Defibrillation of persistent shockable rhythms and survival after in-hospital cardiac arrest

Background Persistent shockable rhythms (refractory to or recurring after three or more defibrillation attempts) are associated with poorer survival following out-of-hospital cardiac arrest, but little is known about this relationship following in-hospital cardiac arrest (IHCA). This study therefore explored the association between the number of defibrillation attempts and 30-day survival following IHCA. Method This was a national retrospective cohort study using prospectively collected data from the Swedish Registry for Cardiopulmonary Resuscitation. All cases of adult IHCA between 1 January 2010 and 31 December 2020 presenting with a shockable rhythm who received at least one defibrillation attempt were included. Comorbidity data originated from the Swedish National Patient Register. The exposure was the total number of defibrillation attempts and the primary outcome was 30-day survival. A descriptive analysis was performed, followed by multivariable logistic regression with adjustment for patient and cardiac arrest factors. Missing data were imputed. Results In total, 5325 IHCA cases were included. Persistent shockable rhythms occurred in 907 (17%) cases. 30-day survival decreased rapidly from 73% in patients receiving one defibrillation attempt to 41% in patients requiring four defibrillation attempts but subsequently plateaued with a minimum value (24%) at nine defibrillation attempts. An unwitnessed arrest (adjusted OR (aOR) 0.50, 95% CI 0.39 to 0.64), the absence of continuous cardiac monitoring (aOR 0.63, 95% CI 0.54 to 0.74) and a longer time to the first defibrillation attempt (aOR 0.89, 95% CI 0.86 to 0.91 per min) were potentially modifiable in-hospital factors associated with decreased survival. Conclusions A persistent shockable rhythm occurred in around one sixth of IHCAs with an initial shockable rhythm. Successive defibrillation attempts were associated with a rapid fall in survival followed by a plateau phase. These findings warrant further investigation, as patients with IHCA may also benefit from novel strategies to more rapidly terminate shockable rhythms.