There is a significant difference in Out of Hospital Cardiac Arrest (OHCA) survival, in the order of 10 to 20 times, between non-shockable(2% survival) and shockable rhythms(25-50% survival) (1).
Ventricular fibrillation is the most common shockable rhythm in OHCA. We know that reducing the time to defibrillation in VF and pulseless VT increases the chances of ROSC and survival, however the inherent 2 minute cycles built into resuscitation algorithms delay defibrillation. The detection of shockable rhythms, using artifact-filtering for ECG analysis, whilst CPR is being performed, can decrease the time to arrhythmia recognition and defibrillation.
We look at the DEFI 2022 study(2) which aimed to assess the ability of this technology to analyse cardiac rhythms during cardiac compressions. They compared the cardiac compression fraction in patients using this technology, to those using conventional defibrillation algorithms.
WHAT THEY DID
This was a cross-sectional study that prospectively looked at OHCA managed by Basic Life Support (BLS) prehospital teams, using an algorithm that analysed during cardiac compressions. They used propensity score matching to compare this to a historical cohort that, used conventional defibrillation.
The study was conducted in the Greater Paris Area.
N = 285 patients were treated in each group
The emergency system in Paris has a two-tiered setup. The BLS is delivered by firefighters using the European Resuscitation guidelines and mobile intensive care units providing assistance on site.
Automated External Defibrillators (AED) were used. The algorithm performed analysis during cardiac compressions. If a shockable rhythm was detected compressions were stopped for 5 seconds to confirm the rhythm. This stop for confirmatory analysis could not occur within one minute of a standard analysis (every two minutes). This ensured that CPR was not interrupted for a lengthy period.
Inclusion Criteria
- Patients over 12 years of age
- A shockable rhythm identified by AED at the first rhythm analysis.
Exclusion Criteria
- Trauma patients
- Patients treated with an on-site AED.
- Patients whose ECG tracings were disturbed by a pacemaker
- Those with electrode disconnection where no “analysis in presence of chest compression” had been performed
- Patients whose families/patients refused to participate.
Primary Outcome
Chest Compression Fraction was chosen. A target rate of over 60% is recommended in resuscitation guidelines.
Secondary Outcomes
They looked at variables related to defibrillation:
- VF storm (time-interval between the first and last shock),
- Number and frequency of shocks
- Time spent in shockable rhythm
- Pre-, post-, and peri-shock pauses
- Quantified the time allocated to analysis versus CPR phases
- Determined the sensitivity and specificity of the algorithms for various cardiac rhythms.
WHAT THEY FOUND
It was found that the 'always sensing algorithm' was associated with a high chest compression ratio'.
The new algorithm:
- resulted in shorter analysis phases
- higher interruptions to cardiac compressions (91% vs 82%)
- analysed rhythms with the following sensitivities/specificities:
- 94.9% [93.7–96.2] for the sensitivity of coarse VF,
- 99.7% [99.4– 99.9] for the specificity of asystole,
- 99.3% [99.0–99.5] for the specificity of other non-shockable rhythms recognition.
- resulted in more shocks at shorter intervals
- resulted in VF recurrences being treated twice as quickly
- resulted in a 40% reduction in the time spent in VF
Survival at hospital discharge did not differ between the new algorithm and traditional analysis, although a subgroup of patients who had OHCA in public places and within a short time between call to AED connection (<12.5 min) did show improved survival.
Authors' Conclusions:
"In our study, the use of the AWC was associated with an improvement in CCF."
My Take on This
This is a cross sectional study. These are observational studies, where variables are set and observed, without any attempt to influence them. Due to this design and the fact that results were obtained from a retrospective, historical group, specific parameters such as time to drug administration could not be compared.
The major concern here is the Primary outcome. Although increased chest compression fraction may indicate that more compressions are delivered in a set time period and in fact they were in this study, I'm interested in survival and specifically neurologically intact survival to hospital discharge. The use of compression fraction is not a clinical outcome.
There was no difference in survival using this new algorithm. It could have been due to the fact that the median time from the call to AED connection was too long, being 13 minutes(11-16) in the traditional group and 12 minutes(10-15) in the new algorithm group. When the AEDs were connected, the median time to first shock was significantly shorter in the new algorithm group (24 vs 19 minutes), although quite long in and of itself.
I wonder what effect an algorithm like this would have in an emergency department situation, where an emergency specialist could read the rhythm and make the decision. We need this study to be done and also to look at improving the filters and algorithms we have.
POINTS TO TAKE AWAY
- Using filters to read the cardiac rhythm whilst performing CPR may result in earlier recognition of shockable rhythms
- Based on this study, there was no improvement in survival in OHCA using AED's
- Perhaps the use of a similar system in emergency departments may make a difference.
References
- Valenzuela TD, et al. Outcomes of rapid defibrillation by security officers after cardiac arrest in casinos. NEJM 2000;343:1206–9.
- Derkenne C et al. Analysis during chest compressions in out-of-hospital cardiac arrest patients, a cross/sectional study; The DEFI 2022 Study. Resuscitation 202 (2024) 110292
