Multi-Detector Spiral Computed Tomography Alone Versus Combined Strategy With Lower Limb Compression Ultrasonography in Outpatients Suspected of Pulmonary Embolism: A Randomised Non-Inferiority Trial [CTEP4]

Suspected pulmonary embolism [PE] is a frequent clinical problem and remains a diagnostic challenge. The diagnostic approach of PE relies on sequential diagnostic tests, such as plasma D-dimer measurement, lower limb compression ultrasonography, ventilation-perfusion lung scan or helical computed tomography [hCT] and pulmonary angiography. In addition, the diagnostic workup is usually stratified according to the clinical probability of pulmonary embolism.

First-generation hCTs were based on a single-detector technique and had a limited 70% sensitivity. Moreover, in two recent outcome studies, a proximal deep venous thrombosis diagnosed by lower limb compression ultrasonography was found in 15% of patients with a normal single-detector hCT. However, in management studies, the association of a normal lower limb compression ultrasonography and a normal single-detector hCT has been proved safe to rule out PE in patients with a non-high clinical probability, with a less than 2% rate of thromboembolic events during a 3-month follow-up in patients left untreated based on that combination. Hence, lower limb compression ultrasonography must be combined with a single-detector CT to safely rule out pulmonary embolism.

More recently, the multi-detector hCT has become widely available. These new scanners allow one to improve image definition and to diminish slice thickness without increasing acquisition time and, hence, to better visualize the segmental and sub-segmental pulmonary arteries. In a recent study [CTEPm], the investigators evaluated the performances of a multi-detector hCT. The rate of false negative results, assessed by the rate of patients with proximal DVT on ultrasonography and a negative hCT, was much lower using the multi-detector CT [0.9%, 95% confidence interval: 0.3-3.3%] than with the single-detector technique [15%]. This raises the possibility that hCT might be used as a single test to rule out PE in patients with an elevated D-dimer level. Indeed, ELISA plasma D-dimer measurement in patients with a non-high clinical probability of PE remains a logical first step since it safely rules out PE in approximately 30% of patients. Such a strategy should now be validated in a prospective randomised outcome study to compare its safety and cost-effectiveness with that of a previously validated strategy combining D-dimer, lower limb compression ultrasonography and hCT.

Therefore, the investigators plan to compare the efficacy and cost-effectiveness of two distinct diagnostic strategies for suspected pulmonary embolism in emergency center patents in a non-inferiority trial. The strategies are: 1) an algorithm based on clinical assessment, D-dimer and multi-detector hCT (DD-hCT); and 2) a previously validated strategy that includes lower limb compression (DD-US-hCT). The main outcome will be the rate of thromboembolic events during a formal 3-month follow-up in patients not anticoagulated on the basis of a PE ruled out by the diagnostic criteria in each study arm. A secondary outcome will be the costs of diagnosis in each study arm, including the costs of suspected and/or confirmed thromboembolic events during follow-up.

In addition, the investigators aim to prospectively and pragmatically validate the revised Geneva score for assessing the clinical probability of PE by using it in the sequential diagnostic work-up for PE. Classification performances of this score will be assessed by checking its capacity to discriminate between patients having a low, intermediate, or high probability of PE.