Development and internal validation of an oxygen saturation-based prehospital cardiac risk assessment index (P-CRAI) for predicting 30-day mortality in acute myocardial infarction: a multicentre registry study from the Mie ACS Registry, Japan
8 affiliations
- 1Cardiology and Nephrology, Mie University Graduate School of Medicine, Tsu, Mie, Japan
- 2Cardiology, Nagai Hospital, Tsu, Mie, Japan
- 3Cardiology, Ise Red Cross Hospital, Ise, Mie, Japan
- 4Cardiology, Kuwana City Medical Center, Kuwana, Mie, Japan
- 5Cardiology, Saiseikai Matsusaka General Hospital, Matsusaka, Mie, Japan
- 6Cardiolory, Matsusaka Chuo General Hospital, Matsusaka, Mie, Japan
- 7Cardiolory, Nabari City Hospital, Nabari, Mie, Japan
- 8Cardiology, Suzuka Chuo General Hospital, Suzuka, Mie, Japan
Abstract
Objectives: Early risk stratification of patients with acute myocardial infarction (AMI) in the prehospital setting remains challenging. The aim of this study was to develop and internally validate a Prehospital Cardiac Risk Assessment Index (P-CRAI) based on peripheral oxygen saturation (SpO₂) for predicting 30-day mortality in patients with AMI.
Design: Retrospective analysis of a prospective multicentre registry.
Setting: 17 cardiovascular centres participating in the Mie ACS Registry in Japan.
Participants: A total of 3584 consecutive patients with AMI who were transported directly by ambulance between 2013 and 2023 were included.
Primary outcome measure: The primary outcome was all-cause mortality within 30-day. Candidate predictors were age, sex, heart rate, systolic blood pressure and peripheral SpO₂ at first medical contact. P-CRAI was developed by adding SpO₂ and sex to the Prehospital-Simple Risk Index (pre-SRI). Model performance was assessed by discrimination, calibration, overall prediction accuracy and decision curve analysis, with bootstrap internal validation.
Results: The P-CRAI was calculated as follows: (heart rate×[age/10]²)/systolic blood pressure+1.1(100−SpO₂)−1.5 (male sex). The model demonstrated good discrimination for predicting 30-day mortality (area under the curve (AUC) 0.830, 95% CI 0.817 to 0.842). Discrimination was significantly improved compared with the pre-SRI (AUC 0.805, p<0.001) and was comparable to that of the Global Registry of Acute Coronary Events score (AUC 0.846, p=0.28). Calibration analysis showed an excellent agreement between the predicted and observed mortality rates, with a mean absolute error of 0.018. Harrell’s C-index was 0.821 and the Brier score was 0.050. Decision curve analysis showed greater net benefit of P-CRAI than the pre-SRI across clinically relevant threshold probabilities. Kaplan-Meier analysis demonstrated significant graded separation of 30-day survival across increasing P-CRAI quartiles (log-rank p<0.001). P-CRAI remained independently associated with 30-day mortality after multivariable analysis (adjusted HR 6.37, 95% CI 4.35 to 9.32; p<0.001).
Conclusions: P-CRAI is a simple prehospital model using variables available at first medical contact that showed good discrimination for 30-day mortality in AMI and may support triage and early transfer of high-risk patients to specialised cardiovascular centres. External validation is required before clinical implementation.
Trial registration number: UMIN000036020.
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BibTeX
@article{kirii2026development,
title = {{Development and internal validation of an oxygen saturation-based prehospital cardiac risk assessment index (P-CRAI) for predicting 30-day mortality in acute myocardial infarction: a multicentre registry study from the Mie ACS Registry, Japan}},
author = {Yosuke Kirii and Tairo Kurita and Hiromasa Ito and Akihiro Takasaki and Keishi Moriwaki and Naoto Kumagai and Takeshi Takamura and Takashi Omura and Toshiki Sawai and Takashi Tanigawa and Eitaro Fujii and Tetsuya Kitamura and Kaoru Dohi},
journal = {BMJ Open},
year = {2026},
month = oct,
doi = {10.1136/bmjopen-2026-124163},
url = {https://bmjopen.bmj.com/lookup/doi/10.1136/bmjopen-2026-124163},
note = {CC BY-NC 4.0},
}
RIS
TY - JOUR
TI - Development and internal validation of an oxygen saturation-based prehospital cardiac risk assessment index (P-CRAI) for predicting 30-day mortality in acute myocardial infarction: a multicentre registry study from the Mie ACS Registry, Japan
AU - Yosuke Kirii
AU - Tairo Kurita
AU - Hiromasa Ito
AU - Akihiro Takasaki
AU - Keishi Moriwaki
AU - Naoto Kumagai
AU - Takeshi Takamura
AU - Takashi Omura
AU - Toshiki Sawai
AU - Takashi Tanigawa
AU - Eitaro Fujii
AU - Tetsuya Kitamura
AU - Kaoru Dohi
PY - 2026
DA - 2026/10/09
JO - BMJ Open
DO - 10.1136/bmjopen-2026-124163
UR - https://bmjopen.bmj.com/lookup/doi/10.1136/bmjopen-2026-124163
AB - Objectives: Early risk stratification of patients with acute myocardial infarction (AMI) in the prehospital setting remains challenging. The aim of this study was to develop and internally validate a Prehospital Cardiac Risk Assessment Index (P-CRAI) based on peripheral oxygen saturation (SpO₂) for predicting 30-day mortality in patients with AMI. Design: Retrospective analysis of a prospective multicentre registry. Setting: 17 cardiovascular centres participating in the Mie ACS Registry in Japan. Participants: A total of 3584 consecutive patients with AMI who were transported directly by ambulance between 2013 and 2023 were included. Primary outcome measure: The primary outcome was all-cause mortality within 30-day. Candidate predictors were age, sex, heart rate, systolic blood pressure and peripheral SpO₂ at first medical contact. P-CRAI was developed by adding SpO₂ and sex to the Prehospital-Simple Risk Index (pre-SRI). Model performance was assessed by discrimination, calibration, overall prediction accuracy and decision curve analysis, with bootstrap internal validation. Results: The P-CRAI was calculated as follows: (heart rate×[age/10]²)/systolic blood pressure+1.1(100−SpO₂)−1.5 (male sex). The model demonstrated good discrimination for predicting 30-day mortality (area under the curve (AUC) 0.830, 95% CI 0.817 to 0.842). Discrimination was significantly improved compared with the pre-SRI (AUC 0.805, p<0.001) and was comparable to that of the Global Registry of Acute Coronary Events score (AUC 0.846, p=0.28). Calibration analysis showed an excellent agreement between the predicted and observed mortality rates, with a mean absolute error of 0.018. Harrell’s C-index was 0.821 and the Brier score was 0.050. Decision curve analysis showed greater net benefit of P-CRAI than the pre-SRI across clinically relevant threshold probabilities. Kaplan-Meier analysis demonstrated significant graded separation of 30-day survival across increasing P-CRAI quartiles (log-rank p<0.001). P-CRAI remained independently associated with 30-day mortality after multivariable analysis (adjusted HR 6.37, 95% CI 4.35 to 9.32; p<0.001). Conclusions: P-CRAI is a simple prehospital model using variables available at first medical contact that showed good discrimination for 30-day mortality in AMI and may support triage and early transfer of high-risk patients to specialised cardiovascular centres. External validation is required before clinical implementation. Trial registration number: UMIN000036020.
SN - 2044-6055
SN - 2044-6055
ER -