How is pulmonary embolism classified and what are the corresponding treatment approaches?

Pulmonary Embolism Classification

Pulmonary embolism is classified into three risk categories based on estimated 30-day mortality: high-risk PE (presence of shock or sustained hypotension), intermediate-risk PE (hemodynamically stable with RV dysfunction and/or elevated cardiac biomarkers), and low-risk PE (hemodynamically stable without RV dysfunction or biomarker elevation), with treatment intensity escalating accordingly. 1

Risk Stratification Framework

Initial Assessment: Hemodynamic Status

The first and most critical step is identifying hemodynamic instability, which immediately classifies patients as high-risk 1:

• High-risk PE is defined by shock or persistent arterial hypotension (systolic BP <90 mmHg or pressure drop ≥40 mmHg for >15 minutes, not caused by new arrhythmia, hypovolemia, or sepsis) 1
• This represents an immediately life-threatening emergency with early mortality rates exceeding 15% 1
• These patients require immediate reperfusion therapy (thrombolysis or embolectomy) without delay 1, 2

Secondary Stratification: Non-High-Risk PE

For hemodynamically stable patients, further classification into intermediate-risk versus low-risk categories is essential 1:

Intermediate-Risk PE is identified by the presence of:

• RV dysfunction on imaging (echocardiography or CTPA showing RV dilatation and/or hypokinesis) 1
• Elevated cardiac biomarkers (troponins or natriuretic peptides) 1
• Early mortality rates range from 3-15% in observational studies, though randomized trials show 2-3% mortality 1

The 2019 ESC guidelines further subdivide intermediate-risk into two categories 1:

• Intermediate-high risk: Both RV dysfunction AND elevated biomarkers present
• Intermediate-low risk: Either RV dysfunction OR elevated biomarkers present (but not both)

Low-Risk PE is characterized by:

• Hemodynamic stability 1
• Absence of RV dysfunction on imaging 1
• Normal cardiac biomarkers 1
• PESI class I-II or sPESI = 0 1
• Early mortality <1% 1, 2

Clinical Prediction Tools

PESI and Simplified PESI (sPESI)

The Pulmonary Embolism Severity Index should be considered for risk assessment in hemodynamically stable patients 1:

• sPESI = 0 identifies low-risk patients suitable for potential outpatient management 1, 2
• However, even with low PESI/sPESI scores, 34% of patients may have RV dysfunction on imaging 1
• Critical caveat: Patients with low PESI or sPESI = 0 but showing RV dysfunction or elevated biomarkers should be reclassified as intermediate-low risk 1

This represents an important nuance where clinical scores and imaging/biomarkers may diverge—the presence of RV dysfunction or biomarker elevation takes precedence over clinical scores alone 1.

Treatment Approaches by Risk Category

High-Risk PE Treatment

Immediate reperfusion therapy is mandatory 1, 2:

• Thrombolytic therapy is first-line unless contraindications exist 1
• Catheter-based or surgical embolectomy if thrombolysis contraindicated or failed 1, 3
• Supportive care with oxygen therapy (target SaO2 >90%) 1
• Avoid intubation if possible; use non-invasive ventilation or high-flow nasal cannula preferentially 1
• If mechanical ventilation required: use tidal volumes ~6 mL/kg lean body weight, keep plateau pressure <30 cmH2O, apply positive end-expiratory pressure cautiously as it reduces venous return and worsens RV failure 1

Intermediate-Risk PE Treatment

Anticoagulation with intensive monitoring is standard 1, 2:

• Full-dose anticoagulation (e.g., rivaroxaban 15 mg twice daily for 21 days, then 20 mg once daily) 4
• Close hemodynamic surveillance in monitored setting 1, 2
• Thrombolysis remains controversial for intermediate-risk PE—the risk-benefit ratio has been inadequately quantified 2, 5
• Consider rescue thrombolysis if clinical deterioration occurs despite anticoagulation 3
• Patients with intermediate-high risk (both RV dysfunction and elevated biomarkers) warrant more intensive monitoring than intermediate-low risk 1

Low-Risk PE Treatment

Anticoagulation alone with consideration for outpatient management 1, 2:

• Full-dose anticoagulation (e.g., rivaroxaban 15 mg twice daily for 21 days, then 20 mg once daily for treatment; 20 mg once daily for extended secondary prevention) 4
• Outpatient treatment is safe and appropriate for properly selected low-risk patients 2, 5
• Minimum 3 months anticoagulation for provoked PE; consider extended therapy for unprovoked PE or recurrent VTE 4

Common Pitfalls and Caveats

Do not rely solely on clinical scores: One-third of patients with low PESI/sPESI scores have RV dysfunction, which increases mortality risk (OR 4.19) 1. Always assess RV function and biomarkers even when clinical scores suggest low risk 1.

Recognize that PE severity exists on a continuum: The artificial separation into risk categories means individual patient risk varies within categories 1. A patient with intermediate-risk PE and severe RV dysfunction may have higher mortality risk than one with mild RV dysfunction 1.

Avoid aggressive positive pressure ventilation: Positive intrathoracic pressure reduces venous return and exacerbates RV failure in high-risk PE 1. Delay intubation whenever possible 1.

Monitor for intracranial hemorrhage with thrombolysis: The rate of intracranial hemorrhage with thrombolytic therapy can reach 3.0% 3. Screen carefully for contraindications before administering thrombolytics 3.

Consider renal function for anticoagulant dosing: Avoid rivaroxaban when CrCl <15 mL/min 4. Dose adjustments may be needed for moderate renal impairment depending on the indication 4.