| Summary: | Aim of the study: Overactivation of the parasympathetic nervous system can lead to reflex syncope (RS) and, in extreme cases, trigger an unusual and underrecognized form of cardiac arrest. We characterized the epidemiology and prognosis of reflex-mediated cardiac arrest (RMCA) and hypothesized it is associated with intervenable patient factors. Methods: This retrospective case-control study examined RMCAs at two academic hospitals from 1/2016 to 6/2022 using a resuscitation quality improvement database. RMCA cases were identified as cardiac arrests preceded by vagal trigger(s). Cases of RS, defined as syncope with bradycardia and hypotension preceded by vagal trigger(s), between 1/2021 and 12/2021 were used as controls. For the secondary analysis, RMCA outcomes were compared to in-hospital cardiac arrest (IHCA) of other causes. Results: We identified 46 RMCA and 67 RS cases. Compared to RS patients, RMCA patients were more likely to have spinal cord injury (13.0% vs 1.5%, p = 0.02). Airway clearance i.e., coughing and suctioning triggered a higher proportion of RMCA events than RS events (23.9% vs 3.0%, p < 0.01). Compared to 1,021 IHCAs of other causes, RMCAs had 100% return of spontaneous circulation, were more likely to survive to discharge (84.8% vs 36.2%, p < 0.001) and have favorable neurological outcomes (cerebral performance category 1 or 2, 58.7% vs 26.9%, p < 0.001). Conclusions: RMCA has a favorable prognosis compared to other IHCAs and is potentially preventable. Spinal cord injury and airway clearance were patient factors significantly associated with RMCA.
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