Abstract 70: External Validation of the Hypothermic to Ischemic Ratio as a Predictor of Survival from Out-of-Hospital Cardiac Arrest for Patients Presenting with a Shockable Rhythm
Objectives: The Hypothermic to Ischemic Ratio (H/I Ratio = total hypothermic time (THT) / total ischemic time (TIT)) was derived to predict survival after out-of-hospital cardiac arrest (OHCA) and found to be highly significant in multivariable models. We sought to externally validate these findings.
Methods: Adult, non-traumatic, OHCA patients presenting with a shockable rhythm (VF/pVT) and surviving to hospital admission between September 1, 2007, and December 31, 2011, were considered for inclusion. Structured data were abstracted from a population-based dataset (Strategies for Post Arrest Care (SPARC) Network database (Toronto, Canada)). THT was measured from initiation in the ED, through therapeutic hypothermia (TH) and rewarming to at least 36.5°C. TIT was estimated from call to 911 or EMS witnessed collapse to return of spontaneous circulation (ROSC). Patients were excluded for age >90 years, TIT <5 or >90 minutes, cooling initiated >6 hours after ROSC, rewarming time >30 hours, or missing relevant intervals. Stepwise logistic regression was used to fit the most parsimonious model. Results: Overall, 1,170 OHCA patients received TH, average age 65 years (SD 15.4), 71% male, 85% witnessed, and 43% with bystander CPR. A total of 497 VF/pVT patients met our criteria, with 52.5% surviving to discharge. In multivariable modeling (Table), TIT, age, and H/I Ratio were the most significant predictors for survival (Chi-Sq 123.43, p<0.0001, R² = 0.25, area under curve = 0.82).
Conclusions: External validation of the H/I Ratio confirmed it is a significant predictor for survival in OHCA patients presenting with a shockable rhythm. Prospective studies should consider H/I Ratio as a potential predictor for investigation.
- © 2012 by American Heart Association, Inc.