A new prehospital cardiac risk assessment index derived from vital signs by first contact emergency medical service, including prehospital oxygen saturation, for accurate prehospital triage of acute m

Abstract Background: Rapid and accurate triage is essential to improve the prognosis of patients with severe acute myocardial infarction (AMI). However, prehospital triage using vital signs, including prehospital oxygen saturation (SpO2), by first medical contact has not been evaluated. Purpose: The purpose of this study was to develop a new risk stratification index for AMI using vital signs including SpO2 for rapid and accurate prehospital triage. Methods: From January 2013 to June 2022, 3006 AMI patients who were directly transported by ambulance were enrolled from the Mie ACS registry. Based on observed risk relationships in 3,006 AMI patients, we developed and evaluated a prehospital cardiac risk assessment index (P-CRAI) using age, heart rate, and systolic blood pressure (SBP) and SpO2 to predict 30-day mortality: (heart rate×[age/10]2)/SBP＋1.1(100-SpO2). We also analyzed whether P-CRAI predicted the need for mechanical circulatory support (MCS) or ventilator use. Results: In the receiver operating characteristic (ROC) curve analysis, P-CRAI 38.1 has a sensitivity of 84.4%, specificity of 72.7%, and accuracy of 84.3% for predicting 30-day mortality, and P-CRAI was a strong predictor of 30-day mortality compared with the other indices and variables (Figure 1A). When divided into two groups with P-CRAI 38, Kaplan-Meier survival curves showed significant differences in 30-day survival between the high and low groups (83.7% vs. 98.7%, P<0.001, Figure 1B). P-CRAI≥38 was the strongest independent predictor of 30-day mortality with a hazard ratio of 7.64 compared to the other factors by multivariate Cox regression analysis. The spline curve of 30-day mortality by P-CRAI shows a correlation with prognosis (Figure 2A). In this study, we then used the bootstrap method to generate a calibration curve and validate P-CRAI. The results showed an excellent fit and that P-CRAI accurately estimated patient prognosis (Figure 2B). In addition, P-CRAI was a robust predictor of the very early events of death at 24 hours and MCS or ventilator use by ROC curve analysis. (c-statistic 0.835 and 0.726, respectively, P<0.01). Conclusion: The P-CRAI was found to be a useful tool for prehospital triage of AMI patients, accurately predicting 30-day mortality and the need for MCS.Figure 1.Figure 2.