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BOSTON -- Clot retrieval for intermediate- to high-risk pulmonary embolism (PE) in patients who don't fit conventional criteria for intervention was safe and associated with immediate hemodynamic and symptom benefits, the FLASH registry showed.

Mechanical thrombectomy using the FlowTriever System resulted in major adverse events (AEs) in 1.8% of patients but no device-related deaths among the 800 patients studied, reported Catalin Toma, MD, of the University of Pittsburgh Medical Center Heart and Vascular Institute, at the Transcatheter Cardiovascular Therapeutics (TCT) meeting hosted by the Cardiovascular Research Foundation. The findings were simultaneously published in .

Hemodynamic changes included a prompt 7.6-mm Hg drop in mean pulmonary artery pressure (down 23.0% from baseline) and a 0.3-L/min/m² increase in cardiac index (up 18.9%) on average in patients with depressed baseline values (both P<0.0001).

Severe dyspnea prevalence dropped from 66.5% at baseline to 15.6% at 48 hours post procedure (P<0.0001).

"The strong safety profile of the procedure, effective thrombus removal, lack of bleeding concerns, and low mortality rates suggest that mechanical thrombectomy may shift the risk-benefit balance towards a more aggressive treatment algorithm for PE patients," Toma's group concluded.

PE guidelines have advocated thrombectomy and other advanced interventions only for patients who decompensate or have absolute contraindications to thrombolytics.

The mortality rate in FLASH was 0.3% at 48 hours, none adjudicated as related to the study device. One patient died from cardiopulmonary arrest on the second day post-thrombectomy; the other died after developing a new PE the day after thrombectomy.

Four other deaths through 30-day follow-up (0.8% all-cause mortality) were also deemed unrelated to the study device. Putting it in context, Toma pointed to 10.2% all-cause mortality at 30 days in the U.S. in the PERT database and 10.0% rate overall or 3.2% with catheter-directed thrombolysis in a prior meta-analysis.

The 30-day all-cause readmission rate in FLASH was 6.2% (1.4% related to PE treatment), compared with 24.4% in the PERT data.

"Encouraging trends here," summarized Toma, although acknowledging that clinical outcomes need to be assessed in randomized trial data, not just for the device used in the study, but also for the many others being developed for use in PE.

Heart rate improvements in the trial along with lower pulmonary arterial pressures are surrogates of improved outcomes, noted TCT press conference panelist Felix Mahfoud, MD, of Saarland University Medical Center in Homburg, Germany. Hard outcomes comparing the procedure against the usual strategies of systemic thrombolytics or heparin are needed, looking at both mortality and ICU stay, he said. "All of these are very relevant endpoints in these very sick patients."

Toma pointed to the ongoing trial to "provide important evidence regarding the safety and effectiveness of FlowTriever mechanical thrombectomy compared with catheter-directed thrombolysis."

In what his group noted is as-yet "the largest prospective interventional study in the field of PE," FLASH enrolled patients treated with mechanical thrombectomy using the FlowTriever System. The analysis included only the 800 patients (mean age 61, 54% male) enrolled at the 50 participating sites in the U.S., while another 200 are planned to be enrolled in Europe.

The cohort was largely at intermediate risk, with submassive PE, by European Society of Cardiology guideline criteria (92.1%); the remaining 7.9% had high-risk, massive PE.

The decision to intervene came from the local heart team, with 32.1% of patients judged by the treating physician to have either an absolute or relative contraindication to thrombolytics.

Most primary endpoint events were major bleeds, which occurred in 1.4% of patients. Intraprocedural events accounted for the remaining major AEs, at a rate of 0.4% at 48 hours.

Mechanical thrombectomy holds a potential advantage in reducing bleeding risk compared with systemic thrombolytics, Toma noted, pointing to a rate of about 10% with systemic thrombolytics.

One concern with the registry data was that some 8% of patients had no 30 day follow-up, pointed out TCT press conference panelist Riyaz Bashir, MD, of Temple University in Philadelphia. A bigger concern was that many patients were consented for participation after the procedure, such that investigators could have selectively decided not to consent patients who developed safety events, he added.

Toma responded that patients who got consent the day of the procedure versus the day after it had similar same major AE rates.

Ultimately, randomized data are the only way to settle whether thrombectomy should be moved into less sick PE patients, affirmed TCT press conference panelist Ajay J. Kirtane, MD, of NewYork-Presbyterian Hospital in New York City. For example, there are potential complications from all these types of devices sucking out blood as they grab the thrombus, which can damage red cells due to shearing even if the blood is returned. "We can have a device a day coming up, but what are we comparing to conventional therapy?"

Not only does thrombectomy need to be compared against systemic therapies but also catheter-based thrombolytics, agreed Robert Bonow, MD, of Northwestern Medicine in Chicago. "This is a really important step forward with a different way of approaching the problem without giving antithrombotic drugs, but we do need randomized trials."

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