High-risk pulmonary embolism (HR-PE) is characterized by hemodynamic instability and marked deformation of the right ventricular (RV) fiber, which can lead to acute RV failure and hemodynamic collapse, with in-hospital mortality close to 25%. While guidelines recommend anticoagulant treatment followed by thrombolytics, these strategy carries a high risk of bleeding and is not suitable for all patients.
In many critical pathology scenarios, high-risk patients have been excluded from most clinical studies. Among such subjects are those related to high-risk PE and its invasive management. Taking note of the difficulties posed by selection and randomization, the American Heart Association (AHA) initially proposed a comparison based on performance goals (PG).
Based on this premise, prospective and multicenter non-randomized study FLAME (FlowTriever for Acute Massive PE) was conducted with the aim of evaluating outcomes in consecutive high-risk PE patients treated with mechanical thrombectomy (MT) following the PG.
The study included adult patients who met at least one of the following criteria: systolic blood pressure (SBP) <90 mmHg or a 40% decrease in systolic blood pressure, need for vasopressor support or resuscitation after cardiac arrest (CA) within 30 minutes. Patients with unwitnessed CA or time elapsed >30 minutes since CA were excluded. Patients were assigned to two groups: the FlowTriever group and the Context group (which received a different treatment from FlowTriever, such as systemic fibrinolysis, anticoagulation, or catheter-directed fibrinolysis).
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The primary endpoint (PEP) consisted of a combination of in-hospital mortality, transition to another thrombus removal procedure (bailout), clinical deterioration, and severe bleeding. These PEP events were compared with predefined PGs. Safety secondary outcomes included ischemic or hemorrhagic stroke (IS) and device-related complications, the use of rescue devices, and the eventual need for extracorporeal membrane oxygenation (ECMO).
The study included a total of 115 HR-PE patients from 11 medical centers in the United States, with 53 in the FlowTriever group and 61 in the Context group. Notably, 41.5% of patients in the FlowTriever group had contraindications for fibrinolysis, compared with 11.7% in the Context group. In the FlowTriever group, an estimated blood loss of 100 mL was reduced to 50 mL with the use of the FlowSaver device.
When evaluating treatment in the Context group, most patients were treated with systemic fibrinolysis (68.9%), followed by anticoagulation alone (23%), while catheter-directed fibrinolysis was used in 6.6% of cases, and surgical embolectomy in 1.6%. The average time to treatment was 6.1 hours in the FlowTriever group and 4.1 hours in the Context group.
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The PEP occurred in 17% of FlowTriever group patients (95% confidence interval [CI]: 8.1%–29.8%), which was significantly better compared with the predefined PG of 32% (p<0.01). In the Context group, the PEP was observed in 63.9% of patients (95% CI: 50.6%–75.8%), with a breakdown showing 66.7% in the fibrinolysis group and 71.4% in the anticoagulation group. In-hospital mortality was 1.9% in the FlowTriever group and 29.5% in the Context group, with a bailout rate of 3.8% in the FlowTriever group, significantly lower than the 26.2% in the Context group.
Regarding safety, severe bleeding was observed in 11.3% of the FlowTriever group patients and 24.6% of the Context group patients. Serious treatment-related adverse events occurred in 18.9% of patients treated with MT, compared with 37.7% of patients who were subjected to other strategies (most of these events did not involve damage to the tricuspid valve or pulmonary vasculature).
Conclusions
The long-awaited FLAME study is the largest prospective study on the interventional treatment of high-risk PE. It is important to note that, as a non-randomized study, only comparisons between two parallel patient groups can be estimated. The composite outcome was 17%, significantly lower when compared to the known PG of 32%, primarily due to a decrease in in-hospital mortality, which was low and substantial (1.9%).
Dr. Omar Tupayachi.
Member of the Editorial Board of SOLACI.org.
Reference: Silver, Mitchell J et al. “Outcomes in High-Risk Pulmonary Embolism Patients Undergoing FlowTriever Mechanical Thrombectomy or Other Contemporary Therapies: Results From the FLAME Study.” Circulation. Cardiovascular interventions vol. 16,10 (2023): e013406. doi:10.1161/CIRCINTERVENTIONS.123.013406.
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