Better Detection of Pulmonary Embolism

Early detection of pulmonary embolism is crucial. Pulmonary embolism leads to death in nearly a third of untreated cases, but therapies can lower the death rate to between 3 and 8%. According to a new study funded by NIH's National Heart, Lung, and Blood Institute, doctors can more accurately diagnose pulmonary embolism by combining a commonly used imaging test of the chest with a scan of the leg, where the clots typically originate. Clinical probability assessments, which determine the likelihood a patient has a pulmonary embolism based on signs and symptoms, heart rate and risk factors, further improve the ability to reach a correct diagnosis.

Pulmonary embolism is a sudden and potentially deadly blockage in a lung artery. In 9 out of 10 cases, it begins as a clot in the deep veins of the leg, a condition known as deep vein thrombosis. The clot breaks free from the vein and travels to the lung, where it can block an artery. Pulmonary embolism affects an estimated 600,000 Americans each year, making it the fourth most common cardiovascular problem in the United States.

The Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) II is the largest collaborative study ever conducted to assess a method called contrast-enhanced multidetector computed tomographic (CT) angiography for diagnosing pulmonary embolism. Researchers compared the accuracy of a chest CT angiogram alone to a chest CT angiogram with a leg CT scan to diagnose blood clots in 824 patients suspected of having pulmonary embolism.

In the June 1, 2006, issue of the New England Journal of Medicine, the PIOPED researchers report that chest CT angiography alone detects suspected pulmonary embolism in 83% of patients. In contrast, combined results of the chest CT angiogram and the leg CT scan detects clots in 90%. With both imaging tests, a clinical probability assessment further improved the accuracy of the results.

"This study suggests that chest CT angiogram for detecting dangerous blood clots in the lung is good, but sometimes it is not enough," noted lead author Dr. Paul D. Stein of Wayne State University and St. Joseph Mercy Oakland Hospital in Pontiac, Michigan. For patients suspected of having a pulmonary embolism, a leg CT scan in addition to a chest CT angiogram can more accurately detect or rule out pulmonary embolism. The researchers also concluded that when the imaging results and clinical probability test don't agree, additional testing is still necessary.