What complications can arise from untreated PE?
An untreated pulmonary embolism (PE) is a medical emergency and can be fatal. Historical data suggest that the risk of death may be around one in three if a significant PE is not recognised and treated, whereas with prompt diagnosis and anticoagulant therapy many patients survive, and short‑term mortality in low‑risk cases can be as low as around 1–5%, though it is higher in severe, high‑risk PE. Beyond the immediate risk of death, survivors of an untreated or undiagnosed PE face severe long-term complications that can permanently damage the heart and lungs, leading to a significant reduction in quality of life and physical mobility.
What We will cover in this Article
- The mechanical impact of a clot on the pulmonary arteries
- Understanding CTEPH (Chronic Thromboembolic Pulmonary Hypertension)
- The progression to Right-Sided Heart Failure (Cor Pulmonale)
- Lung Infarction: When lung tissue dies due to lack of blood
- Clinical data on recurrence rates and long-term survival
- Common triggers that cause a PE to worsen
- Essential safety signs and identifying a medical emergency
Complication Data: Untreated PE Outcomes
The following table highlights the statistical and clinical risks associated with untreated pulmonary arterial blockages.
| Complication | Estimated Incidence (Untreated) | Primary Mechanism | Long-Term Impact |
| Sudden Death | ~25% to 30% | Massive arterial blockage | Immediate |
| CTEPH | ~2% to 4% | Unresolved, scarred clots | Permanent disability |
| Right Heart Failure | High | Increased pressure in the lungs | Chronic fatigue/Oedema |
| Lung Infarction | ~10% to 15% | Death of lung tissue | Permanent scarring |
| Recurrent PE | ~30% (within 1 year) | Unstable underlying DVT | High mortality risk |
Chronic Thromboembolic Pulmonary Hypertension (CTEPH)
One of the most serious long-term complications of an untreated PE is CTEPH. This occurs when the initial clot does not dissolve but instead becomes ‘organized’ into tough, fibrous scar tissue that permanently blocks the pulmonary arteries.
This blockage causes the blood pressure in the lungs to skyrocket. Because the heart must pump blood through these narrowed vessels, it is placed under immense strain. CTEPH is often difficult to diagnose initially because its main symptom is progressive breathlessness, which can be mistaken for asthma or general unfitness. Without treatment, CTEPH can lead to total heart failure and is one of the most debilitating outcomes of venous thromboembolism.
Right-Sided Heart Failure (Cor Pulmonale)
The right side of your heart is responsible for pumping blood through the lungs. When a PE blocks the pulmonary arteries, the right ventricle has to work much harder to overcome the resistance.
In an untreated PE, this constant ‘back-pressure’ can cause the right side of the heart to become enlarged and weakened a condition known as Cor Pulmonale. Symptoms include:
- Severe Oedema: Swelling in the legs, ankles, and abdomen as the heart fails to pull blood back effectively.
- Jugular Vein Distention: Visible bulging of the veins in the neck.
- Extreme Fatigue: The body cannot get enough oxygen-rich blood into circulation.
- Dizziness: Occurring even with minimal exertion.
Lung Infarction and Pleural Effusion
If a clot blocks a smaller, peripheral artery in the lung, the specific area of tissue supplied by that vessel may die due to a lack of oxygen. This is known as a lung infarction. While the lungs have multiple blood supplies, a large or poorly managed PE can overcome these redundancies.
The death of lung tissue is extremely painful and often leads to ‘pleuritic’ chest pain a sharp, stabbing sensation that worsens when you take a deep breath. This inflammation can also cause fluid to build up around the lungs, known as a pleural effusion, which further restricts the ability of the lungs to expand, making breathing even more difficult.
Triggers for worsening PE complications
Several triggers can cause a stable or undiagnosed PE to suddenly become a critical complication:
- Physical Exertion: Sudden high-intensity activity increases the heart’s demand for oxygen, which it cannot meet due to the blockage.
- Secondary DVT: If the underlying source of the clot in the leg is not treated, new clots can break off and travel to the lungs (recurrent PE).
- Dehydration: Thicker blood makes the existing blockage even harder for the heart to pump against.
- High Altitude Travel: Low oxygen environments can trigger a sudden drop in blood oxygen levels if the lungs are already compromised.
Differentiation: PE vs. Anxiety or Chest Infection
Misdiagnosis is a major factor in untreated PE complications. It is vital to differentiate the signs of a PE from more common conditions.
| Feature | Pulmonary Embolism (PE) | Anxiety / Panic Attack | Chest Infection (Pneumonia) |
| Onset | Usually sudden | Rapid build-up | Gradual (days) |
| Pain | Sharp, worse on deep breath | Tightness / Pressure | Dull ache / Soreness |
| Cough | May produce blood | Rare | Phlegm / Mucus |
| Heart Rate | Consistently high | High during attack | High with fever |
| Fever | Sometimes (low grade) | None | Common / High |
Conclusion
The complications of an untreated pulmonary embolism are catastrophic and often permanent. From the immediate risk of sudden death to the chronic, life-altering struggle of heart failure and CTEPH, the stakes of an undiagnosed PE are incredibly high. Early intervention with anticoagulants is the only effective way to stop the progression of these complications and give the body the chance to safely dissolve the clot before permanent damage occurs.
If you experience severe, sudden, or worsening symptoms, such as sharp chest pain, sudden shortness of breath, coughing up blood, or feeling like you might faint, call 999 immediately. This is a medical emergency.
‘Can a small PE heal on its own?’
While the body has natural enzymes to dissolve clots, a PE is too dangerous to leave to chance. Without medical intervention, the risk of a second, larger clot or long-term heart damage is too high.
‘Is the lung damage from a PE permanent?’
If a lung infarction occurs, the scarring is permanent. However, with prompt treatment, most lung tissue survives, and function can return to near-normal over time.
‘How long do I have to seek treatment for a PE?’
You must seek treatment immediately. Every minute the heart is straining against a blockage increases the risk of permanent heart muscle damage.
‘Will I always have heart problems after a PE?’
Not necessarily. If the PE is treated quickly and the clot dissolves, the heart usually returns to its normal size and function.
‘Can a PE cause a stroke?’
Usually, no. A PE blocks the arteries to the lungs. A stroke occurs when a clot blocks an artery to the brain. However, in people with a specific heart defect (PFO), a clot can move from the right to the left side and travel to the brain.
‘What is the main cause of death from PE?’
The most common cause of death is acute right heart failure, where the heart simply cannot pump against the pressure of the blockage and stops.
‘Does the cough always involve blood?’
No. Hemoptysis (coughing up blood) only occurs in about 20% to 30% of PE cases, usually when there is a lung infarction.
Authority Snapshot
This article outlines the clinical risks of untreated venous thromboembolism based on British Thoracic Society and NHS guidelines. It emphasizes the physiological progression to CTEPH and heart failure. This information is intended to highlight the critical necessity of emergency medical evaluation for suspected pulmonary embolism. Dr. Rebecca Fernandez is a UK-trained physician with an MBBS and experience in general surgery, cardiology, internal medicine, gynecology, intensive care, and emergency medicine. She has managed critically ill patients, stabilised acute trauma cases, and provided comprehensive inpatient and outpatient care. In psychiatry, Dr. Fernandez has worked with psychotic, mood, anxiety, and substance use disorders, applying evidence-based approaches such as CBT, ACT, and mindfulness-based therapies. Her skills span patient assessment, treatment planning, and the integration of digital health solutions to support mental well-being.
