Double Sequential External Defibrillation for Refractory Ventricular Fibrillation
Ilya Litvak, DO Mikhail Podlog, DO Anna Van Tuyl, MD
Ventricular fibrillation (VF) is the most common initial dysrhythmia after out-of-hospital cardiac arrest(OHCA) occurring in approximately 70 % of the cases. VF is also considered the rhythm with the highest likelihood of neurologically intact survival (1). Unfortunately, there is a subset of patients who do not respond to standard ACLS algorithm for VF and are termed to have refractory ventricular fibrillation (RVF).
What is refractory ventricular fibrillation?
The exact definition of RVF is subject of debate. However, the literature in the past has used persistent VF without response to at least five single defibrillations (including AED) as the definition of RVF. One intervention that has been reported to terminate RVF is double sequential defibrillation (DSD).
What factors affect successful defibrillation?
Successful defibrillation depends on several variables, including pad placement, total energy used, length of stay in VF, and patient’s body habitus (2). Zhang et al. demonstrated in swine models that body mass had inverse relationship with the success of defibrillation (3). Other studies have shown lower success rates in cardioversion of atrial fibrillation in patients with BMI >25 (4).
The amount of energy is also an important factor in successful defibrillation. Although there are concerns that higher energy may result in myocardial injury or chest wall trauma, several studies have shown safety of high energy defibrillation in humans. For example, Stiell et al. found no deleteriouseffects of biphasic defibrillation up to 360 J (5). Multiple other studies have found no deleterious effects in subjects cardioverted for atrial fibrillation with energy levels of up to 720 J monophasic.
What is Double Sequential Defibrillation?
Double sequential external defibrillation refers to the use of two simultaneous defibrillator pads to deliver the shock. In addition, to increased energy, another theory behind this set-up is that the addition of a second pair of defibrillator pads allows for two alternative vectors of energy delivered to fibrillating myocytes. This allows the energy to overcome limiting factors, such as poorly placed electrodes and the air in the lungs, which otherwise divert the vectors from fibrillating myocardium.(6). Yet another theory postulates that the first defibrillation serves to lower the threshold for successful shock with the second defibrillation (7).
How should the pads be positioned?
There is no clear evidence on which pad placement is ideal. Two sets of pads can be placed in anterior-posterior (AP) orientation, antero-lateral (AL) or AP/AL orientation.
The first report of DSD in VF patient was described in 1994 by Hoch et al. in the electrophysiology literature (8). This case series paper described 5 patients with WPW or other cardiomyopathies undergoing routine studies in the electrophysiology lab. All five subjects had VF intentionally induced as part of their evaluation. In this study, patients failed to convert to normal sinus rhythm with monophasic energies ranging from 200-360 J, but all of them responded to double shock with a total of 720 J. However, until recently there has been paucity of data (limited mostly to case reports) supporting the use of DSD in the Emergency Department or OHCA.
One recent paper in Resuscitation by Cortez et. Al from August 2016 shows promising evidence for the use of DSD for RVF in OHCA (9). In this retrospective chart review, 2428 OHCA events were reviewed with 12 patients treated with DSD. Nine patients out of twelve were successfully converted out of ventricular fibrillation. Of the patients treated with DSD, three patients survived to hospital discharge with good neurologic function.
Also important to note is that the median time to DSD was 27 minutes in the above study. This is significantly shorter than reported values in other papers. This may mean that DSD maybe more effective when incorporated earlier in resuscitation efforts of VF arrest.
Although the above paper provides promising evidence for DSD it has several important limitations including small sample size and retrospective case series nature of the study. Unfortunately, to date there are no double blind randomized control studies on DSD to determine its efficacy.
Management of RFV remains challenging and when standard ACLS measures have failed DSD may be another tool that can be utilized to achieve ROSC in RVF patients.
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2 Morrison LJ, Dorian P, Long J. et al Out- of- hospital cardiac arrest rectilinear biphasic to mopnophasic damped sine defibrillation waveforms with advanced life support intervention trial (ORBIT). Resuscitation 2005; 66 :149-57
3 Zhang Y, Clark CB, Davies LR, Karlsson G, Zimmerman MB, Kerber R. Body weight is a predictor of biphasic shock success for low energy thranthorasic defibrillation. Resuscitation 2002; 54:281-7.
4 Glover BM, Walsh SJ, McCann CJ, et al. Biphasic energy selection for transthoracic cardioversion of atrial fibrillation. The BEST AF Trial. Heart 2008;94:884-7
5 Stiell IG, Walker RG, Nesbitt LP, et al, BIPHASIC Trial: a randomized comparison of fixed lower versus escalating higher energy levels for defibrillation in out-of-hospital cardiac arrest. Circulation 2007;115:1511-7
6 Ristagno G, Yu T, Quan W, Freeman G, Li Y. Comparison of defibrillation efficacy between two pads placements in a pediatric porcine model of cardiac arrest. Resuscitation 2012;83:755-9
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8 Hoch DH, Batsford WP, Greenberg SM, et al Double sequential external shocks for refractory ventricular fibrillation. J Am Coll Cardiol 1994;23:1141-5
9 Cortez E et al. Use of Double Sequential External Defibrillation for Refractory Ventricular Fibrillation During Out-of-Hospital Cardiac Arrest. Resuscitation 2016. S0300-9572(16): 30398 – 7.