Background Pulseless electrical activity (PEA) is increasingly observed in out-of-hospital cardiac arrest (OHCA), but outcomes are still poor. We aimed to assess the relationship between QRS characteristics and outcomes of patients with OHCA with initial PEA (OHCA-P).

Methods This prospective observational study included patients aged at least 18 years who developed OHCA-P between 1 January 2016 and 31 December 2018, and were enrolled in the Daegu Emergency Medical Services registry, South Korea. We performed multivariable logistic regression analyses to identify the associations between QRS characteristics and OHCA-P outcomes, in which QRS complexes were considered separately (model 1) and simultaneously (model 2). The primary outcome was survival to hospital discharge and the secondary outcome was a favourable neurological outcome.

Results Of the 3659 patients with OHCA, 576 were enrolled (median age 73 years; 334 men). A higher QRS amplitude was associated with survival to hospital discharge and a favourable neurological outcome in model 1 (adjusted OR (aOR) 1.077 and 1.106, respectively; 95% CI 1.021 to 0.136 and 1.029 to 1.190, respectively) and model 2 (aOR 1.084 and 1.123, respectively; 95% CI 1.026 to 1.145 and 1.036 to 1.216, respectively). A QRS width of <120 ms was associated with survival to hospital discharge and a favourable neurological outcome in model 1 (aOR 3.371 and 4.634, respectively; 95% CI 1.633 to 6.960 and 1.562 to 13.144, respectively) and model 2 (aOR 3.213 and 5.103, respectively; 95% CI 1.568 to 6.584 and 1.682 to 15.482, respectively). Survival to hospital discharge and neurological outcome were not associated with QRS frequency.

Conclusion OHCA-P outcomes were better when the initial QRS complex showed a higher amplitude or narrower width.