Impact of cause of arrest, initial rhythm and its conversion on the outcome of extracorporeal cardiopulmonary resuscitation in out-of-hospital cardiac arrest

Background:
The use of extracorporeal cardiopulmonary resuscitation (eCPR) for out-of-hospital cardiac arrest (OHCA) is increasing. The inclusion of patients with an initial non-shockable rhythm is controversial. However, this group is heterogeneous in terms of the cause of arrest. Furthermore, there is a lack of data on the role of rhythm conversion in the outcome of eCPR. In our study, we aim to evaluate the role of initial rhythm and its conversion, as well as the cause of arrest, on eCPR outcomes in a real-life cohort of patients.

Methods:
In a single centre retrospective study, consecutive 281 patients (median age 58 [45-70] years, 82% male) undergoing eCPR for OHCA from 01/2016 to 10/2023 were divided based on initial (shockable (SR, n=159) vs non-shockable (NSR, n=122)) and hospital admission rhythm. Patients were also stratified by cause of arrest and initial rhythm.  The outcome was defined as survival to discharge and favourable neurological function at discharge, defined by a cerebral performance category ≤ 2.

Results:
Baseline characteristics were similar except for a higher prevalence of previous coronary artery disease in SR (77 vs 47% in NSR, p<0.001). There were no significant differences in resuscitation and ECMO parameters and times.

OHCA was significantly more often caused by primary coronary and arrhythmogenic events in SR and by aortic dissection, pulmonary embolism and unknown cause in NSR. Causes of arrest did not differ between patients with initial pulseless electrical activity (PEA) and asystole (ASY).

In SR, only 47% of patients remained in a shockable rhythm on admission, while 38% converted to PEA and 16% to asystole. The conversion from non-shockable to shockable rhythm on admission was 8% in both PEA and ASY. In NSR, most patients remained in the initial rhythm (PEA - 71%, ASY - 63%).

In general, survival (23.9% vs. 7.4%) and favourable neurological outcome (17% vs. 4.1%) were significantly higher in SR compared to NSR (p<0.001). In the NSR, patients with PEA had significantly higher survival (12.7% vs. 1.7%, p=0.02) but similar neurological outcome at discharge (6.4% vs. 1.5%, p=0.19) compared to ASY.  
Asystole on admission was associated with the worst survival and neurological outcome, regardless of the initial rhythm.  Converting from PEA to a shockable rhythm on admission significantly improved survival (66.6 vs. 12.7%) and neurological outcome (33.3 vs. 3.2%), but it only occurred in 3 patients (p<0.001). Conversion to PEA from an initial shockable rhythm did not affect outcome. (p=0.67)

Regardless of the cause of arrest, an initial shockable rhythm was associated with a better outcome. Interestingly, when OHCA was caused by pulmonary embolism, survival with a favourable neurological outcome in NSR was 25% in PEA and 14.7% in ASY, which is notably higher than in NSR for other causes.

Conclusions:
Conversion of the initial PEA to a shockable rhythm seems to have a positive effect on the outcome of eCPR. Asystole at any time, whether initially or on hospital admission, is associated with a poor prognosis. This supports the idea of adding rhythm change to the decision-making process when deciding on eCPR. However, it requires further investigation. Routine use of eCPR in NSR cannot be recommended, but selected patients (e.g. with pulmonary embolism) may benefit given the diversity of causes of OHCA in this subgroup. Further multicentre and randomised trials are needed.