Classification of Pulmonary Embolism Types
Pulmonary embolism is correctly classified into three main severity categories based on hemodynamic status and risk of early mortality: high-risk (massive), intermediate-risk (submassive), and low-risk PE. 1
Primary Classification System (Acute PE)
The most current and clinically relevant classification divides acute PE into three categories based on hemodynamic stability and mortality risk:
1. High-Risk (Massive) PE
This represents the most severe form with the highest early mortality risk (>15%). High-risk PE is defined by sustained hypotension (systolic blood pressure <90 mmHg for at least 15 minutes) or requiring vasopressor support, pulselessness, or persistent profound bradycardia (heart rate <40 bpm with signs of shock). 2, 1 The key distinguishing feature is hemodynamic instability not attributable to other causes such as arrhythmia, hypovolemia, or sepsis. 3
2. Intermediate-Risk (Submassive) PE
This category identifies hemodynamically stable patients who nonetheless have evidence of right ventricular dysfunction or myocardial injury, placing them at moderate risk (3-15% early mortality). 4 Intermediate-risk PE is diagnosed when at least one marker of RV dysfunction (echocardiographic RV dilatation/hypokinesis, elevated BNP/NT-proBNP, RV dilatation on CT) or myocardial injury (positive cardiac troponin) is present in a normotensive patient. 3, 4
The European Society of Cardiology initially proposed the term "submassive" for this group, recognizing that these patients have a different prognosis than those with completely normal right ventricular function. 3
3. Low-Risk PE
Low-risk PE is characterized by hemodynamic stability with all checked markers of RV dysfunction and myocardial injury being negative, conferring a <1% early mortality risk. 4 These patients may be candidates for early discharge or outpatient management.
Important Clinical Nuances
The 2025 ACR guidelines and most recent consensus statements have moved away from older anatomic classifications (based on Miller Index or clot burden) because these do not reliably predict clinical outcomes. 1, 2 The hemodynamic and risk-based approach better guides treatment decisions and prognosis.
Common Pitfall to Avoid
Do not confuse the acute PE classification with the chronic thromboembolic disease classification. The American Heart Association describes a separate four-type classification system (Types 1-4) specifically for chronic thromboembolic pulmonary hypertension (CTEPH), which is based on anatomic location and vessel wall pathology relevant to surgical endarterectomy outcomes. 2 This chronic classification is NOT used for acute PE management.
Alternative Historical Classification
Older literature sometimes references a four-type clinical classification: acute minor embolism, acute massive embolism, subacute massive embolism, and chronic thromboembolic pulmonary hypertension. 5 However, this classification has been superseded by the current three-tier risk stratification system, which better aligns with evidence-based treatment algorithms and mortality prediction.
The shift in terminology from "massive/submassive/non-massive" to "high-risk/intermediate-risk/low-risk" reflects the understanding that severity should be defined by early mortality risk rather than anatomic clot burden alone. 4