A mechanical-based thrombectomy using the FlowTriever (FT) System is viable as a front-line treatment for high-risk pulmonary embolism (PE), according to findings presented at the American College of Cardiology Annual Scientific Sessions 2023 in New Orleans.

In a Clinical and Investigative Horizons session on Sunday, researchers pointed to the “significant, high-quality evidence,” and “positive outcome” of the FlowTriever for Acute Massive PE (FLAME) study.

In the enrollment of 53 patients for the FT arm of the study, the primary endpoint composite was 17% versus the performance goal of 32% (P=0.017).

“The FLAME study is the largest prospective interventional trial in high-risk PE,” said Mitchell J. Silver, director of the Center for Critical Limb Care and Endovascular Research at OhioHealth Group, Columbus, Ohio, on behalf of the FLAME investigating team.

“Large-bore mechanical thrombectomy with FlowTriever was associated with a significantly lower occurrence of meaningful in-hospital adverse clinical outcomes.”

Guidelines for hemodynamically unstable (high-risk or massive) PE recommend immediate reperfusion treatment due to the associated short-term mortality of over 30%.

Systemic thrombolytics are the recommended front-line treatment but carry high bleeding risks.

Mechanical thrombectomy has shown excellent survival outcomes in small studies of high-risk PE; however, data are limited.

The largest prospective interventional study in high-risk PE

The FLAME study adopted a prospective, multicenter, non-randomized, parallel-group, observational study approach.

The research team said a non-randomized study with a prespecified performance goal approach was taken to guard against inherent randomization challenges.

These challenges are related to the emergent presentation, low incidence (5% of all PE), and high rate of crossover or combined treatments.

Enrollment included 53 patients treated with front-line FlowTriever mechanical thrombectomy (FT arm) and 61 patients treated using other therapies (context arm), along with a prior therapy arm that was not shown due to low enrollment (n=1).

Patients selected were ≥18 years of age, presented with high-risk PE and had a systolic blood pressure of  <90 mmHg or drop of >40 mmHg for at least 15 minutes.

The research team, from the New York University Grossman School of Medicine, said the study enrollment was stopped after the positive interim analysis result met the criteria for early termination.

The primary endpoint is an in-hospital composite of all-cause mortality, bailout to an alternative thrombus removal strategy, clinical deterioration and major bleeding.

The FT arm's primary endpoint was compared to a prespecified performance goal of 32% based on a meta-analysis of the literature.

FLAME study results

Results revealed that the primary endpoint occurred in 17.0% of FT arm patients, a significantly lower rate than the performance goal of 32.0% (P = 0.017), and in 63.9% of context arm patients (P = 0.999).

Further findings revealed that components were numerically lower in the FT arm than the context arm, including in-hospital mortality (1.9% vs. 29.5%), bailout strategy (3.8% vs. 26.2%), clinical deterioration (15.1% vs. 21.3%), and major bleeding (11.3% vs. 24.6%).

Notable safety outcomes

Regarding safety outcomes, there was one incidence of stroke in the FT arm compared to four in the context arm. A total of 12 subjects encountered device-related complications in the FT arm compared to 10 in the context arm of the study.

There were no reports of device-related tricuspid valve injuries, cardiac injuries, or pulmonary vascular injuries in the FT arm.

In the context arm, out of 42 patients, there were two incidences (4.8%) of intracerebral hemorrhage (ICH), who received systemic thrombolytics.

Silver concluded by adding that the FlowTriever was associated with a remarkably low mortality rate of 1.9% compared to the context arm’s mortality rate of 29.5% and performance goal rate of 28.5%.

“Large-bore mechanical thrombectomy with the FlowTriever System likely reduces mortality in high-risk PE patients by rapidly unloading the RV,” said Silver. “This quickly reverses the obstructive shock death spiral and simultaneously improves oxygenation.

“A care pathway similar to STEMI and stroke may benefit high-risk PE patients.”

The study was sponsored by Inari Medical, the manufacturer of the FlowTriever device.