Does transthoracic impedance influence termination and recurrence of ventricular fibrillation during impedance-compensated shocks for out-of-hospital cardiac arrest? A retrospective study

Abstract

Aim: To examine the association between transthoracic impedance (TTI) and termination of ventricular fibrillation or pulseless ventricular tachycardia (VF/pVT) and recurrent VF/pVT in out-of-hospital cardiac arrest (OHCA).

Methods: We conducted a retrospective observational study of non-traumatic OHCA in patients aged ≥16 years with an initial shockable rhythm between January 2019 and October 2022. Termination of VF/pVT was defined as the absence of a shockable rhythm within 5 s following shock delivery, resulting in asystole or an organised rhythm. The relationship between TTI and VF/pVT termination and recurrence were assessed using mixed-effects logistic regression models applied to shock level data with a random intercept for clustering by patient.

Results: Between 2019 and 2022, 1880 cases met the inclusion criteria, comprising 8333 analysable shocks. The unadjusted probability of VF/pVT termination declined at TTI values ≥100 Ω, whereas no clear relationship was observed at TTI <100 Ω. In adjusted analyses, TTI <100 Ω was not associated with VF/pVT termination (adjusted odds ratio [OR] per 1-Ω increase 0.999; 95% CI 0.993-1.006; p = 0.860), while TTI ≥100 Ω was associated with lower odds of termination (adjusted OR per 1-Ω increase 0.994; 95% CI 0.988-0.999; p = 0.016). Among shocks that resulted in VF/pVT termination, TTI was not associated with recurrent VF/pVT (adjusted OR per 1-Ω increase 1.003; 95% CI 0.999-1.006; p = 0.082).

Conclusion: Despite impedance-compensated defibrillation, TTI ≥100 Ω remains associated with reduced likelihood of VF/pVT termination in OHCA. In contrast, TTI does not appear to influence the risk of recurrent VF/pVT following successful termination.

Keywords: Cardiac arrest; Defibrillation; Out-of-hospital cardiac arrest; Thoracic impedance; Ventricular fibrillation.