Imperative Care has reported encouraging sex-specific safety and effectiveness findings from the SYMPHONY-PE clinical trial, showing that women with intermediate-risk pulmonary embolism experienced substantial clot removal and improvement in right-heart function after treatment with the Symphony Thrombectomy System. Announced on November 3, 2026, the prespecified analysis examined 106 patients across 17 United States centres, including 42 women and 64 men, and found no deaths or device-related serious adverse events in either group through 30 days.
The findings, presented at Transcatheter Cardiovascular Therapeutics 2026 and published in the Journal of the Society for Cardiovascular Angiography and Interventions, address a clinically important concern about the safety of large-bore thrombectomy in women. Despite having similar initial clot burdens, female participants showed greater evidence of cardiac stress before treatment. At 48 hours, their mean right ventricular-to-left ventricular diameter ratio was 1.03, compared with 1.14 among men, a statistically significant difference that remained after multivariable adjustment.
However, the results do not establish that women benefit more from Symphony thrombectomy or that the procedure eliminates sex-related differences in complications. The study was not randomised against anticoagulation alone, its female subgroup was relatively small, and a separate scientific report identified two major bleeding events among women compared with none among men with available follow-up. The findings support further investigation rather than a definitive conclusion of equivalent safety.
Why is sex-specific evidence important for pulmonary embolism thrombectomy?
Pulmonary embolism occurs when a blood clot obstructs one or more arteries carrying blood from the heart to the lungs. Depending on the size and location of the obstruction, the condition can increase pressure within the pulmonary circulation and place substantial strain on the right ventricle. Severe cases can produce cardiovascular collapse, while intermediate-risk patients may have preserved blood pressure despite evidence of right-heart dysfunction.
Treatment decisions are influenced by clinical severity, haemodynamic stability and the patient’s underlying risk factors. Anticoagulation remains the foundation of management for most patients, while catheter-directed interventions may be considered in selected circumstances. The benefits of removing a clot mechanically must be weighed against the risks associated with introducing a large catheter into the vascular system.
Women may differ from men in body size, vascular anatomy, underlying health conditions and physiological responses to pulmonary embolism. Previous studies of large-bore cardiovascular procedures have raised concerns about bleeding and vascular complications in female patients. These observations make sex-specific evaluation relevant when introducing technologies requiring substantial vascular access.
Arman Qamar, director of the Center for Cardiovascular Personalized Medicine at Endeavor Health Cardiovascular Institute and a senior author of the analysis, identified this evidence gap as an important reason for examining the SYMPHONY-PE population separately. The investigators wanted to determine whether baseline differences translated into different procedural or short-term outcomes.
The new analysis contributes prospective evidence from patients undergoing the same general treatment strategy. Nevertheless, it cannot establish how outcomes would have differed if women and men had received another form of pulmonary embolism treatment.
What did the SYMPHONY-PE study reveal about baseline differences between women and men?
The original SYMPHONY-PE trial enrolled 109 patients across 17 United States centres. The full population included 43 women and 66 men, while the modified intention-to-treat population used for the principal effectiveness analyses comprised 42 women and 64 men. The smaller population excluded patients receiving certain additional treatments that could complicate interpretation of the device’s effect.
Investigators found that women had greater evidence of cardiac stress before thrombectomy despite broadly similar clot burdens. A separate scientific summary described more frequent elevation of cardiac injury or strain biomarkers and higher shock-risk scores among female participants. These differences suggest that clot burden alone may not fully describe the physiological consequences of pulmonary embolism.
A patient with a similar extent of arterial obstruction may experience a different degree of right ventricular dysfunction depending on existing cardiovascular conditions and physiological reserve. This makes clinical severity assessment more complicated than measuring the amount of clot visible on imaging. Biomarkers, ventricular dimensions and haemodynamic information can provide complementary insights.
However, the relationship between sex and these variables cannot be resolved completely in a small observational subgroup. Differences may reflect patient characteristics that were unevenly distributed between women and men. Statistical adjustment can account for selected measured factors but cannot eliminate every possible source of confounding.
The finding is therefore most useful in highlighting the importance of assessing right-heart stress directly. It should not be interpreted as establishing that pulmonary embolism is universally more severe in women.
How did right ventricular function change after Symphony thrombectomy?
One of the principal measures in pulmonary embolism device studies is the ratio between right ventricular and left ventricular size. Pulmonary arterial obstruction can increase the workload on the right ventricle, causing it to enlarge relative to the left ventricle. Reduction in the right ventricular-to-left ventricular ratio after treatment can indicate improvement in this aspect of cardiac strain.
In the sex-specific analysis, the mean ratio at 48 hours was 1.03 among women and 1.14 among men. The difference was statistically significant, with a reported p-value of 0.006. It remained significant after multivariable adjustment, with a p-value of 0.010.
These results indicate that women had a more favourable measured ratio at the 48-hour assessment. However, the comparison concerns the post-treatment values rather than demonstrating that female patients experienced a greater treatment effect than they would have achieved under another therapy. Baseline characteristics and the extent of change must also be considered.
In the original trial population, the mean reduction in the ventricular ratio was 0.44 at 48 hours. That result exceeded the study’s prespecified effectiveness performance goal and provided important evidence supporting the Symphony system’s clinical development. It also helps place the new subgroup findings within the larger study.
The limitation is that improvement in right ventricular dimensions is an intermediate physiological outcome. It may be clinically meaningful, but it does not independently establish improved survival or lower rates of recurrent pulmonary embolism.
Why was the reduction in pulmonary artery pressure particularly interesting among women?
Pulmonary artery pressure reflects the resistance encountered as blood moves from the right ventricle into the lungs. An obstructing clot can increase this resistance, creating a greater workload for the right side of the heart. Mechanical removal of thrombus may reduce obstruction and lower pulmonary artery pressure during or after the procedure.
Women in the SYMPHONY-PE subgroup experienced an unadjusted mean pulmonary artery pressure reduction of 28%, compared with 19% among men. The difference reached statistical significance before adjustment, with a reported p-value of 0.02. This suggested a potentially larger immediate haemodynamic improvement in the female group.
However, the association between sex and post-thrombectomy mean pulmonary artery pressure was no longer statistically significant after multivariable adjustment. This distinction is important because the unadjusted result may reflect differences in baseline characteristics rather than an independent effect associated with sex.
A larger reduction in pressure also does not necessarily mean a patient has achieved a better long-term outcome. Pulmonary artery pressure is influenced by multiple physiological factors, including vascular resistance, blood flow and right ventricular function. Changes during a procedure provide valuable information but require clinical context.
The adjusted findings therefore limit the strength of any claim that Symphony thrombectomy produces superior pressure reduction in women. The study supports substantial haemodynamic improvement in both groups while leaving the reasons for the numerical difference unresolved.
What do the zero 30-day deaths and device-related serious adverse events establish about safety?
No deaths or device-related serious adverse events were reported in either sex group through the 30-day follow-up period. This is an encouraging finding because pulmonary embolism can cause serious deterioration, and large-bore thrombectomy introduces procedural risks of its own. The absence of these outcomes supports the short-term safety experience reported in the study.
The original SYMPHONY-PE trial also met its prespecified primary safety endpoint. Across the full intention-to-treat population of 109 patients, one major adverse event was identified within 48 hours, corresponding to an event rate of 0.9%. The result was below the study’s predefined safety performance goal.
However, device-related serious adverse events and major bleeding are not interchangeable measures. A patient may experience a bleeding complication without that event being classified as a device-related serious adverse event under the applicable definitions. This makes it essential to examine individual safety outcomes rather than rely solely on the absence of device-related serious events.
The scientific communication accompanying the sex-specific analysis identified two major bleeding events among women and none among men with available follow-up. The small number of events prevents a reliable statistical conclusion about whether female patients face a higher risk. Nevertheless, the events should not be omitted from an assessment of sex-specific safety.
A 30-day observation period also cannot establish the full longer-term risk profile. The study provides reassuring short-term evidence while supporting the need for additional evaluation of bleeding, vascular complications and subsequent clinical outcomes.
How does the Symphony Thrombectomy System remove pulmonary embolism clots?
Symphony is a pump-driven aspiration thrombectomy system designed to remove thrombus from blood vessels through catheter-based intervention. The platform includes 24-French and 16-French catheter options intended to provide access to different parts of the pulmonary arterial anatomy. Its aspiration mechanism is designed to draw clot material into the catheter for removal.
The larger 24-French catheter was used in 91% of women and 94% of men in the analysed population. This indicates that the majority of procedures involved large-bore aspiration rather than the smaller catheter alone. The similarity in catheter use also provides useful context when comparing outcomes between groups.
The system incorporates real-time feedback intended to help operators understand aspiration conditions during treatment. It also includes ProHelix Mechanical Assist, a component designed to help facilitate clot ingestion when additional mechanical assistance is needed. These features are intended to support efficient thrombus extraction.
However, the use of larger catheters creates important vascular-access considerations. Inserting and removing the device requires attention to vessel anatomy, bleeding risk and haemostasis. The system’s technical features cannot eliminate complications associated with vascular access.
The key clinical question is whether clot removal produces a sufficient benefit to justify these procedural risks. The new subgroup findings provide information about patients who underwent thrombectomy but do not directly compare that strategy with anticoagulation alone.
How do the latest findings compare with the original SYMPHONY-PE trial results?
The original multicentre investigation was a prospective, single-arm study involving patients with acute intermediate-risk pulmonary embolism. Published findings showed a mean right ventricular-to-left ventricular ratio reduction of 0.44 within 48 hours. The investigators also reported substantial improvements in pulmonary artery pressure and clot burden.
Mean pulmonary artery pressure declined from approximately 29.1 mmHg to 22.2 mmHg, representing a 24% reduction. The modified Miller index, an imaging-based measure of pulmonary arterial clot burden, declined by approximately 38%. These findings supported the conclusion that the device could remove clot material and improve selected physiological measures.
The trial’s primary efficacy and safety results met their respective performance goals. However, those goals were based on historical evidence rather than direct randomisation against an alternative treatment. Consequently, the original study did not establish that Symphony was superior to anticoagulation, thrombolysis or another mechanical thrombectomy system.
The new sex-specific analysis extends that evidence by examining whether outcomes differed between women and men. Its main contribution is not a new overall procedural success claim but more detailed information about baseline risk and short-term response in the two groups.
The distinction matters because subgroup findings can be clinically informative without changing the evidentiary strength of the original study design. A larger randomised comparison would provide stronger evidence about the incremental benefit of thrombectomy.
What is the regulatory status of Symphony, and how does it differ from the company’s developing technologies?
The Symphony Thrombectomy System is part of Imperative Care’s commercial vascular treatment portfolio. The FDA issued a 510(k) substantial-equivalence decision covering the Symphony Thrombectomy System and a related 16-French configuration on August 28, 2025. The company’s current clinical analysis therefore concerns an established device platform rather than an unapproved experimental system awaiting its first marketing authorisation.
However, the FDA’s clearance should not be interpreted as endorsement of a sex-specific superiority claim. The subgroup analysis was published after the earlier regulatory decision and provides additional evidence relevant to clinical use. The manufacturer’s authorised indications and product instructions remain the appropriate framework for device selection.
Imperative Care also offers products for stroke and peripheral vascular thrombectomy, including its Zoom Stroke System and Prodigy Thrombectomy System. These technologies address different anatomical and clinical needs and should not be treated as interchangeable with Symphony. Their regulatory status and supporting evidence must be evaluated individually.
The company is separately developing the Telos Robotic Platform, which remains in development and is not cleared or approved for commercial use. Its inclusion in Imperative Care’s broader research strategy does not change the status of the currently marketed Symphony system.
For hospitals, the commercial relevance of the new analysis lies in supporting a more detailed discussion of patient selection and expected outcomes. It does not establish a new indication or demonstrate that the device is appropriate for every patient with pulmonary embolism.
Why does the absence of randomisation limit conclusions about thrombectomy effectiveness?
The SYMPHONY-PE trial enrolled patients selected to receive mechanical thrombectomy and followed their outcomes after the procedure. This design can provide information about technical success, changes in physiological measurements and treatment-associated adverse events. However, it cannot directly determine how the same patients would have performed with anticoagulation alone.
Many patients with intermediate-risk pulmonary embolism improve under anticoagulant treatment and appropriate monitoring. Some may experience clinical deterioration and require more intensive intervention. Identifying which patients benefit most from early thrombectomy remains an important question in pulmonary embolism care.
The new analysis also compares women and men rather than randomly assigning patients to different treatment strategies. Sex-related differences in anatomy, biomarkers and clinical history may influence the results. Even adjusted analyses cannot completely eliminate these potential differences.
The results therefore should not be interpreted as establishing identical procedural risk between women and men. The sample was too small to exclude clinically meaningful differences in uncommon events such as major bleeding. Likewise, the absence of deaths in both groups is reassuring but cannot establish a survival advantage.
Future research could examine whether specific risk characteristics predict a more favourable benefit-risk balance. Such evidence would help clinicians determine when thrombectomy is preferable to continued anticoagulation or other interventions.
What could the findings mean for Imperative Care’s position in pulmonary embolism treatment?
Imperative Care is a privately held medical technology company headquartered in Campbell, California. Its commercial products focus on removing blood clots from neurovascular and peripheral circulations. The Symphony system represents its presence within the pulmonary embolism treatment market, where several competing catheter-based technologies are already available.
The new analysis may support discussions with clinicians concerned about large-bore access in female patients. Demonstrating comparable short-term outcomes in a prospective cohort could increase confidence in considering the device for appropriately selected women. However, the findings do not establish a direct competitive advantage over other pulmonary embolism thrombectomy platforms.
Commercial adoption will continue to depend on physician experience, procedural performance, product cost and the quality of clinical evidence. Hospitals may also evaluate the availability of pulmonary embolism response teams and the ability to manage complications. The device’s clinical results must therefore be considered within a broader treatment pathway.
The company has not disclosed new sales figures, financing or commercial contracts associated with the November analysis. Its potential financial benefit cannot be quantified from the study publication. The main value is additional evidence supporting a product already within its portfolio.
The published findings could also inform future research examining treatment outcomes in women and other patient subgroups. Such studies would strengthen the evidence base while helping clinicians understand which patients are most likely to benefit.
What evidence is needed before sex-specific thrombectomy recommendations can become more precise?
Larger studies are needed to determine whether women and men experience genuinely different complication rates or treatment responses. Such investigations should be sufficiently powered to evaluate uncommon but important outcomes, including major bleeding, vascular injury and clinical deterioration. Longer follow-up would help determine whether early physiological improvement translates into durable benefit.
Randomised treatment comparisons would provide stronger evidence about the incremental value of thrombectomy. The appropriate clinical question is not simply whether patients improve after mechanical clot removal, but whether outcomes are better than those achieved through another suitable management strategy. This distinction matters particularly in intermediate-risk pulmonary embolism.
Researchers may also need to examine the relationship between baseline cardiac stress, catheter size and patient anatomy. The latest findings suggest that women can present with greater evidence of right-heart strain despite similar clot burden. Understanding why this occurs may improve risk assessment and treatment selection.
Imperative Care’s new SYMPHONY-PE analysis offers reassuring evidence that female patients can experience substantial clot reduction and right-heart improvement following large-bore aspiration thrombectomy. However, the small sample, observed bleeding events and lack of a randomised comparator prevent definitive claims about comparative safety or clinical superiority. Its lasting contribution may be helping clinicians ask more precise questions about patient selection and sex-specific procedural risk.
