Thrombolysis in Intermediate-Risk Pulmonary Embolism: Who Should Receive Early Reperfusion?

Introduction

The central controversy in intermediate-risk pulmonary embolism is not whether thrombolysis can reduce thrombus burden or right ventricular strain. Multiple trials have demonstrated rapid physiologic and imaging effects.[3,5–9]

The clinically important question is subtler. Does intervening before overt cardiopulmonary failure prevent enough meaningful deterioration to justify exposing patients, who might otherwise recover with anticoagulation alone, to hemorrhagic and procedural risk?[1,3]

For more than a decade, PEITHO defined this dilemma. Systemic tenecteplase reduced hemodynamic decompensation but substantially increased major extracranial bleeding and stroke, without demonstrating a statistically significant mortality benefit.[3] During the same period, catheter-based therapies expanded largely on the strength of improved right ventricular-to-left ventricular diameter ratios, pulmonary artery pressures, or thrombus burden measurements, rather than definitive randomized clinical-outcome advantages over anticoagulation.[5–9]

The evidence landscape changed in 2026.

The new AHA/ACC multisociety guideline introduced a more granular acute pulmonary embolism severity classification that separates stable Category C disease from incipient cardiopulmonary failure in Category D and established cardiopulmonary failure in Category E.[1] Soon afterward, HI-PEITHO provided randomized evidence that ultrasound-facilitated catheter-directed fibrinolysis can reduce early adverse clinical events in a carefully selected subset of patients with intermediate-risk pulmonary embolism and additional cardiorespiratory distress.[10]

The implication here is not that every intermediate-risk pulmonary embolism should undergo intervention. Rather, the term “intermediate-risk” is no longer sufficiently precise by itself to determine whether anticoagulation alone is the best initial strategy.

Why Risk Stratification Matters

Patients conventionally grouped together as having intermediate-risk pulmonary embolism can follow substantially different clinical trajectories.[1,2]

Think about it this way. A patient with an abnormal biomarker but otherwise preserved physiology is clinically different from a patient with right ventricular dilation, myocardial injury, tachycardia, borderline systemic pressure, and tachypnea. Treating them identically ignores that distinction.

The 2026 guideline reflects this heterogeneity. It recommends hospitalization for symptomatic patients in Categories C through E and multidisciplinary pulmonary embolism response team (PERT) assessment for patients in those categories who are at increased risk of adverse outcomes.[1] For Category C3 pulmonary embolism, a mean arterial pressure below 80 mm Hg may help identify patients who could require escalation of therapy.[1] Category D moves beyond biomarker and imaging abnormalities toward incipient cardiopulmonary failure, including transient hemodynamic instability or evidence of impaired perfusion.[1]

The therapeutic question, therefore, should not be reduced to whether CT imaging shows a large embolus. The more relevant issue is whether pulmonary vascular obstruction is producing a physiologic trajectory in which anticoagulation alone may not adequately protect the patient from early deterioration.

From Intermediate-Risk PE to the 2026 AHA/ACC Categories

The 2019 European Society of Cardiology framework separates pulmonary embolism into low-, intermediate-low-, intermediate-high-, and high-risk categories.[2] Intermediate-high-risk disease generally requires an elevated clinical severity score plus both right ventricular dysfunction and elevated cardiac biomarkers.[2]

The 2026 AHA/ACC framework takes a different approach, categorizing acute pulmonary embolism from A through E according to symptoms, clinical severity, right ventricular findings, biomarkers, hemodynamic abnormalities, hypoperfusion, and cardiopulmonary failure.[1]

Clinically Relevant Categories

Category	Clinical Phenotype	Reperfusion Implication
C2	Elevated clinical severity with either an RV abnormality or abnormal biomarker.[1]	Systemic thrombolysis should not be used over anticoagulation alone; the benefit of catheter-directed thrombolysis remains unclear.[1]
C3	Elevated clinical severity with both RV abnormality and abnormal biomarker.[1]	Systemic thrombolysis is uncertain; the benefit of catheter-directed thrombolysis over anticoagulation was considered unclear in the guideline evidence review.[1]
D1–D2	Incipient cardiopulmonary failure with important hemodynamic or perfusion abnormalities.[1]	Systemic thrombolysis, catheter-directed thrombolysis, and mechanical thrombectomy may be considered when advanced treatment is being contemplated.[1]
E1	Cardiopulmonary failure with persistent hypotension and cardiogenic shock.[1]	Advanced reperfusion therapies are reasonable when clinically appropriate.[1]

The guideline classifies systemic thrombolysis in Categories A1–C2 as Class 3: Harm, because increased major bleeding and intracranial hemorrhage outweigh the expected benefit.[1] For Category C3, systemic thrombolysis carries a Class 2b designation, with benefit considered uncertain when advanced therapy is being contemplated.[1] For Categories D1–D2 with acceptable bleeding risk, systemic thrombolysis may be considered to prevent further clinical deterioration.[1]

Catheter-directed thrombolysis likewise may be considered in D1–D2, whereas its benefit over anticoagulation in Categories C2–C3 was considered unclear by the guideline evidence review.[1]

What PEITHO Established About Systemic Thrombolysis

PEITHO randomized 1,006 normotensive patients with acute pulmonary embolism, right ventricular dysfunction, and positive cardiac troponin testing to tenecteplase plus heparin or placebo plus heparin.[3]

The primary composite endpoint of death or hemodynamic decompensation within 7 days occurred in 2.6% of patients receiving tenecteplase versus 5.6% receiving placebo, an odds ratio of 0.44.[3] This reduction in deterioration, however, came with substantial hemorrhagic toxicity. Major extracranial bleeding occurred in 6.3% of tenecteplase-treated patients compared with 1.2% of controls.[3] Stroke occurred in 2.4% versus 0.2%, respectively, with most strokes in the tenecteplase group being hemorrhagic.[3] Mortality was not notably reduced at either 7 or 30 days.[3]

PEITHO therefore established a clinically important distinction: systemic fibrinolysis can prevent hemodynamic deterioration without necessarily producing a favorable overall benefit-harm balance when used routinely in hemodynamically stable intermediate-risk pulmonary embolism.

Anticoagulation With Rescue Reperfusion Remains a Valid Strategy

The PEITHO experience also supports an anticoagulation-first strategy combined with close monitoring and escalation when deterioration occurs.[1,3] This does not mean that intermediate-high-risk pulmonary embolism can be treated with anticoagulation and subsequently forgotten.

The 2026 guideline emphasizes that patients at elevated risk of deterioration require hospitalization, appropriate monitoring, and reassessment of hemodynamics and perfusion.[1] A patient initially categorized as C3 who develops transient hypotension, impaired perfusion, worsening organ function, or other features of Category D no longer presents the same therapeutic problem encountered at admission.[1]

The practical success of an anticoagulation-first strategy depends on recognizing deterioration early enough for rescue therapy to remain effective.

Long-Term Outcomes After Systemic Thrombolysis

One rationale for early thrombolysis has been the hope that rapid reperfusion might protect the right ventricle and reduce long-term dyspnea, pulmonary hypertension, or post-pulmonary embolism functional limitation.

Long-term PEITHO follow-up did not demonstrate that advantage.[4] At a median follow-up of 37.8 months, mortality was 20.3% after tenecteplase and 18.0% after placebo, without a noteworthy difference.[4] Persistent dyspnea or functional limitation occurred in 36.0% versus 30.1%, respectively.[4] Residual pulmonary hypertension or right ventricular dysfunction did not differ markedly between treatment groups, and confirmed chronic thromboembolic pulmonary hypertension occurred in 2.1% versus 3.2%.[4]

These findings do not support routine systemic thrombolysis in intermediate-risk pulmonary embolism for the purpose of preventing long-term symptoms or chronic right ventricular abnormalities.[4]

Could Reduced-Dose Systemic Thrombolysis Improve the Tradeoff?

The 2026 guideline states that a lower systemic thrombolytic dose may be considered when systemic thrombolysis is being administered, with the goal of reducing bleeding risk.[1] However, definitive evidence establishing the clinical benefit-risk profile of reduced-dose systemic fibrinolysis remains incomplete.

PEITHO-3 is a randomized, placebo-controlled Phase 3 trial evaluating reduced-dose alteplase plus anticoagulation in intermediate-high-risk pulmonary embolism.[11] As of the ClinicalTrials.gov update posted July 1, 2026, PEITHO-3 was active but not recruiting, with actual primary completion on April 13, 2026, and no results posted.[11] The current registry lists an estimated enrollment of 800 patients.[11]

Until outcome data are available, reduced-dose systemic fibrinolysis should not be described as a proven solution to the bleeding liability demonstrated with full-dose systemic thrombolysis.

Catheter-Directed Fibrinolysis Before HI-PEITHO

The rationale for catheter-directed fibrinolysis is straightforward: deliver a smaller amount of fibrinolytic drug directly into the pulmonary arterial thrombus while attempting to achieve rapid reperfusion.[5–9] Before HI-PEITHO, however, much of the supporting evidence centered on surrogate outcomes.

ULTIMA

ULTIMA randomized 59 patients with intermediate-risk pulmonary embolism and an RV/LV ratio of at least 1.0 to ultrasound-assisted catheter-directed thrombolysis plus unfractionated heparin or unfractionated heparin alone.[5] Patients in the catheter group received 10–20 mg of recombinant tissue plasminogen activator over 15 hours.[5]

The mean RV/LV ratio decreased by 0.30 in the catheter group compared with 0.03 in the anticoagulation group at 24 hours.[5] No major bleeding occurred through 90 days.[5] ULTIMA demonstrated rapid reversal of right ventricular dilation but was too small and too dependent on an imaging endpoint to establish a mortality or clinical-deterioration benefit.

SEATTLE II

SEATTLE II was a prospective single-arm study of 150 patients with massive or submassive pulmonary embolism treated with a total alteplase dose of 24 mg through ultrasound-facilitated catheters.[6] Mean RV/LV ratio decreased from 1.55 to 1.13 at 48 hours, and pulmonary artery systolic pressure and angiographic thrombus burden also decreased.[6] One GUSTO-defined severe bleeding event occurred, and 16 moderate bleeding events occurred in 15 patients; no intracranial hemorrhage was reported.[6]

Because SEATTLE II lacked an anticoagulation-only comparator, it could not determine whether catheter-directed treatment improved clinical outcomes compared with anticoagulation alone.

OPTALYSE PE

OPTALYSE PE randomized 101 patients among four shorter-duration ultrasound-facilitated thrombolysis regimens using 4–12 mg alteplase per lung over 2–6 hours.[7] All regimens produced remarkable reductions in RV/LV ratio compared with baseline.[7] Four major bleeding events occurred, and two intracranial hemorrhages were reported, one of which was attributed to catheter-delivered alteplase.[7]

The trial established that shorter and lower-dose regimens can produce measurable right ventricular improvement, but it contained no anticoagulation-only control group.[7]

CANARY

CANARY provided another randomized comparison of catheter-directed treatment against anticoagulation alone.[8] Ninety-four patients with intermediate-high-risk pulmonary embolism were randomized to conventional catheter-directed thrombolysis plus anticoagulation or anticoagulation alone.[8]

The trial was terminated prematurely because of the COVID-19 pandemic and was underpowered.[8] Its primary endpoint, the proportion of patients with an RV/LV ratio above 0.9 at 3 months, was not significantly different between groups: 4.3% with catheter-directed therapy versus 12.8% with anticoagulation alone.[8] Other imaging measures suggested improved right ventricular recovery, but these findings remained hypothesis-generating.[8]

Does Ultrasound Facilitation Add Benefit?

SUNSET sPE randomized 81 analyzed patients to ultrasound-assisted or standard catheter-directed thrombolysis using similar alteplase doses and infusion durations.[9] Pulmonary arterial thrombus reduction was similar between groups.[9] Major bleeding occurred in two patients, both assigned to ultrasound-assisted treatment.[9] SUNSET therefore does not support assuming that the ultrasound component itself is superior to standard catheter-directed fibrinolysis.[9]

HI-PEITHO Changes the Evidence Base

HI-PEITHO addressed a central limitation of the earlier catheter-directed literature by randomizing patients against anticoagulation alone and using a clinically adjudicated primary outcome rather than an isolated imaging endpoint.[10]

The intention-to-treat population included 544 patients: 273 assigned to ultrasound-facilitated catheter-directed fibrinolysis plus anticoagulation and 271 assigned to anticoagulation alone.[10] Patients had an RV/LV end-diastolic diameter ratio of at least 1.0 and elevated troponin.[10]

Importantly, they also had to demonstrate at least two indicators of cardiorespiratory distress:

• Systolic blood pressure at or below 110 mm Hg
• Heart rate at or above 100 beats/min
• Respiratory rate above 20 breaths/min[10]

These enrollment criteria are central to interpretation. HI-PEITHO was not a trial of every normotensive patient with incidental CT evidence of right ventricular enlargement.

Primary Outcome

The 7-day composite of pulmonary embolism-related death, cardiorespiratory decompensation or collapse, or symptomatic recurrent pulmonary embolism occurred in 4.0% of the catheter-directed fibrinolysis group versus 10.3% of the anticoagulation-alone group.[10] The relative risk was 0.39 (95% CI, 0.20–0.77; P = 0.005).[10] The treatment effect was driven primarily by reduced cardiorespiratory decompensation or collapse.[10]

Bleeding

Major bleeding within 7 days occurred in 4.1% of the catheter-directed group and 2.2% of the anticoagulation group (P = 0.32).[10] At 30 days, major bleeding occurred in 4.1% and 3.0%, respectively (P = 0.64).[10] No intracranial hemorrhage occurred.[10]

What HI-PEITHO Demonstrates

HI-PEITHO provides randomized evidence that ultrasound-facilitated catheter-directed fibrinolysis can reduce a clinically meaningful composite of early adverse outcomes in selected patients with intermediate-risk pulmonary embolism and additional cardiorespiratory distress.[10]

What HI-PEITHO Does Not Demonstrate

It is equally important to recognize the trial’s boundaries. HI-PEITHO does not establish a mortality benefit.[10] It does not establish benefit for all patients with intermediate-risk pulmonary embolism.[10] It does not establish superiority of ultrasound-facilitated catheter delivery over conventional catheter-directed fibrinolysis.[9,10] It does not establish superiority over mechanical thrombectomy.[10,12] And it has not yet established improved long-term exercise capacity, quality of life, prevention of post-PE syndrome, or prevention of chronic thromboembolic disease.[10]

HI-PEITHO and the 2026 Guideline: Timing Matters

The 2026 AHA/ACC guideline was published before HI-PEITHO became available.[1,10] Its systematic evidence review therefore did not incorporate the randomized clinical-outcome results subsequently reported in HI-PEITHO.[1,10]

This sequence matters when interpreting the guideline’s conclusion that catheter-directed thrombolysis has unclear benefit over anticoagulation in Categories C2–C3.[1] HI-PEITHO narrows that evidence gap for a selected higher-risk population. It does not invalidate the guideline or justify applying catheter-directed therapy to every Category C3 patient. Instead, the new evidence argues for more precise identification of the subset whose physiology resembles the HI-PEITHO population.

Who Most Closely Resembles the HI-PEITHO Population?

The randomized HI-PEITHO evidence applies most directly to patients meeting a combination of imaging, biomarker, and clinical-severity criteria.[10] Required features included:

• RV/LV ratio of at least 1.0
• Elevated troponin
• At least two of three indicators: systolic pressure at or below 110 mm Hg, heart rate at or above 100 beats/min, or respiratory rate above 20 breaths/min[10]

This differs substantially from treating isolated RV enlargement on CT as a sufficient indication for catheter intervention.

The 2026 AHA/ACC classification independently emphasizes moving beyond imaging and biomarker abnormalities toward hemodynamic and perfusion assessment.[1] In Category C3, a mean arterial pressure below 80 mm Hg may help identify patients who could require escalation.[1] Features of impaired perfusion, including elevated lactate, acute kidney injury, reduced urine output, altered mental status, reduced cardiac index, or other shock markers, become particularly relevant when assessing progression toward Category D physiology.[1]

Practical Phenotype-Based Approach

Category C2

Systemic thrombolysis should not be used over anticoagulation alone because the guideline classifies this strategy as harmful.[1] The benefit of catheter-directed thrombolysis or mechanical thrombectomy over anticoagulation remains unclear.[1]

Category C3 Without Additional Physiologic Deterioration

Hospitalization, therapeutic anticoagulation, and close monitoring are appropriate.[1] Routine systemic thrombolysis is not supported because its benefit remains uncertain and the bleeding hazard demonstrated in PEITHO is substantial.[1,3] An RV abnormality plus elevated troponin should not automatically trigger catheter intervention.

Category C3 With a HI-PEITHO-Like Phenotype

The evidence for considering early catheter-directed fibrinolysis is stronger when the patient has RV dysfunction, myocardial injury, and multiple manifestations of cardiorespiratory stress similar to the HI-PEITHO inclusion criteria.[10] In that population, HI-PEITHO demonstrated a significant reduction in the early clinical composite compared with anticoagulation alone.[10] The expected benefit should still be framed as prevention of early deterioration rather than proven improvement in survival.[10]

Progression Toward Category D

Transient hypotension, worsening perfusion, elevated lactate, acute organ dysfunction, or other evidence of incipient cardiopulmonary failure materially changes the clinical problem.[1] For Categories D1–D2, systemic thrombolysis, catheter-directed thrombolysis, and mechanical thrombectomy may each be considered when advanced therapy is appropriate.[1]

Selection should incorporate hemodynamic trajectory, bleeding risk, contraindications, procedural availability, institutional expertise, time to treatment, local PERT assessment, and remaining uncertainty regarding comparative effectiveness.

Category E

Persistent hypotension with cardiogenic shock represents cardiopulmonary failure rather than intermediate-risk pulmonary embolism.[1] Advanced reperfusion assumes substantially greater urgency in this setting.[1]

Systemic Versus Catheter-Directed Fibrinolysis

The appeal of catheter-directed fibrinolysis is the ability to administer a smaller fibrinolytic dose within the pulmonary arteries compared with conventional systemic alteplase dosing.[5-7] That does not, however, eliminate bleeding risk. Major bleeding has occurred with catheter-directed treatment, including intracranial hemorrhage in OPTALYSE PE.[7]

The 2026 guideline states that among Categories D1–E1 in whom thrombolysis is being considered, catheter-directed thrombolysis may be considered over systemic thrombolysis to reduce major bleeding risk, although superiority for clinical deterioration, long-term survival, functional capacity, or quality of life remains unclear.[1] No adequately powered randomized trial has directly established that contemporary catheter-directed low-dose fibrinolysis is superior to full-dose systemic thrombolysis for patient-centered clinical outcomes.

Evidence Comparison

Strategy	Evidence Signal	Principal Limitation
Anticoagulation with surveillance	Standard treatment for many hemodynamically stable patients.[1,2]	Higher-risk patients can deteriorate and require rescue reperfusion.[3]
Systemic thrombolysis	Reduces hemodynamic deterioration.[3]	Major bleeding and hemorrhagic stroke substantially increased in PEITHO; mortality benefit unproven.[3]
Catheter-directed fibrinolysis	HI-PEITHO reduced early clinical deterioration in a selected higher-risk population.[10]	Mortality and long-term functional benefit remain unproven.[10]
Mechanical thrombectomy	Randomized comparative evidence against catheter-directed thrombolysis is available.[12]	Definitive superiority over anticoagulation for the relevant intermediate-risk population remains unresolved.[1,12]

Mechanical Thrombectomy

Mechanical thrombectomy offers reperfusion without exposing the patient to a catheter-delivered fibrinolytic drug and can therefore be attractive when bleeding risk is a concern.[1,12] The 2026 guideline states that mechanical thrombectomy may be considered in Categories D1–D2 when advanced therapy is being considered.[1]

PEERLESS randomized 550 patients with intermediate-risk pulmonary embolism and additional risk factors to large-bore mechanical thrombectomy or catheter-directed thrombolysis.[12] Its hierarchical primary endpoint favored large-bore mechanical thrombectomy, driven largely by differences in clinical deterioration or bailout therapy and intensive care utilization.[12] Thirty-day mortality and major bleeding did not differ significantly.[12]

Because PEERLESS compared two invasive strategies rather than an invasive strategy against anticoagulation alone, it cannot establish that either intervention is superior to anticoagulation in otherwise similar patients.[12] HI-PEITHO and PEERLESS therefore answer different clinical questions.

Newly Published 2026 Pilot Evidence

A randomized pilot trial published online July 19, 2026, compared a combined catheter-interventional approach incorporating local fibrinolysis and mechanical thrombectomy with conventional guideline-directed treatment in 20 patients with intermediate-high-risk pulmonary embolism.[13] Patients were randomized 2:1.[13]

At 24 hours, the catheter-intervention group demonstrated improvements in a composite physiologic endpoint and RV/LV ratio compared with control treatment.[13] In-hospital mortality and bleeding were reported as similar between groups.[13]

The trial is notable because it was randomized and directly compared an interventional strategy with standard treatment. Its sample size of only 20 patients, single-center design, and short-term predominantly physiologic endpoints, however, make the findings hypothesis-generating rather than practice-defining.[13]

Regulatory Considerations

Alteplase

Current U.S. Activase prescribing information indicates alteplase for lysis of acute massive pulmonary embolism.[14] The label defines acute massive pulmonary embolism as acute pulmonary emboli obstructing blood flow to a lobe or multiple lung segments, or acute pulmonary emboli accompanied by unstable hemodynamics.[14] The labeled pulmonary embolism regimen is alteplase 100 mg intravenously over 2 hours.[14]

This regulatory terminology predates and does not directly map onto contemporary ESC intermediate-risk terminology or the 2026 AHA/ACC Categories A–E.[1,2,14] Consequently, hemodynamic stability alone does not establish that systemic alteplase use is outside the labeled indication, because the Activase label also includes an anatomic criterion.[14] In contrast, catheter-directed administration and the reduced local doses used in catheter-directed trials are not the labeled pulmonary embolism administration regimen.[5–10,14]

Tenecteplase

Current U.S. TNKase labeling includes acute ischemic stroke and ST-elevation myocardial infarction but does not include pulmonary embolism.[15] Tenecteplase use for pulmonary embolism, including the regimen evaluated in PEITHO, is therefore off-label in the United States.[3,15]

Safety and Bleeding Risk

Bleeding remains the principal limitation of thrombolytic therapy.

Current Activase labeling contraindicates treatment for acute myocardial infarction or pulmonary embolism in circumstances including active internal bleeding, history of recent stroke, intracranial or intraspinal surgery or serious head trauma within the preceding 3 months, intracranial conditions that increase bleeding risk, bleeding diathesis, and current severe uncontrolled hypertension.[14] Activase can cause severe and sometimes fatal internal or external bleeding, particularly at arterial or venous puncture sites.[14] Anticoagulants and platelet-inhibiting drugs can further increase bleeding risk.[14]

PEITHO illustrates why these risks materially affect the intermediate-risk decision: the reduction in hemodynamic deterioration was accompanied by substantially greater major bleeding and hemorrhagic stroke.[3] HI-PEITHO is reassuring in that no intracranial hemorrhage occurred and major bleeding did not differ significantly between study groups, but the study does not establish that catastrophic hemorrhage cannot occur with catheter-directed fibrinolysis.[10]

The treatment decision therefore requires simultaneous assessment of the probability of PE-related deterioration and the probability and consequence of treatment-related bleeding.

Pulmonary Embolism Response Teams

The 2026 guideline recommends multidisciplinary PERT assessment for patients with acute pulmonary embolism at increased risk of adverse outcomes in Categories C through E.[1] This is particularly relevant when choosing among continued anticoagulation, systemic thrombolysis, catheter-directed fibrinolysis, mechanical thrombectomy, and surgical reperfusion.

No single interventional strategy has definitively demonstrated superiority across the entire spectrum of intermediate-risk pulmonary embolism.[1,10,12] A multidisciplinary process can therefore integrate hemodynamic trajectory, bleeding risk, comorbidity, local expertise, procedural feasibility, and patient-specific considerations into a coherent treatment decision.

Should We Be Doing More?

The evidence supports better selection rather than indiscriminate escalation.

PEITHO remains a strong warning against expanding routine systemic fibrinolysis across hemodynamically stable intermediate-risk pulmonary embolism.[3] HI-PEITHO provides the strongest randomized evidence to date that catheter-directed fibrinolysis can prevent early adverse clinical events in a carefully selected group with intermediate-risk pulmonary embolism plus substantial cardiorespiratory distress.[10] These conclusions are not contradictory. They reflect different treatment strategies, fibrinolytic exposures, and patient-selection approaches.

A patient with isolated RV enlargement on imaging is not clinically equivalent to a patient with RV dysfunction, elevated troponin, tachycardia, borderline systemic pressure, and tachypnea.[1,10] The practical question is therefore evolving from whether intermediate-risk pulmonary embolism requires thrombolysis to which intermediate-risk phenotype has sufficient risk of imminent deterioration to justify early reperfusion.

Limitations of the Evidence

Several uncertainties remain.

Mortality is relatively uncommon in contemporary intermediate-risk pulmonary embolism trials, making survival advantages difficult to demonstrate.[3,10] HI-PEITHO’s positive primary result was driven primarily by prevention of cardiorespiratory decompensation or collapse rather than mortality.[10] Its enriched entry criteria limit generalizability to less severely affected intermediate-risk populations.[10] Long-term functional outcomes following early catheter-directed fibrinolysis remain incompletely established.[10]

Among the earlier trials, CANARY was prematurely terminated and underpowered.[8] ULTIMA was small and primarily evaluated right ventricular recovery.[5] SEATTLE II lacked a randomized comparator.[6] OPTALYSE compared catheter dosing regimens rather than catheter therapy against anticoagulation.[7] SUNSET does not demonstrate that ultrasound-assisted catheter delivery is superior to standard catheter-directed fibrinolysis.[9] PEERLESS did not include an anticoagulation-only arm.[12] The July 2026 randomized combined-intervention pilot included only 20 patients and cannot establish a definitive clinical advantage.[13]

Reduced-dose systemic thrombolysis also remains unresolved because PEITHO-3 has completed collection of its primary endpoint but had no results posted at the August 7, 2026, evidence cutoff.[11]

Future Directions

PEITHO-3 should provide important randomized evidence regarding whether reduced-dose systemic alteplase can preserve efficacy while reducing the bleeding liability associated with conventional systemic thrombolysis.[11] As of July 1, 2026, the study was active but not recruiting, with primary completion on April 13, 2026, and no results posted.[11]

PE-TRACT is testing catheter-directed therapy plus anticoagulation against anticoagulation alone in 500 planned patients with intermediate-risk pulmonary embolism and proximal clot with right ventricular dilation.[16] The trial incorporates functional outcomes and is estimated to complete its primary endpoint in March 2027.[16]

These studies matter because preventing an early decompensation event is not necessarily equivalent to improving long-term exercise capacity, functional status, quality of life, or survival. Future comparative studies must also determine whether observed benefit derives principally from fibrinolysis itself, local delivery, mechanical clot removal, faster right ventricular unloading, or particular combinations of these mechanisms.

Clinical Implications

Five conclusions are supported by the current evidence.

First, anticoagulation remains appropriate initial therapy for many hemodynamically stable patients with intermediate-risk pulmonary embolism.[1,2]

Second, full-dose systemic thrombolysis should not be expanded routinely across intermediate-risk pulmonary embolism.[1,3]

Third, clinicians should actively distinguish Category C3 disease from evolving Category D physiology rather than treating “intermediate-risk” as a static diagnosis.[1]

Fourth, HI-PEITHO provides randomized evidence supporting consideration of early catheter-directed fibrinolysis in carefully selected patients with RV dysfunction, myocardial injury, and additional cardiorespiratory distress.[10]

Fifth, neither right ventricular strain nor clot burden alone should automatically trigger invasive reperfusion. Patient selection, hemodynamic trajectory, bleeding risk, expected natural history, and applicability of the randomized evidence remain central.[1,10]

References

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8. Sadeghipour P, Jenab Y, Moosavi J, et al. (2022). Catheter-Directed Thrombolysis vs Anticoagulation in Patients With Acute Intermediate-High-Risk Pulmonary Embolism: The CANARY Randomized Clinical Trial. JAMA Cardiology, 7(12), 1189–1197. DOI: 10.1001/jamacardio.2022.3591. PMID: 36260302.
9. Avgerinos ED, Jaber W, Lacomis J, et al; SUNSET sPE Collaborators. (2021). Randomized Trial Comparing Standard Versus Ultrasound-Assisted Thrombolysis for Submassive Pulmonary Embolism: The SUNSET sPE Trial. JACC: Cardiovascular Interventions, 14(12), 1364–1373. DOI: 10.1016/j.jcin.2021.04.049. PMID: 34167677. Published correction: JACC Cardiovascular Interventions, 14(19), 2194. DOI: 10.1016/j.jcin.2021.07.010.
10. Rosenfield K, Klok FA, Piazza G, et al; HI-PEITHO Investigators. (2026). Ultrasound-Facilitated, Catheter-Directed Fibrinolysis for Acute Pulmonary Embolism. New England Journal of Medicine, 394(20), 1979–1990. DOI: 10.1056/NEJMoa2516567. PMID: 41910345.
11. Sanchez O, Charles-Nelson A, Ageno W, et al; PEITHO-3 Investigators. (2022). Reduced-Dose Intravenous Thrombolysis for Acute Intermediate-High-Risk Pulmonary Embolism: Rationale and Design of the Pulmonary Embolism International THrOmbolysis (PEITHO)-3 Trial. Thrombosis and Haemostasis, 122(5), 857–866. DOI: 10.1055/a-1653-4699. PMID: 34560806. ClinicalTrials.gov NCT04430569; registry status verified August 7, 2026.
12. Jaber WA, Gonsalves CF, Stortecky S, et al; PEERLESS Committees and Investigators. (2025). Large-Bore Mechanical Thrombectomy Versus Catheter-Directed Thrombolysis in the Management of Intermediate-Risk Pulmonary Embolism: Primary Results of the PEERLESS Randomized Controlled Trial. Circulation, 151(5), 260–273. DOI: 10.1161/CIRCULATIONAHA.124.072364. PMID: 39470698.
13. Shahidi P, Mentzel L, Sulimov D, et al. (2026). A Randomized Pilot Trial Comparing Combined Catheter-Interventional Treatment Versus Standard of Care in Intermediate High-Risk Pulmonary Embolism. Catheterization and Cardiovascular Interventions. Published online July 19, 2026. DOI: 10.1002/ccd.70758. PMID: 42473023.
14. Genentech, Inc. Activase (alteplase) for injection prescribing information. DailyMed. Current record updated January 20, 2026; prescribing-information revision date January 2026. Accessed August 7, 2026.
15. Genentech, Inc. TNKase (tenecteplase) for injection prescribing information. DailyMed. Current record verified August 7, 2026.
16. Sista AK, Troxel AB, Tarpey T, et al. (2025). Rationale and Design of the PE-TRACT Trial: A Multicenter Randomized Trial to Evaluate Catheter-Directed Therapy for the Treatment of Intermediate-Risk Pulmonary Embolism. American Heart Journal, 281, 112–122. DOI: 10.1016/j.ahj.2024.11.016. PMID: 39638275. ClinicalTrials.gov NCT05591118; registry status verified August 7, 2026.