Respect the Small Pulmonary Embolism

Samuel Z. Goldhaber, MD


November 18, 2013

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Hello. This is Dr Sam Goldhaber from the ClotBlog at speaking to you from Brigham and Women's Hospital and Harvard Medical School on an important topic: don't ignore subsegmental pulmonary embolism (SSPE).

Our imaging of pulmonary embolism (PE) with CT scanning has become so good that we can identify a tiny, SSPE the size of a pencil tip—even as small as a sharpened piece of lead at the pencil tip. That is how good we are, and so the question arises: when we find these teeny, tiny blood clots, what do they mean? Are they clinically significant? Are normal people forming blood clots all the time and then endogenously lysing them? It would be nice to think that we could dismiss these as part of a normal physiologic process. After all, a little clotting is good for us. It should be, because it prevents us from having excessive hemorrhages.

Along come some important data that tell another tale. In fact, a group of Dutch investigators, led by den Exter, have published an important study in Blood[1] looking at chest CT pulmonary angiograms in about 3000 patients from two large and very well-done trials. They identified PE in approximately 750 patients. Of these patients with PE, 15% had small SSPE. They followed these patients over time to evaluate their outcomes compared with patients who had much larger, more dangerous-looking PE.

Perhaps counterintuitively, they found that patients with the small SSPE have death rates that are just as high as those of patients who have larger PE, and the likelihood that the patients with tiny SSPE will have recurrent events despite anticoagulation is the same as the likelihood of recurrence in patients with larger PE.

It goes back to risk factors. The risk factors for a thrombosis (and cancer is a particularly strong risk factor) were the same in patients with small SSPE as in patients with larger and more proximal PE. So the bottom line is, if we see a PE on the chest CT scan, we should treat it, and if we don't treat it, we should have a really great reason for not treating it.

Many of us have tended to treat PE with anticoagulants anyway, even if it they are small, because there was no study telling us that we shouldn't do so. Now we have good observational data published in a high-impact journal telling us that we should be careful and respect the small SSPE.

This is Dr Sam Goldhaber signing off for the ClotBlog.


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