Pulmonary embolism classification scheme

Associate Editors-in-Chief: Ujjwal Rastogi, MBBS [mailto:urastogi@perfuse.org]

Overview
Pulmonary embolism (PE) is classified in two different ways based upon:
 * 1) Time of appearance of symptoms & size of embolus : Acute vs '''Chronic
 * 2) Severity of the disease : Massive vs Submassive vs Low-risk (the incidence Massive, Submassive and Low-risk PE are 5%, 40% and 55% respectively).

Acute PE
Pulmonary embolism is called acute, if the embolism is
 * Based on time of appearance of symptoms:
 * Develop symptoms and signs immediately after obstruction of pulmonary vessels.
 * Based on characteristic of the embolus:
 * Situated centrally within the vascular lumen
 * Occludes a vessel
 * It also causes distention of the involved vessel.

Acute PE can be further classified as massive pulmonary embolism, submassive pulmonary embolism or low-risk pulmonary embolism.

Chronic PE
Chronic pulmonary embolism is a consequence of incomplete resolution of pulmonary embolism. It can be characterized:
 * Based on time of appearance of symptoms:
 * Develop slowly progressive dyspnea over a period of years due to pulmonary hypertension.


 * Based on characteristic of the embolus:
 * Embolus is eccentric and contiguous with the vessel wall
 * Embolus reducing the arterial diameter by ≥50%
 * Evidence of recanalization within the thrombus
 * Presence of an arterial web

Massive PE
In the past, massive pulmonary embolism has been defined on the basis of angiographic burden of emboli by using the Miller Index. This is a retrospective diagnosis based upon the pulmonary angiogram that does not inform prospective decisions.

Recently the American Heart Association has proposed the following definition for massive PE: Acute pulmonary embolism with sustained hypotension (systolic blood pressure <90 mm Hg for at least 15 minutes or requiring inotropic support, not due to a cause other than PE, such as arrhythmia, hypovolemia, sepsis, or left ventricular [LV] dysfunction), pulselessness, or persistent profound bradycardia (heart rate <40 bpm with signs or symptoms of shock).

Submassive PE
The American Heart Association has proposed the following definition for submassive PE: Acute PE without systemic hypotension (systolic blood pressure ≥90 mm Hg) but with either RV dysfunction or myocardial necrosis.

Submassive PE patient population has the following characteristics:
 * Significantly higher rate of in-hospital complications.
 * Have potential for long-term pulmonary hypertension and cardiopulmonary disease.

These patient, though hemodynamic stable and may initially appear to be clinically stable, but patient can undergo a cycle of progressive RV failure. Thus watchful waiting of such patients could lead to irreversible damage and death.

Low-risk PE
The American Heart Association has proposed the following definition for Low-risk PE: Acute PE and the absence of the clinical markers of adverse prognosis that define massive or submassive PE.

Saddle PE
A saddle PE is one that lodges at the bifurcation of the main pulmonary artery into the right and left pulmonary arteries. Most of the saddle PE are submassive.