Occult Ventricular Fibrillation Visualized by Echocardiogram During Cardiac Arrest: A Retrospective Observational Study From the Real-Time Evaluation and Assessment for Sonography-Outcomes Network (REASON).

Objectives: Cardiac arrest patients with a shockable rhythm are more likely to survive an out-of-hospital cardiac arrest (OHCA) compared with a nonshockable rhythm. An electrocardiogram (ECG) is the most common way to identify a shockable rhythm, but it can miss patients with clinically significant ventricular fibrillation (vfib). We sought to determine the percentage of nonshockable OHCA patients that demonstrated vfib on echo.

Methods: Secondary analysis of echo images recorded from a prior study from our group, Real-Time Evaluation and Assessment for Sonography-Outcomes Network (REASON), a multicenter, observational study of OHCA patients presenting to the emergency department with nonshockable rhythms. Using ECG and echocardiogram images recorded during the initial cardiopulmonary resuscitation (CPR) pause, 2 independent emergency physicians determined the presence of vfib. Two experienced emergency physicians (R.G. and T.G.) reviewed echo images with adjudication by a third if necessary. ECG interpretation was unblinded to patient information. The primary outcome was the proportion of patients in occult vfib.

Results: During the first CPR pause, reviewers noted occult vfib in 22/685 (3.2%; 95% CI, 2.1%-4.8%) subjects. Patients with ECG vfib (n = 55) were defibrillated immediately during the first pause in CPR, but no patients with occult vfib during the first pause in CPR were defibrillated. Subsequently, 50% (11 of 22) of occult vfib patients were defibrillated when ECG vfib was recognized during an ensuing pause in CPR.

Conclusion: One in 33 OHCAs with a nonshockable ECG rhythm exhibits VF on echocardiogram. Patients presenting to the emergency department in a presumed nonshockable rhythm following OHCA may benefit from prompt defibrillation if personnel recognize occult vfib on echo.