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Should cardiac arrest patients in asystole be shocked? Is there any advantage to this?

What do we know about asystole in cardiac arrest?

Patients in asystole are known to have a very poor prognosis, with 0% to 2% surviving to hospital discharge. There is a slightly better prognosis if the rhythm converts spontaneously to a shockable rhythm early(1).

The Advanced Life Support guidelines do not recommend defibrillation in asystole. They consider shocks to confer no benefit, and go further claiming that they can cause cardiac damage; something not really founder in the evidence.

So why am I writing about this?

…..because not all asystole is true asystole. We know that false asystole can appear on our monitors and occur secondary to technical error() and that the measured amplitude, is altered by several factors including; recording conditions, movement artefact, body habits and recording devices.(3)

The above video comes from one of many case studies where the patient is in asystole, however the echo demonstrates fibrillation(4).

The FEEL Study(5) demonstrated that 38% of patients with an ECG diagnosis of asystole had coordinated cardiac motion and 58% of patients in PEA had coordinated cardiac motion.

Multiple case studies show that patients in asystole receiving shocks return to an organised rhythm, implying that they were probably in ventricular fibrillation.(6,7,8,9)

One study showed(10), that an initial defibrillatory countershock resulted in 8.4% of patients with asystole developing QRS complexes, indicating that they were in ventricular fibrillation.

Where is the evidence for the guidelines’ push for NO SHOCK in Asystole?

In 1992 the American Heart Association stated that delivering shocks in asystole was considered dangerous (11). There was a strong concern that delivering shocks could result in parasympathetic storm(12,13). Evidence is lacking in respect to an approach to asystole, as it is in most of the resuscitation-related guidelines. Two studies are cited in the guidelines as evidence of the poor survival from shocking asystole(14,15). One is a paediatric study, which is really not applicable in the adult population as the rate of ventricular fibrillation is very different in the two groups. The second found that patients with asystole did better with no shocks delivered.

The 2015 European Resuscitation Guidelines advise that in cases of asystole, that the rhythm be checked for P waves, as these may respond to cardiac pacing. They advise against defibrillation if there is doubt as to the rhythm being asystole, or extremely fine VF. The recommendation is to continue chest compressions and ventilation, with the aim of improving the amplitude and frequency of the VF and thus the chance of a successful defibrillation(16,17,18). However the guidelines have stayed firm on no shock in asystole(19)

What do we know?

  1. We know that most adults in cardiac arrest(76%), have ventricular fibrillation as their initial rhythm and this can deteriorate to asystole(15).
  2. We also know that defibrillation is very effective in those patients with ventricular fibrillation. The average out of hospital cardiac arrest survival rate of 8%,  increases to 20% in those patients with ventricular fibrillation and early defibrillation(20).
  3. We also know that about 8% of patients in the pre-hospital environment, that present in asystole, are actually in ventricular fibrillation and this is the group of patients that may benefit.
  4. For every minute that defibrillation is delayed, the survival drops by 7-10%. This is because as the duration of the cardiac arrest increases the amplitude of the ventricular fibrillation decreases. Thus, the greater the amplitude of VF, the better the outcome, with the best outcome in those patients that have a VF amplitude of > 0.5mV. Those patients with an amplitude of <0.2mV, when shocked developed asystole.

Why might we be missing VF and calling it asystole?

Our monitors simply don’t pick it up. The defibrillators we use are usually set to read one lead only, with no capacity to scan the leads and we are not seeing all possible leads. We may not increasing the amplitude in the asystole patient, which might assist us in seeing low amplitude VF.

We may also not be using cardiac echo enough in arrests. It can show  fibrillation even when the monitor reads asystole.

Will it make a difference?

All studies done show that defibrillation of VF in the first 4 minutes make a significant difference. After this time, it may be that we are fighting an uphill battle. The evidence is not great. In a study by Steil(21) in out of hospital cardiac arrest, defibrillation made little difference to survival if too delayed.

I am not saying that all asystole should be shocked, with a hope of a return to an organised rhythm.

What I am saying is that not all asystole is the same. Some patients are not in this rhythm and may benefit from defibrillation, if we can identify them.

What could we be doing?

My own view is:

  • Commence CPR, this perfuses the myocardium and can increase the amplitude of VF if it is present, improving the chances of a successful cardioversion. One cycle is adequate.
  • Increase the amplitude reading on the cardiac monitor(defibrillator), to pick up fine VF
  • During the rhythm check phase, scan the leads for any signs of ventricular fibrillation- you have about 5-7 seconds (in some difibrillators, this can be achieved by disabling the VF/VT alarms)
  • Simultaneously perform a cardiac echo looking for fibrillation or coordinated cardiac motion.You have about 5-7 seconds. It is better to record this, so it can be viewed away from the arrest.
  • Start CPR Immediately after this.
  • If there is ventricular fibrillation and you believe you have maximised perfusion, deliver a shock. One shock, to see if there is any return of an organised rhythm. if nothing, I would not continue shocking.

What if you are in a situation where you can’t echo or change leads. Can you just deliver a shock? My answer is definitely yes. Deliver a shock, one shock and deliver it early. If it is unseuccessful, no further shocks need be given.

We can’t really cause harm by doing this. These patients have no chance of survival if we do nothing. They are effectively deceased by all measures. The survival is poor even if we do. However it is an approach we must consider, especially in the early stages ie., out of hospital cardiac arrest by first responders, or in hospital cardiac arrest.

WATCH THE 60 SECOND SYNOPSIS                 

A/Prof Peter Kas – I will be speaking on this topic in detail at EMCORE Byron Bay 2019


  1. Luo S, Zhang Y, Zhang W, et al. Prognostic significance of spontaneous shockable rhythm conversion in adult out-of-hospital cardiac arrest patients with initial non-shockable heart rhythms: A systematic review and meta-analysis. Resuscitation 2017; 121:1.
  2. Cummins RO, Austin Jr D. The frequency of ‘occult’ VF masquerading as a flat line in prehospital cardiac arrest. Ann Emerg Med 1988;17:813-7
  3. Callaway CW, Menegazzi JJ. Waveform analysis of ventricular fibrillation to predict defibrillation. Currently Open Crit Care 2005 Jun;11(3):192-9.
  4. Limb C, Siddiqui M.A. Apparent Asystole: are we missing a lifesaving opportunity? BMJ Case Rep. 2015 Mar 16. PMID: 25777487
  5. Brown DC, Lewis AJ, Criley JM. Asystole and its treatment: the possible role of the parasympathetic nervous system in cardiac arrest. JACEP 1979;8:448-52.
  6. J.P. Ornato, E.R. Gonzales, A.R. Morkunas, M.R. Coyne, C.L. Beck Treatment of presumed asystole during pre-hospital cardiac arrest: superiority of electrical countershock. Am J Emerg Med, 3 (5) (1985), pp. 395-399
  7. Amaya SC, Langsam A: Ultrasound detection of ventricular fibrillation disguised as asystole. Ann Emerg Med March 1999;33:344-346.
  8. Ewy GA, Dahl CF, Zimmerman M, et al: Ventricular fibrillation masquerading as ventricular standstill. Crit Care Med 1981;9:841-844.
  9. McDonald JL: Coarse ventricular fibrillation presenting as asystole or very low amplitude ventricular fibrillation. Crit Care Med 1982;10:790-792.
  10. Thompson BM, Brooks RC, Pionkowski RS et al. ‘Immediate countershock treatment of asystole’. Ann Emerg Med 1984;9:827–9
  11. Emergency Cardiac Care Committee and Subcommittees, American Heart Association: Guidelines for cardiopulmonary resuscitation and emergency cardiac care, part III: Adult advanced cardiac life support. JAMA 1992;268:2199-2241.
  12. Brown DC, Lewis AJ, Criley JM. Asystole and its treatment: the possible role of the parasympathetic nervous system in cardiac arrest. JACEP 1979;8:448-52.
  13. Vassalle M. On the mechanisms underlying cardiac standstill: factors determining success or failure of escape pacemakers in the heart. J Am Coll Cardiol 1985;5:35B-42B.
  14. J.D. Losek, H. Hennes, P.W. Glaeser, D.S. Smith, G. Hendley Prehospital countershock treatment of pediatric asystole. Am J Emerg Med, 7 (6) (1989), pp. 571-575
  15. Martin DR, Gavin T, Bianco J, Brown CG, Stueven H, Pepe PE, et al.Initial countershock in the treatment of asystole. Resuscitation 1993;26:63-8.
  16. Berg RA, Hilwig RW, Kern KB, Ewy GA. Precountershock cardiopul- monary resuscitation improves ventricular fibrillation median frequency and myocardial readiness for successful defibrillation from prolonged ventri- cular fibrillation: a randomized, controlled swine study. Ann Emerg Med 2002;40:563–70.
  17. Eftestol T, Sunde K, Aase SO, Husoy JH, Steen PA. “Probability of successful defi- brillation” as a monitor during CPR in out-of-hospital cardiac arrested patients. Resuscitation 2001;48:245–54.
  18. Kolarova J, Ayoub IM, Yi Z, Gazmuri RJ. Optimal timing for electrical defi- brillation after prolonged untreated ventricular fibrillation. Crit Care Med 2003;31:2022–8.
  19. Stewart JA. The prohibition on shocking apparent asystole: A history and critique of the argument. AJEM 2008, 26.618-622.
  20. McNally R, Vellano Al V, Pw Y, C S, A C, et al. Out-of-hospital cardiac arrest surveillance—Cardiac Arrest Registry to Enhance Survival (CARES), United States, October 1, 2005—December 31, 2010. Morb Mortal Wkly Rep Surveill Summ Wash DC 2002. 2011;60: 1–19.
  21. Steil et al Advanced Cardiac life support in out of hospital cardiac arrest August 12, 2004N Engl J Med 2004; 351:647-656


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