Incidence and Predictors of Repeated Computed Tomographic Pulmonary Angiography in Emergency Department Patients

Study objective: Use of contrast-enhanced computed tomography (CT) of the pulmonary arteries to evaluate for pulmonary embolism has increased, raising concern about radiation and contrast toxicity. We sought to measure the frequency of repeat CT pulmonary angiography in emergency department (ED) patients. Methods: This was a prospective, longitudinal follow-up of ED patients who underwent first-time CT pulmonary angiography as part of a research protocol for diagnosis of pulmonary embolism in 2001 to 2002. Two authors (DMB and MCK) searched electronic medical record databases to measure the frequency of repeated CT scans performed within 5 years. Primary outcome was greater than or equal to I repeated CT pulmonary angiography examination. Radiologist-written interpretations of CT pulmonary angiography were categorized by 2 observers (DMB and JAK). Cox regression was used to estimate hazard ratios for 24 clinical variables. Results: A cohort of 675 ED patients was observed for a median of 1,989 days: 226 of 675 (33%) had at least 1 additional CT pulmonary angiography scan, and 60 died with no repeated CT pulmonary angiography, leading to a mortality-adjusted frequency of repeated CT pulmonary angiography scanning of 226 of 615, or 37%. Seventy-three percent of the cohort had I or more subsequent CT scans of any body part, and 31 patients (5%) had 5 or more repeated CT pulmonary angiography scans. The pulmonary embolism (positive) prevalence was 57 of 675 (8.4%; 95% confidence interval [CI] 6.5% to 10.8%) on the first CT pulmonary angiography versus 8 of 226 (3.5%; 95% CI 1.5% to 6.9%) on the second CT pulmonary angiography scan. Hazard ratios indicated that respiratory rate, active malignancy, previous coronary artery disease, and previous or new diagnosis of venous thromboembolism were positively associated with repeated CT pulmonary angiography scanning. Conclusion: At least one third of ED patients who undergo CT pulmonary angiography scanning will have a second CT pulmonary angiography result that will be negative for pulmonary embolism. New methods are needed to exclude pulmonary embolism recurrence without use of ionizing radiation. [Ann Emerg Med. 2009;54:41-48.]