17. Massive & Submassive PE — Reperfusion Therapy Decision (HI-PEITHO Update)

Quick Recap

Cross-cutting protocol — companion to the Pulmonary Embolism protocol (Respiratory System), addressing the specific reperfusion-therapy decision (systemic thrombolysis vs. catheter-directed therapy vs. anticoagulation alone) across the PE risk spectrum. ⚠️ This protocol incorporates the HI-PEITHO trial, presented as a Late-Breaking Clinical Trial at ACC.26 (March 2026) and simultaneously published in NEJM — genuinely new, practice-changing evidence that postdates typical knowledge cutoffs and represents the first large RCT demonstrating a clinical-outcome advantage for catheter-directed therapy over anticoagulation alone in intermediate-risk PE.

1. Definition

PE risk stratification (per current ESC/AHA frameworks): high-risk (massive) — PE with hemodynamic instability/shock; intermediate-risk (submassive) — normotensive PE with right ventricular (RV) dysfunction and/or elevated cardiac biomarkers, further stratified into intermediate-low-risk and intermediate-high-risk based on the presence of both RV dysfunction on imaging AND positive cardiac troponin (intermediate-high) versus either alone (intermediate-low); low-risk — normotensive PE without RV dysfunction or biomarker elevation.

Systemic thrombolysis: full-dose intravenous fibrinolytic therapy (e.g., tenecteplase, alteplase) administered systemically — the traditional reperfusion strategy, effective but carrying a substantial bleeding risk (Section 11).

Ultrasound-facilitated, catheter-directed thrombolysis (USCDT): a percutaneous, catheter-based approach delivering a substantially lower dose of thrombolytic agent directly into the pulmonary artery thrombus, augmented with ultrasound energy to enhance drug dispersion into the clot — designed to achieve local clot-directed efficacy while minimizing the systemic bleeding risk associated with full-dose systemic lytic therapy.

2. Pathophysiology

Acute PE causes right ventricular pressure overload as the RV acutely confronts a sudden increase in pulmonary vascular resistance from the obstructing thrombus burden — the RV, normally a thin-walled, low-pressure chamber, is poorly adapted to this acute afterload increase, leading to RV dilation, septal shift compromising left ventricular filling, and, in severe cases, progressive RV failure and cardiogenic shock. RV dysfunction (assessed via RV/LV diameter ratio on imaging) and myocardial injury (elevated troponin) are the key markers identifying patients at meaningfully elevated risk of early hemodynamic decompensation, even when the patient is currently normotensive — this is the physiological basis for risk-stratifying beyond simple presence/absence of hypotension, and for considering reperfusion therapy in appropriately selected normotensive (intermediate-risk) patients, not only in overt shock.

Why catheter-directed, lower-dose local thrombolysis is mechanistically attractive: by delivering thrombolytic agent directly into the clot at substantially reduced total systemic dose, USCDT aims to achieve meaningful local clot burden reduction and RV afterload relief while avoiding the systemic fibrinolytic state (and associated bleeding risk, particularly intracranial hemorrhage) that full-dose systemic thrombolysis produces.

3. Immediate Stabilization (ABCDE) — Reperfusion Therapy Decision Point

Not a standalone acute stabilization scenario; this protocol addresses the reperfusion-therapy decision within the broader PE management framework (cross-reference Pulmonary Embolism protocol):

Checklist:

4. Focused History

• Time since symptom onset/diagnosis (relevant to thrombus organization and treatment window)
• Bleeding risk factors: recent surgery, active bleeding, prior intracranial hemorrhage, anticoagulant use, age (older age associated with higher extracranial bleeding risk with systemic thrombolysis, though not statistically significant in PEITHO specifically)
• Hemodynamic trajectory since presentation (worsening vs. stable vs. improving)
• Symptoms/signs of cardiorespiratory distress beyond the biomarker/imaging risk stratification itself

5. Comprehensive System-wise Examination

• Cardiovascular: heart rate, blood pressure trend (confirming normotensive intermediate-risk status vs. evolving hypotension), signs of RV strain (elevated JVP, RV heave)
• Respiratory: work of breathing, oxygenation
• Neurological: baseline assessment relevant to bleeding risk stratification (any focal deficit warranting exclusion of thrombolysis)

POCUS integration: central to this protocol — bedside echocardiographic RV assessment (RV dilation, septal flattening, TAPSE) both for initial risk stratification and for tracking response to therapy.

6. Syndrome Identification — Reframed as Risk-Category-Specific Management Pathway

• High-risk (massive) PE with hemodynamic instability: systemic thrombolysis (or catheter-directed therapy where systemic thrombolysis is contraindicated/unavailable, or surgical/mechanical embolectomy in refractory cases) remains the established, guideline-endorsed approach — not the primary focus of the newer evidence discussed here, which concerns the normotensive intermediate-risk population
• Intermediate-high-risk PE (RV dysfunction AND elevated troponin, normotensive): the population specifically studied in both PEITHO (systemic thrombolysis) and HI-PEITHO (catheter-directed thrombolysis) — the current evidence base most directly informs management in this specific substratification (Section 11)
• Intermediate-low-risk PE (either RV dysfunction OR elevated troponin, not both): a lower-risk population where reperfusion therapy is less clearly indicated; anticoagulation alone remains standard
• Low-risk PE: anticoagulation alone; reperfusion therapy not indicated

7. Differential Diagnosis — Not a Traditional Differential

Cross-reference the Pulmonary Embolism protocol (Respiratory System) for the full diagnostic differential of the underlying PE itself; this protocol addresses the reperfusion-therapy decision once PE is confirmed and risk-stratified.

8. Severity/Risk Assessment

RV/LV diameter ratio: the key imaging-based severity marker — HI-PEITHO specifically used a threshold of ≥1.0 as part of its intermediate-risk enrollment criteria; observational data has associated an RV/LV ratio ≥0.9 with substantially higher mortality (6.6% vs. 1.9% in one single-center registry) compared to below this threshold, underscoring the marker's genuine prognostic weight rather than being an arbitrary cutoff.

Cardiac troponin: elevated troponin, combined with RV dysfunction, defines the intermediate-high-risk category that has been the specific focus of both PEITHO and HI-PEITHO.

National Early Warning Score (NEWS): used as an additional clinical severity indicator in HI-PEITHO's enrollment criteria (mean NEWS of 6 at baseline in the trial population), reflecting the trial's specific focus on patients with genuine, multi-marker evidence of elevated risk rather than RV dysfunction/troponin elevation alone.

9. Investigations

Immediate bedside: echocardiographic RV assessment, vital sign trend

Routine labs: cardiac troponin, BNP/NT-proBNP as an adjunct severity marker

Imaging: CT pulmonary angiography for diagnosis and RV/LV ratio assessment; echocardiography for RV function assessment and treatment response monitoring

10. Point-of-Care Ultrasound

Central to risk stratification (RV/LV ratio, RV function assessment) and to monitoring treatment response — serial echocardiographic reassessment can help confirm improving RV function following reperfusion therapy and inform the overall trajectory assessment.

11. Evidence-Based Management

Systemic Thrombolysis in Intermediate-High-Risk PE — PEITHO (2014)

• PEITHO trial (Meyer et al., NEJM 2014, n=1,006, intermediate-high-risk PE — normotensive with both RV dysfunction on imaging AND positive troponin): single-dose, weight-based systemic tenecteplase plus heparin vs. heparin alone — primary composite outcome (death or hemodynamic decompensation within 7 days) significantly reduced: 2.6% (tenecteplase) vs. 5.6% (placebo), corresponding to a number needed to treat of 33
• However, this efficacy came at a substantial, statistically significant bleeding cost: major bleeding in 11.5% (tenecteplase) vs. 2.4% (placebo); hemorrhagic stroke 2% vs. 0.2%; major extracranial hemorrhage 6.3% vs. 1.2% — corresponding to a meaningful number needed to harm alongside the NNT of 33 for the primary efficacy outcome
• No mortality benefit specifically was definitively established — the composite primary outcome was driven substantially by the hemodynamic decompensation component rather than mortality alone
• Practical synthesis of PEITHO: established that systemic thrombolysis reduces short-term hemodynamic decompensation in intermediate-high-risk PE, but the bleeding risk (particularly hemorrhagic stroke) is substantial enough that systemic thrombolysis has not become routine practice for this normotensive intermediate-risk population, despite the statistically significant efficacy finding — this bleeding-risk-driven reluctance is precisely the clinical gap that motivated development of lower-dose, catheter-directed alternatives

Catheter-Directed Thrombolysis — The Evolving, Now-Definitive Evidence Base

• ULTIMA trial (Kucher et al., Circulation 2014): an earlier, smaller RCT of ultrasound-facilitated catheter-directed thrombolysis (USCDT) vs. anticoagulation alone in acute intermediate-risk PE — found USCDT associated with significantly improved RV function recovery with no increase in bleeding risk, but was a smaller trial spanning a broad range of intermediate-risk severity (both intermediate-low and intermediate-high), and was not powered for hard clinical outcomes
• SEATTLE II (Piazza et al., JACC Cardiovasc Interv 2015): a prospective, single-arm (not randomized) multicenter trial of ultrasound-facilitated, catheter-directed, low-dose fibrinolysis for acute massive and submassive PE — supportive but non-randomized, uncontrolled evidence
• This left a genuine evidence gap: prior to HI-PEITHO, there was no large, adequately powered RCT directly comparing catheter-directed therapy against anticoagulation alone for hard clinical outcomes specifically in the intermediate-high-risk population — practice had been guided by smaller trials, registries, and extrapolation from the systemic thrombolysis evidence (PEITHO)

HI-PEITHO (2026) — The New, Definitive, Practice-Changing Trial

• ⚠️ HI-PEITHO trial (presented as a Late-Breaking Clinical Trial at ACC.26, March 2026, simultaneously published in NEJM — this is genuinely recent evidence): a multinational, multicenter RCT (n=544, 59 sites across the US and 8 European countries) directly comparing ultrasound-facilitated catheter-directed thrombolysis (USCDT) plus anticoagulation vs. anticoagulation alone in patients with intermediate-high-risk PE, defined by an RV/LV diameter ratio ≥1.0, elevated troponin, and at least two additional indicators of cardiorespiratory distress (a more stringent, multi-marker enrollment criterion than PEITHO's RV dysfunction + troponin alone)
• Primary outcome (7-day composite of PE-related death, cardiorespiratory decompensation/collapse, or symptomatic PE recurrence): 61% relative risk reduction with USCDT (P=0.005), a difference largely driven by a lower rate of cardiorespiratory decompensation/collapse rather than mortality alone (mirroring PEITHO's own outcome-driver pattern, but with catheter-directed rather than systemic delivery)
• At 30 days: composite endpoint occurred in 4% (USCDT) vs. 10.3% (anticoagulation alone)
• Critically, and in contrast to PEITHO's systemic thrombolysis findings: no excess bleeding risk or other serious adverse events were observed with the catheter-directed approach — this is the key distinguishing feature from the systemic thrombolysis evidence base, and the central reason this trial is being described as practice-changing
• This is explicitly described as the first randomized trial demonstrating a clinical-outcome advantage for a catheter-based intervention in intermediate-risk PE, addressing the specific evidence gap left by the smaller ULTIMA trial and non-randomized SEATTLE II data
• Expert commentary accompanying the trial (Spyropoulos and Vedantham, editorial) suggests the findings "support a lower threshold for the use of ultrasound-facilitated, catheter-directed thrombolysis in patients with PE who would have been categorized as having intermediate-high risk", while explicitly cautioning that "the wisdom of applying this approach to patients with less severe intermediate-risk PE [i.e., intermediate-low-risk] remains unclear and will benefit from additional studies" — an important, explicit boundary on how far to extrapolate this new evidence

Practical Synthesis

For intermediate-high-risk PE specifically (RV dysfunction + elevated troponin + additional markers of cardiorespiratory distress), the evidence now favors ultrasound-facilitated catheter-directed thrombolysis over both anticoagulation alone (per HI-PEITHO's clear efficacy benefit without excess bleeding) and, by comparison, likely over systemic thrombolysis (per the favorable bleeding profile relative to PEITHO's substantial bleeding cost), in institutions with the capability to deliver USCDT. This represents a genuine, very recent shift in the evidence landscape for this specific patient population. This evidence should NOT be extrapolated to intermediate-low-risk PE (per the accompanying editorial's explicit caution) or to high-risk (massive, hemodynamically unstable) PE, where different, established management pathways apply (cross-reference Pulmonary Embolism protocol). Institutional capability for USCDT delivery remains a genuine practical constraint, analogous to the systems-dependency theme discussed in the ECPR protocol — this is an interventional, resource- and expertise-dependent therapy, not a universally deliverable pharmacologic default.

12. Organ Support

Interacts with standard hemodynamic support principles (cross-reference Vasopressor & Inotrope Selection & Titration protocol) if RV failure progresses despite reperfusion therapy, and with the broader PE management framework in the Pulmonary Embolism protocol.

13. Disease-Specific Therapy

• Systemic tenecteplase: weight-based single-dose regimen per PEITHO protocol — reserved for high-risk (massive) PE with hemodynamic instability, or select intermediate-high-risk cases where catheter-directed therapy is unavailable, given the substantial bleeding risk profile
• Ultrasound-facilitated catheter-directed thrombolysis (USCDT): substantially lower total thrombolytic dose than systemic therapy (in HI-PEITHO, mean total alteplase dose approximately 8.85 mg for unilateral catheter placement, 16.92 mg for bilateral placement, versus full systemic weight-based dosing) delivered directly into the pulmonary artery thrombus over a mean infusion duration of approximately 7 hours in the trial protocol
• Anticoagulation: continues as the backbone of therapy across all risk categories and reperfusion strategies, not replaced by either thrombolytic approach

14. Consultation Matrix

15. Monitoring Framework

• Clinical: hemodynamic trajectory closely monitored, given that both PEITHO and HI-PEITHO's primary outcomes were substantially driven by early (7-day) decompensation risk rather than later mortality
• Echocardiographic: serial RV function assessment to track treatment response
• Bleeding monitoring: intensified surveillance during and after thrombolytic therapy (systemic or catheter-directed), given the established bleeding risk profile, particularly with systemic thrombolysis

16. ICU Bundle Checklist

17. Complications

Systemic thrombolysis-specific:

• Major bleeding (11.5% in PEITHO), hemorrhagic stroke (2%), major extracranial hemorrhage (6.3%) — the dominant, well-established risk with this approach

Catheter-directed thrombolysis-specific:

• Access-site complications (vascular injury, bleeding at catheter insertion site) — reported but generally manageable conservatively in registry data
• Notably, no excess bleeding risk or serious adverse events relative to anticoagulation alone in the definitive HI-PEITHO RCT — the key distinguishing safety feature from systemic thrombolysis

Prevention: careful risk-category-specific reperfusion strategy selection per Section 11; explicit bleeding risk assessment before any thrombolytic approach

Rescue: standard bleeding management protocols if hemorrhagic complications occur; escalation to mechanical circulatory support/embolectomy for refractory RV failure despite reperfusion therapy

18. Escalation & De-escalation

Escalation: progressive hemodynamic decompensation despite anticoagulation alone in intermediate-high-risk PE → consider USCDT per current evidence (or systemic thrombolysis/embolectomy if evolving toward frank hemodynamic instability, cross-reference Pulmonary Embolism protocol).

De-escalation: stable, improving trajectory on anticoagulation alone in lower-risk categories → continue anticoagulation without reperfusion therapy, per the risk-category-specific framework in Section 6.

19. ICU Discharge Criteria — Not Directly Applicable

Cross-reference Pulmonary Embolism protocol and ICU Discharge Criteria & Step-Down protocol for the relevant discharge framework once the acute reperfusion-therapy decision period has resolved.

20. Documentation & Medicolegal Checklist

• Risk stratification (RV/LV ratio, troponin, additional cardiorespiratory distress markers) documented explicitly
• Reperfusion therapy decision and rationale documented, referencing the specific supporting evidence (PEITHO for systemic thrombolysis; HI-PEITHO for catheter-directed therapy)
• Bleeding risk assessment documented before any thrombolytic intervention
• Institutional capability considerations documented if USCDT was considered but unavailable
• Treatment response (serial echocardiographic RV assessment, clinical trajectory) documented

21. Key Guidelines

• Current ESC/AHA PE guidelines predate HI-PEITHO's publication (March 2026) and are expected to be updated to reflect this new evidence — clinicians should specifically seek updated guideline incorporation of HI-PEITHO findings rather than relying solely on pre-2026 guidance for the intermediate-high-risk PE reperfusion decision
• Prior guidance (e.g., 2015 CHEST guidelines) recommended systemic thrombolysis specifically for PE associated with hypotension without high bleeding risk — reflecting the pre-HI-PEITHO evidence landscape this protocol updates

22. Landmark Trials

23. Controversies

• Extrapolation boundary explicitly flagged by the trial's own accompanying editorial: HI-PEITHO's population was specifically intermediate-high-risk PE with additional cardiorespiratory distress markers, a more stringent enrollment criterion than simple RV dysfunction + troponin elevation alone — the editorial explicitly cautions against extending this favorable risk-benefit profile to intermediate-low-risk PE without further dedicated study; this boundary should be respected rather than treating HI-PEITHO as license for broader catheter-directed therapy use across the full intermediate-risk spectrum.
• Relative efficacy of USCDT versus other catheter-based approaches remains unknown: HI-PEITHO specifically tested ultrasound-facilitated catheter-directed thrombolysis; other catheter-based therapies (e.g., mechanical thrombectomy devices) were not compared head-to-head in this trial, and their relative efficacy versus USCDT remains an open question for future research, as explicitly noted by commentary on the trial.
• Institutional capability and equity of access: as with ECPR, USCDT is a resource- and expertise-intensive intervention requiring interventional cardiology/radiology availability — the trial's favorable findings do not resolve the practical, systems-level question of how broadly this capability can or should be distributed, an issue this protocol shares conceptually with the ECPR protocol's systems-dependency discussion.
• This is very recent evidence: given HI-PEITHO's publication in March 2026, formal guideline incorporation, broader real-world validation, and longer-term outcome data (beyond the 30-day endpoint reported at presentation) are still pending — clinicians should treat this as important, credible, but still-maturing evidence rather than fully established, guideline-endorsed standard of care at the time of this protocol's writing.

24. References

1. Meyer G, Vicaut E, Danays T, et al; PEITHO Investigators. Fibrinolysis for patients with intermediate-risk pulmonary embolism. N Engl J Med. 2014;370(15):1402-1411.
2. Kucher N, Boekstegers P, Muller OJ, et al. Randomized, controlled trial of ultrasound-assisted catheter-directed thrombolysis for acute intermediate-risk pulmonary embolism (ULTIMA). Circulation. 2014;129(4):479-486.
3. Piazza G, Hohlfelder B, Jaff MR, et al. A prospective, single-arm, multicenter trial of ultrasound-facilitated, catheter-directed, low-dose fibrinolysis for acute massive and submassive pulmonary embolism: the SEATTLE II study. JACC Cardiovasc Interv. 2015;8(10):1382-1392.
4. Klok FA, Piazza G, Sharp ASP, et al. Ultrasound-facilitated, catheter-directed thrombolysis vs anticoagulation alone for acute intermediate-high-risk pulmonary embolism: rationale and design of the HI-PEITHO study. Am Heart J. 2022;251:43-53.
5. Konstantinides SV, et al; HI-PEITHO Investigators. Ultrasound-facilitated catheter-directed thrombolysis vs. anticoagulation alone for acute intermediate-high-risk pulmonary embolism: primary results of the HI-PEITHO randomized clinical trial. N Engl J Med. 2026 (presented ACC.26).
6. Spyropoulos AC, Vedantham S. Advanced therapy for intermediate-risk pulmonary embolism [editorial]. N Engl J Med. 2026.
7. Barco S, Vicaut E, Klok FA, et al. Improved identification of thrombolysis candidates amongst intermediate-risk pulmonary embolism patients: implications for future trials. Eur Respir J. 2018;51(1):1701775.
8. The Washington Manual of Critical Care, 4th ed. 2025 — pulmonary thromboembolism chapter.
9. ICU Protocols: A Step-wise Approach, 2nd ed. — pulmonary thromboembolism chapter.