Pathophysiology
Clinical meaning
Pulmonary embolism (PE) occurs when a thrombus, most commonly originating from deep veins of the lower extremities (DVT), embolizes to the pulmonary arterial vasculature. Virchow's triad (venous stasis, endothelial injury, hypercoagulability) underlies thrombus formation. The embolus lodges in pulmonary arteries, creating dead space ventilation (ventilated but unperfused alveoli), increasing V/Q mismatch, and causing hypoxemia. In massive PE, acute right ventricular (RV) pressure overload occurs as pulmonary vascular resistance rises abruptly, leading to RV dilation, septal bowing into the left ventricle (reducing LV filling), and obstructive shock.