Thank you doctor for finding that blood clot in my lung--you saved my life! (not)

Pulmonary embolism is a condition in which a blood clot that forms somewhere in the veins of the body moves with flowing blood into the right heart and then out into the lung (or lungs.) It is a common cause of sudden death, since a very large clot can cause the heart to fail and reduce the oxygen level in the blood. The blood clots that cause pulmonary emboli usually form in the deep veins of the legs, sometimes in the large veins of the pelvis and rarely form in the heart. Some people with pulmonary embolism have symptoms that are vague, like dizziness, cough, chest pain or shortness of breath. When they are evaluated they usually have an increased pulse rate, often a low-ish oxygen level, and occasionally report coughing up blood. A person who has a small pulmonary embolus may have really mild symptoms and then flip a very large clot later which can be devastating, so we evaluate many people for pulmonary embolism who have very atypical symptoms. We have a blood test, the d dimer, which, if it is low and symptoms are minimal, is enough to be pretty sure there is no clot. We have a couple of good imaging tests, the CT angiogram and the ventilation perfusion scan, which are even more accurate unless a person has pretty significant underlying lung disease.

When I was just a wee baby newly fledged doctor, we had to do a test called a pulmonary angiogram if we wanted to be really sure that a person didn't have a pulmonary embolism. This involved putting a catheter into a large vein and threading it into the right hear to inject a contrast material into the pulmonary arteries whereafter an x-ray could show the pulmonary arteries and delineate any clot that obstructed them. We tried not to do this test because it could kill people, either by causing rhythm disturbances in an already stressed heart or by killing their kidneys with a large load of potentially toxic contrast material. The catheter in the large vein was also potentially harmful. We can still do this test but the CT angiogram, which uses a smaller amount of contrast material in a smaller vein and gives us great images has mostly replaced it.

The CT angiogram is not without risk. It can cause kidney damage and does deliver a sizeable dose of radiation. It is also hard on the national budget, since we do it very often now at a few thousand dollars a pop.

CT scanners have gotten faster and more accurate, with multiple detector machines becoming increasingly common. These machines can see really little clots. How cool is that? 

It turns out that the new multidetector machines detect many more small clots than the standard machines, about twice as many. A study that looked at 22 studies comparing the two types of machines and the outcomes of patients scanned with them, showed that even though the standard single detector machines probably missed a portion of clots, the people who walked away with no treatment, because their tiny clots were not detected, were no more likely to have evidence of blood clots three months later than were the people screened with the multidetector machines and thus treated with anticoagulant medications. This is the link: http://www.ncbi.nlm.nih.gov/pubmed/20546118

Treating a pulmonary embolism is no small endeavor. People usually spend several nights in the hospital on medications that reduce blood clotting, and receive oral medications that will work when they go home. There is a not so small risk of bleeding, either in the hospital or after discharge, and a first blood clot is then treated with an anticoagulant medication for at least 3 months, requiring multiple blood draws and visits to the doctor. All of this is a reasonable price to pay for not dying, but not if the tiny blood clot was meaningless.

Today a patient was admitted to me to the hospital who had come to the emergency department with shortness of breath and a swollen leg after a long car trip. Long car or airplane trips are classic inciting events for blood clots. He had a d dimer that was a bit high and a CT angiogram showing that he had, maybe, a subsegmental pulmonary embolus. Even with the multidector machines, these tiny clots are hard to be sure of. He was also already on a therapeutic dose of a standard anticoagulant for a heart arrhythmia he'd had for years. The level of that was fine. He shouldn't have gotten a clot. 

But did he have a clot? Or if he did, was it significant? 

It turns out that his shortness of breath had started before he even went on his car trip, that he had a weakened heart from previous valve disease, and that both legs were actually swollen and he had been eating higher than normal amounts of salt as he headed across country. So he probably doesn't have a clot and his symptoms are probably due to congestive heart failure. But I can't really know that.

If this were an unusual case it wouldn't be worth mentioning at all. But it wasn't. It is more and more common to see tiny maybe pulmonary emboli in patients who have symptoms that have another likely cause, but then they require months of treatment and are forever worried about their risk of blood clots. Aargh. What messes we make for ourselves with our everso nifty technology.