Are the pulmonary arteries the vessels of interest in a pulmonary embolism?

Pulmonary Arteries in Pulmonary Embolism

Yes, the pulmonary arteries are definitively the primary vessels of interest in pulmonary embolism, as they are the site where emboli lodge and cause obstruction to blood flow. 1

Pathophysiology of Pulmonary Embolism

• Pulmonary embolism (PE) is characterized by occlusion of blood flow in the pulmonary arteries, typically due to a thrombus that travels from a vein in a lower limb 2
• The emboli travel through the venous system and right heart chambers before lodging in the pulmonary arterial system, causing obstruction 1
• Spiral CT angiography enables direct visualization of PE within the pulmonary arteries as low attenuation filling defects within the vessel, partly or completely surrounded by opacified blood 1

Diagnostic Imaging of Pulmonary Arteries

• Pulmonary angiography is considered the reference method for detecting emboli in the pulmonary arteries, with sensitivity around 98% and specificity between 95-98% 1
• Spiral CT provides excellent results for detecting emboli located in the main, lobar, and segmental pulmonary arteries, though its sensitivity is limited for subsegmental and more peripheral arteries 1
• Direct angiographic signs of PE include complete obstruction of a pulmonary vessel or filling defects within the pulmonary arteries 1

Hemodynamic Effects of Pulmonary Artery Obstruction

• Obstruction of pulmonary arteries leads to increased right ventricular (RV) afterload, which can cause RV dilatation, dysfunction, and potentially hemodynamic collapse 1
• The imbalance between oxygen supply and demand resulting from pulmonary arterial obstruction can damage cardiomyocytes and further reduce contractile forces 1
• In high-risk PE, obstruction of pulmonary arteries can lead to obstructive shock and systemic hypotension, critically impairing coronary driving pressure to the overloaded right ventricle 1

Types of Emboli in Pulmonary Arteries

• The most common cause of pulmonary arterial obstruction is thromboemboli from deep vein thrombosis 2
• Other types of emboli that can lodge in pulmonary arteries include fat emboli (associated with trauma and long bone fractures), air emboli, and intravascular foreign bodies 1
• Intravascular foreign bodies that can embolize to the pulmonary arteries include broken catheters, guidewires, vena cava filters, coils for embolization, and endovascular stent components 1

Clinical Implications

• PE is the third leading cause of cardiovascular mortality, with approximately 60,000-100,000 deaths annually in the US 2, 1
• Mortality is directly related to the degree of pulmonary arterial obstruction and subsequent right ventricular dysfunction 1
• In chronic thromboembolic pulmonary hypertension (CTEPH), persistent obstruction of pulmonary arteries leads to progressive pulmonary hypertension and right heart failure 1

Diagnostic Pitfalls

• Breathing artifacts during imaging can create pseudo-hypoattenuating areas that mimic clots in pulmonary arteries 1
• Prominent perivascular tissue may sometimes be confused with intravascular thromboembolic material in the pulmonary arteries 1
• A normal spiral CT does not rule out isolated subsegmental pulmonary arterial emboli, which can occur in 6-17% of PE cases 1

Understanding that pulmonary arteries are the vessels of interest in PE is crucial for proper diagnosis and management of this potentially fatal condition, which represents a significant cause of cardiovascular mortality.