# Clinical Significance of Initial and Converted Cardiac Rhythms in Extracorporeal Cardiopulmonary Resuscitation for Patients with Refractory Out-of-Hospital Cardiac Arrest: A Nationwide Observational Study

## TL;DR

This study shows that converting non-shockable rhythms to shockable rhythms before ECPR improves survival and neurological outcomes in cardiac arrest patients.

## Contribution

The study identifies rhythm conversion as a novel prognostic marker and resuscitation target in ECPR for refractory OHCA.

## Key findings

- Survival and favorable neurological outcomes were highest in patients with initial shockable rhythms.
- Rhythm conversion to shockable rhythms before ECPR significantly improved neurological outcomes compared to refractory non-shockable rhythms.
- Persistent non-shockable rhythms were independently linked to poor neurological outcomes.

## Abstract

Background/Objectives: Initial cardiac rhythm is a known prognostic indicator in out-of-hospital cardiac arrest (OHCA). However, the impact of rhythm conversion during cardiopulmonary resuscitation (CPR) on outcomes in patients undergoing extracorporeal CPR (ECPR) remains unclear. This study evaluated the association between initial and converted cardiac rhythms and outcomes in patients with refractory OHCA treated with ECPR. Methods: This nationwide retrospective observational study analyzed data from the Out-of-Hospital Cardiac Arrest Surveillance registry in South Korea (2008–2022). Patients were categorized into three groups: initial shockable rhythm (SR), non-shockable rhythm (NSR) converted to SR, and refractory NSR. The primary outcome was survival to hospital discharge; the secondary outcome was favorable neurological status (CPC 1–2). Results: Among 681 patients, 161 had initial SR, 345 had converted SR, and 175 had refractory NSR. Before matching, survival and CPC 1–2 rates were highest in the initial SR group (21.1% and 15.5%), followed by the converted SR group (19.4% and 11.6%), and lowest in the refractory NSR group (9.7% and 4.0%) (p < 0.01). After matching, CPC 1–2 remained significantly higher in the initial SR group (14.4%) and in the converted SR group (9.3%) vs. the refractory NSR group (5.1%, p = 0.016; 3.7%, p = 0.042). Persistent NSR was independently associated with poor neurological outcomes compared to both initial SR (AOR 0.337, p = 0.037) and converted SR (AOR 0.283, p = 0.020). Conclusions: Rhythm conversion from NSR to SR before ECPR was associated with significantly improved neurological outcomes. Rhythm conversion may serve as a prognostic marker and resuscitation target to guide ECPR decisions.