OC 04.3 - A pilot study to assess feasibility of evaluating the safety and efficiency of a simplified diagnostic approach for pulmonary embolism

Background: Decision rules designed to reduce pulmonary embolism (PE) imaging are seldom used by emergency physicians because of their complexity and poor credibility. We designed a simple decision rule for emergency department PE testing – the ‘Adjust-Unlikely’ rule.

Aims: To assess the feasibility of, and to inform the planning of a large study, which will determine the safety and efficiency of the Adjust-Unlikely rule for diagnosing PE in the emergency department.

Methods: We conducted a prospective pilot study in two emergency departments in Ontario, Canada. Adult patients tested for PE using Adjust-Unlikely consented to enrollment by telephone. Patients were followed for 90 days by chart review plus telephone, text or email to identify subsequent venous thromboembolism (VTE) diagnoses. PE and deep vein thrombosis testing during follow-up was independently adjudicated. We reported recruitment, missed eligible and loss to follow-up rates (feasibility outcomes). We estimated the average research assistant time to consent and follow-up one patient.

Results: We recruited 200 patients (from a total 474 eligible patients) between March 24 and June 10, 2023. The median age was 58, 70.7% female, 14.6% had prior VTE history, 8.1% taking anticoagulants, 4.5% had cancer and 3.5% were diagnosed with PE on index emergency department visit. The recruitment rate averaged 18 patients/week. Missed eligible rate averaged 11 patients/week. Time to obtain consent to enrollment was 1.5 hours per enrolled patient. After 90 days, 2 patients withdrew and 191/198 (96.5%) were contacted in follow-up, taking an average of 0.2 hours per patient. Of the 143 patients with a negative Adjust-Unlikely rule on index visit, 1 patient was diagnosed with PE at the segmental level during follow-up 0.7% (95% CI 0.1, 3.9%).

Conclusion(s): We showed the feasibility of our study methods. Our results are informing the design of a multicentre study assessing the safety of Adjust-Unlikely PE testing.