TUESDAY, Oct. 20, 2009 (HealthDay News) -- New research raises doubts about the long-held medical dogma that dangerous blood clots in the lungs, known as pulmonary emboli, originate from clots in the deep veins of the legs or other parts of the lower body, which then break up and travel up through the body.
A study appearing in the October issue of the Archives of Surgery found that 85 percent of trauma patients with pulmonary emboli showed no sign of deep vein thrombosis, or blood clots in the lower extremities.
The lead author of the study, Dr. George Velmahos, chief of the division of trauma, emergency surgery and surgical critical care at Massachusetts General Hospital and professor of surgery at Harvard Medical School in Boston, said the findings also cast doubt on the use of filters to prevent the clots from traveling.
But an outside expert said the findings need to be received cautiously, at least for now.
"I think it's an interesting report. I wouldn't call it a bombshell", said Dr. Jack Ansell, chairman of the department of medicine at Lenox Hill Hospital in New York City. "I think this study by no means answers this question or reverses the original concept that most pulmonary embolisms originate as venous thrombosis [blood clots] in the deep veins of leg or sometimes in pelvis or abdomen."
According to Velmahos, the concept of clots in the lungs originating as clots in the legs has never been challenged, despite evidence in the literature that some patients suffering from pulmonary embolism did not show signs of having had a blood clot in the lower extremities.
For this study, Velmahos and co-authors looked back over medical records of 247 trauma patients who had undergone CT pulmonary angiography and CT venography.
Among 46 patients with PE, only 7 also had DVT, or 15 percent.
There are possible explanations, the team said. It's possible that the entire original clot detached itself, leaving no traces. However, cadaver studies suggest that only a part of the leg clot breaks away, and a remnant is typically left behind. Or it could be that small clots exist and were not picked up by imaging techniques or even that the clots start in the upper extremities, which are not routinely examined.
Ansell also pointed to what he believes are several shortcomings in the study.
"There are still some issues that could account for why they didn't see DVTs," Ansell said. "The screening methods may not be ideal [and] small clots in calf veins are difficult to visualize by various techniques."
"Having said that, there certainly is the possibility with certain types of injury that there could be clots formed just primarily in the lungs and not necessarily travel from other spots," he added.
Velmahos felt that he had already excluded potential reasons for not seeing lower-extremity clots in pulmonary embolism patients, and said he is "very confident that a correlation cannot be established." Yet he also acknowledged that "every retrospective study [which this is] should be viewed with a grain of salt."
More studies need to be conducted, particularly to explore the hypothesis that pulmonary emboli actually form first in the lungs.
If it turns out that DVTs do not travel far from the legs, do tiny filters now used to trap them remain useful therapy? One expert said that issue may be a minor one.
"Pulmonary embolism and DVT are huge problems in trauma patients. The question is how to treat them," said Dr. David Gillespie, a professor of surgery at the University of Rochester Medical Center. "Anticoagulants such as heparin have been the standard of care... The interpretation here should not be that all filters are bad [but] anticoagulants should be the main therapy."
Finally, even if DVTs don't detach and travel to the lungs, "this does not mean that DVT is unimportant," Ansell said. "It is clearly established that most or many pulmonary emboli do originate in the legs in the lower extremities and one still needs to provide appropriate anticoagulant [blood-thinning] prophylaxis in patients who are at risk, whether they are trauma patients or just patients immobilized for other reasons in the hospital."
More information
There's more on deep vein thrombosis at the U.S. National Heart, Lung, and Blood Institute.
