Pathophysiology and Hemodynamic Impact
Obstruction of the pulmonary arterial bed disrupts both circulation and gas exchange simultaneously. The clinical severity of the condition depends on the thrombus burden. For pulmonary artery pressure to rise significantly, the embolus must occlude at least 30–50% of the vessels. The situation is exacerbated by concomitant reflex vasoconstriction.
The sharp increase in pulmonary vascular resistance forces the right ventricle (RV) to work against an excessive load, leading to its dilatation. Acute right ventricular failure is the primary cause of death in patients with massive obstruction. Meanwhile, the viability of the lung tissue itself is usually preserved thanks to collateral blood supply from the bronchial arteries. Classic pulmonary infarction with coagulation necrosis forms rarely and, as a rule, against the background of pre-existing venous congestion.
Probability Assessment and Screening (D-dimer)
Routine bedside tests, such as ECG or arterial blood gas analysis, are unable to confirm the diagnosis; they are useful only to rule out other emergencies (such as myocardial infarction).
The diagnostic algorithm begins with the assessment of clinical probability using scoring systems (most commonly the Wells score). If the probability is low or intermediate, the blood level of D-dimer is measured.
- A negative test reliably rules out pulmonary embolism. Further investigations are unnecessary.
- A positive test is not a 100% confirmation, as this marker elevates in inflammation, trauma, or pregnancy.
- To improve diagnostic accuracy in patients over 50 years of age, an age-adjusted cutoff is applied: the threshold value is calculated using the formula age × 10 µg/L.
Radiography and Ultrasound: Baseline Modalities
Standard chest radiography is performed primarily to look for alternative causes of dyspnea (pneumothorax, pleurisy). In 40% of patients with pulmonary embolism, the radiographs are completely normal. Specific radiographic signs are rare:
- Hampton's hump (Hampton hump) is a wedge-shaped pleural-based opacity indicating an infarction zone.
- Westermark's sign (Westermark sign) is localized hypertranslucency due to reduced blood flow (oligemia).
- Knuckle sign is enlargement of the central pulmonary artery with a sharp cutoff of the distal vessels.
Compression ultrasound of the lower extremity veins (CUS) plays a crucial role. If a patient with dyspnea is found to have deep vein thrombosis, treatment is initiated immediately without waiting for chest imaging. However, clear leg veins do not rule out the presence of emboli in the chest.
Echocardiography is used only in patients with cardiorespiratory instability (for bedside assessment of RV function).
CT Angiography and Scintigraphy
Today, computed tomography pulmonary angiography (CTPA) is the standard and modality of choice. Its sensitivity reaches 83–100%. CTPA not only visualizes thrombi but also assesses prognosis: if the ratio of the RV diameter to the left ventricular diameter exceeds 1.0, the risk of early mortality increases significantly.
An alternative method is ventilation-perfusion scintigraphy (V/Q scan). It is indicated when CT is contraindicated (iodine allergy, renal failure). A radiopharmaceutical is administered intravenously, and if the scan reveals a perfusion defect in the presence of normal ventilation and a clear chest radiograph (a so-called mismatch or mismatch), the diagnosis is considered confirmed with a probability greater than 95%.
Radiological signs of PE are rare but easy to remember: Hampton = Hump (wedge) at the pleura, Westermark = Wind (radiolucent field without vessels), Knuckle = Knotted/enlarged root.
Class and exam questions
Does the classic clinical triad occur in PE?
Sudden chest pain, dyspnea, and hemoptysis combined are observed in only a small minority of patients. Non-specific symptoms are much more common: isolated dyspnea or tachypnea.
Is traditional invasive angiography still used?
The historical "gold standard" is rarely used today due to its invasiveness. It is resorted to only if CT is unavailable, uninformative, or if catheter-directed thrombolysis is planned.
What should be done if CT reveals isolated small subsegmental emboli?
This is a clinical dilemma. The question of whether the risk from such small thrombs outweighs the bleeding risk from therapy remains open. Treatment is usually prescribed in the presence of reduced cardiopulmonary reserve or concurrent venous thrombosis.
What else to study on this topic
- Criteria for assessing clinical probability using the Wells score
- Pathogenesis and stages of pulmonary infarction formation
- Specifics of applying age-adjusted cutoffs for D-dimer levels
- Radiopharmaceuticals for V/Q scintigraphy and interpretation of indeterminate results
- Low-dose CT pulmonary angiography protocols
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