Saddle Pulmonary Embolism: Definition and Treatment
A saddle pulmonary embolism is a large thrombus that straddles the bifurcation of the main pulmonary artery, causing obstruction to blood flow in both pulmonary arteries and potentially leading to hemodynamic collapse.
Definition and Pathophysiology
A saddle PE is a radiological term referring to a thrombus that lodges at the bifurcation of the main pulmonary artery, extending into both right and left pulmonary arteries. This location is particularly dangerous because:
- It obstructs blood flow to both lungs simultaneously
- It can cause rapid right ventricular failure
- It carries a high risk of hemodynamic instability and sudden death
Diagnosis
Diagnosis of saddle PE relies on:
- CT pulmonary angiography (CTPA) - the gold standard imaging test showing the characteristic "saddle" appearance of thrombus at the bifurcation
- Bedside transthoracic echocardiography - essential for immediate assessment of right ventricular function and strain 1
- D-dimer testing - useful in low/intermediate probability cases, though often bypassed in high clinical suspicion cases 2
Risk Stratification
Saddle PE is classified based on hemodynamic status:
High-risk (massive) PE:
- Presents with shock or hypotension (systolic BP <90 mmHg)
- Requires immediate aggressive intervention
Intermediate-risk (submassive) PE:
- Normotensive but with right ventricular dysfunction
- May require more aggressive treatment than standard anticoagulation
Low-risk PE:
- Normotensive with normal right ventricular function
- Can typically be managed with standard anticoagulation
Treatment Algorithm
1. Immediate Management
For high-risk (massive) PE with shock/hypotension:
For intermediate-risk PE with RV dysfunction but normal BP:
- Immediate full anticoagulation
- Close monitoring for deterioration
- Consider reperfusion therapy if clinical deterioration occurs 1
2. Anticoagulation Options
Traditional anticoagulation:
- LMWH followed by warfarin (target INR 2-3)
- Used when NOACs are contraindicated
3. Advanced Interventions (for high-risk PE or when thrombolysis fails/contraindicated)
Surgical embolectomy 1:
- Performed via median sternotomy
- Indicated when thrombolysis is contraindicated or has failed
- Requires rapid institution of cardiopulmonary bypass
Catheter-directed therapy 2, 5, 6:
- Mechanical thrombectomy and/or catheter-directed thrombolysis
- Lower risk of bleeding than systemic thrombolysis
- Increasingly used for submassive saddle PE with RV strain
Special Considerations
- Contraindications to thrombolysis include recent surgery, active bleeding, previous hemorrhagic stroke, or ischemic stroke within 6 months 1
- IVC filter placement may be considered in patients with contraindications to anticoagulation or recurrent PE despite adequate anticoagulation 1
- ECMO may be necessary in cases of refractory circulatory collapse 2
Follow-up
- Clinical evaluation 3-6 months after acute PE
- Assess for persistent symptoms, signs of recurrence, or bleeding complications
- Consider extended anticoagulation for unprovoked PE or persistent risk factors 2
- Evaluate for chronic thromboembolic pulmonary hypertension (CTEPH) in patients with persistent symptoms 1, 2
Common Pitfalls
- Delay in diagnosis - saddle PE can present with nonspecific symptoms or even be subclinical 7
- Underestimating severity - normal oxygen saturation does not rule out saddle PE 2
- Inadequate risk stratification - failure to assess for RV dysfunction can lead to suboptimal treatment decisions 8
- Premature discontinuation of anticoagulation increases risk of recurrent thrombotic events 3
The management of saddle PE requires rapid assessment, risk stratification, and appropriate intervention. While anticoagulation is the foundation of treatment for all PE patients, those with saddle PE often require more aggressive approaches due to the high risk of hemodynamic collapse.