CTA could improve and complicate management for pulmonary embolism

December 21, 2007

Researchers in Canada and the U.S. have found CT angiography to be as safe and accurate as ventilation/perfusion lung scans for ruling out pulmonary emboli. Results in what could be the first study of its kind suggest, however, that CTA could also spot many clinically irrelevant thrombi.

Researchers in Canada and the U.S. have found CT angiography to be as safe and accurate as ventilation/perfusion lung scans for ruling out pulmonary emboli. Results in what could be the first study of its kind suggest, however, that CTA could also spot many clinically irrelevant thrombi.

The investigators published findings in the Dec. 19 issue of the Journal of the American Medical Association.

About a quarter million people die each year in the U.S. due to pulmonary embolism. A swift diagnosis allows proper management of patients with the condition and keeps those who are disease-free from the risks of unwarranted treatment. The accurate diagnosis of PE remains a challenging task, however. Ventilation-perfusion (V/Q) lung scanning, the noninvasive imaging standard of care for three decades, can reliably exclude PE in normal studies, but its predictive power drops when results are abnormal.

A strategy combining clinical exam, blood testing, sonography of the legs, and CTA could be just as good as one using V/Q scanning to diagnose or rule out PE, according to the investigative team led by Dr. David R. Anderson, a professor of medicine, community health, epidemiology, and pathology at Dalhousie University in Halifax, NS.

Anderson and colleagues at one U.S. and four Canadian tertiary-care centers enrolled 1417 consecutive patients suspected with PE between May 2001 and April 2005. Patients were randomized to undergo either V/Q scanning (n = 716) or CTA (n = 701). Patients with a negative diagnosis did not receive antithrombotic therapy and were followed for three months.

Almost 20% of patients randomized to CTA were diagnosed with PE or deep vein thrombosis during the initial evaluation period, while 14.2% of patients in the V/Q scanning group had a similar diagnosis.

Two out of 561 patients randomized to CTA who completed follow-up developed venous thromboembolism. Six of 611 patients randomized to V/Q scanning who finished the three-month monitoring period developed deep vein thrombosis and/or PE.

"The results of our study are reassuring given previous reports of relatively low sensitivity of CTA for the diagnosis of pulmonary embolism," researchers wrote in the study.

CTA resulted, however, in approximately 30% more venous thromboembolism diagnoses than did V/Q scanning. The finding could have undesired consequences, the researchers said. CTA diagnosis could result in increasing numbers of patients exposed to anticoagulant therapy, with the subsequent life risk derived from bleeding complications. Management of patients suspected with PE based exclusively on CTA could become less cost-effective than with V/Q scans.

Further research should confirm whether some pulmonary emboli or vein thrombi detected by CTA may be clinically unimportant and not require anticoagulant therapy, the researchers said.

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