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CTPA and V/Q Have Similar Sensitivities for Pulmonary Embolism

January 6, 2008
Written by: , Filed in: Chest Radiology
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A recent study was conducted to determine whether CT pulmonary angiography (CTPA) is a safe alternative to ventilation-perfusion (V/Q) lung scanning as the initial procedure for excluding the diagnosis of pulmonary embolism (PE) in acutely symptomatic patients.

The frequency of pulmonary thromboembolism was not clinically or statistically different for patients with negative V/Q scans versus those with negative CT pulmonary angiography.

The study was a randomized, single-blinded noninferiority multicenter clinical trial.

Participants
1,417 patients considered likely to have acute PE participated.

Methodology
Patients were randomly assigned to undergo either V/Q scanning (n=716) or CTPA (n=701) performed using standard Methodology. When patients had positive V/Q scans or CTPA, they were considered to have PE and were treated. If V/Q was normal, they were considered to be without PE and were not treated.

Patients with negative CTPA and nondiagnostic V/Q underwent ultrasound (US) leg imaging to look for deep venous thrombosis. Based on these US findings, patients in these groups were diagnosed as having or not having PE. Those patients in whom PE was excluded were not put on antithrombotic therapy and were followed up for 3 months by telephone.

Review for Practicing Radiologists The University of California, San Francisco School of Medicine, Department of Radiology and Biomedical Imaging Review for Practicing Radiologists an intensive clinical radiologic review and self-assessment covering the following radiology subspecialties: Vascular-Interventional, Breast, Neuro, Gastrointestinal and Pulmonary Imaging. The program is designed for radiologists in clinical practice. Click here to read more or order: Review for Practicing Radiologists --

 

Body Imaging: Abdominal, Thoracic and Vascular University of California, San Francisco, Department of Radiology Course Director: Judy Yee, MD This program is designed for the radiologist in clinical practice, and is intended to provide an overview and update on clinically relevant topics in diagnostic imaging and interventional techniques. Click here to read more or order: Body Imaging

Results
133 CTPA patients (19.2%) and 101 V/Q patients (14.2%) were diagnosed as having PE on the initial study. Of the patients in whom PE was considered excluded, 2 of 561 CTPA patients (0.4%) and 6 of 611 V/Q patients (1.0%) subsequently developed venous thromboembolism in the 3-month follow-up, including one patient with fatal PE in the V/Q group. These frequencies were not clinically or statistically different.

Conclusions
CTPA was not inferior to V/Q scanning in excluding PE. CTPA diagnosed 35% more PEs than did V/Q, with a very similar outcome in patients in whom the studies were negative, indicating that some of the positive CTPA cases were either insignificant emboli or false-positives.

Reviewer’s Comments
By definition, this study was designed to show if CTPA was a safe alternative to V/Q. The other way to look at the data is that V/Q is clinically and statistically equivalent to CTPA in sensitivity.

If we are truly concerned with minimizing patient exposure, why use higher-radiation CTPA over tried and true V/Q scanning? There were 35% more emboli diagnosed with CTPA, compared to V/Q, despite a similar morbidity in each group. These must either represent false-positives or small subclinical emboli.

There surely is an economic and health cost to anticoagulating an additional 35% of patients. This will need to be analyzed in the future.

Author: Lionel S. Zuckier, MD

Reference:
Anderson DR, Kahn SR, et al. Computed Tomographic Pulmonary Angiography versus Ventilation-Perfusion Lung Scanning in Patients With Suspected Pulmonary Embolism: A Randomized Controlled Trial. JAMA; 2007; 298 (December 19): 2743-2753

Review for Practicing Radiologists The University of California, San Francisco School of Medicine, Department of Radiology and Biomedical Imaging Review for Practicing Radiologists an intensive clinical radiologic review and self-assessment covering the following radiology subspecialties: Vascular-Interventional, Breast, Neuro, Gastrointestinal and Pulmonary Imaging. The program is designed for radiologists in clinical practice. Click here to read more or order: Review for Practicing Radiologists --

 

Body Imaging: Abdominal, Thoracic and Vascular University of California, San Francisco, Department of Radiology Course Director: Judy Yee, MD This program is designed for the radiologist in clinical practice, and is intended to provide an overview and update on clinically relevant topics in diagnostic imaging and interventional techniques. Click here to read more or order: Body Imaging
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