Does occult Ventricular Fibrillation occur? If so what is the incidence and how does it appear on our ECGs?
This study answered these questions.
The Study
Gaspari R et al. Incidence and Clinical Relevance of Echocardiographic Visualisation of Occult Ventricular Fibrillation: A Multicenter Prospective Study of Patients presenting to the Emergency Department After Out-of-Hospital Cardiac Arrest. Ann of Emergency Med Oct 2025;Vol 86.No 4 pp 328-336
What They Did
This was a multicenter, prospective, observational trial in 28 Emergency Departments in the US and Canada.
Inclusion Criteria
- Adult patients (> 18yo)
- Atraumatic out-of-hospital cardiac arrest, with resuscitation continuing to the Emergency Department
- Patients who have had at least one simultaneous echo and ecg (during CPR)
Primary Outcome: Prevalence of VF visualised by echo and not identified by the ECG
Secondary Outcomes
- Survival to hospital discharge
- Defibrillation resulting in termination of VF and return of spontaneous circulation(ROSC)
n=811
What They Found
5.3% (43/811) (95%CI 3.9-7.1) of patients had occult VF during the first 3 pauses of CPR
ECG in VF was identified earlier in cardiac arrest and those patients were more likely to be defibrillated compared to those with occult VF.
Of all non-shockable rhythms found on ECG in patients in occult VF
- 81.4%(35) showed PEA and
- 18.6%(8) showed asystole
61.4% (124) who had ECG VF showed no VF on ECHO.
Survival to discharge for all patients was 3.1%(25/811), with no difference in survival between occult and ECG VF. Although defibrillation was more likely to to terminate occult VF, compared to ECG VF 75% vs 55.6% and ROSC was also more likely in occult VF (39.5% vs 24.8%)
Discussion
There were some limitations to this study, including small numbers of patients in active arms
The main limitation in my view was that the ECHO recordings were reviewed by experienced sonographers who could view the recordings several times. In the resus scenario, we don’t have that opportunity. At most we have 6 seconds of recording(so we don’t interrupt CPR) and then we take the ultrasound machine away and review and have to make a repid decision.
5.3% of patients in this study had occult VF found on ECHO. Although survival outcomes were no different,, occult VF was less likely to be defibrillated. In my view this simply rienforces what we have been teaching and doing for so long. If unsure one shock, may be beneficial.
Of greatest interest to me was the fact that 61% of patients that showed VF on ECG, had non on ECHO.
A related blog here on resus is “Should We Shock Patients in Asystole?”
