Conversion to shockable rhythms during resuscitation and survival for out-of hospital cardiac arrest

BACKGROUND: In out of hospital cardiac arrest (OHCA), the prognostic influence of conversion to shockable rhythms during resuscitation for initially non-shockable rhythms remains unknown. This study aimed to assess the relationship between initial and subsequent shockable rhythm and post-arrest survival and neurological outcomes after OHCA.

METHODOLOGY: This was a retrospective analysis of all OHCA cases collected from the Pan-Asian Resuscitation Outcomes Study (PAROS) registry in 7 countries in Asia between 2009 and 2012. We included OHCA cases of presumed cardiac etiology, aged 18-years and above and resuscitation attempted by EMS. We performed multivariate logistic regression analyses to assess the relationship between initial and subsequent shockable rhythm and survival and neurological outcomes. 2-stage seemingly unrelated bivariate probit models were developed to jointly model the survival and neurological outcomes. We adjusted for the clustering effects of country variance in all models.

RESULTS: 40,160 OHCA cases met the inclusion criteria. There were 5356 OHCA cases (13.3%) with initial shockable rhythm and 33,974 (84.7%) with initial non-shockable rhythm. After adjustment of baseline and prehospital characteristics, OHCA with initial shockable rhythm (odds ratio/OR=6.10, 95% confidence interval/CI=5.06-7.34) and subsequent conversion to shockable rhythm (OR=2.00,95%CI=1.10-3.65) independently predicted better survival-to-hospital-discharge outcomes. Subsequent shockable rhythm conversion significantly improved survival-to-admission, discharge and post-arrest overall and cerebral performance outcomes in the multivariate logistic regression and 2-stage analyses.

CONCLUSION: Initial shockable rhythm was the strongest predictor for survival. However, conversion to subsequent shockable rhythm significantly improved post-arrest survival and neurological outcomes. This study suggests the importance of early resuscitation efforts even for initially non-shockable rhythms which has prognostic implications and selection of subsequent post-resuscitation therapy.