Percutaneous mechanical thrombectomy using the AcoStream thrombus aspiration system for intermediate-high-risk pulmonary embolism

Introduction

Pulmonary embolism (PE) is the third leading cause of cardiovascular death after coronary artery disease and stroke (1,2). Despite advances in diagnosis and treatment, PE remains a major global health issue, contributing to significant morbidity and mortality (3,4). Accurate risk stratification is critical in the management of PE, as it directly determines treatment strategies and the patient’s care setting (5). PE is typically categorized into low-risk, intermediate-risk, and high-risk groups based on hemodynamic stability, imaging evidence of right ventricular (RV) dysfunction, and levels of cardiac biomarkers (3).

Patients with intermediate-high-risk of PE, despite being hemodynamically stable, exhibit evidence of RV dysfunction and myocardial injury, with significantly higher short-term mortality rates compared to those at intermediate-low risk (3,6,7). Due to concerns about bleeding risks associated with systemic thrombolysis, current guidelines continue to recommend anticoagulation as the treatment for intermediate-high-risk PE (3,8). However, real-world registry data reflect a higher-risk and less-selected population, where the 30-day mortality rate can range from 8% to 15%, with a significant proportion experiencing early clinical deterioration (9). This real-world risk underscores the need to explore escalation therapies beyond standard anticoagulation. Thus, more effective treatment methods are needed. Previous studies have documented the positive outcomes of mechanical thrombectomy (MT) and catheter-directed thrombolysis (CDT) in treating intermediate-high-risk PE (10-14). Compared to CDT, MT does not rely on thrombolytic agents—reserving them strictly for bailout scenarios—thereby immediate reducing pulmonary artery thrombus burden while significantly lowering the bleeding complications associated with thrombolysis (15). MT devices have been deployed in numerous medical centers and are gaining widespread adoption. Previous research has demonstrated that intravascular reperfusion therapy for PE can be successfully achieved using MT devices such as the FlowTriever system and the Indigo Aspiration System (16,17).

However, there are few reports on the application of the AcoStream thrombus aspiration system (Acotec, China), which was approved for market release by the China National Medical Products Administration in 2021. This retrospective case series reports our initial experience and primary outcomes in the treatment of patients with intermediate-high risk PE by the AcoStream system. We present this article in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2026-0913/rc).

Methods

Ethical consideration

This single-center retrospective study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of Jinhua Municipal Central Hospital [No. (Research) 2026-Ethical Review-174] and individual consent for this retrospective analysis was waived. The data used in this study are available upon reasonable request for collaboration, secondary analysis, or further investigation.

Study participants

We retrospectively reviewed patients with acute PE who underwent MT using the AcoStream system (Acotec, Beijing, China) between July 2021 and February 2025. Patients were eligible for inclusion if they met the following criteria: (I) age ≥18 years; (II) symptomatic acute PE (symptom onset ≤14 days) confirmed by computed tomography pulmonary angiography (CTPA); and (III) classified as intermediate-high-risk PE. Exclusion criteria were: (I) presence of subsegmental PE; (II) chronic thromboembolic pulmonary hypertension (CTEPH) at baseline; (III) contraindications to anticoagulation; and (IV) life expectancy <6 months due to comorbid conditions. Intermediate-high-risk PE was defined according to the 2019 ESC guidelines as patients presenting with hemodynamic stability, accompanied by both evidence of RV dysfunction on imaging and elevated cardiac biomarkers.

Treatment

Patients were selected for MT over anticoagulation alone based on a multidisciplinary team assessment, primarily driven by clinical signs of impending deterioration (e.g., upward heart rate trajectory, escalating oxygen requirements) or high thrombus burden.

Anticoagulation

All patients received therapeutic anticoagulation. During hospitalisation, they were administered weight-adjusted low-molecular-weight heparin every 12 hours (e.g., enoxaparin 1 mg/kg). In patients with contraindications to heparin, argatroban was used with dose adjustment to achieve a target activated partial thromboplastin time of 1.5–2.5 times baseline, with regular laboratory monitoring. After discharge, switch from low molecular weight heparin or argatroban to direct oral anticoagulants (e.g., rivaroxaban).

MT

A 5-F vascular sheath (Terumo, Tokyo, Japan) was inserted via the right femoral vein. For patients with thrombosis of the right iliofemoral vein, the procedure was performed via the left femoral vein. For patients who had concomitant extensive proximal deep vein thrombosis, a retrievable inferior vena cava filter was placed prior to MT therapy, and the filter will be retrieved within 2 weeks. A 5-F pigtail catheter was inserted into the main pulmonary artery to perform pulmonary angiography, thereby identifying the thrombus location and corresponding pulmonary perfusion status to evaluate the baseline Miller index. A disposable pressure transducer (Biotek, Nanchang, China) was connected to measure the baseline pulmonary artery systolic pressure (PASP). Subsequently, a 10-F 700 mm-long Fustar vascular sheath was replaced, and a 10-F AcoStream (Acotec, Beijing, China) thrombus aspiration catheter system was advanced to the thromboembolic site for thrombus aspiration. Continuous or pulsed aspiration was applied under negative pressure to extract the thrombus. The number of aspiration passes was determined by the operating physician based on angiographic clearance and real-time hemodynamic improvement. Typically, aspiration within the same pulmonary artery is performed no more than three times. Following completion of all aspiration procedures, repeat angiography was conducted to reassess the post-procedural Miller index, while the post-procedural PASP was immediately remeasured using the disposable pressure transducer. Vital signs were continuously monitored throughout the procedure. Procedural success was defined as a reduction in the angiographic Miller index by at least 30%, alongside improvement of vital signs within 48 hours after the procedure. To evaluate the early recovery of RV function, all patients underwent repeat transthoracic echocardiography at 48 hours post-procedure.

Study endpoints

The efficacy endpoints evaluated in this study included the immediate reduction in the Miller index (including obstruction score and perfusion score) and the decrease in PASP. Furthermore, the reduction in cardiac biomarkers (BNP and Troponin I), and the ratio of partial oxygen pressure (PaO₂) to the fraction of inspired oxygen (FiO₂) (PaO₂/FiO₂) within the first 48 hours post-procedure was also assessed.

Follow-up transthoracic echocardiography was additionally performed to descriptively assess recovery of RV function. PASP was recorded during the procedure using a pressure transducer system. Mean pulmonary artery pressure (mPAP) was not consistently available in the retrospective dataset and therefore was not included in the present analysis.

The primary safety endpoints included procedure-related serious adverse events and major bleeding defined by the International Society on Thrombosis and Haemostasis (ISTH) criteria during hospitalization (18). The secondary safety endpoint was clinically relevant non-major bleeding (CRNMB) according to the ISTH criteria (19).

Follow-up

Patients were followed up in the outpatient clinic or by telephone at 1, 3, 6, and 12 months after discharge. During outpatient follow-up, clinical status was evaluated based on self-reported residual symptoms (such as dyspnea and chest tightness). Systematic functional assessments, such as the 6-minute walk test, were not routinely performed. Follow-up CTPA was scheduled as part of a routine post-PE institutional protocol at 3 to 6 months to evaluate for residual thrombi, rather than being strictly symptom-triggered. Long-term endpoints included recurrent PE, the presence of residual thrombi on repeat CTPA, residual symptoms (e.g., chest tightness or dyspnea after physical activity), and the incidence of chronic thromboembolic pulmonary disease (CTEPD) or CTEPH.

CTEPD was suspected in patients who presented with residual symptoms and residual thrombi on repeat CTPA. For these suspected cases, right heart catheterization (RHC) was mandatory to confirm the diagnosis of CTEPH, defined as a mPAP of >20 mmHg, pulmonary artery wedge pressure of ≤15 mmHg, and pulmonary vascular resistance of >2 Wood units (20).

Statistical analysis

Continuous variables are expressed as the mean ± standard deviation (SD) or median with interquartile range (IQR), depending on their distribution. Categorical variables are presented as numbers with percentages. To evaluate the efficacy, pre- and post-procedural variables were compared using the paired Student’s t-test or the Wilcoxon signed-rank test, as appropriate. For parameters with missing data, analyses were performed only on patients with complete paired baseline and follow-up measurements. A two-tailed P value <0.05 was considered statistically significant. Statistical analysis was performed using R (v4.2.3; R Foundation for Statistical Computing, Vienna, Austria).

Results

Patient characteristics

A total of 45 consecutive patients with acute intermediate-high-risk PE underwent percutaneous MT using the ACOSTREAM aspiration system and were included in the final analysis. The baseline demographic and clinical characteristics of the cohort are summarized in Table 1. The mean age of the patients was 66.6±10.7 years, and 26 patients (57.8%) were male. Upon admission, syncope was documented in 20 patients (44.4%). The cohort demonstrated substantial RV strain and hypoxemia at presentation, with a mean baseline right ventricular to left ventricular (RV/LV) diameter ratio of 1.30±0.11 and a median PaO₂/FiO₂ ratio of 260 mmHg (IQR, 204–286 mmHg). The MT procedure was successfully performed in all 45 patients, with a mean operation time of 94.9±17.8 minutes and an average blood loss of 108.6±27.2 mL.

Procedural outcomes and acute hemodynamic improvement

A representative image of an intermediate-high-risk PE case at the initial and follow-ups after MT is shown in Figure 1. The changes in angiographic and physiological parameters before and immediately after treatment are shown in Table 2 and Figure 2. Following the procedure, a significant reduction in thrombus burden was observed, with the total Miller index decreasing from 16.00 (IQR, 15.00, 18.00) at baseline to 6.00 (IQR, 5.00, 8.00) (P<0.001). This was accompanied by a rapid decline in PASP [46.00 (IQR, 41.00, 50.00) vs. 30.00 (IQR, 26.00, 32.00) mmHg, P<0.001]. Gas exchange and vital signs also improved profoundly: the PaO₂/FiO₂ ratio increased [260.00 (IQR, 204.00, 286.00) vs. 381.00 (IQR, 367.00, 395.00) mmHg, P<0.001], heart rate significantly decreased [104.00 (IQR, 95.00, 112.00) vs. 80.00 (IQR, 76.00, 85.00) bpm, P<0.001], and respiratory rate improved [21.00 (IQR, 20.00, 23.00) vs. 18.00 (IQR, 16.00, 19.00) breaths/min, P<0.001]. Concurrently, tissue perfusion was rapidly restored as lactate levels significantly decreased [1.90 (IQR, 1.70, 2.40) vs. 1.50 (IQR, 1.30, 1.80) mmol/L, P<0.001], although a procedure-related drop in hemoglobin was noted [131.00 (IQR, 123.00, 137.00) vs. 120.00 (IQR, 114.00, 127.00) g/L, P<0.001]. Furthermore, 34 out of 45 patients (75.6%) completed the repeat echocardiographic evaluation at 48 hours post-procedure; at this time point, the median RV/LV diameter ratio was 0.91 (IQR, 0.87, 0.97). Cardiac biomarkers also decreased significantly within 48 hours, as the BNP and troponin I dropped to near-normal levels [484.00 (IQR, 300.00, 801.00) vs. 106.00 (IQR, 74.00, 281.00) pg/mL, P<0.001; 0.25 (IQR, 0.08, 1.24) vs. 0.08 (IQR, 0.03, 0.19) ng/mL, P<0.001, respectively].

Figure 1 Pre-procedural and follow-up imaging of a 75-year-old female patient with acute pulmonary embolism. (A) Baseline pulmonary angiography demonstrating significant filling defects and high thrombus burden in the right pulmonary artery. The arrow indicates pulmonary artery filling defect. (B) Baseline axial CTPA showing RV dilation. The maximal RV diameter is 38.2 mm, and the LV diameter is 31.1 mm, yielding an RV/LV ratio of 1.23, which is indicative of acute RV dysfunction. (C) Baseline coronal reformatted CTPA image revealing extensive thrombus in the pulmonary artery. The arrow indicates pulmonary artery thrombus. (D) Immediate post-procedural pulmonary angiography following mechanical thrombectomy showing restored blood flow and a significant reduction in thrombus burden. The arrow indicates restored pulmonary blood flow. (E) 3-month follow-up axial CTPA demonstrating normalization of the cardiac chambers. The RV diameter decreased to 36.3 mm, and the LV diameter increased to 41.2 mm, resulting in a normalized RV/LV ratio of 0.88 and relief of RV strain. (F) 3-month follow-up coronal reformatted CTPA image confirming complete resolution of the pulmonary thrombus with a fully patent arterial tree. CTPA, computed tomography pulmonary angiography; LV, left ventricular; RV, right ventricular.

Figure 2 Comprehensive evaluation of clinical, hemodynamic, and biomarker changes pre- and post-mechanical thrombectomy using the AcoStream system. Box plots display medians and interquartile ranges for nine key efficacy parameters, with individual patient trajectories overlaid (gray lines). Following the ACOSTREAM procedure, all parameters demonstrated highly significant improvements (all P<0.001, Wilcoxon signed-rank test). BNP and troponin I are plotted on a logarithmic scale. BNP, B-type natriuretic peptide; FiO₂, fraction of inspired oxygen; PaO₂, partial oxygen pressure; PASP, pulmonary artery systolic pressure.

Safety and complications

No device-related serious adverse events, including pulmonary artery perforation, cardiac tamponade, or hemodynamic collapse, were observed during hospitalization. No patient (0.0%) experienced a major bleeding event according to the ISTH criteria or any device-related serious adverse events during hospitalization. Three (6.7%) patients had CRNMB during hospitalization, which primarily presented as minor hematomas at the puncture site and were managed successfully with manual compression.

Twelve-month follow-up

During the 12-month follow-up period, two patients experienced a recurrence of PE after discontinuing their anticoagulant medication on their own initiative. Six patients still had residual thrombi on repeat CTPA scans, and three continued to experience chest tightness after physical activity. Following the diagnostic protocol, these patients underwent RHC. CTEPH was confirmed in 1 patient, while the remaining 2 patients were classified as CTEPD without pulmonary hypertension (Table 3).

Discussion

For all patients with acute PE, including those at intermediate risk, anticoagulation is the primary treatment (3,21). Given the high mortality rate and risk of clinical deterioration among intermediate-high risk patients with PE, anticoagulation alone may not be sufficient to prevent adverse events (8,15). Due to the potential bleeding risks associated with CDT, MT has attracted increasing attention (11,22). Therefore, we conducted this retrospective case series to report the performance of the AcoStream MT system; our results suggest that this aspiration system achieved an acceptable safety profile and was highly effective in rapidly reducing thrombus burden.

In this study, the total Miller index decreased significantly from 16.00 (IQR, 15.00, 18.00) to 6.00 (IQR, 5.00, 8.00) immediately following the procedure (P<0.001). This reduction in angiographic thrombus burden is consistent with results from the meta-analysis conducted by Milioglou et al. (23). While CDT has been shown to be effective in reducing thrombus burden, it generally requires a continuous infusion over 12 to 24 hours to achieve optimal results (11). In contrast, MT relies on physical extraction, providing immediate debulking. As reported in the PEERLESS study, MT may be significantly superior to CDT in terms of improving clinical outcomes and treatment efficacy (24). Follow-up echocardiographic assessments in a subset of patients suggested improvement in RV strain after thrombectomy. However, because baseline and follow-up RV/LV measurements were derived from different imaging modalities, these findings should be interpreted cautiously and regarded as descriptive observations rather than validated longitudinal quantitative changes. But a rapid decline in RV/LV was observed in previous trials evaluating large-bore mechanical suction therapy, including the FLASH and EXTRACT-PE studies (16,17). Such a rapid structural recovery is likely attributable to the early clearance of the pulmonary artery thrombus burden, as represented by the Miller index, which subsequently led to a profound decrease in RV afterload. In the current study, we also observed a rapid improvement in cardiac biomarkers within 48 hours, with BNP and troponin I levels dropping to near-normal level (all P<0.001). These findings suggest that the prompt removal of mechanical obstruction may not only immediately alleviate RV pressure overload, but may also limit further myocardial damage. Although cardiac biomarkers declined substantially within 48 hours, these changes should be interpreted cautiously because biomarker improvement may also reflect the natural clinical trajectory following anticoagulation and supportive care.

The oxygenation status of patients with PE is also a focus of attention; the 2026 AHA guideline have, for the first time, incorporated oxygenation status into the risk stratification system (21). The P/F ratio in blood gas analysis is significantly associated with in-hospital mortality from PE and is used to predict risk stratification for PE (25,26). We therefore compared the P/F ratio at admission with that 48 hours post procedure, the P/F ratio increased from 260.00 to 381.00 mmHg. In the FLASH study, following thrombectomy, the modified Medical Research Council dyspnea scores decreased from 2.7±1.4 at baseline to 1.1±1.2 after 48 hours, and supplemental oxygen requirements improved for 87.4% of patients within 48 hours (17). The phenomenon of accelerated recovery observed in this study suggests that the prompt removal of mechanical obstruction can improve pulmonary perfusion and restore oxygenation.

Regarding safety, no major bleeding events occurred in this cohort, and the rate of CRNMB was 6.7% (3/45), primarily presenting as access-site hematomas managed with manual compression. This finding aligns with trials like STORM-PE, which demonstrated that interventional therapies do not necessarily increase bleeding rates compared to anticoagulation alone (27). However, compared to systemic anticoagulation, catheter-based interventions generally exhibit a slightly higher rate of minor access-site bleeding, as observed in our CRNMB data. A key difference between our protocol and CDT is the complete avoidance of thrombolytic agents. Apistar et al. found that CDT involving thrombolytic agents carries a 2.47-fold higher risk of major bleeding than anticoagulant therapy (28). Thrombolytics also carry an inherent risk of intracranial hemorrhage, and their omission in mechanical aspiration theoretically improves the safety profile for patients at high risk of bleeding (29). The observed incidence of CTEPH (1/45) lies within the expected epidemiological range following acute PE. Given the lack of a control group and systematic screening, this cannot be interpreted as evidence of long-term disease modification by the intervention. Overall, our findings are descriptive and hypothesis-generating, warranting future randomized controlled trials to establish true comparative efficacy and safety.

Several important limitations should be acknowledged. First, this was a single-center, retrospective observational study without a randomized control group. This design precludes direct comparisons with CDT or anticoagulation alone and introduces potential selection bias. Second, the evaluation of the RV/LV ratio relied on two different imaging modalities (baseline CTPA and post-procedural echocardiography). These two modalities utilize different physical principles, which can lead to discrepancies in measuring cardiac chamber dimensions. While both methods are clinically validated for assessing right heart strain, the lack of a uniform imaging protocol throughout the study period may have introduced minor measurement errors that could affect the precision of our RV/LV ratio recovery analysis. Third, due to the retrospective nature of the study and varying clinical practices, follow-up echocardiographic data at 48 hours were only available for 34 of the 45 patients. This missing data reduces the statistical power for this specific endpoint. Fourth, the angiographic Miller index was assessed by the operating physicians rather than an independent core laboratory, which may introduce assessor bias and inter-observer variability. Fifth, the sample size of 45 patients is relatively small and lacks the statistical power to adequately assess rare procedural complications, such as pulmonary artery perforation. Finally, although 12-month clinical outcomes were documented, standardized functional assessments, such as the 6-minute walk test or quality-of-life questionnaires, were not systematically collected. As anatomical success does not always translate into functional improvement, the impact of this intervention on preventing post-PE syndrome remains to be fully elucidated. Future prospective, multicenter trials with independent core laboratory adjudication and long-term functional follow-up are required to validate these preliminary findings.

Conclusions

In conclusion, MT using the AcoStream system was feasible in this retrospective case series of patients with acute intermediate-high-risk PE and was associated with rapid reduction in angiographic thrombus burden and improvement in short-term hemodynamic parameters without major bleeding events. Given the observational design and lack of a comparator group, these findings should be considered hypothesis-generating and require confirmation in larger prospective studies.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2026-0913/rc

Data Sharing Statement: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2026-0913/dss

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2026-0913/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2026-0913/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Ethics Committee of Jinhua Municipal Central Hospital [No. (Research) 2026-Ethical Review-174] and individual consent for this retrospective analysis was waived.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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