Cardiopulmonary Resuscitation Performance of Professional Rescuers With a New Defibrillation Algorithm

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    French Defence Health Service
Updated on 15 October 2021


In the Paris (France) Medical Emergency system, in the early phase of Out-of-hospital Cardiac Arrest (OHCA), the treatment of a Ventricular Fibrillation (VF) consists of delivering an External Electric Shock (EES) by a rescuer with the use of an Automated External Defibrillator (AED). This latter realizes a cardiac rhythm analysis every two minutes. This analysis requires that chest compressions (CC) be interrupted for a while. However, CC interruptions are potentially harmful due to the brain, and heart perfusions decrease.

On the other hand, the recurrence of VF occurs mostly during the first minute after the shock, whereas the delay between 2 rhythm analysis is 2 minutes. The consequence is excessive time spent in VF, which is deleterious in terms of coronary and cerebral perfusion.

The investigator implements a new AED algorithm whose operating principle is as follows. One minute after an EES administration, the AED realizes a cardiac rhythm analysis during which the rescuers do not need to interrupt the chest compressions (CC): this is called the rhythm analysis " in presence of CC" The detection of a VF " in presence of CC " needs to be confirmed, " in absence of CC " The CC's are therefore interrupted for new rhythm analysis. Once the presence of VF is approved, the AED proposes a shock to be administred

The aim of the study

Study Design:

This is a prospective observational study.

The eligibility criteria are as follows:

  • Patients in Out-Of-Hospital Cardiac Arrest.
  • Basic Life support care with an AED.

The primary endpoint is the " chest-compression fraction (CCF) " that represents the CPR-time performance during the ten first minutes of BLS care ( or < 10 min in case of Return Of Spontaneus Circulation (ROSC))



For Out-Of-Hospital Cardiac Arrest (OHCA) patients suffering from ventricular fibrillation (VF) or ventricular tachycardia (VT), BLS care consists of administering external electric shocks (EES) and cardiopulmonary resuscitation (CPR). However, despite successful defibrillation, VF recurs in 50% of cases. Rescuers are forced to repeat EES as often as needed, without the recommendations specifying a maximum number.

International guidelines recommend a 2-min CPR time between 2 rhythm analysis, that means one shock every 2 min. Since refibrillation occurs mostly during the first-minute post-shock, the patient will have to wait until the end of the 2 minutes before receiving the next EES. During that time, the chest compressions (CC) provide a reduced fraction of physiologic blood flow.

The new AED algorithm provides the following changes :

  • After a 60-second post-shock CPR-period, the AED performs an analysis "in presence of CC" i.e., without CC interruption is performed.
  • Each time the AED detects a VF "in presence of CC" the algorithm requires the CC to be interrupted to perform an analysis "in absence of CC " to confirm the rhythm shockability.
  • Analyses "in presence of CC" are triggered every minute, possibly followed or not by an analysis " in absence of CC "
  • at least, the algorithm performs an analysis " in absence of CC " systematically every 2 minutes.

This new algorithm fits in between two historical CPR algorithms used in western medical systems - the one-minute and the two-minute CPR cycle- depending on the rhythm shockability detected " in presence of CC "


The main objective is to measure the " CC fraction " during the ten first minutes of Fire Fighter BLS care in OHCA.

The secondary objectives :

  1. Report on the available CPR quality parameters (CC frequency, hands-off maximum).
  2. Report on the AED's diagnostic performance when analyzing the rhythm "in presence of CC "
  3. Report on the AED's diagnostic performance when analyzing the rhythm " in absence of CC "
  4. Report on the overall AED's diagnostic performance that results from the combination of two consecutive analyses " in presence of CC " and " in absence of CC"

(3) Report on post-shock rhythms and their incidence (4) Report on the number of EES per patient (5) Report on the time distribution for the shocks administered per-patient to describe the rhythmic storm.

(5) Report on the incidence of Return Of Spontaneous Circulation (ROSC), survival at hospital admission, and survival at hospital discharge.

(6) Compare these reports to a historical cohort (2017).


This is a prospective observational study.

  • The observation window is limited to CPR cycles within the first 10 minutes of BLS care, or less if ROSC is presumed.
  • The choice of 10 minutes is intended to observe the BLS team's action, without interfering with the ALS team that arrives later.
  • The three following criteria define a presumptive ROSC:
  • 1. presence of QRS complexes of broadly similar morphology
  • 2. synchronous impedance curve variation with the QRS complexes (indicating intrathoracic movement, in that case, cardiac mechanical activity)
  • 3. no on-going CC
  • A CPR cycle is defined by the delay between two " in absence of CC " analyses.

The study does not imply any change in current practice. There is no planned interim analysis.

All consecutive participants with inclusion criteria and no exclusion criteria will be analyzed.


A study size for a before-after comparison, with 2017 as the "before" period and 2020 as the "after" period has been calculated

In our healthcare system, the average CC ratio was 65% in 2017, whereas the ERC guidelines recommend a minimum of 60%.

With the use of the 2020 algorithm, for CA with shockable rhythm, the CC ratio is expected to decrease slightly, as the analyses become closer in time.

It is assumed a CCratio in 2020 being " equivalent " to 2017 (65%) and consider that a difference in CCratio rate as large as 10% in favor of the 2017 period still allows the new algorithm to be non-inferior (delta = 0.1). The sample size calculation is based on an 80% power to confirm non-inferiority and a one-sided confidence level of 97.5%.

As a result, the number of subjects to be included in each period is 282, i.e., six months of observation in each period.


The sponsor has the responsibility to report, to the national health authority, any serious and unexpected adverse events attributable to the new AED algorithm.


A full report on the risks, the description of incidents, accidents and adverse events will be the subject of a chapter in the results section and also in the discussion.


Funding for the study is provided by the Paris Fire Brigade (promoter, following acceptance of the survey under French policy for clinical research projects)


The study will report on the CC fraction of an AED algorithm designed to analyze "under CC."

Condition Arrhythmia, Sudden Cardiac Death, Tachycardia, Ventricular tachycardia, Ventricular Fibrillation, Fast Heart Rate (Tachycardia), Dysrhythmia
Clinical Study IdentifierNCT04691089
SponsorFrench Defence Health Service
Last Modified on15 October 2021


Yes No Not Sure

Inclusion Criteria

Non-traumatic OHCA in adults, treated by a BLS team and connected to an AED equipped either with the 2017 or with the 2020 algorithm

Exclusion Criteria

Use of AED in a pediatric mode
CPR administered in 15:2 mode
Patient already connected to another defibrillator at the arrival of the BLS Team
No shock administration within the first 10 minutes after the first analysis has started
Secondary Exclusion Criteria
Surviving patients' opposition to the use of their data
Patients with unreadable electrocardiographic or impedance data
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