Incidence and Clinical Relevance of Echocardiographic Visualization of Occult Ventricular Fibrillation: A Multicenter Prospective Study of Patients Presenting to the Emergency Department After Out-of-Hospital Cardiac Arrest

Study objectives: Ventricular fibrillation (VF) is traditionally identified on ECG but echocardiography can visualize myocardial fibrillation. The prevalence and importance of occult VF defined as a nonshockable ECG rhythm but VF by echocardiography is unknown. Methods: In this multicenter, prospective study, emergency department patients presenting following out-of-hospital cardiac arrest were eligible for inclusion if echocardiography and ECG were performed simultaneously. Recorded echocardiography and ECG were interpreted separately by physicians blinded to all patient and resuscitation information. The primary outcome was percentage of occult VF. The secondary outcomes included survival to hospital discharge, termination of defibrillated VF, and return of spontaneous circulation (ROSC). Termination of VF is described as a postdefibrillation change in ECG rhythm to a nonshockable rhythm. Multivariate modeling accounted for confounding variables. Results: Of 811 patients enrolled, 5.3% (95% confidence interval [CI] 3.9 to 7.1) demonstrated occult VF. An additional 24.9% (95% CI 22.1 to 28.0) demonstrated ECG VF. Of the patients with occult VF, 81.4% demonstrated ECG pulseless electrical activity (PEA) and 18.6% demonstrated ECG asystole. Occult VF was less likely to be defibrillated compared with ECG VF. Defibrillation was not significantly more likely to terminate occult VF (75.0% vs 55.6%; odds ratio [OR], 2.3; 95% CI 0.42 to 15.24). ROSC was not statistically different for occult VF compared with ECG VF (39.5% vs 24.8%; OR, 2.26; 95% CI 0.87 to 5.9). Survival to hospital discharge was no different for patients with occult VF compared with ECG VF (7.0% vs 5.4%; OR, 3.6; 95% CI 0.63 to 19.2) despite fewer defibrillation attempts for patients with occult VF. Conclusion: Occult VF was seen in 5.3% of patients following out-of-hospital cardiac arrest. Recognizing and treating occult VF who otherwise would have been treated as PEA or asystole led to survival outcomes indistinguishable to traditionally recognized VF.