Mechanical Thrombectomy Outcomes in Intermediate-risk Pulmonary Embolism Patients: Insights from the FLASH Registry

The optimal treatment strategy for intermediate-risk pulmonary embolism (PE) remains uncertain, confounded by a diverse array of clinical presentations. We report baseline characteristics and outcomes for intermediate-risk PE patients undergoing mechanical thrombectomy (MT) with the FlowTriever System (Inari Medical) from the complete US cohort of the FLASH Registry.

Materials and Methods:

Patients enrolled in the prospective, multicenter FLASH Registry were risk-stratified according to ESC guidelines, including intermediate-high and intermediate-low risk subgroups. The primary endpoint was a major adverse event (MAE) composite within 48 hours. Additional safety and clinical outcomes were assessed through 6 months.

Results:

Among 800 patients enrolled in FLASH, 734 (91.9%) had intermediate-risk PE, including 76.7% with intermediate-high risk and 7.4% with intermediate-low risk. Baseline characteristics (Table 1) included notably high rates of sPESI ≥ 1, elevated lactate, and low cardiac index (CI), even among intermediate-low risk patients. Following MT, mean PA pressure reduced from 32.6±8.9 to 25.0±8.8 mmHg and CI improved from 1.7±0.3 to 1.9±0.6 L/min/m² in patients with low baseline CI. MAEs occurred in 14 (1.9%) patients. All-cause mortality was 0.3% at 48 hours, 0.9% at 30 days, and 7.0% at 6 months.  At follow-up, significant improvements from baseline included reduced rates of severe dyspnea (mMRC 3+, 66.0% to 13.4% at 48h and 3.1% at 6m, p< 0.0001) and moderate-to-severe RV dysfunction (64.8% to 23.3% at 48h and 1.2% at 6m, p< 0.0001) as well as improved quality of life (PEmb-QoL Frequency of Complaints score, 12.5 at 48h to 3.1 at 6m, p< 0.0001).

Conclusion:

Patients with intermediate-high and intermediate-low risk PE present with a diverse spectrum of clinically significant disease despite hemodynamic stability. Among such patients, MT with the FlowTriever System demonstrated favorable safety with low mortality, immediate hemodynamic benefits, and sustained clinical improvements through 6 months.