Can we distinguish refractory VF from other types of VF?

Poor clinical outcomes occur in patients with refractory Ventricular Fibrillation (VF), which is defined as persistent VF following three consecutive defibrillation attemps and standard Advanced Life Support (ALS) treatment.

Double sequential defibrillation and vector change defibrillation, have been identified as showing superior outcomes to standard defibrillation (1).

In managing VF we need to differentiate between:

1. Shock Refractory VF (5-20%) which is continuous VF before and after each shock and
2. Recurrent VF: (> 50%)Which is the absence of VF for > 5 sec after any shock, followed by refibrillation

Patients with recurrent VF have a higher rate of survival, however it is sometimes difficult to ascertain which type of VF we have, as it can occur during the time that CPR is recommenced.

The ability to predict which VF type is occurring, becomes important to allow the provision of tailored resuscitation, affecting administration of antiarrhythmic agents, adrenaline use and the type of shock delivery employed, as well as early use of ECPR.

One method that is highly accurate in VF waveform analysis and prediction of defibrillation outcome, is Amplitude Spectral Area (AMSA) (2).

The objective of this study was to determine if pre-shock AMSA could identify cases of  shock-refractory VF and refractory-recurrent VF in a large database of OHCAs with shockable rhythm.

The Study
Magliocca A, et al. Amplitude spectrum area to predict true shock-refractory ventricular fibrillation during out-ofhospital cardiac arrest. Resuscitation 2025. https://doi.org/10.1016/j. resuscitation.2025.110695.

What They Did

This was a multicenter retrospective observational cohort study. All cases of OHCA with a first recorded shockable rhythm of VF or pulseless Ventricular Tachycardia (VT) were included and  ECG traces recorded by automatic external defibrillators (AEDs) in 8 city-areas in Italy. 

N= 1646

Outcome Definitions

1. Refractory VF:  VF still observed after three shocks with associated 2-min CPR cycles.
2. Non-refractory VF: Successful defibrillation (one or two shocks) without VF recurrence.
3. True shock-refractory VF: VF that continuously persisted over the period of delivery of the first 3 shocks, without termination by any of the shock attempts.
4. Refractory-recurrent VF: VF recurrence after a transient initial termination of VF and/or a successful defibrillation, at any time after each of the first three shock attempts.

Defibrillation outcome was assessed at 5, 30, and 60 s after each shock and immediately prior to shock administration. 

What They Found

Following exclusions, 1619 patients with ECGs for VF waveform analysis were identified:

• 360 patients (22 %) were classified as pragmatic-refractory VF. Of these, 66 (18 %) were true shock-refractory VFs and 294 (82 %) were refractory-recurrent VF
  • A lower number of patients in this group, achieved ROSC, survival to hospital discharge, at 6 months and at 1 year.
  • A lower AMSA was associated with the presence of refractory VF
  • Pragmatic-refractory VF and lower AMSA values were associated with lower likelihood of ROSC and survival to hospital discharge and at one year. 
• 1259 patients (78 %) were non-refractory VF

Discussion

The authors' conclusion was:

"This study reveals AMSA as a promising predictor for differentiating true shock-refractory VF from refractory-recurrent VF in OHCA."

This is a retrospective study, with a decent sample, but missing data. There is no information on time to defibrillation, the underlying cause of the VF, CPR quality, or treatment given by EMS. 

Selection bias is likely, as only patients with refractory VF, who were randomized to the AMSA-guided CPR arm of the trial were included,

Real-time AMSA, (frequency-domain analysis of VF waveform), may be a new approach to guide defibrillation during CPR. AMSA has been shown to correlate with myocardial viability, defibrillation outcomes, and overall survival(3).

The use of AMSA requires further prospective evaluation, however it may guide, pharmacological treatment, timing of defibrillation and risk stratification of patients.

References

1. Cheskes S, et al. Defibrillation strategies for Refractory Ventricular Fibrillation. N Engl J Med 2022;387:1947–56.
2. Meessen JMTA, et al. High amplitude spectrum area measured in real-time during cardiopulmonary resuscitation is associated with favourable long-term neurological outcome after out-of-hospital cardiac arrest. J Clin Anesth 2024;93:111323.
3. Ruggeri L, et al. Amplitude spectrum area measured in real-time during cardiopulmonary resuscitation – how does this technology work?. Resuscitation 2023;191:109941.