What Is the Best Approach to Diagnosing Pulmonary Embolism?

Computed tomographic pulmonary angiography is as accurate as ventilation-perfusion scan, but detects many smaller emboli.

Computed tomographic pulmonary angiography (CTA) has increasingly replaced ventilation-perfusion (V/Q) scanning in the diagnosis of pulmonary embolism (PE), despite a lack of data comparing the two.

In an investigator-blinded, international, multisite, randomized trial, 1417 patients with a high clinical probability of PE (Wells score, 4.5) or positive D-dimer assay underwent CTA or V/Q scan. Subjects with high-probability V/Q scans or with positive CTA were considered to have PE and received anticoagulation. Those with normal V/Q scans were considered to have PE excluded. All others had lower extremity venous ultrasound; those positive for proximal deep venous thrombosis (DVT) were also anticoagulated. A small number of patients crossed over between groups, usually for technical reasons or physician preference. Of 694 patients randomized to CTA, 19.2% were positive for PE or proximal DVT, compared with 14.2% of patients randomized to V/Q scan. Of the remaining 561 CTA patients, 0.4% developed symptomatic thromboembolic events, compared with 1.0 of) V/Q patients.

Comment: CTA appears to be as accurate as V/Q scanning in detecting thromboembolic events. However, it also detected 30% more pulmonary emboli than did V/Q scanning, of which nearly 40% of the total was segmental or subsegmental. The rate of undetected significant clinical events was not higher in the V/Q patients, suggesting that CTA may detect pulmonary emboli of limited clinical significance and expose patients to unnecessary anticoagulation. The authors and an editorialist both suggest that a structured approach to PE assessment — including Wells score, D-dimer assay, lower extremity ultrasound, CTA unless contraindicated, and V/Q scan if available and needed — seems appropriate.

— Thomas L. Schwenk, MD

Published in Journal Watch General Medicine January 3, 2008

Citation(s):

Anderson DR et al. Computed tomographic pulmonary angiography vs ventilation-perfusion lung scanning in patients with suspected pulmonary embolism: A randomized controlled trial. JAMA 2007 Dec 19; 298:2743.