Prognostic impact of the conversion to a shockable rhythm from a non-shockable rhythm for patients suffering from out-of-hospital cardiac arrest.

Objective: For patients suffering from an out-of-hospital cardiac arrest (OHCA), having an initial shockable rhythm is a marker of good prognosis. It has been suggested as one of the main prognosticating factors for the selection of patients for extracorporeal resuscitation (E-CPR). However, the prognostic implication of converting from a non-shockable to a shockable rhythm, as compared to having an initial shockable rhythm, remains uncertain, especially among patients that can otherwise be considered eligible for E-CPR. The objective of this study was to evaluate the association between the initial rhythm and its subsequent conversion and survival following an OHCA, for the general population and for the general population and for E-CPR candidates. Methods: This study used a registry of OHCA in Montreal, Canada. Adult patients suffering from a non-traumatic OHCA for whom the initial rhythm was known were included. The association between the initial rhythm and its subsequent conversion or not and survival to discharge was assessed using a multivariable logistic regression. Results: Of 6681 included patients, 1788 (27%) had an initial shockable rhythm, 1749 (26%) had pulseless electrical activity (PEA) and no subsequent shockable rhythm, 295 (4%) had PEA and a subsequent shockable rhythm, 2694 (40%) had asystole and no subsequent shockable rhythm, and 155 (2%) asystole and a subsequent shockable rhythm. As compared to patients having an initial shockable rhythm, patients in all other groups had significantly lower odds of survival to hospital discharge (p < 0.001 for all comparisons). Univariate analyses were performed for E-CPR candidates. Among these 556 (8%) patients, more patients with an initial shockable rhythm survived than patients in all other groups (p < 0.001 for all comparisons). Conclusions: The initial rhythm remains a much better prognostic marker than subsequent rhythms for all patients suffering from an OHCA, including in the subset of potential E-CPR candidates.