Guest Post

by Mark Ramzy, DO, EMT-P
(@MRamzyDO)
EM Resident Physician
Drexel University, Department of Emergency Medicine

Editors Note

Mark just published his research on Dual External Defibrillation in Prehospital Emergency Care.

Hamilton R, Ramzy M. Dual defibrillation is highly variable: an analysis of pulse interval delivered in dual defibrillation. Prehospital Emergency Care. 2019 (PMID 31116612)

EMS calls ahead:
They are bringing in a 54-year-old male who collapsed while walking on a college campus. By-stander hands-only CPR was performed and one shock was delivered by an AED. The EMS crew arrives and states that the initial rhythm was ventricular fibrillation (VF). A total of three shocks, and two doses of epinephrine were given en route all with on-going CPR. Ventricular fibrillation is noted on the hospital monitor and a fifth shock is delivered. CPR is resumed, and Amiodarone is also administered. On the next rhythm check, VF is seen again, so another shock is delivered. Calcium gluconate is given in addition to another dose of epinephrine, all while good-quality CPR is being continued. VF is seen yet again, and a seventh shock is administered. At this point, someone in the resuscitation team suggests getting a second defibrillator and your medical student loudly wonders “Wait, what’s wrong with this defibrillator?”

Your Answer:
ABSOLUTELY NOTHING. You need another defibrillator because this patient is in Refractory ventricular fibrillation (RVF) and you’re about to do Dual External Defibrillation (DED). Before getting into the details about DED we have to define RVF, which is persistent ventricular fibrillation (VF) with no response to three or more defibrillations.^1-5

What’s some of the literature say on RVF and DED?
RVF depends on multiple variables: time in VF, body habitus (despite animal models showing inverse relationship with defibrillation), total defibrillator energy used, chronic lung disease and use of antiarrhythmic agents.^6,7 Multiple case reports have shown the effectiveness of a second defibrillator in terminating RVF.^3-5,8,9. In a large literature review, DED terminated RVF in 77% of the 39 cases. More importantly 11 of those patients who received DED were discharged with a Cerebral Performance Category (CPC) score of 2 or less, indicating good neurologic outcomes. ² (Figure 1)

FIGURE 1: Breakdown of Cerebral Performance Category (CPC) scale. Source: REBELem

How much do you REALLY know about a defibrillator?
A defibrillator potential is specific to the manufacturer and the model. Most hospitals and ambulance companies are using biphasic devices which deliver up to a MAX of 360 Joules (J) in a reticilinear or high-peak distribution. The type of waveform for DED doesn’t matter as much as the duration of the defibrillator potential. Using an oscilloscope, one can measure the exact duration of each part of a potential down to the microsecond. Each biphasic defibrillation potential has to have a positive deflection and a negative deflection. Some older models have a neutral period where the two vectors of electricity cross. In the high-peak biphasic defibrillator model shown below the total time of the defibrillation potential is, 13.2 milliseconds, the cumulative total of the positive, neutral and negative deflections (Figure 2)

FIGURE 2: An oscilloscope screenshot of a High-Peak Biphasic Defibrillator. Note the positive deflection measures 7.4 milliseconds (green), followed by the neutral period measures 0.8 milliseconds (orange) and lastly the negative deflection  in 5.04 milliseconds (red). The cumulative sum of all these is, 13.2 milliseconds (blue), the total time of the defibrillation potential for this particular model

After a defibrillator discharges, there is a refractory or vulnerable period where it physically can not administer another shock. During this period, the device is analyzing and recording exactly how much energy was given. It’s also verifying its internal protective resistor was not damaged as sometimes its own electrical energy, although often very minimal, can revert back unto itself. Once all these internal checks are clear, often taking 30 seconds to a minute, the defibrillator is ready to be used again.

TYPES? Yes, Double Defibrillation is NOT ALL Sequential

DED  can either be simultaneous (Figure 3) or sequential (Figure 4) depending on the duration of the defibrillation potential and the intershock or pulse interval between the two defibrillator shocks.^4,9-12

FIGURE 3: Oscilloscope depicting true simultaneous double defibrillation. The inter-shock interval from the start of one defibrillation potential (blue) to the start of the second (yellow) is 12.4 milliseconds (red arrow). This is less than the total time of a single defibrillation potential of 13.2 milliseconds as previously mentioned

FIGURE 4: Oscilloscope depicting true sequential double defibrillation. The inter-shock interval from the start of the first defibrillation potential (yellow) to the start of the second (blue) is 14.4 milliseconds. This is more than the total time of a single defibrillation potential of 13.2 milliseconds, again on this particular defibrillator model, that was mentioned before.

There is currently no evidence suggesting sequential or simultaneous is more effective. There are three main hypothesized theories as to why DED is effective:

1. More Power Theory: Several studies have shown that higher energy has improved success on subsequent defibrillation.^4,13-16. This is why DED is often termed “Double Simultaneous Defibrillation (DSiD)”. Lack of real-time measuring devices and subsequent delay in human response times, makes it difficult to consistently perform true simultaneous defibrillation in the clinical setting. One of the most common fears with DED is the high amount of energy (ie. 400 J). It’s important to note that several studies have shown safety in patients receiving up to 720 J of monophasic energy for conversion of RVF and atrial fibrillation.^8,13,16-18          
2. Setting Up Theory: It is suggested that the first shock lowers the defibrillation threshold thus increasing the second shock’s success in converting any remaining fibrillating myocytes.^8,18 This is where DED gets its alternate name of “Double Sequential Defibrillation (DSD)”. It is also the more likely method of administration in clinical setting.
3. Multiple Vector Theory: This proposed theory suggests that more pads increase the number of vectors that the electricity can use to reach the myocardium.^8,18

ACTUALLY Performing DED and Pad Placement:

• If ventricular fibrillation is noted on the second rhythm check, start looking for a second IDENTICAL defibrillator early so it is ready to use on the third pulse check if needed
• There are two common pad placement options:
  • 1) Anterior (ie. Adjacent to first set at apex and right sternum) (Figure 5)
  • 2) Anterior-posterior (Figure 6)

FIGURE 5: Anterior pad placement for double defibrillation. Notice none of the pads are in contact with one another, ensuring safe DD administration and preservation of equipment for future use.

FIGURE 6: Anterior-posterior pad placement for double defibrillation. This approach is preferred as it decreased the likelihood that the pads will be in contact with one another.

• LIKE PARKING YOUR CAR IN A BUSY CITY:
  Defibrillator pads should be CLOSE but NEVER be touching!

• If attempting DSiD, having one provider push “shock” on both defibrillators decreases the chances for delay and optimizes the probability of simultaneous administration
• If attempting DSD, having two providers each push “shock” on both defibrillators ensures a slightly delayed administration of the shocks in sequential fashion

It’s important to remember that performing DED is operating outside of the advanced cardiac life-support (ACLS) guidelines and this is because not enough research has been done on the topic to provide any formal recommendation by the American Heart Association. In a 2015 ACLS guideline update they do acknowledge a gap in regard to optimal waveform, pad placement and ideal dose of subsequent and maximum energy.¹⁹                       

Remember that patient you had…
Well he received a total of three DEDs that resulted in ROSC after 61 total minutes of resuscitation. Hypothermia protocol was initiated, he was found to have a 100% occlusion of the Left Anterior Descending coronary artery in the percutaneous catheter lab. He was extubated the next day and subsequently discharged without any neurologic deficits.⁹

^­­Defibrillator Damage

There was a case report that came out that detailed damage of one of the defibrillators after synchronized dual-dose cardioversion was performed. Having performed 2000 simulated double defibrillations with different models of defibrillator (without any damage to any of the devices)¹⁹ and several in the clinical setting, I want to highlight some important points in this article.

• Their pad placement was correct and not the issue as it was in the AP position we discussed earlier (also no mention of them “accidentally” touching)
• The electrophysiologists in the paper used two DIFFERENT brands AND models of defibrillators which each have different waveforms.
• While it has been performed before, Double defibrillation is NOT indicated for ventricular tachycardia let alone synchronization. In fact, hitting that sync button is the WORST thing you could be doing if you’re trying to avoid damaging your defibrillators. Remember that vulnerable period a defibrillator goes through after delivering a shock so it can do some analysis? Well imagine another shock being delivered at a very specific time reverting back to the resistor of that first defibrillator which isn’t expecting THAT much energy in the first place and thus overloading it. The defibrillator senses this, just like the authors mentioned in the paper, produces the message “Abnormal energy delivered”, and likely resulted in the malfunctioning of the device
• To simply say it was the use of two defibrillators for an indication it’s not typically used for and not considering all of the confounding variables is premature.

Bottom Line   

Further research is needed to better understand DED. Knowing about the pulse interval and differentiating between DSiD and DSD helps to add to the current research, but double defibrillation continues to remain highly variable.¹⁹ Remember that VF survival rates in out of hospital cardiac arrest can reach as high as 40-60% when combined with high quality CPR and early defibrillation.^20-24 Double defibrillation, despite not yet being part of ACLS guidelines, serves as another tool during resuscitation and should be considered with other lifesaving interventions.

Use identical devices, pad placement should be close but not touching, and don’t hit that sync button.

Update

Double Sequential External Defibrillation for Refractory Ventricular Fibrillation: The DOSE VF Pilot Randomized Controlled Trial. Resuscitation. 2020 May;150:178-184. doi: 10.1016/j.resuscitation.2020.02.010. Epub 2020 Feb 19.

REFERENCES:

1. Slovis CM, et al. The technique of reversing ventricular fibrillation: improve the odds of success with this five-phase approach. J Crit Illn. 1994. PMID: 10147464
2. Hajjar K et al. Dual defibrillation in patients with refractory ventricular fibrillation. Am J Emerg Med 2018. PMID: 29730094
3. Cabañas JG, et al. Double sequential external defibrillation in out-of-hospital refractory ventricular fibrillation: a report often cases. Prehosp Emerg Care 2015. PMID: 25243771
4. Leacock B, Double Simultaneous Defibrillators for Refractory Ventricular Fibrillation. J Emerg Med. 2014; PMID: 24462025
5. Cortez E, et al. Use of double sequential external defibrillation for refractory ventricular fibrillation during out-of-hospital cardiac arrest. Resuscitation. 2016 PMID: 27521470
6. Sirna SJ, et al. Factors affecting transthoracic impedance during electrical cardioversion. Am J Cardiol 1988 PMID: 3189167
7. Sirna SJ, et al. Mechanisms responsible for decline in transthoracic impedance after DC shocks. Am J Phys Heart Circ Phys. 1989. PMID: 2801977
8. Hoch D, et al. Double sequential external shocks for refractory ventricular fibrillation. J Am Coll Cardiol. 1994. PMID: 8144780
9. El Tawil C, et al. Double sequential defibrillation for refractory ventricular fibrillation. Am J Emerg Med. 2017; PMID: 28978402
10. Bell C, et al. Make it two: A case report of dual sequential external defibrillation. CJEM. 2017; PMID: 28587703
11. Boehm K. et al. First Report of Survival in Refractory Ventricular Fibrillation After Dual-Axis Defibrillation and Esmolol Administration. Western Journal of Emergency Medicine. 2016; PMID: 27833686
12. Johnson E, et al. Effect of pulse separation between two sequential biphasic shocks given over different lead configurations on ventricular defibrillation efficacy. Circulation 1992; PMID: 1591840
13. Stiell I, 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; PMID: 17353443
14. Koster R, et al. Recurrent ventricular fibrillation during advanced life support care of patients with prehospital cardiac arrest. Resuscitation. 2008; PMID: 18556106
15. Walsh SJ, et al. Efficacy of distinct energy delivery protocols comparing two biphasic defibrillators for cardiac arrest. Am J Cardiol 2004. PMID: 15276112
16. Morgan JP, et al. High-energy versus low-energy defibrillation: experience in patients at Mayo Clinic-affiliated hospitals. Mayo Clin Proc. 1984 PMID: 6503363
17. Saliba W et al. Higher energy synchronized external direct current cardioversion for refractory atrial fibrillation. J Am Coll Cardiol 1999. PMID: 10588220
18. Pourmand A et al. The controversial role of dual sequential defibrillation in shockable cardiac arrest. Am J Emerg Med. 2018. PMID: 29880409
19. Hamilton R, Ramzy M. Dual defibrillation is highly variable: an analysis of pulse interval delivered in dual defibrillation. Prehospital Emergency Care. 2019 PMID: 31116612
20. Daya MR, et al. Out-of-hospital cardiac arrest survival improving over time: results from the Resuscitation Outcomes Consortium (ROC). Resuscitation 2015 PMID: 25676321
21. Institute of Medicine. Strategies to improve cardiac arrest survival: a time to act. Washington, DC: The National Academies Press; 2015. PMID: 26225413
22. Berdowski J, et al. Global incidences of out-of-hospital cardiac arrest and survival rates: systematic review of 67 prospective studies. Resuscitation 2010 PMID: 20828914
23. King County, WA, Has World's Highest Survival Rate for Cardiac Arrest | Sudden Cardiac Arrest Foundation. http://www.sca-aware.org/sca-news/king-county-wa-has-worlds-highest-survival-rate-for-cardiac-arrest. 2018.
24. Rezaie S. Beyond ACLS: Is It Time to Abandon Epinephrine in Out-Of-Hospital Cardiac Arrest? – REBEL EM – Emergency Medicine Blog. REBEL EM – Emergency Medicine Blog. http://rebelem.com/time-abandon-epinephrine-hospital-cardiac-arrest/. 2018

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