Pulmonary Embolism — Pathophysiology & Diagnosis

What is a pulmonary embolism (PE)?

A clot obstructing pulmonary arterial blood flow, potentially causing life-threatening complications.

What pathway does a leg thrombus follow to become a PE?

Leg veins → inferior vena cava → right atrium → right ventricle → pulmonary artery.

Why can pulmonary embolism be fatal?

Obstructed pulmonary circulation impairs blood flow through the lungs.

What are the major signs and symptoms of PE?

Dyspnea, chest pain, tachycardia, hypotension, and hemoptysis; PE can also be silent.

What is the primary imaging test for PE?

CT pulmonary angiography (CTPA), using IV contrast to visualize pulmonary artery clots.

What does D-dimer indicate in suspected PE?

Possible clot breakdown, but not confirmation; negative results can help exclude PE in low/intermediate-risk patients.

What does a ventilation-perfusion (V/Q) scan compare?

Airflow and blood flow in the lungs; PE may cause ventilation without adequate perfusion.

When might a V/Q scan replace CTPA?

When CTPA is unsuitable, such as certain IV contrast contraindications.

What ABG changes may occur with PE?

Decreased PaO2 and early respiratory alkalosis from hyperventilation; normal ABGs do not exclude PE.

What ECG changes may occur with PE?

Sinus tachycardia or signs of right ventricular strain.

What is the role of a chest X-ray in suspected PE?

Helps evaluate alternative causes; cannot reliably diagnose PE.

How can leg ultrasound support suspected PE?

It may detect a DVT, supporting suspected venous thromboembolism.