Introduction
Pulmonary thromboembolism is occlusion of the pulmonary arterial tree by thromboemboli. It is the most common and most fatal form of venous thromboembolism and occurs more in hospitalised or bed-ridden patients. The thrombus comes from peripheral vessels or the right atrium; the majority arise from deep veins of the lower extremities, and the most fatal ones from the iliofemoral veins.
Conditions favouring its development
- Stasis (heart failure, chronic venous insufficiency)
- Injury (trauma, surgery, childbirth)
- Hormonal imbalance (oral contraceptive usage)
- Advanced age
- Immobilization (paralysis, bed rest)
- Sickle cell disease
Pathogenesis
- Thrombi detach from their sites of origin (e.g. DVT); the thromboembolus flows through venous drainage into large veins (vena cava), the right side of the heart and the pulmonary artery.
- A large thrombus is impacted at the bifurcation of the main pulmonary artery (saddle embolus) or found in the right ventricle.
- More commonly, a large embolus is fragmented into multiple smaller ones, which lodge in different places of the pulmonary tree depending on size.
- Pulmonary edema and pulmonary hypertension (to counteract the permeability edema) can follow, and cor pulmonale (right heart failure) develops because the right ventricle overworks.
Paradoxical embolism
An embolus may pass from the right side of the heart into the left through an atrial or ventricular septal defect.