Residency · Residency · Interventional Radiology

Pulmonary Embolism: Catheter-Based Interventions

PE Classification and Risk Stratification

Hemodynamic Classification

Massive PE (high-risk) presents with systemic hypotension (SBP below 90 mmHg for more than 15 minutes), requirement for vasopressors, or cardiac arrest, carrying a mortality of 25-65% without treatment and requiring immediate reperfusion therapy. Submassive PE (intermediate-risk) involves hemodynamically stable patients with evidence of RV dysfunction (RV/LV ratio greater than 0.9 on CTA or echo, RV hypokinesis, septal bowing, elevated BNP) and/or myocardial injury (elevated troponin). Intermediate-low risk patients have one marker positive, while intermediate-high risk patients have both positive, with overall mortality of 3-15%. Low-risk PE involves hemodynamically stable patients without RV dysfunction or biomarker elevation, carrying less than 1% mortality and managed with anticoagulation alone.

Risk Scores

The PESI and simplified PESI (sPESI) are validated risk stratification tools. The Bova score specifically assesses intermediate-risk PE for clinical deterioration. PERT (Pulmonary Embolism Response Team), a multidisciplinary team approach, is increasingly adopted for intermediate- and high-risk PE.

Treatment Overview by Risk Category

Low-risk PE is treated with anticoagulation alone (LMWH, DOAC, or unfractionated heparin) and patients may be candidates for outpatient treatment. For submassive PE, anticoagulation is the standard of care, with catheter-based interventions or systemic thrombolysis considered for intermediate-high risk patients, those deteriorating on anticoagulation, or those with high clot burden and impending hemodynamic compromise. For massive PE, systemic thrombolysis (alteplase 100 mg IV over 2 hours) is first-line per most guidelines, catheter-based therapy is used when systemic thrombolysis is contraindicated or has failed, and surgical embolectomy is the last resort.

Catheter-Based Therapies

Catheter-Directed Thrombolysis (CDT)

A multi-sidehole infusion catheter is placed within the pulmonary artery thrombus, and tPA is infused at 0.5-1.0 mg/hr per catheter (bilateral placement yields a total of 1-2 mg/hr). The typical total dose is 12-24 mg over 12-24 hours, which is significantly less than the systemic dose of 100 mg, reducing systemic bleeding risk. ICU monitoring is required during infusion.

Ultrasound-Assisted Catheter-Directed Thrombolysis (UACDT)

The EKOS/EkoSonic system (Boston Scientific) combines low-power ultrasound with lytic infusion. Ultrasound energy disrupts fibrin cross-links and enhances tPA penetration into the thrombus. Bilateral catheter placement is performed via bilateral femoral or single jugular approach. The SEATTLE II study protocol used 24 mg tPA over 12-24 hours (1 mg/hr per side). This approach has a large evidence base for intermediate-risk PE.

Aspiration Thrombectomy

The FlowTriever (Inari Medical) is a large-bore mechanical aspiration system using a 24 French catheter with self-expanding nitinol disks that engage and extract thrombus. No lytic agent is required, making it a single-session procedure. The FLASH study demonstrated significant RV/LV ratio reduction at 48 hours with very low bleeding rates. This device is rapidly becoming the dominant catheter-based PE treatment. The Indigo system (Penumbra), originally designed for stroke, uses continuous aspiration through the catheter tip. The EXTRACT-PE study showed significant RV/LV ratio reduction with no intracranial hemorrhage. It is a smaller bore than FlowTriever and may require multiple passes.

Rheolytic Thrombectomy

The AngioJet uses high-velocity saline jets to create a Venturi effect that fragments and aspirates thrombus, with a power pulse mode for lytic delivery. It is associated with transient bradycardia and hypotension from adenosine release from hemolyzed red cells, which can be fatal in hemodynamically unstable patients. It has largely fallen out of favor for PE compared with newer devices.

Key Trials

PEITHO Trial (2014)

This trial studied submassive PE with systemic tenecteplase versus placebo. Thrombolysis reduced hemodynamic decompensation but increased major bleeding (6.3% vs. 1.2%) and stroke (2.4% vs. 0.2%), without showing a mortality benefit. The conclusion is that systemic thrombolysis should not be routine for submassive PE but is indicated for clinical deterioration.

SEATTLE II (2015)

This single-arm study of EKOS UACDT in massive and submassive PE showed significant RV/LV ratio reduction and improvement in PA pressures. Major bleeding was 10% (mostly access-site related) with no ICH, establishing UACDT as a viable reduced-dose alternative to systemic thrombolysis.

FLASH Study (2023)

This multicenter single-arm study of FlowTriever for intermediate-risk PE showed mean RV/LV ratio reduction from 1.65 to 1.15 at 48 hours. Major bleeding was only 1.3%, significantly lower than lytic-based approaches, with no ICH. The single-session procedure requires no ICU lytic infusion.

EXTRACT-PE (2021)

Indigo aspiration thrombectomy for submassive PE reduced RV/LV ratio from 1.47 to 1.04 at 48 hours, with 1.7% major bleeding and no ICH.

HI-PEITHO Trial (2024)

This was the first RCT of UACDT versus anticoagulation alone for intermediate-high risk PE. UACDT reduced the composite endpoint of death, hemodynamic decompensation, or clinical worsening without increasing major bleeding. This is the first RCT to demonstrate benefit of catheter-based therapy in submassive PE.

PERT (Pulmonary Embolism Response Team)

PERT is a multidisciplinary team including IR, pulmonary/critical care, cardiology, hematology, and cardiac surgery. It is activated for intermediate- and high-risk PE, provides rapid consensus on treatment strategy, improves outcomes and reduces time to treatment, and is increasingly standard at major academic centers.

Procedural Considerations

Access

Common femoral vein access (unilateral or bilateral depending on device) is standard. Internal jugular vein access is an alternative for EKOS catheter placement. Right heart catheterization is performed to measure PA pressures before and after intervention.

Technique

CT pulmonary angiography guides catheter placement. The catheter is advanced through the right heart into the pulmonary arteries. For CDT/EKOS, infusion catheters are placed within the clot in bilateral PAs. For FlowTriever, the device is positioned in the PA with the most clot burden for aspiration and extraction. Hemodynamics are monitored throughout due to risk of arrhythmia and RV outflow tract irritation.

Periprocedural Anticoagulation

Systemic heparin is initiated before the procedure unless the patient has massive PE with imminent arrest. Anticoagulation is continued throughout and transitioned to a DOAC or warfarin after the procedure.

<image>Flowchart for the management of acute pulmonary embolism based on risk stratification. Starting with CTA confirming PE, branching into massive (hemodynamic instability), submassive (RV dysfunction and/or elevated troponin), and low-risk categories. Massive PE branches to systemic thrombolysis as first-line, with catheter-based therapy and surgical embolectomy as alternatives. Submassive PE branches to anticoagulation with PERT consultation, with catheter-based therapy considered for intermediate-high risk or deterioration. Low-risk PE leads to anticoagulation alone with possible outpatient management. Decision nodes include contraindications to systemic lysis, PERT recommendation, and clinical deterioration triggers.</image>

<image>Illustration of catheter-based PE treatment devices. Four panels: (1) EKOS ultrasound-assisted catheter with bilateral placement in the pulmonary arteries, showing ultrasound transducers along the infusion zone and tPA infusing through sideholes, with a magnified inset of the ultrasound waves disrupting fibrin; (2) FlowTriever system showing the large-bore aspiration catheter in the pulmonary artery with self-expanding nitinol disks engaging the thrombus and being retracted into the aspiration guide catheter; (3) Indigo aspiration system with continuous aspiration through the catheter tip and a separator wire advancing through the thrombus; (4) Before and after pulmonary angiograms showing a large saddle embolus in the main pulmonary artery pre-treatment and restored bilateral PA flow post-aspiration thrombectomy.</image>

<image>CT pulmonary angiography demonstrating submassive PE with RV strain. Two panels: (1) Axial CTA showing a large saddle embolus straddling the main pulmonary artery bifurcation with extension into bilateral lobar arteries; (2) Four-chamber view (axial CTA at the cardiac level) showing RV dilation with RV/LV ratio >1.0, interventricular septal bowing toward the LV, and contrast reflux into the hepatic veins indicating RV failure. Measurements of RV and LV diameters are annotated with the calculated ratio.</image>

Clinical Pearls

Risk stratification drives treatment: low-risk PE receives anticoagulation, massive PE needs immediate reperfusion, and the controversy centers on submassive PE. Catheter-based therapies use significantly less tPA (12-24 mg) than systemic thrombolysis (100 mg), theoretically reducing bleeding risk. FlowTriever and Indigo aspiration devices avoid lytic agents entirely, offering single-session treatment, no ICU infusion, and very low bleeding rates. PERT activation is critical for intermediate- and high-risk PE because multidisciplinary input improves decision-making. HI-PEITHO is the first RCT showing benefit of catheter-based therapy in submassive PE and will shape future guidelines. PA pressures should always be measured before and after intervention to document hemodynamic improvement. The AngioJet should be used with extreme caution in PE due to bradycardia and hypotension risk.

References

• Meyer G et al. Fibrinolysis for patients with intermediate-risk pulmonary embolism (PEITHO). N Engl J Med 2014
• Piazza G et al. A prospective, single-arm, multicenter trial of UACDT for acute massive and submassive PE (SEATTLE II). JACC Cardiovasc Interv 2015
• Tu T et al. FlowTriever for acute massive and submassive PE (FLASH). Circulation 2023
• Defined by the ESC/ERS Guidelines on Acute Pulmonary Embolism 2019
• Defined by the AHA Scientific Statement on Catheter-Based Therapy for PE 2019
• Kucher N et al. Randomized trial of UACDT for intermediate-high risk PE (HI-PEITHO). Lancet 2024

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