How can I determine whether a patient with pulmonary embolism is low‑risk or high‑risk?

Risk Stratification of Pulmonary Embolism

The first and most critical step is to assess for haemodynamic instability at presentation—patients with cardiac arrest, obstructive shock, or persistent hypotension (systolic BP <90 mmHg or drop ≥40 mmHg lasting >15 minutes) are classified as high-risk PE and require immediate reperfusion therapy. 1

High-Risk PE (Immediate Life-Threatening)

High-risk PE is defined by the presence of haemodynamic instability at presentation, which includes any of the following 1:

• Cardiac arrest requiring cardiopulmonary resuscitation
• Obstructive shock with end-organ hypoperfusion (altered mental status, cold/clammy skin, oliguria/anuria, elevated lactate)
• Persistent hypotension: systolic BP <90 mmHg OR systolic BP drop ≥40 mmHg lasting >15 minutes (not caused by new arrhythmia, hypovolemia, or sepsis)

These patients have approximately 19% short-term mortality and require emergency bedside echocardiography or CTPA for diagnosis, immediate UFH anticoagulation with bolus, and systemic thrombolysis 1, 2, 3.

Intermediate-Risk and Low-Risk PE (Hemodynamically Stable Patients)

For all hemodynamically stable patients, you must perform further risk stratification using a combination of clinical assessment tools, right ventricular dysfunction markers, and cardiac biomarkers 1.

Step 1: Clinical Risk Assessment

Use validated clinical prediction scores:

• Pulmonary Embolism Severity Index (PESI) or simplified PESI (sPESI): These identify patients at low risk of 30-day mortality (<1%) 2, 4, 5
• sPESI = 0 indicates low-risk if combined with absence of RV dysfunction 4

The sPESI assigns 1 point each for:

• Age >80 years
• Cancer
• Chronic cardiopulmonary disease
• Heart rate ≥110 bpm
• Systolic BP <100 mmHg
• Oxygen saturation <90%

Step 2: Assess Right Ventricular Dysfunction

RV dysfunction is the key determinant separating intermediate-risk from low-risk PE 3, 6. Assess using:

• Echocardiography: Look for RV dilation, RV hypokinesis, interventricular septal flattening, tricuspid regurgitation
• CT pulmonary angiography: RV/LV diameter ratio >1.0 indicates RV dysfunction 4
• Clinical signs: Elevated jugular venous pressure, RV heave, loud P2

Step 3: Cardiac Biomarkers

Measure troponin and BNP/NT-proBNP to assess myocardial injury 6, 5:

• Elevated biomarkers indicate myocardial strain and higher risk
• Combined with RV dysfunction, this identifies intermediate-high-risk patients

Final Risk Classification Algorithm

Low-Risk PE

• sPESI = 0 AND
• No RV dysfunction on imaging AND
• Normal cardiac biomarkers
• 30-day mortality <1% 2, 4
• Management: Consider early discharge and outpatient anticoagulation 1, 5

A more stringent low-risk definition: Modified sPESI (heart rate cutoff 100 bpm instead of 110) = 0 AND CT RV/LV ratio ≤1.0 identifies patients with only 0.4% 30-day mortality 4

Intermediate-Low-Risk PE

• Hemodynamically stable BUT
• Either positive sPESI OR RV dysfunction OR elevated biomarkers (not both RV dysfunction AND biomarkers)
• Management: Hospital admission with standard anticoagulation and monitoring 1, 5

Intermediate-High-Risk PE

• Hemodynamically stable BUT
• RV dysfunction on imaging AND elevated cardiac biomarkers
• Higher risk of deterioration requiring escalation to reperfusion therapy 6, 5
• Management: Hospital admission to monitored unit, anticoagulation, close observation with contingency plan for rescue thrombolysis if deterioration occurs 1

Critical Pitfalls to Avoid

1. Do not rely solely on clinical gestalt—use validated scoring systems 1
2. Do not skip RV assessment in normotensive patients—this is essential for identifying intermediate-risk patients who may deteriorate 3, 6
3. Do not use D-dimer in high clinical probability patients—it will not safely exclude PE 1
4. Plasma lactate is emerging as a sensitive marker of circulatory failure and may help identify patients at higher risk of adverse outcomes 6
5. The combination of modified sPESI with CT-assessed RV/LV ratio has the lowest false-negative rate (0.4% 30-day mortality) for identifying truly low-risk patients 4

The ESC guidelines emphasize that risk stratification must be performed immediately after PE diagnosis to guide treatment intensity, monitoring level, and disposition decisions 1. The newer 2026 AHA/ACC guidelines introduce enhanced clinical categories for more precise severity classification 7, though the fundamental approach remains assessment of hemodynamic stability followed by evaluation of RV dysfunction and biomarkers in stable patients.