Pulmonary Embolism Diagnosis and Evaluation

Clinical protocols for detecting pulmonary clots and evaluating heart strain.

Pulmonology focuses on diagnosing and treating lung and airway conditions such as asthma, COPD, and pneumonia, as well as overall respiratory health.

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Diagnosis and Evaluation

Diagnosing a pulmonary embolism can be challenging because the symptoms are often vague. At Liv Hospital, we use proven checklists, advanced scans, and lab tests to confirm or rule out the diagnosis safely. We look for the clot, check its size and location, and see how it affects the heart. This helps us decide if a patient can be treated at home or needs more intensive care.

Clinical Probability Assessment

Before ordering tests, clinicians assess the likelihood of PE using standardized scoring systems.

Wells Criteria: The most widely used scoring system. It assigns points based on symptoms (like hemoptysis), signs (like tachycardia), risk factors (like cancer or recent surgery), and the likelihood of an alternative diagnosis. A high score indicates a high probability of PE and necessitates imaging. A low score may allow for a D-dimer test to rule out PE.
Geneva Score: This scoring system relies entirely on objective clinical variables, such as age, prior VTE, and heart rate, independent of the physician’s subjective judgment (alternative diagnosis less likely).
PERC Rule: The Pulmonary Embolism Rule-out Criteria is used in low-risk patients. If a patient meets all criteria (e.g., age <50, pulse <100, no hormone use, no surgery), no further testing is needed as the risk is negligible.

D-Dimer Testing

The D-dimer test is an important first step for patients who are at low or moderate risk.

Mechanism: D-dimer is a protein fragment produced when a blood clot dissolves in the body. It is a degradation product of cross-linked fibrin.
Interpretation: A negative D-dimer result is highly effective at ruling out pulmonary embolism in patients with low clinical probability. It has a high negative predictive value. However, a positive D-dimer is nonspecific; it can be elevated due to infection, inflammation, pregnancy, cancer, or recent surgery, not just blood clots. Therefore, a positive result requires follow-up imaging.

Computed Tomography Pulmonary Angiography (CTPA)

CTPA is the main imaging test used to diagnose pulmonary embolism.

Procedure: This test involves injecting a contrast dye into a vein and taking high-resolution CT scans of the chest. The dye highlights the pulmonary arteries, allowing radiologists to detect filling defects indicative of clots.
Advantages: It is fast, widely available, and highly accurate. It allows visualization of the main pulmonary arteries down to the subsegmental branches. It also provides information about the heart (right ventricular strain) and the lung parenchyma (infarction, pleural effusion, or other diagnoses such as pneumonia).
Considerations: It involves radiation exposure and the use of iodinated contrast, which requires caution in patients with kidney disease or contrast allergies.

Ventilation-Perfusion (V/Q) Scan

This test is another option for patients who cannot have a CTPA scan.

Procedure: It involves two parts. The ventilation scan uses an inhaled radioactive gas to show airflow in the lungs. The perfusion scan uses injected radioactive particles to show blood flow.
Interpretation: A mismatch, where an area of the lung has good airflow (ventilation) but poor blood flow (perfusion), indicates a high probability of a blood clot.
Indications: It is preferred in pregnant women (lower radiation to the breast tissue), patients with renal failure (no contrast dye), or those with severe contrast allergies.

Echocardiography

A heart ultrasound is very important for checking risk, especially in patients who are not stable.

Bedside Assessment: In patients with suspected massive PE who are too unstable for a CT scan, a bedside echocardiogram can reveal signs of right heart strain.
McConnell’s Sign: A specific finding in which the right ventricular apex moves normally while the free wall is akinetic (not moving), highly suggestive of acute PE.
Right Ventricular Dilation: Enlargement of the right ventricle and increased pressure in the pulmonary artery suggest a significant clot burden and a submassive or massive PE classification. This finding underscores the need for more aggressive therapies, such as thrombolysis.

Lower Extremity Venous Ultrasound

Because most pulmonary embolisms start in the legs, checking the leg veins is part of the diagnosis process.

Compression Ultrasonography: This test uses sound waves to visualize the deep veins of the legs. If the veins do not compress under pressure from the probe, it indicates a thrombus is present.
Utility: Finding a DVT in a patient with respiratory symptoms can sometimes be sufficient to initiate anticoagulant therapy without a CT scan, particularly if CT is contraindicated. However, a negative leg ultrasound does not rule out PE, as the entire clot may have already embolized.

Pulmonary Angiography

This test used to be the main way to diagnose pulmonary embolism, but now it is rarely used just for diagnosis.

Procedure: A catheter is threaded through the veins into the right side of the heart and pulmonary arteries to inject dye directly.
Current Role: It is mainly reserved for patients undergoing catheter-directed therapies (such as thrombolysis or embolectomy), rather than for purely diagnostic purposes, and has been primarily replaced by the non-invasive CTPA.

Cardiac Biomarkers

Blood tests for heart damage provide prognostic information.

Troponin: Elevated troponin levels indicate damage to the heart muscle cells, specifically right ventricular microinfarction caused by the strain of pumping against the blockage. High troponin levels are associated with a worse prognosis and define submassive PE.
Brain Natriuretic Peptide (BNP): Elevated BNP or NT-proBNP levels indicate that the heart muscle is being stretched due to pressure overload. Like troponin, high levels signal right ventricular strain and a higher risk.

Magnetic Resonance Imaging (MRI)

MRI is a newer tool for finding pulmonary embolism, but it is not usually the first choice.

Utility: MRI can visualize pulmonary emboli without radiation. However, technical challenges with breathing motion and lower sensitivity for small clots limit its routine use. MR angiography is sometimes used in pregnant patients or those who cannot tolerate CT contrast, but availability and scan time are determining factors in emergency settings.

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FREQUENTLY ASKED QUESTIONS

What is the gold standard test for pulmonary embolism?

Computed Tomography Pulmonary Angiography (CTPA) is currently considered the gold standard for diagnosing a pulmonary embolism due to its speed, accuracy, and ability to visualize the clots directly.

What is a D-dimer test used for?

A D-dimer test measures a substance released when clots break down; a typical result is beneficial for ruling out a pulmonary embolism in low-risk patients, avoiding the need for further imaging.

Can an echocardiogram diagnose a PE?

While an echocardiogram cannot see the clot in the lungs directly, it can show strain on the right side of the heart, which strongly supports the diagnosis in unstable patients.

Is a V/Q scan safe during pregnancy?

Yes, a V/Q scan is often preferred over CT during pregnancy because it exposes the mother’s breast tissue to less radiation, although both tests are considered relatively safe with proper protocols.

What does a Wells score tell the doctor?

The Wells score is a calculation based on your symptoms and history that tells the doctor how likely it is that you have a pulmonary embolism, guiding which test to order next.