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.
Diagnosis & workup
Diagnostics & workup: - Apply Wells criteria to stratify pre-test probability (low, moderate, high) - D-dimer for low-probability patients (high negative predictive value) - CT pulmonary angiography (CTPA) — gold standard confirmatory imaging - RV strain markers: elevated troponin and BNP - ECG findings: sinus tachycardia (most common), S1Q3T3, right axis deviation, new RBBB - ABG: respiratory alkalosis with hypoxemia and elevated A-a gradient - Echocardiography for hemodynamically unstable patients (RV dilation, McConnell sign)