CardioNerds co-chairs Dr. Dinu Balanescu and Dr. Billy Joe Mullinax, along with FIT lead Dr. Shiavax Rao, discuss the evolving landscape of randomized controlled trials in pulmonary embolism with Dr. Jay Giri, interventional cardiologist, Associate Professor of Medicine, and Director of the Cardiovascular Catheterization Laboratories at the Hospital of the University of Pennsylvania. This episode examines the historical evidence behind systemic thrombolysis, the emergence of catheter-directed therapies and mechanical thrombectomy, and the landmark RCTs – STORM-PE, PEERLESS, HI-PEITHO, and PEERLESS II – that are reshaping intermediate-risk PE management. The discussion highlights challenges in PE trial design, the critical importance of clinical deterioration as an endpoint, and why this era represents an unprecedented wave of evidence generation in PE. Audio editing for this episode was performed by CardioNerds Intern, Dr. Julia Marques Fernandes. Dr. Dinu Balanescu and Dr. Billy-Joe Mullinax are Co-chairs for the CardioNerds PE Series, developed in collaboration with the PERT Consortium. Enjoy this Circulation 2022 Paths to Discovery article to learn about the CardioNerds story, mission, and values. CardioNerds Pulmonary Embolism PageCardioNerds Episode PageCardioNerds AcademyCardionerds Healy Honor Roll CardioNerds Journal ClubSubscribe to The Heartbeat Newsletter!Check out CardioNerds SWAG!Become a CardioNerds Patron! Pearls: Systemic thrombolysis in intermediate-risk PE reduces hemodynamic decompensation but at the cost of ~1.5–2% intracranial hemorrhage risk – a near-zero net benefit that has driven the search for safer catheter-based alternatives. “Focus on clinical deterioration, not mortality” – Due to crossover design in contemporary PE RCTs, control-arm patients who decompensate are rescued with advanced therapies, biasing mortality toward the null. Clinical deterioration is the most informative endpoint to watch in HI-PEITHO, PRAGUE-26, and PEERLESS II. HI-PEITHO is the first large RCT to demonstrate that catheter-directed fibrinolysis plus anticoagulation significantly reduces the composite of PE-related death, cardiorespiratory decompensation, or PE recurrence versus anticoagulation alone (RR 0.39; 95% CI 0.20–0.77; P=0.005), with no intracranial hemorrhage in either arm. The four major upcoming/recently reported PE RCTs (HI-PEITHO, PRAGUE-26, PEERLESS II, PE-TRACT) enroll progressively different risk populations – from the most enriched (HI-PEITHO) to the most permissive (PE-TRACT, which includes intermediate-low risk patients) – enabling a nuanced understanding of which patients benefit most from intervention. PE device clearance follows a fundamentally different FDA pathway than structural heart devices (single-arm safety/efficacy studies vs. mandated RCTs), yet market forces and clinical need have ultimately driven industry and government to sponsor large-scale RCTs – a lesson in how evidence development can evolve organically alongside regulatory frameworks. Notes: Notes drafted by Dr. Shiavax Rao. Question #1: What is the current evidence behind advanced PE therapies? Systemic thrombolysis: Sixteen RCTs over 40 years (1972–2014) enrolling nearly 2,000 patients have studied systemic thrombolysis in intermediate-risk PE. The landmark PEITHO trial (n=1,006) showed that tenecteplase reduced the composite of death or hemodynamic collapse (2.6% vs. 5.6%; P=0.015), driven primarily by reduced hemodynamic decompensation (1.6% vs. 5.0%; P=0.002). However, this came at the cost of increased major bleeding (6.3% vs. 1.5%; P<0.001) and a ~2% rate of intracranial hemorrhage. Meta-analyses of systemic thrombolysis trials show a small absolute mortality benefit (~1–2%) that is closely offset by bleeding risk, explaining why guidelines have not broadly recommended systemic thrombolysis for intermediate-risk PE. Catheter-directed thrombolysis (CDT): The ULTIMA trial (n=59) was the first RCT of ultrasound-assisted CDT (EkoSonic/EKOS system) vs. anticoagulation alone in intermediate-risk PE. CDT showed superior RV/LV ratio improvement at 24 hours (decrease of 0.30 ± 0.20 vs. 0.03 ± 0.16; P<0.001), but this difference was no longer significant at 90 days. The CANARY trial, initiated in Iran in 2019, was halted prematurely due to the COVID-19 pandemic but largely verified ULTIMA’s findings, with a signal that RV benefits may persist at 90 days. Mechanical thrombectomy – single-arm data: The FLARE trial demonstrated a 25% reduction in RV/LV ratio at 48 hours with large-bore aspiration thrombectomy (FlowTriever). The EXTRACT-PE trial showed significant RV/LV ratio reduction with the Indigo aspiration system with a low major adverse event rate. The FLASH registry (FlowTriever) reported a mean 7.6 mmHg drop in mean PA pressure and RV/LV ratio decrease from 1.23 to 0.98 at 48 hours. STORM-PE (2025): The first RCT of mechanical thrombectomy (computer-assisted vacuum thrombectomy [CAVT] with the Indigo/Penumbra system) vs. anticoagulation alone. One hundred patients were randomized across 22 sites. CAVT was superior for the primary endpoint of 48-hour RV/LV ratio reduction (0.52 vs. 0.24; difference 0.27; P<0.001), with earlier normalization of vital signs and comparable major adverse event rates (4.3% vs. 7.5%; P=0.681). Two PE-related deaths occurred in the CAVT arm. The trial was not powered for mortality or longer-term outcomes. PEERLESS (2025): The first RCT comparing two interventional strategies head-to-head – large-bore mechanical thrombectomy (FlowTriever) vs. CDT – in 550 patients with intermediate-risk PE. The primary hierarchical win ratio composite favored LBMT (win ratio 5.01; 95% CI 3.68–6.97; P<0.001), driven primarily by fewer clinical deterioration/bailout events (1.8% vs. 5.4%; P=0.04) and substantially less post-procedural ICU use (41.6% vs. 98.6% admission rates). No significant differences in mortality, intracranial hemorrhage, or major bleeding were observed. RV/LV ratio reduction was similar between arms. LBMT was associated with shorter hospital stays and fewer 30-day readmissions. Question #2: What are the challenges with conducting RCTs in PE? Crossover and rescue therapy: Unlike early TAVR trials where control-arm patients could not cross over to the device arm, contemporary PE trials allow crossover upon clinical deterioration. This is ethically necessary given available therapies but biases mortality toward the null, making it unlikely that any individual trial – or even a meta-analysis of the four major trials (~2,400–3,000 patients combined) – will demonstrate a mortality difference. Heterogeneity of intermediate-risk PE: Two patients meeting ESC intermediate-high risk criteria (RV dysfunction + elevated troponin) can look clinically very different – one may be tachypneic on 5 liters of oxygen, while another is comfortable on room air. This heterogeneity complicates enrollment, endpoint detection, and generalizability. Endpoint selection: Early PE trials relied on surrogate imaging endpoints (RV/LV ratio, PA pressure reduction, Miller score). While these demonstrate proof-of-concept, they have not moved guidelines. Clinically relevant endpoints – mortality, clinical deterioration, functional status, quality of life – are needed but require larger sample sizes and longer follow-up. Funding and maturation of the field: Trials require buy-in from government or industry funders. It took time for the field to mature enough to estimate effect sizes for trial powering, accumulate sufficient operator experience to ensure internal validity, and for industry to recognize that market adoption required randomized evidence despite existing FDA clearance. FDA regulatory pathway: PE devices are cleared via a 510(k) pathway requiring single-arm studies (~100–150 patients) demonstrating safety and RV/LV ratio improvement – a much lower bar than the pre-market approval pathway requiring RCTs mandated for structural heart devices (e.g., TAVR, MitraClip). While this has enabled rapid innovation and market competition, it initially reduced the incentive for industry-sponsored RCTs. Question #3: What are the upcoming/recently reported RCT trials in PE? HI-PEITHO (published 2026, NEJM): Multinational adaptive-design RCT of ultrasound-facilitated CDT (EkoSonic system, alteplase 2 mg bolus + 1 mg/hr/catheter × 7 hours) plus anticoagulation vs. anticoagulation alone in 544 patients with enriched intermediate-high risk PE (RV/LV ≥1.0, elevated troponin, plus ≥2 of: SBP ≤110, HR ≥100, RR 20). Primary composite of PE-related death, cardiorespiratory decompensation/collapse, or symptomatic PE recurrence within 7 days: 4.0% intervention vs. 10.3% control (RR 0.39; 95% CI 0.20–0.77; P=0.005). Effect driven by reduced cardiorespiratory decompensation. Major bleeding at 7 days: 4.1% vs. 2.2% (P=0.32). No intracranial hemorrhage in either arm. Clinical deterioration measured using the National Early Warning Score (NEWS), a validated ordinal scoring system incorporating vital signs – more sensitive at detecting decompensation than binary clinical criteria. PRAGUE-26: Czech Republic government-sponsored RCT with a design essentially identical to HI-PEITHO in terms of sample size and primary endpoint, but using standard (non-ultrasound-assisted) CDT catheters in the interventional arm. Enrolling well; results anticipated in the near term. PEERLESS II: Industry-sponsored (Inari/Boston Scientific) RCT of large-bore mechanical thrombectomy (FlowTriever) plus anticoagulation vs. anticoagulation alone in up to 1,200 patients with enriched intermediate-high risk PE (enrichment criteria slightly less stringent than HI-PEITHO). Five-component hierarchical primary endpoint assessed via win ratio: (1) mortality, (2) clinical deterioration (defined by binary clinical criteria – pressor initiation, SBP <90 for sustained period, mechanical circulatory support, or significant respiratory decompensation/intubation – a less sensitive measure than NEWS), (3) recurrent PE admission, (4) non-deterioration-based bailout crossover at day 3, and (5) 48-hour dyspnea score. The larger sample size compensates for the less sensitive clinical deterioration definition. PE-TRACT: NIH-sponsored, open-label, assessor-blinded RCT of CDT (any FDA-cleared device – CDT or mechanical thrombectomy, strategy trial) plus anticoagulation vs. anticoagulation alone in 500 patients with intermediate-risk PE (most permissive enrollment – includes intermediate-low risk patients). Co-primary endpoints at 3 months (peak VO₂ on cardiopulmonary exercise testing) and 12 months (NYHA functional class), analyzed sequentially. Designed to answer the longer-term functional question rather than early clinical deterioration. Question #4: What does the future of PE research look like? Unprecedented evidence generation: Across STORM-PE, PEERLESS, HI-PEITHO, PEERLESS II, PE-TRACT, PRAGUE-26, PEITHO-3, and high-risk PE trials (PERSEVERE, TORPEDO-NL), approximately 8–9 RCTs are enrolling or recently completed – an unparalleled volume of comparative evidence in any cardiovascular subspecialty over such a short period. Guideline impact: The 2026 AHA/ACC PE Guideline already reflects the evolving evidence landscape, with Class 2a–2b recommendations for CDT and MT in select PE categories. Results from HI-PEITHO, PEERLESS II, PRAGUE-26, and PE-TRACT have the potential to substantially strengthen these recommendations, particularly if clinical deterioration endpoints are positive. PERT evolution: As evidence clarifies which patients benefit from intervention, PERT programs may transition from primarily clinical decision-making bodies to systems-of-care delivery engines – analogous to STEMI systems – focused on efficient, protocol-driven care and real-world evidence generation for quality improvement. Innovation ecosystem: The relatively permissive FDA clearance pathway has fostered a competitive device landscape with multiple manufacturers and device types, contrasting with the prolonged duopoly in the TAVR space. This competition may drive technological improvement and more favorable economics. Caution with real-world evidence: While real-world evidence is valuable for quality improvement and systems-of-care assessment, it should be used cautiously for comparative effectiveness analyses due to irreconcilable confounding and limitations in causal inference. RCTs remain the gold standard for comparative questions. References: ★ Rosenfield K, Klok FA, Piazza G, et al. Ultrasound-facilitated, catheter-directed fibrinolysis for acute pulmonary embolism. N Engl J Med. 2026;394(22):2131-2141. doi:10.1056/NEJMoa2503539 ★ Lookstein RA, Konstantinides SV, Weinberg I, et al. Randomized controlled trial of mechanical thrombectomy with anticoagulation versus anticoagulation alone for acute intermediate-high risk pulmonary embolism: primary outcomes from the STORM-PE trial. Circulation. 2026;153(1):21-34. doi:10.1161/CIRCULATIONAHA.125.077232 ★ Jaber WA, Gonsalves CF, Stortecky S, et al. 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. 2025;151(5):260-273. doi:10.1161/CIRCULATIONAHA.124.072364 ★ Gonsalves CF, Gibson CM, Stortecky S, et al. Randomized controlled trial of mechanical thrombectomy vs catheter-directed thrombolysis for acute hemodynamically stable pulmonary embolism: rationale and design of the PEERLESS study. Am Heart J. 2023;266:128-137. doi:10.1016/j.ahj.2023.09.002 ★ Sista AK, Troxel AB, Tarpey T, et al. 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. Am Heart J. 2025;281:112-122. doi:10.1016/j.ahj.2024.11.016 ★ Giri J, Sista AK, Weinberg I, et al. Interventional therapies for acute pulmonary embolism: current status and principles for the development of novel evidence: a scientific statement from the American Heart Association. Circulation. 2019;140(20):e774-e801. doi:10.1161/CIR.0000000000000707 ★ Zhang RS, Maqsood MH, Sharp ASP, et al. Efficacy and safety of anticoagulation, catheter-directed thrombolysis, or systemic thrombolysis in acute pulmonary embolism. JACC Cardiovasc Interv. 2023;16(22):2781-2793. doi:10.1016/j.jcin.2023.09.014 Additional References Rosovsky RP, Konstantinides SV, Moriarty JM, et al. A prospective, multicenter, randomized controlled trial evaluating anticoagulation alone vs anticoagulation plus computer assisted vacuum thrombectomy for the treatment of intermediate-high-risk acute pulmonary embolism: rationale and design of the STORM-PE study. Am Heart J. 2025;288:1-14. doi:10.1016/j.ahj.2025.03.018 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. doi:10.1016/j.ahj.2022.05.011 Creager MA, Barnes GD, Giri J, et al. 2026 AHA/ACC/ACCP/ACEP/CHEST/SCAI/SHM/SIR/SVM/SVN guideline for the evaluation and management of acute pulmonary embolism in adults. J Am Coll Cardiol. 2026;87(7):e77-e206. doi:10.1016/j.jacc.2025.11.027 Piazza G. Advanced management of intermediate- and high-risk pulmonary embolism: JACC focus seminar. J Am Coll Cardiol. 2020;76(18):2117-2127. doi:10.1016/j.jacc.2020.05.028 Zuo Z, Yue J, Dong BR, et al. Thrombolytic therapy for pulmonary embolism. Cochrane Database Syst Rev. 2021;4(4):CD004437. doi:10.1002/14651858.CD004437.pub6 Kroupa J, Buk M, Weichet J, et al. A pilot randomised trial of catheter-directed thrombolysis or standard anticoagulation for patients with intermediate-high risk acute pulmonary embolism (CANARY). EuroIntervention. 2022;18(8):e657-e665. doi:10.4244/EIJ-D-22-00194 Zuin M, Lang I, Chopard R, et al. Innovation in catheter-directed therapy for intermediate-high-risk and high-risk pulmonary embolism. JACC Cardiovasc Interv. 2024;17(20):2390-2408. doi:10.1016/j.jcin.2024.07.037 Harvey JJ, Huang S, Uberoi R. Catheter-directed therapies for the treatment of high risk (massive) and intermediate risk (submassive) acute pulmonary embolism. Cochrane Database Syst Rev. 2022;8(8):CD013083. doi:10.1002/14651858.CD013083.pub2 Kim JM, Horbal SR, Mewaldt C, et al. Mechanical thrombectomy and catheter-directed thrombolysis in acute pulmonary embolism: trends and practice patterns in the PERT Consortium Registry (2016-2024). J Am Coll Cardiol. 2026;87(13):1271-1283. doi:10.1016/j.jacc.2025.12.044 Planer D, Yanko S, Matok I, et al. Catheter-directed thrombolysis compared with systemic thrombolysis and anticoagulation in patients with intermediate- or high-risk pulmonary embolism: systematic review and network meta-analysis. CMAJ. 2023;195(24):E833-E843. doi:10.1503/cmaj.221655 Farmakis IT, Binder H, Chopard R, et al. Reperfusion strategies for acute pulmonary embolism: design and rationale of RECONNECT-PE – a living systematic review and meta-analysis. Am Heart J. 2026;295:107365. doi:10.1016/j.ahj.2026.107365 Rashedi S, Leyva H, Hamade N, et al. Fibrinolytic therapy for thromboembolic diseases: approved indications and future directions. J Am Coll Cardiol. 2025;86(14):1395-1416. doi:10.1016/j.jacc.2025.07.048 Creager MA, Barnes GD, Giri J. A field in transition: catheter-based therapy in the 2026 AHA/ACC acute pulmonary embolism guideline. J Am Coll Cardiol. 2026;87(13):1284-1288. doi:10.1016/j.jacc.2026.01.024

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