Pulmonary Embolism

Pulmonary embolism is the acute obstruction of one or more pulmonary arteries, most often by a thrombus that has travelled from the deep veins of the legs or pelvis. It is the lung manifestation of venous thromboembolism and can range from a clinically silent event to sudden obstruction severe enough to cause acute right-ventricular failure.

Definition

Pulmonary embolism is obstruction of the pulmonary arterial circulation by embolic material, characteristically a venous thrombus, producing increased pulmonary vascular resistance, impaired gas exchange, and a variable degree of right-ventricular strain (Tapson, 2008; Konstantinides, 2020).

Scope

This topic covers pulmonary embolism as an acute pulmonary vascular obstruction: its origin in venous thrombosis, the physiologic consequences of obstructing the pulmonary arterial bed, the spectrum of severity from low-risk to high-risk presentations, and its place within venous thromboembolic disease. It is a reference account and does not provide diagnostic algorithms or treatment guidance.

Core questions

• Where do the emboli that obstruct the pulmonary arteries usually originate?
• How does acute obstruction of the pulmonary bed affect gas exchange and the right ventricle?
• What distinguishes low-risk from high-risk (haemodynamically unstable) presentations?
• How is pulmonary embolism related to deep vein thrombosis and venous thromboembolism?

Key concepts

• Venous thromboembolism and deep vein thrombosis as the source
• Acute increase in pulmonary vascular resistance
• Ventilation-perfusion mismatch and increased dead space
• Acute right-ventricular pressure overload
• Risk stratification by haemodynamic stability and right-ventricular strain
• Pre-test probability assessment

Mechanisms

Most pulmonary emboli arise from thrombi in the deep veins of the lower limbs or pelvis that dislodge and lodge in the pulmonary arteries. The obstruction abruptly raises pulmonary vascular resistance and creates regions that are ventilated but not perfused, increasing dead space and impairing gas exchange. When obstruction is extensive, the sudden rise in afterload can overwhelm the thin-walled right ventricle, producing acute right-ventricular dilatation and, in severe cases, circulatory collapse; the extent of right-ventricular strain underpins risk stratification (Tapson, 2008; Konstantinides, 2020).

Clinical relevance

Pulmonary embolism is suspected when acute breathlessness, chest pain, or unexplained haemodynamic compromise occurs, often in the setting of risk factors for venous thrombosis, and severity is judged largely by haemodynamic stability and signs of right-ventricular strain. This entry describes how the condition is conceived and stratified and is not a basis for individual diagnosis or treatment.

Epidemiology

Pulmonary embolism is a common acute cardiovascular condition and, together with deep vein thrombosis, constitutes venous thromboembolism, one of the leading vascular causes of acute morbidity; its incidence rises with age and with provoking factors such as immobilisation, surgery, and cancer (Konstantinides, 2020).

Evidence & guidelines

Contemporary definition and risk stratification of acute pulmonary embolism are summarised in the 2019 ESC guideline (Konstantinides, 2020), with foundational clinical description provided by a widely cited review (Tapson, 2008); both are cited for orientation rather than as care directives.

History

Pulmonary embolism was linked to venous thrombosis through the classical understanding of thrombus formation and embolisation, and its modern framing as one pole of venous thromboembolism, with structured risk stratification by haemodynamic status and right-ventricular strain, was consolidated in successive expert guidelines (Konstantinides, 2020).

Key figures

• Stavros Konstantinides
• Victor Tapson

Seminal works

• konstantinides-2020
• tapson-2008

Frequently asked questions

Where do most pulmonary emboli come from?

They typically originate as thrombi in the deep veins of the legs or pelvis, which dislodge and travel through the venous system to lodge in the pulmonary arteries.

Why can a large pulmonary embolism be dangerous?

Extensive obstruction of the pulmonary arteries abruptly raises the load on the right ventricle, which can fail acutely and cause circulatory collapse.