Initial cardiac rhythm and rhythm conversion recorded by public access defibrillators

Out-of-hospital cardiac arrest (OHCA) research primarily focus on events after emergency medical services arrive. Public access defibrillators (PADs) record cardiac rhythms during bystander resuscitation and contain knowledge on early cardiac rhythms. This study investigated cardiac rhythms in OHCA cases recorded by PADs used by bystanders.

PAD data from 2016 to 2021 were merged with OHCA cases from the Danish Cardiac Arrest Registry. The cardiac rhythm analyses from the PAD (performed automatically every 2-3 min) were manually reviewed. Cardiac rhythms were classified as shockable (ventricular fibrillation or ventricular tachycardia) or non-shockable. Survival was assessed using multivariable logistic regression.

Among 3179 OHCA cases, 559 had PAD data and 26 % (n = 152) had an initial shockable rhythm. Compared to the non-shockable group, the shockable group included more males (75.7 % vs 58.7 %) and median age was lower (69 vs 74 years). The rate of return of spontaneous circulation (ROSC) and 30-day survival for shockable rhythms were 61 % (n = 93), and 40 % (n = 61), respectively (odds ratio 9.02 [95 %CI: 4.99-16.9] compared to non-shockable). In non-shockable cases, ROSC and survival were 17 % (n = 69) and 5 % (n = 20), respectively. Conversion to shockable rhythms occurred in 8.8 % (n = 30), however not associated with improved survival (odds ratio 0.82 [95 %CI: 0.25-2.25]; survival with conversion 10 %, without conversion 4.5 %, p = 0.41). No patients with more than five consecutive shockable rhythms survived.

Initial PAD-recorded rhythm is an important prognostic factor in OHCA. Survival is poor in non-shockable cases, even with rhythm conversion. Utilizing PAD data may support clinical decision-making in OHCA care.