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NEW ORLEANS -- Large-bore mechanical thrombectomy for high-risk pulmonary embolism (PE) was associated with fewer major adverse outcomes than other approaches, the FLAME study showed.

Clot removal with the FlowTriever device exceeded the performance goal for the in-hospital composite risk of all-cause mortality, bailout to alternate thrombus removal strategy, clinical deterioration, and major bleeding (17.0% vs 32.0%, P<0.01).

The procedure also bested contemporary comparison with primary treatment using non-FlowTriever therapies, for which the primary endpoint rate was 63.9%, reported Mitchell J. Silver, DO, of OhioHealth Heart and Vascular in Columbus, at the American College of Cardiology annual meeting.

"The big lesson here is that this large-bore thrombectomy device works in patients with high-risk PE," Silver told attendees.

While the observational study couldn't say so definitively, he suggested that, based on the study findings, the FlowTriever "likely reduced mortality in high-risk PE patients by rapidly unloading the right ventricle, reversing the shock spiral, improving oxygenation."

The in-hospital mortality rate was 1.9% in the FlowTriever-treated patients, compared with 29.5% among patients treated with other primary therapies.

Other primary endpoint components also favored FlowTriever use, including bailout (3.8% vs 26.2%), clinical deterioration (15.1% vs 21.3%), and major bleeds (11.3% vs 24.6%).

"After years and years of very little happening, we now have a lot of things going on and this is one of four significant clinical trials that should be completed in 2023," said session panelist Joshua A. Beckman, MD, of UT Southwestern Medical Center in Dallas. "The field will be changing dramatically by next year."

One of those changes needs to be a shift in approach to one like ST-elevation myocardial infarction, Silver argued.

"I think the one issue is the approach to this population of high-risk PE patients has become too algorithmic," he said. "That's because the guidelines do say systemic thrombolysis is the frontline treatment. But in centers who have a lot of experience with large-bore thrombectomy, there's an 'aha' moment. Systemic thrombolytics aren't necessarily at the front of the mind, it's call the interventionalist, get the cath lab team in, and do thrombectomy."

However, he acknowledged that achieving results like these -- which came from centers experienced in large-bore thrombectomy -- widely across the field will take time "as we all teach each other. It's that perfect storm of rapid diagnosis to the cath lab with the right operator. I do think it will be generalizable over time."

Silver noted that this was not a randomized trial, which was a limitation. Rather, all high-risk PE patients at 11 centers were concurrently enrolled using electronic medical records without need for patient consent, such that there would be no bias in enrollment, he explained. Given how hard a randomized trial would be to enroll, this design had been suggested by an American Heart Association scientific statement as the way to generate evidence in high-risk PE, he added.

Treatment strategy was at the treating physician's discretion. For the 61 patients treated without FlowTriever thrombectomy among the total of 115 patients in the study, systemic thrombolytics were used in 68.9%, anticoagulation alone in 23.0%, catheter-directed thrombolytics in 6.6%, and surgical thrombectomy in 1.6%. No patients underwent mechanical thrombectomy with non-FlowTriever devices, although it was allowed.

The trial enrolled adults (average ages 62-64) for whom PE was determined to be the cause of shock who were high risk based on a systolic blood pressure less than 90 mm Hg or a drop of more than 40 mm Hg for at least 15 minutes, a need for vasopressor support, resuscitation after cardiac arrest with less than 30 minutes of CPR and a Glasgow Coma Scale score over 8, or a combination of those factors.

Exclusion criteria included COVID-19 positive status, out-of-hospital cardiac arrest with a low Glasgow Coma Scale sore or ongoing CPR for more than 30 minutes, and chronic medical conditions with short life expectancy.

The study was stopped early after the prespecified interim analysis at 50 patients due to efficacy.

The FlowTriever trial included many more patients with contraindications to lytics (41.5% vs 11.7% in non-FlowTriever patients), more patients with deep vein thrombosis (30.8% vs 20.0%) and active cancer (13.5% vs 8.5%), and fewer advanced shock patients (11.3% vs 32.8% in SCAI shock stage E).

In terms of safety, there was one stroke case in the FlowTriever arm (1.9%) compared with four in the other contemporary treatment group (6.6%) and device-related complications in 22.6% and 16.4%, respectively. None of the FlowTriever events were device-related tricuspid valve injury, cardiac injury, or pulmonary vascular injury. Intracerebral hemorrhage occurred in two of the systemic thrombolysis-treated patients.

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