Rapid prediction of adverse outcomes for acute normotensive pulmonary embolism: derivation of the Calgary Acute Pulmonary Embolism score

Background: Acute pulmonary embolism (PE) has a wide spectrum of outcomes, but the best method to risk-stratify normotensive patients for adverse outcomes remains unclear. Methods: A multicentre retrospective cohort study of acute PE patients admitted from emergency departments in Calgary, Canada, between 2012 and 2017 was used to develop a refined acute PE risk score. The composite primary outcome of in-hospital PE-related death or haemodynamic decompensation. The model was internally validated using bootstrapping and the prognostic value of the derived risk score was compared to the Bova score. Results: Of 2067 patients with normotensive acute PE, the primary outcome (haemodynamic decompensation or PE-related death) occurred in 32 (1.5%) patients. In simplified Pulmonary Embolism Severity Index highrisk patients (n=1498, 78%), a multivariable model used to predict the primary outcome retained computed tomography (CT) right-left ventricular diameter ratio.1.5, systolic blood pressure 90-100 mmHg, central pulmonary artery clot and heart rate.100 beats.min(-1) with a C-statistic of 0.89 (95% CI 0.82-0.93). Three risk groups were derived using a weighted score (score, prevalence, primary outcome event rate): group 1 (0-3, 73.8%, 0.34%), group 2 (4-6, 17.6%, 5.8%), group 3 (7-9, 8.7%, 12.8%) with a C-statistic 0.85 (95% CI 0.78-0.91). In comparison the prevalence (primary outcome) by Bova risk stages (n=1179) were stage I 49.8% (0.2%); stage II 31.9% (2.7%); and stage III 18.4% (7.8%) with a C-statistic 0.80 (95% CI 0.74-0.86). Conclusions: A simple four-variable risk score using clinical data immediately available after CT diagnosis of acute PE predicts in-hospital adverse outcomes. External validation of the Calgary Acute Pulmonary Embolism score is required.