Pulmonary embolism (blood clots in the lungs)

A pulmonary embolism (PE) happens when a blood clot blocks one or more arteries in the lungs. Almost always, the clot started in a deep vein of the leg or pelvis, a condition called deep vein thrombosis (DVT). A piece breaks off, travels through the heart and lodges in the lung arteries.

A clot in the lungs does two kinds of harm. It blocks part of the lung from picking up oxygen, so you feel short of breath. And it makes the right side of the heart, which pumps blood into the lungs, push against a blockage. A large clot can strain that side of the heart to the point of failure, which is why a big PE is an emergency.

The risk factors are the same as for DVT: recent surgery or hospital stay, not moving for long periods, cancer, pregnancy and the weeks after delivery, estrogen-containing hormones, a past clot and inherited clotting tendencies.

Some people have only mild breathlessness on stairs or feel unusually tired. Small clots can cause few symptoms.

In the emergency room, the main test is a CT pulmonary angiogram: a CT scan of the chest taken while contrast dye flows through the lung arteries. It takes only a few minutes. Clots show up as dark gaps in the bright arteries. If you cannot have contrast dye, a lung scan called a V/Q scan may be used instead.

Your team then works out how serious the PE is. They check your blood pressure and oxygen, look at the size of the right side of the heart on the CT or an echocardiogram (heart ultrasound), and measure blood tests that show heart strain, such as troponin and BNP. A leg ultrasound may look for the DVT the clot came from.

On the CT scan, the lung arteries normally fill bright white with contrast. A clot appears as a dark gray plug inside the white. A large clot may sit where the main artery splits into left and right, called a saddle embolus.

Blood thinners (anticoagulants) are the foundation for everyone with a PE. They stop the clot from growing and stop new ones from forming while your body dissolves the clot over weeks to months. Treatment usually starts in the hospital with an injection or IV drip, then switches to pills such as apixaban (Eliquis) or rivaroxaban (Xarelto), or to warfarin. Most people take them for at least 3 months, and some longer. See our blood thinners guide.

For larger clots that strain the heart, doctors may also try to clear the clot faster. Many hospitals have a PE response team, where lung, heart, emergency and interventional specialists decide together on the best plan.

Catheter treatment is done by an interventional radiologist in a procedure room with X-ray imaging. It is usually done with moderate sedation, which keeps you relaxed and drowsy, and numbing medicine at the skin. There is no incision.

1. 1
   Access

   We numb the skin at the groin or neck and place a thin tube into a vein using ultrasound.

2. 2
   Measure and map

   The tube is guided through the heart into the lung arteries. We measure pressures and inject contrast to see the clots.

3. 3
   Remove the clot

   Using suction catheters or a clot-removal device, we pull out as much clot as is safe. Sometimes we leave small tubes in place to drip clot-dissolving medicine for several hours instead.

4. 4
   Finish and recover

   The tubes are removed and the site is closed with a stitch or pressure. You recover in a monitored bed and continue blood thinners.

Many people feel their breathing ease within hours. Most go home after 1 to 3 days, depending on how sick they were before the procedure.

When I am called about a PE, the first thing I look at is not the clot, it is the right side of the heart. If the heart is coping, blood thinners usually do the job. If it is straining and the patient is getting worse, I talk with the team about going in to remove the clot. Watching someone's oxygen level climb and their heart rate settle on the table is one of the most satisfying parts of my work.

Fabio Komlos, MD, interventional radiologist · About Dr. Fabio Komlos

1. First days
   Breathlessness and chest discomfort start to ease. Walking is encouraged. You leave the hospital on a blood thinner.
2. First weeks
   Tiredness and breathlessness with effort are common. Increase activity gradually. Most people return to desk work within a few weeks.
3. About 3 months
   Follow-up visit to decide how long to continue blood thinners. If you are still short of breath, you may have a heart ultrasound or lung scan.
4. Long term
   Most people recover fully. A small number develop lasting breathlessness from scarred lung arteries, which can be treated.

A few people are left with long-term breathlessness because the clots do not fully dissolve and scar the lung arteries. This is called chronic thromboembolic pulmonary hypertension (CTEPH). It is uncommon, about 2 to 4 in 100 people after a PE, but it is important to catch because it can be treated with medicine, surgery or a balloon procedure.