Amplitude spectrum area to predict true shock-refractory ventricular fibrillation during basic life support-treated out-of-hospital cardiac arrest.

AIM: Refractory ventricular fibrillation (VF) is associated with decreased survival. Guideline definition of refractory VF, i.e. a VF persisting after 3 shocks, includes cases of true shock-refractory VF or recurrent VF with transient defibrillation response. Predicting true shock-refractory VF before repeated shock failure could prioritize targeted interventions to improve out-of-hospital cardiac arrest (OHCA) outcomes. We hypothesized that amplitude spectrum area (AMSA) may predict cases of true refractory VF.

METHODS

ECGs recorded by automated external defibrillators were obtained from OHCAs in 8 cities in Italy. A 2-second VF window before each defibrillation was analyzed to calculate Amplitude Spectrum Area (AMSA). Defibrillation success was defined by occurrence of a perfusing rhythm, while refractory VF was defined as: "pragmatic-refractory" (based on guideline definition); or within this category, as "True shock-refractory", if VF continuously persisted over the period needed to deliver the first 3 shocks; or "refractory-recurrent", if VF recurred after any of the first three shocks transiently terminated VF.

RESULTS

1646 OHCAs with shockable presenting rhythm were included, 360 (22 %) of whom met the definition of pragmatic-refractory VF. Among the 360 cases of pragmatic-refractory VF, 18 % were true shock-refractory and 82 % were refractory-recurrent VF. AMSA was significantly lower in true shock-refractory VF than in refractory-recurrent VF. A lower first AMSA was associated with occurrence of true shock-refractory VF (aOR:0.81; 95 %CI: 0.73-0.88; p < 0.0001).

CONCLUSIONS

Lower AMSA is associated with true shock-refractory VF, a subtype associated with persistent defibrillation failure and worse long-term survival. Identifying different VF subtypes early may help guide advanced resuscitation strategies in OHCA.