What is a pulmonary embolism, the condition that led to Catherine O’Hara’s death?

By Katia Hetter, CNN

(CNN) — A pulmonary embolism was the immediate cause of death for actor and comedian Catherine O’Hara. It’s a serious condition in which a blood clot lodges in the lungs.

O’Hara’s sudden passing on January 30 at age 71 has drawn attention to a medical emergency that can unfold rapidly. What makes this condition especially alarming is that it can strike people who seem otherwise well, and symptoms can be mistaken for other problems. Understanding the warning signs is especially important.

To explain what a pulmonary embolism is and who is most at risk, I spoke with CNN wellness expert Dr. Leana Wen. Wen is an emergency physician and clinical associate professor at George Washington University. She previously was Baltimore’s health commissioner.

CNN: What is a pulmonary embolism, and how does it develop?

Dr. Leana Wen: A pulmonary embolism, or PE, happens when a blood clot travels to the lungs and blocks one of the pulmonary arteries. Most often, the clot forms elsewhere — typically in the deep veins of the legs or pelvis — in a condition known as deep vein thrombosis. If part of that clot breaks off, it can travel through the bloodstream, pass through the right side of the heart and become lodged in the arteries of the lungs.

When that blockage occurs, it interferes with blood flow needed to pick up oxygen. Depending on the size and location of the clot, this can reduce oxygen delivery to the body and increase pressure on the heart.

Large clots can obstruct major pulmonary arteries and cause sudden cardiovascular collapse. Smaller clots may block smaller vessels and can still impair breathing and strain the heart. A PE is a potentially life-threatening emergency that requires prompt diagnosis and treatment.

CNN: What symptoms should people watch for, and which ones require immediate emergency care?

Wen: The most common symptoms include sudden shortness of breath, chest pain that may worsen with deep breathing and an unexplained rapid heart rate. Some people also cough up blood and experience lightheadedness or fainting.

However, symptoms can vary. Some individuals have dramatic onset of severe breathing difficulty, while others have more subtle signs, such as mild shortness of breath with exercise or vague chest discomfort. In some cases, the first sign of a PE may be sudden collapse.

Certain symptoms should prompt immediate medical attention. These include difficulty breathing, chest pain, fainting or signs of shock such as confusion and clammy skin. Because a PE can worsen quickly, it is better to err on the side of caution and seek emergency evaluation if these symptoms arise.

CNN: Why can a pulmonary embolism affect people who appear otherwise healthy?

Wen: Blood clots tend to develop when three factors are present: slowed blood flow, injury to the lining of blood vessels and increased tendency of the blood to clot. Because these factors may not be outwardly visible, someone may appear healthy until a blood clot occurs. That unpredictability is one reason why clinicians and patients need to be aware of a PE and consider it as part of the diagnostic possibilities.

CNN: Who is at highest risk for developing a PE?

Wen: People with a history of blood clots are at significantly increased risk of developing another. Other high-risk groups include people over 60; those who have recently had major surgery or trauma; those who have been hospitalized or immobilized for extended periods; and people with certain medical conditions such as cancer, obesity, atrial fibrillation and inherited blood clotting disorders.

Notably, O’Hara’s death certificate listed rectal cancer as an underlying cause of death. According to some studies, PE is the second leading cause of death among patients with cancer after the cancer itself.

CNN: Are there other common situations that increase risk outside of medical conditions?

Wen: Yes. Long-distance travel can contribute when people remain seated for prolonged periods without moving their legs. While the absolute risk from travel alone is relatively low for healthy individuals, it rises in those who have additional risk factors.

In addition, pregnancy and the weeks after delivery create a natural hypercoagulable state, meaning the blood is more prone to clotting and increases PE risk. Estrogen-containing therapies in some birth control pills and menopause hormone therapies can similarly increase clotting tendency. Smoking is also a risk factor for developing blood clots.

CNN: How is a PE diagnosed, and why can it sometimes be difficult to recognize?

Wen: Diagnosis typically begins with clinical suspicion based on symptoms and risk factors. Clinicians may use scoring systems to estimate the probability of a PE. These scoring systems and blood tests such as a D-dimer can help rule out clots in low-risk patients.

The definitive imaging test is usually a CT pulmonary angiogram, which uses contrast dye to visualize clots in the pulmonary arteries. In some cases, for instance if contrast cannot be used, a ventilation-perfusion scan (VQ scan) may be performed. Ultrasound of the legs can also detect blood clots in the legs, which supports the diagnosis.

Recognition can be challenging because symptoms overlap with other conditions, including heart attack, heart failure, pneumonia, anxiety or musculoskeletal chest pain. In older adults or those with other illnesses, the symptoms may not be typical, which is why maintaining awareness of risk factors is critical.

CNN: How urgent is treatment, and what does treatment typically involve?

Wen: Pulmonary embolism is a medical emergency, and treatment should begin as soon as the diagnosis is made or strongly suspected. The mainstay of therapy is anticoagulation, commonly referred to as blood thinners. These medications prevent the clot from growing and reduce the risk of additional clots forming.

In severe cases, such as when a large clot is causing heart failure, more aggressive treatments may be required. These include thrombolytic medications that dissolve clots, procedures to remove or break up clots or, rarely, surgery.

Most patients require anticoagulation for at least three months. The duration may be longer depending on whether the clot was provoked by a temporary risk factor or reflects an ongoing predisposition.

CNN: What can people do to reduce their risk? And what should they do if they are concerned about possible symptoms?

Wen: Risk reduction depends on individual circumstances. Staying active and avoiding prolonged immobility are important preventive measures. During long travel, people can periodically stand, walk and perform calf exercises. For those undergoing surgery or hospitalization, physicians often prescribe preventive anticoagulation or use compression devices around the legs to reduce clot risk.

People with known risk factors should discuss prevention strategies with their clinicians, especially before major procedures or long trips. Maintaining a healthy weight and avoiding smoking also play roles in prevention.

If someone develops symptoms suggestive of a pulmonary embolism, they should not delay emergency medical evaluation. Because early treatment significantly improves outcomes, prompt attention can be lifesaving.

The-CNN-Wire
™ & © 2026 Cable News Network, Inc., a Warner Bros. Discovery Company. All rights reserved.