Abstract Body: Background:
Cardiac rearrest post-return of spontaneous circulation (ROSC) is a critical concern in emergency care, as it is associated with worse outcomes. Patient characteristics and arrest factors associated with rearrest remain poorly understood, making predicting rearrest after out of hospital cardiac arrest (OHCA) challenging.

Aim: To examine rearrest patterns, identify patient-specific risk factors for rearrest, and assess the impact of rearrest on patient outcomes.

Hypothesis: Patients that experience rearrest after OHCA will have greater cardiac comorbidities, unfavorable arrest characteristics, and greater mortality.

Methods:
We performed an observational single-site clinical trial of consecutive adult EMS OHCA patients with ROSC (1/01/2018 to 3/31/24). EMS reports, continuous EMS ECG recordings, and electronic health records were analyzed to determine rearrest occurrence at any time during EMS and ED care. Patient demographics, comorbidities, and arrest/rearrest characteristics were determined. The primary outcome was survival at 6 months. Statistical significance was determined using Chi-square and logistic regression (LR) analyses.

Results:
We examined 344 patients with OHCA and ROSC, of whom 173 patients rearrested and 171 did not. Patients experiencing rearrest were older (p<0.003) and more likely to be female (p<0.013). They were also more likely to have ED resuscitation medications and interventions (epinephrine, amiodarone, lidocaine, defibrillation, all p<0.001) and a higher incidence of underlying cardiovascular comorbidities, including HTN and CAD (p<0.03). Notably, PEA and asystole were the most common rearrest rhythms, and time from arrest to ROSC was greater (30±16 vs. 25±15 min, p<0.007) in rearrest patients vs. those who did not rearrest. Patients with rearrest were less likely to receive TTM (p<0.003) and importantly, had higher rates of in-hospital and six-month mortality (both p<0.001). In a LR model, no rearrest (OR 2.4, 1.1-5.2), shockable arrest rhythm (OR 9.3, 4-22), female sex (OR 3.3, 1.6-6.5), and therapeutic hypothermia (OR 3.3, 1.7-6.4), were associated with survival (all p<0.04).

Conclusions:
Rearrest is independently associated with mortality. Increased age, male sex, and underlying cardiac comorbidities were associated with rearrest. Patient and arrest characteristics may predict rearrest. Improved understanding of why these factors promote rearrest will be important to prevent rearrest to enhance OHCA outcomes.