Early risk stratification of patients after successfully resuscitated out-of-hospital cardiac arrest without ST-segment elevation - the TOMAHAWK risk score

Abstract Background Mortality after out-of-hospital cardiac arrest (OHCA) remains high. Early risk stratification is crucial to make adequate treatment decisions. Existing OHCA risk scores are either medically outdated, limited to registry data, small cohorts, certain healthcare systems only or include complex calculations. Purpose The aim of this study was to develop an easy-to-use, readily available risk prediction score for short-term mortality in patients with successfully resuscitated OHCA without ST-segment elevation, derived from the TOMAHAWK (Angiography after Out-of-Hospital Cardiac Arrest without ST-Segment Elevation) trial. Methods The risk score was developed using a backward stepwise regression analysis. The risk score was externally validated in the COACT (Coronary Angiography after Cardiac Arrest Trial) cohort, which included patients with shockable rhythms only. Results Development and validation of the risk score was performed across 50 centres in three countries. Five variables emerged as independent predictors for 30-day mortality and were used as risk score parameters: age ≥72 years, known diabetes, unshockable initial electrocardiogram rhythm, time until return of spontaneous circulation ≥23 minutes and admission serum lactate level above 7.9 mmol/L. Between 1 and 4 points were attributed to each variable, leading to a score with three risk categories: low (0 to 2), intermediate (3 to 6) and high (7 to 10). The observed 30-day mortality rates were 23.6%, 68.8% and 86.2%, respectively (p<0.001) with a very good discrimination at an area under the curve of 0.82. Kaplan-Meier analysis revealed a stepwise increase in mortality between the different risk score categories (p<0.001 for low vs. intermediate, intermediate vs. high and low vs. high; see Figure). External validation in the COACT cohort showed short-term mortality rates of 23.1% (score 0 to 2), 44.8% (score 3 to 6) and 78.9% (score 7 to 10), respectively (each p<0.001). Conclusion The TOMAHAWK risk score can be easily calculated in daily clinical practice and is strongly correlated with mortality in patients with successfully resuscitated OHCA without ST-segment elevation. It may help stratify patient risk for short-term mortality and facilitate clinical decision making.