Abstract Body: Introduction: Transcutaneous pacing (TCP) is used to treat bradycardia with hemodynamic compromise. A single-center study found that sustained electrical capture (SEC) was uncommon during prehospital TCP, but no prior multi-center study has investigated SEC during TCP or evaluated the relationship between SEC and outcomes.

Research Questions: What proportion of prehospital TCP attempts result in SEC? What factors are associated with SEC? Is SEC associated with time to post-TCP cardiopulmonary resuscitation (CPR) or odds of mortality prior to hospital discharge?

Methods: Four emergency medical services agencies contributed patients who received >60 seconds of TCP from 2017 to 2024. Data were abstracted from electronic health records and cardiac monitor files. SEC was defined as a wide QRS complex with a T-wave after at least 90% of pacer impulses until TCP stopped or CPR started. The association between variables of interest and SEC was estimated using univariable logistic regression. A multivariable Cox proportional hazards model estimated the association between SEC and time to post-TCP CPR. A multivariable logistic regression model estimated the association between SEC and mortality. Age, sex, pre-TCP CPR, and pre-TCP heart rate were used as covariables.

Results: In our cohort of 299 patients, 29 (9.7%) had SEC. The median pre-TCP heart rate was 38 [30, 45] bpm, the median body weight was 78 [68, 95] kg and maximum TCP current was 90 [70-110] mA. Lower body weight (odds ratio [OR]: 0.95 [0.93, 0.98] per kg; n=208), lower pre-TCP heart rate (OR: 0.96 [0.93, 0.99] per bpm; n=297), and higher current (OR: 1.18 [1.06, 1.32] per 10 mA; n=299) were associated with higher odds of SEC. Overall, 124/299 (41.5%) had post-TCP CPR, and 88/237 (37.1%) with outcome data died prior to hospital discharge. SEC was not associated with the hazard of post-TCP CPR (15/29 [51.7%] vs. 109/270 [40.4%]; adjusted hazard ratio: 1.12 [0.64, 1.96]; n= 297), but was associated with higher odds of mortality prior to hospital discharge (18/23 [78.3%] vs. 131/214 [61.2%]; adjusted OR: 3.92 [1.29, 11.92]; n=235).

Conclusions: We found that SEC during prehospital TCP was rare and associated with mortality but not post-TCP CPR. Limitations include potential residual confounding, the retrospective design, and limited sample size. These findings suggest that prehospital TCP is frequently ineffective, highlighting the potential to improve care for this patient population.