A pulmonary embolism (PE) is a type of blood clot in your lungs. It usually develops as a result of a blood clot in another part of the body breaking and traveling to a lung artery. Most start as deep vein thrombosis (DVT) in the lower leg.

Pulmonary embolism (PE) is a serious condition that can be life threatening without prompt treatment.

But before recommending specific treatment measures, a doctor will first need to classify the type of PE you have. A PE is primarily classified based on:

  • how long you’ve had related symptoms
  • how severe the symptoms are
  • where the blood clot is located

In diagnosing PE, a doctor may consider how long you’ve been experiencing symptoms. Doctors may classify these as acute, subacute, or chronic PE.


Acute PE refers to a sudden onset of symptoms that may occur from a blood clot in your lungs. These may include shortness of breath, chest pain, and coughing up blood. Acute PE is dangerous and can lead to pulmonary hypertension if left untreated.

The most important form of treatment for acute PE is anticoagulation, which consists of blood thinners that help stop blood clots from growing and help prevent future clots from developing.


Subacute PE develops gradually over 2 to 12 weeks and carries a higher mortality rate. This type of PE may also be more resistant to treatments that help break up the blood clot.


Chronic PE may develop due to residual blood clots that are left behind along the lungs’ vessel walls despite treatment. Chronic PE is less common than acute and subacute forms. Sometimes, doctors classify chronic PE as a separate group.

Having chronic PE could increase your risk of developing a complication called chronic thromboembolic pulmonary hypertension (CTEPH). Scar tissue in the pulmonary arteries causes CTEPH.

You should talk with a doctor about getting tested for CTEPH if you continue to have symptoms 6 months after your initial PE treatment. CTEPH may require surgery, such as balloon pulmonary angioplasty or a thromboendarterectomy to remove blood clots and scar tissue.

PE may cause severe and life threatening complications, such as:

  • low blood pressure
  • low oxygen levels
  • organ damage
  • permanent lung damage

Accordingly, a doctor will classify your PE as low, intermediate, or high-risk. Your doctor will assess your risk via a six-point scoring system called the PE severity index (PESI). The higher your score, the more at risk you are for adverse outcomes.

A PESI score considers the following:

Low risk

Having low risk PE means you have a 0 PESI score. Subsequently, the risk of death within 30 days is relatively low at an estimated 1 percent. With low-risk PE, your condition may be treatable with blood thinners only.

Intermediate risk (submassive)

Intermediate, or submassive, PE carries a slightly higher risk of complications. A PESI score of 1 or higher might indicate submassive PE. Doctors also look for other factors, including dysfunction of the right ventricle or elevated biomarkers, such as troponins, that can indicate a damaged heart.

At this stage, blood thinners are the main treatment. Doctors may also consider medicine or procedures to break up blood clots.

High risk (massive)

High risk PE is the most severe form and is associated with a higher risk of death. With a massive PE, it’s common to see acute right ventricle failure or low blood oxygen in body tissues (hypoxia).

Treatment for massive PE can be more complex. In addition to blood thinners, treatment may include medication or procedures to break up clots. Doctors do this to help reduce pressure in the lungs’ arteries and reduce your heart rate.

Finally, the location of PE is important in classifying this condition and determining the best treatment options. PE may develop in the saddle, lobar, or distal areas of the pulmonary arteries.


Saddle PE refers to a large blood clot that has formed in the main pulmonary artery. In general, larger blood clots are more dangerous due to blocked blood flow to your lungs.

Still, a saddle PE is uncommon. Having acute PE may increase your risk of developing this type of blood clot.


A lobar PE is located within one of the large branches of the pulmonary artery. These branches extend from the main pulmonary artery on each side of the lungs. The left lung has two lobes (upper and lower), while the right has three (upper, middle, and lower lobes).


Distal PE refers to a blood clot located in the small branches of the pulmonary artery, which extend from each of the lungs’ lobes. Also called subsegmental PE, this type of blood clot tends to be less severe and may not require treatment.

While PEs may be difficult to diagnose at first, they are categorized based on a combination of the following tests:

  • a physical exam, where a doctor may also ask you about the history and severity of your symptoms
  • a computerized tomography (CT) scan of the chest with contrast dye to gain images of your pulmonary arteries
  • an echocardiogram, a type of ultrasound of the heart, to help determine whether a PE is affecting overall heart function
  • blood testing to help detect clotting abnormalities, organ damage, or signs of heart problems, such as elevated troponin proteins

A pulmonary embolism is a serious condition that has the best outcomes when caught as early as possible. Due to the complexities of this type of blood clot and the anatomy of the lungs, PE may be categorized based on the onset of symptoms, location, and severity.

Talk with a doctor if you experience possible symptoms of PE, especially if you have certain risk factors, such as:

Additionally, preventive measures can help prevent future blood clots, even if you already have had PE. You can help reduce your risk by:

  • continuing anticoagulant medications as directed by a doctor
  • moving regularly, especially during long trips and after surgery
  • exercising regularly
  • quitting smoking