Most emboli are thought to arise from lower extremity proximal veins (iliac, femoral, and popliteal), whereas a thrombus of the distal veins (calf) resolves spontaneously ⅔ of the time [1][2][3]
Pulmonary emboli can be classified according to the level along the pulmonary arterial tree.
Epidemiology
In the US, approximately 370,000-390,000 PE’s are diagnosed annually [4][5]
Mortality
Hemodynamically stable (AHA/ACC Class A & B or ESC Low Risk) patients with a PE have a direct mortality of about 1%, however hemodynamically unstable patients mortality ranges from 25-50% [6]
For almost one quarter of PE patients, the initial clinical presentation is sudden death [7]
Clinical Features
DVT of right leg
Diagnosis of PE is challenging, with less than 10% of patients evaluated for a PE ultimately diagnosed with a PE [8]
ECG of a person with pulmonary embolism, showing sinus tachycardia of approximately 100 beats per minute, large S wave in Lead I, moderate Q wave in Lead III, inverted T wave in Lead III, and inverted T waves in leads V1 and V3.
Assessing Pretest Probability
A thorough H&P is paramount to assess probability of PE
Objective scoring systems (Wells, revised Geneva) performs similarly to experienced clinician gestalt in assessing pretest probability[9][10]
PE's can be associated with ECG changes that indicate acute pulmonary hypertension and right heart strain
Abnormal in 70% of patients with a PE, however nonspecific [20]
Sinus tachycardia
Most common arrhythmia associated with PE
Symmetric T wave inversions in the anterior leads (V1-V4)
McGinn-White S1Q3T3 pattern
Incomplete or complete right bundle branch block
ST elevations in aVR
Atrial fibrillation
Classification
Both the ESC and the AHA/ACC proposed classification of patients with acute PE into categories based on their potential risk for adverse outcomes
ESC 2019 Guidelines: Updated the 2011 AHA/ACC tool by splitting the intermediate or previously referred to as "submassive" patient group into those that present with low-risk features and those that present with high-risk features while maintaining stable hemodynamics.
ESC 2019 PE Classification
AHA/ACC 2026 Guidelines: A new, 5 tier, non-validated tool using an A-E category system with multiple subcategories is presented in a way to capture higher risk patients who may not have underlying RV dysfunction or cardiac biomarker abnormalities but appear to have a higher risk for adverse outcomes as noted in their proposed D group
AHA 2026 PE Classification
Categorization of PE patients allows for guidance in management decisions
Management
Anticoagulation
Anticoagulation is the cornerstone of PE management and should be started in the ED
If bleeding risk is very high, based on tools such as VTE Bleed or RIETE, consider discussing anticoagulation strategies with hematology, pulmonology, or PERT (if available at your institution) prior to initiating anticoagulation
80 units/kg bolus; then 18 units/kg/hr continuous infusion
5mg daily
Indication
Preferred oral treatment
All CKD stages
Preferred oral treatment
CKD Stages II-III (GFR 30-90 mL/min)
CKD Stages II-III (GFR 30-90 mL/min)
Preferred parenteral treatment
Can be used in patients undergoing advanced therapies
Can be used in patients undergoing advanced therapies
Patients with mechanical prosthetic heart valve
Patients with confirmed anti-phospholipid syndrome
Patients with mechanical prosthetic heart valve
Contraindications
Pregnancy
Breastfeeding
Child-Pugh Class C Liver Disease
CKD Stage V (GFR <15mL/min)
Pregnancy
Breastfeeding
Child-Pugh Class C Liver Disease
CKD Stage IV-V (GFR <30mL/min)
Pregnancy
Breastfeeding
Child-Pugh Class C Liver Disease
Pregnancy
Dose Adjustments
If BMI >40kg/m2, reduce dose (0.8mg/kg BID of enoxaparin)
If Stage IV or greater CKD (GFR<30 mL/min), adjust to 1mg/kg QD
Consider starting at 2.5mg PO if frail, elderly, malnourished, or with a history of liver disease
Duration
3-6 mo, if time limited risk factor (post-op, trauma, estrogen use)
6 mo to life, if idiopathic etiology or recurrent
Advanced Therapies
Systemic thrombolytics, catheter directed therapy, and less often surgical embolectomy may be considered for specific patients with acute PE, typically in categories C-E in the AHA/ACC guidelines or the intermediate-high risk/high risk in ESC guidelines
However, decisions to pursue these therapies should be made with multidisciplinary specialty input
Thrombolytic therapies are a group of IV medications that activate fibrinolysis and break up clots
In general, should only be reserved for patients in categories D/E or High risk, however some evidence suggests it may be beneficial for specific patients within category C3 [21][22][23]
Thrombolytics should NOT be used over anticoagulation due to increased risk of major bleeding and ICH in patients within categories A-C2 [24][25]
Thrombolytic dosing is debated, however current standard dosing of rt-PA (alteplase) is 100mg IV over 2hrs
Some evidence supports 25-50mg IV tPA,[26][27][28] highlighting similar efficacy and a lower bleeding risk, but no high quality trials have definitively proven this
PEITHO-3 trial currently ongoing and hopes to elucidate this question
Tenecteplase, while studied in certain trials, has not been FDA approved for PE thrombolysis, and has no head to head data comparing it with tPA [29][30]
Thrombolytics in Cardiac Arrest
For patients in cardiac arrest with a presumed PE, thrombolytics may be considered, but there is no clear benefit and a paucity of evidence [31]
Duration of CPR after lytic administration is not quantified, however best estimates are to continue high quality CPR for 30-60min after administration of thrombolytic medication
Catheter Directed Therapies
Catheter directed therapies continue to be studied for varying PE classifications with wide heterogeneity in methodology, leading to difficulty comparing treatment strategies
Generally considered for patients in categories C-E and often on a case by case basis
Mechanical thrombectomy
Catheter-directed thrombolysis
Combination of mechanical thrombectomy and catheter based thrombolytic administration
Surgical Embolectomy
Efficacy of surgical embolectomy vs anticoagulation alone has not been studied
Majority of evidence is retrospective and often for patients who have had CPR and as a salvage therapy after systemic thrombolytics
IVC filters can be used when standard anticoagulation therapy is contraindicated or when patients develop recurrent PE despite being on anticoagulation
Be cautious about intubation as the increase in intrathoracic pressure from positive pressure can worsen RV preload and precipitate cardiovascular collapse
Fluids
Small (250-500mL) fluid boluses may be used as part of resuscitation in patients who are hemodynamically unstable
Excessive IV fluids can worsen RV dilation and further compress LV, worsening hemodynamics
Vasopressors
May be used once fluids are no longer helpful
Norepinephrine is generally first line
Has a favorable SVR/PVR ratio with doses < 15 μg/min
Vasopressin is a second line agent
Consider adding once norepinephrine doses exceed 15 μg/min, as norepi at higher doses can lead to an increase in PVR
Disposition
20-30% of patients with a PE can be discharged from the ED, presuming they are able to start anticoagulation and have a stable social situation in which they are able to return for appropriate follow-up with an outpatient provider
Hestia Criteria [32] can be used to guide decision making for patients who are safe to discharge from the ED
Enoxaparin 1 mg/kg SC q12h SC — Preferred in cancer, liver disease, coagulopathy, pregnancyHeparin (UFH) 80 units/kg IV bolus, then 18 units/kg/hr continuous infusion IV drip — Short half-life; preferred if considering thrombolytics or bleeding riskRivaroxaban 15 mg PO BID x3 weeks, then 20 mg PO daily PO — Preferred if parenteral therapy to be avoidedApixaban 10 mg PO BID x1 week, then 5 mg PO BID PO
Additional Topics
PERT Teams
Pulmonary embolism response team (PERT) is a multidisciplinary group that provide real time expertise in management of patients at higher risk for adverse events in the setting of an acute PE
Often composed of emergency medicine, pulmonology, critical care, interventional radiology, vascular surgery, cardiology, as well as nursing and pharmacy
60% of all PERT activations originate in the ED and have been shown to improve overall care and reduce disposition times, as well as facilitate advanced therapies [34]
Clot in Transit
A ‘clot in transit’, a free floating blood clot discovered within the cardiac chambers either on echocardiogram or CT, is found in 2-4% of patients with PE
Patients with renal failure are at increased risk of both VTE as well as bleeding
Treatment
DOACs are preferred to VKA in Stage II-III CKD (GFR 30-89 ml/min) [37][38][39]
Patients with Stage IV, V, or on renal replacement therapy were excluded from randomized trials, but data from US Renal Data System shows apixaban is as safe and effective as warfarin in Stage IV and higher CKD[40][41]
When LMWH is used, transition to once daily dosing due to extended half-life
Morbid obesity
Patients who are obese have less lean body mass, often leading to supratherapeutic anticoagulation when using standard LMWH dosing
Evidence supports reduced dosing of LMWH to 0.8 mg/kg BID in BMI ≥40 kg/m2 with no clear increased thrombotic events, but less rate of major bleeding and lower rates of supratherapeutic events[42]
Active Cancer
Patients with cancer are at increased VTE risk
Treatment for most stable patients is preferred with a DOAC, however LMWH may be indicated if;
oral ingestion or gastrointestinal absorption is limited
Severe thrombocytopenia related to chemotherapy
Calculators
A-a O₂ Gradient
Alveolar-arterial (A-a) O₂ Gradient
Parameter
Value
Age (years)
FiO₂ (%)
PaCO₂ (mmHg)
PaO₂ (mmHg)
A-a Gradient
mmHg
Expected A-a
mmHg (age-adjusted normal)
Interpretation
Normal A-a gradient ≈ (Age/4) + 4 on room air
Elevated A-a gradient suggests: V/Q mismatch, shunt, or diffusion impairment
Normal A-a gradient + hypoxia suggests: hypoventilation or low FiO₂
Kanber GJ, et al. The alveolar-arterial oxygen gradient in young and elderly men during air and oxygen breathing. Am Rev Respir Dis. 1968;97(3):376-381. PMID 5637791.
Wells Score for PE
Wells' PE Score Calculator
Criteria
No
Yes
Points
Clinical signs and symptoms of DVT (leg swelling, pain with palpation)
1
+3.0
PE is #1 diagnosis OR equally likely
1
+3.0
Heart rate >100 bpm
1
+1.5
Immobilization (≥3 days) OR surgery in previous 4 weeks
Malignancy (treatment within 6 months or palliative)
1
+1.0
Wells' Score
points
Three-Tier Model
0–1
Low Risk — 1.3% incidence of PE. Consider D-dimer to rule out. Consider PERC rule.
2–6
Moderate Risk — 16.2% incidence of PE. Consider high-sensitivity D-dimer or CTA.
>6
High Risk — 37.5% incidence of PE. Consider CTA. D-dimer not recommended.
Two-Tier Model (Preferred by guidelines)
0–4
PE Unlikely — 12.1% incidence. Consider high-sensitivity D-dimer; if negative, stop workup.
>4
PE Likely — 37.1% incidence. Consider CTA testing.
References
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