The Current State of Refractory VF

The following guest post is written by MD candidate Joseph N. Ponce at McGovern Medical School, Houston TX, and describes the current state of evidence with adjunctive techniques to treat refractory VF.

Refractory ventricular fibrillation (RVF) is a life-threatening cardiac arrhythmia unresponsive to traditional methods of defibrillation and advanced cardiovascular life support (ACLS). Current literature lacks a uniform definition for RVF, however, some studies provide more specific clinical definitions of refractory ventricular fibrillation such as ventricular fibrillation that is resistant to at least three defibrillation attempts, 300 mg of amiodarone, and does not exhibit return of spontaneous circulation (ROSC) after > 10 min of cardiopulmonary resuscitation (CPR).10 Without an established effective treatment, the current approach for RVF is standard ACLS care with three possible strategies focused on converting RVF to a perfusing rhythm: β-blockade with esmolol, dual sequential defibrillation (DSD), and withholding or decreasing epinephrine administration.

 

Dual sequential defibrillation

Dual sequential defibrillation (DSD) has been used as an additional method of cardioversion when a patient has been non-responsive to biphasic defibrillation. Multiple case reports have demonstrated the usefulness and feasibility of the technique.2-4,9 The mechanism behind DSD’s apparent efficacy involves expansion of the defibrillation vector and an ability to overcome the electrical threshold for defibrillation. For example, if an anterior-lateral pad placement is already on the patient, an anterior-posterior placement can be applied from a second defibrillator. This extra set of pads provides an additional area of defibrillation and allows for depolarization of a larger mass of myocardium when compared to two pad defibrillation.3,4 Two matching orientation but adjacent sets of defibrillator pads can also be used to expand the already existing defibrillation vector or placed in a second direction. Also, the increased electrical vector may compensate for any user errors or patient abnormalities that would normally lower the efficacy of a defibrillating shock, such as poor pad placement or inadequate pad contact.4 DSD may also overcome any additional elevations in the threshold for successful defibrillation. Investigation of two sequential shocks in animal models has demonstrated an overall reduction in total energy and peak voltage required for successful termination of VF.3 The relatively simple approach of using a second set defibrillator makes DSD an easy first choice for treatment of RVF and a feasible pre-hospital therapy.4 Despite some documented success utilizing DSD, it is not FDA approved and neither defibrillator equipment standard operating protocol or manufacturer instruction endorse its use8.

 

Beta-blockade

Esmolol, also offers promise as an adjunctive therapy for stopping RVF.5,10,11 During RVF and cardiac arrest, increased sympathetic tone through administration of multiple rounds of epinephrine results in increased myocardial oxygen demand, exacerbation of myocardial ischemia, and depression of the VF threshold5. In practice administration consists of 500mcg/kg loading bolus followed by 50-100mcg/kg/min while continuing standard ACLS care.  The decreased sympathetic tone via β-1 antagonism may assist in terminating RVF.5,9 Despite the potential positive effects that have been published in the literature, more robust evidence is required before β -blockade can be recommended as a widespread therapeutic option for the treatment for RVF.5,10

 

Withholding Epinephrine

Often paired with esmolol administration, intermittent decreases or skipped doses of epinephrine during subsequent rounds of ACLS may lessen the sympathetic surge promoting RVF.  Epinephrine has traditionally been recommended for use during resuscitation of cardiac arrest due to the increase in aortic diastolic pressure and coronary artery perfusion.1  Even dosing at 0.01mg/kg, epinephrine increases myocardial oxygen demand due to positive ionotropic and chronotropic effects and may contribute to the myocardial dysfunction and electrical instability that leads to RVF.1,5,10 It is possible although unproven that after administering 3-4 rounds of epinephrine, the threshold for myocardial stress is overcome in patients with RVF.  Although unproven, withholding dosages of epinephrine during RVF while either performing a DSD or administering esmolol may increase successful defibrillation.5

 

Conclusion

Among these techniques none are proven to offer benefit when compared to standard therapy but given the difficulty in converting RVF to a perfusing rhythm all should be considered as options. With DSD being the easiest to perform it is often cited as a first attempted adjunct, while cessation of epinephrine can be paired with esmolol administration.

 

 

References

 

  • Attaran RR, Ewy GA. Epinephrine in Resuscitation: Curse or Cure? Future Cardiology. 2010; 6: 473-482.
  • Cabañas JG, Myers JB, Williams JG, De Maio VJ, Bachman MW. Double sequential external defibrillation in out-of-hospital refractory ventricular fibrillation: a report of ten cases. Prehosptial Emergency Care. 2015;19:126-130.
  • Chang M, Inoue H, Kallok MJ, Zipes DP. Double and triple sequential shocks reduce ventricular defibrillation threshold in dogs with and without myocardial infarction. Journal of the American College of Cardiology. 1986;8:1393-1405.
  • Cortez E, Krebs W, Davis J, Keseg DP, Panchal AR. Use of double sequential external defibrillation for refractory ventricular fibrillation during out-of-hospital cardiac arrest. Resuscitation. 2016;108:82-86.
  • Driver BE, Debaty G, Plummer DW, Smith SW. Use of esmolol after failure of standard cardiopulmonary resuscitation to treat patients with refractory ventricular fibrillation. Resuscitation. 2014;85:1337.
  • Gao D, Sapp JL. Electrical storm: definitions, clinical importance, and treatment. Current Opinion in Cardiology. 2013;28:72-79
  • Hoch DH, Batsford WP, Greenberg SM, et al. Double sequential external shocks for refractory ventricular fibrillation. Journal of the American College of Cardiology. 1994;23:1141-1145.
  • Krusor B. Recent Resuscitation Research. 2016
  • Leacock BW. Double simultaneous defibrillators for refractory ventricular fibrillation. The Journal of emergency medicine. 2014;46:472.
  • Lee YH, Lee KJ, Min YH, et al. Refractory ventricular fibrillation treated with esmolol. Resuscitation. 2016;107:150.
  • Nademanee K, Taylor R, Bailey WE, Rieders DE, Kosar EM. Treating electrical storm : sympathetic blockade versus advanced cardiac life support-guided therapy. Circulation. 2000;102:742-747.

 

 

 

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