- In a prospective, multicenter trial of the FlowTriever Retrieval/Aspiration System in 106 patients with acute intermediate-risk PE, the average reduction in the right ventricular/left ventricular ratio was 0.38
- Four patients (3.8%) experienced major adverse events, including one who had a pulmonary hemorrhage; an independent committee judged that none of the events were device-related
- There were no intracerebral hemorrhages, major vascular complications or device-related pulmonary or cardiac injuries
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In patients with intermediate-risk pulmonary embolism (PE), catheter-directed thrombolysis (CDT) has been shown to be more effective than anticoagulation alone. It reduces the right ventricular/left ventricular (RV/LV) ratio more quickly. However, CDT is contraindicated for many patients with PE because of the risk of major bleeding.
Percutaneous mechanical thrombectomy may avoid the potential complications of thrombolytic therapy, but it has not been studied systematically. The American College of Chest Physicians currently recommends catheter-based mechanical thrombectomy only for hypotensive patients with acute PE who are at high bleeding risk, have life-threatening shock or did not respond to thrombolysis.
Kenneth Rosenfield, MD, section head for Vascular Medicine and Intervention at Massachusetts General Hospital, recently participated in FLARE, the first investigational device exemption trial of mechanical thrombectomy for acute intermediate-risk PE. In JACC: Cardiovascular Interventions, the FLARE investigators report that catheter-directed mechanical thrombectomy was as effective as CDT in this setting and had a favorable safety trial.
The FlowTriever System
The FLARE was a manufacturer-sponsored study of the FlowTriever Retrieval/Aspiration System, a single-use mechanical thrombectomy device that requires large-bore femoral venous access. An aspiration guide catheter is advanced over a guidewire through the right ventricle to the level of the right or left pulmonary artery, just proximal to the clot. The FlowTriever Catheter is then advanced through the catheter, and self-expanding mesh disks are deployed into the clot. Once engaged, the clot is extracted via aspiration. The procedure can be repeated several times per side if necessary.
Prospective Multicenter Trial
FLARE enrolled 106 patients at 18 U.S. sites between April 2016 and October 2017. Eligibility criteria were:
- Age 18 to 75 years
- Symptomatic proximal PE, documented by computed tomography (CT), of no more than 14 days duration
- Hemodynamic stability: no vasopressor requirement, heart rate <130 beats/minute and systolic blood pressure ≥90 mm Hg
- RV/LV ratio ≥0.9
Immediately following thrombectomy, local thrombolytic therapy could be provided at the physician's discretion. Two patients (1.9%) received adjunctive thrombolysis because of large clots, and per protocol, they were not included in the effectiveness analysis.
Primary Effectiveness Endpoint
The primary effectiveness endpoint was the change in RV/LV ratio from baseline to 48 hours. In the 101 patients who had both baseline and post-thrombectomy measurements, the RV/LV ratio decreased by an average of 0.38 (P < .0001).
The researchers note that this reduction compares favorably with the 0.34 value reported in a recent meta-analysis of CDT trials.
Most FLARE study sites enrolled fewer than five patients, but there was no difference between sites in effectiveness outcomes. Regression analysis did not detect any demographic or clinical characteristic that predicted effectiveness.
Primary Safety Outcomes
The primary safety endpoint was the composite rate of major adverse events (MAEs), defined as any of the following within 48 hours of treatment: device-related death, major bleeding, or treatment-related clinical deterioration, pulmonary vascular injury or cardiac injury.
Four patients (3.8%) experienced MAEs, a rate significantly lower than the performance goal of <25% (P < .0001) and similar to the incidence with CDT. An independent committee judged that all MAEs represented treatment-related clinical deterioration but were not device-related:
- One patient (0.9%) had a major bleeding event, an intraprocedural pulmonary hemorrhage that required a lower lobectomy. It was considered to be due to pulmonary infarction and reperfusion injury; no injury to the pulmonary artery was observed
- Two patients with minimal thrombus removal during thrombectomy experienced respiratory deterioration during or immediately after the procedure that required emergent intubation
- One patient became agitated during the procedure, received increasing sedation and had ventricular fibrillation that required cardioversion and emergent intubation. Underlying coronary disease with ST-segment elevation was diagnosed, and coronary angioplasty and stenting were performed before thrombectomy resumed
There were no intracerebral hemorrhages, major vascular complications or device-related pulmonary or cardiac injuries.
Advantages of Percutaneous Mechanical Thrombectomy
Percutaneous mechanical thrombectomy has several advantages over other therapeutic approaches:
- Its hemodynamic benefit is potentially similar to that of systemic or local thrombolysis, but it occurs faster
- The FlowTriever device can be used in patients who are at high risk of bleeding, such as postoperative patients, who represent about 30% of the PE population
- Mechanical thrombectomy has the potential to reduce hospital costs: in this study the average length of intensive care unit stay was 1.5 days, with 41% of patients not needed intensive care unit admission, and the average hospital stay was 4.1 days
The FlowTriever received U.S. Food and Drug Administration approval for the PE indication in May 2018.
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