-hospital cardiac arrest (OHCA) remains high. In London alone, over 10,000 patients suffer an OHCA each year; approximately half have resuscitation attempted by the ambulance service, and an overall 9% survive to hospital discharge [1]. Despite recent advances in treatment, survival rates have remained relatively stable over time, a pattern that is seen in other cities across the world [2].
It is well known that patients who receive early, high quality cardiopulmonary resuscitation (CPR) and whose presenting cardiac rhythm is ‘shockable’ are most likely to survive [3], [4]. Defibrillation is an essential component of resuscitation for individuals presenting with ventricular fibrillation or pulseless ventricular tachycardia (VF/pVT) [3], [5]. While the majority of OHCA patients presenting in VF are successfully defibrillated after 1–2 shocks [6], there is a subset of patients who remain in VF after receiving multiple shocks [7], [8]. This unique population are often referred to as having refractory ventricular fibrillation (RVF). There is currently no unified clinical definition of RVF [7], [9], [10], although it is generally considered to exist after 3 or more sustained episodes of VF [9]. Additionally, there are no specific guidelines as to how Emergency Medical Services (EMS) should defibrillate patients who may be experiencing RVF [5], [10]. With recent findings showing a decrease in survival as the number of defibrillation attempts increase [11], RVF poses a particular challenge in the out-of-hospital setting and new approaches are needed to terminate VF earlier during the resuscitation attempt.
Double sequential defibrillation (DSD) has shown clinical potential as a treatment for RVF [12]. DSD is a technique that utilises two separate defibrillators and two sets of electrode pads on the same patient in order to deliver two shocks in close succession. By utilising a second defibrillator and electrodes with a new pad position, one can hypothesise that an alternate vector of electricity is provided across the myocardium, depolarising a higher proportion of tissue [12], [13]. It has also been suggested that simply administering a larger current may be enough to overcome fibrillation [14]. However, the exact mechanism underlying the physiological benefits of DSD is currently unknown and further research is needed.
Across the UK, current defibrillation practice for patients in VF is three standard defibrillation attempts, in the anterior-lateral position, followed by a single dose of anti-arrhythmic medication [5]. When this procedure is utilised without effect, the London Ambulance Service (LAS) uses a local standardised protocol that allows a specific group of Advanced Paramedics, with an extended skill set, to perform DSD. This protocol instructs three standard single shocks, followed by three shocks in the anterior-posterior position (i.e. pads front and back), then DSD. Using this protocol, patients receive a total of six standard shocks before DSD is attempted. To deliver DSD, both the original and additional defibrillators are charged to their maximum energy (360J) and utilised one after the other, by the same operator, in quick succession (approximately 3–4 s apart). This technique provides two shocks sequentially, using both the anterior-lateral and anterior-posterior positions.
Little published evidence currently exists, in the form of a handful of case reviews [9], [10], [15], [16], [17], [18], [19], describing the use of DSD to terminate RVF in the pre-hospital setting. As a consequence, the use of DSD in OHCA remains controversial and requires further investigation.
By describing DSD utilisation, reporting patient outcomes, and observing a comparison of standard defibrillation attempts, our study aims to contribute to understanding the potential clinical benefit of using DSD to treat RVF during OHCA.
Section snippets
Study design
This is a retrospective, observational analysis of 18 months’ worth of data (1st July 2015–31st December 2016) for OHCA patients treated by LAS Advanced Paramedics using DSD. The study period selected reflects the time from implementation of our local DSD protocol until data analysis commenced. Ethical approval was not required as this study reports anonymised registry data collected as part of an on-going quality assurance and monitoring programme.
Patient population
All patients who experienced an OHCA and were
Results
A total of 45 patients were treated with DSD. During the same period, 175 patients received more than 6 consecutive standard defibrillation attempts, but not DSD. Descriptive characteristics are summarised in Table 1.
The majority of patients who received DSD presented with an initial arrest rhythm of VF/pVT (87%), and the remaining patients converted from asystole to VF/pVT after CPR. This compares with 82% presenting in VF/pVT amongst the standard defibrillation group. Three patients in the
Discussion
A third of patients who were treated with DSD in our observational study achieved a pre-hospital ROSC, and 7% survived to hospital discharge. However, similar outcomes were observed for patients who had more than 6 consecutive standard shocks, and no DSD. A previously published case series that compared DSD with standard defibrillation amongst a mixed sample (n = 50) of both recurrent and RVF [10], similarly found no statistical differences in survival or neurological outcome. Ross et al. showed
Conclusions
While we did not find any clear benefit for DSD use by EMS for the treatment of RVF, we did find that 3 patients who were treated with DSD after numerous failed resuscitation attempts with single shocks, survived. This finding, combined with the multiple factors that may have impacted on our results, supports the need to investigate the effectiveness of DSD in the pre-hospital setting through well designed and controlled prospective clinical trials.
Conflict of interest
None
Acknowledgements
We would like to thank Scott Picton and Gary Merritt for assisting with data collection for the London Ambulance Service cardiac arrest registry as well as all London hospitals for helping us obtain patient outcomes. We are also grateful to Dr Heloise Mongue-Din for her advice and guidance throughout.
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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.2017.06.011”.