Acute outcomes for the full US cohort of the FLASH mechanical thrombectomy registry in pulmonary embolism

Abstract

Background: Evidence supporting interventional pulmonary embolism (PE) treatment is needed.

Aims: We aimed to evaluate the acute safety and effectiveness of mechanical thrombectomy for intermediate- and high-risk PE in a large real-world population.

Methods: FLASH is a multicentre, prospective registry enrolling up to 1,000 US and European PE patients treated with mechanical thrombectomy using the FlowTriever System. The primary safety endpoint is a major adverse event composite including device-related death and major bleeding at 48 hours, and intraprocedural adverse events. Acute mortality and 48-hour outcomes are reported. Multivariate regression analysed characteristics associated with pulmonary artery pressure and dyspnoea improvement.

Results: Among 800 patients in the full US cohort, 76.7% had intermediate-high risk PE, 7.9% had high-risk PE, and 32.1% had thrombolytic contraindications. Major adverse events occurred in 1.8% of patients. All-cause mortality was 0.3% at 48-hour follow-up and 0.8% at 30-day follow-up, with no device-related deaths. Immediate haemodynamic improvements included a 7.6 mmHg mean drop in mean pulmonary artery pressure (-23.0%; p<0.0001) and a 0.3 L/min/m² mean increase in cardiac index (18.9%; p<0.0001) in patients with depressed baseline values. Most patients (62.6%) had no overnight intensive care unit stay post-procedure. At 48 hours, the echocardiographic right ventricle/left ventricle ratio decreased from 1.23±0.36 to 0.98±0.31 (p<0.0001 for paired values) and patients with severe dyspnoea decreased from 66.5% to 15.6% (p<0.0001). Conclusions: Mechanical thrombectomy with the FlowTriever System demonstrates a favourable safety profile, improvements in haemodynamics and functional outcomes, and low 30-day mortality for intermediate- and high-risk PE.

Figure 1. On-table improvements in mean pulmonary artery pressure.

Alluvial graph of the number and proportion of patients with normal (<25 mmHg), mildly elevated (≥25 and <35 mmHg), moderately elevated (≥35 and <45 mmHg), and severely elevated mPAP (≥45 mmHg) pre- and post-thrombectomy, showing a significant change (p<0.0001). The lines flowing between the columns indicate the movement of patients from their prethrombectomy mPAP category to their post-thrombectomy category, with the width of the lines proportional to the number of patients. mPAP: mean pulmonary artery pressure

Figure 2. Right ventricular echocardiographic parameters, dyspnoea, and supplemental oxygen use at baseline compared to 48 hours post-thrombectomy.

A) Change in RV/LV ratio (p<0.0001 for available paired assessments; McNemar’s test). B) Change in RV systolic pressure (p<0.0001 for available paired assessments; McNemar’s test). C) Change in the distribution of patients’ RV function (p<0.0001 for available paired assessments; McNemar-Bowker’s test). D) Dyspnoea was assessed at baseline and at 48 hours using the modified Medical Research Council (mMRC) assessment tool (higher score=worse dyspnoea). The proportion of patients with each score (0-4) is presented, showing a significant change in score distribution (p<0.0001 for available paired assessments; McNemar-Bowker’s test). E) The proportion of patients whose use of supplemental oxygen decreased from baseline to 48 hours is presented. A decrease was defined as a reduction in the oxygen volume used, or in the type of supplemental oxygen required (types of supplemental oxygen were ranked as a reduction if a patient moved from one type to another type in order as follows: intubation, face mask, nasal cannula, room air). F) The proportion of patients on room air at baseline and 48 hours post-thrombectomy is presented (p<0.0001 for paired assessments; McNemar’s test). hr: hours; LV: left ventricle; RV: right ventricle

Central illustration. Acute outcomes of the full US cohort of the FLASH mechanical thrombectomy registry in pulmonary embolism.

Baseline characteristics, in-hospital safety and effectiveness outcomes, and acute mortality for the fully enrolled US cohort of the FLASH registry in pulmonary embolism. Between December 2018 and December 2021, 800 patients with acute pulmonary embolism were enrolled across 50 US sites in the FLASH registry for mechanical thrombectomy using the FlowTriever System. Patient characteristics, immediate changes in haemodynamics, in-hospital safety outcomes including major adverse events, effectiveness outcomes including RV function recovery and dyspnoea symptom improvement, hospital stay details, and all-cause mortality and readmissions through 30-day follow-up are reported. Images provided by Dr. Michael Brown, Missouri Cardiovascular Specialists, Columbia, MO, USA. *Depressed cardiac index is defined as <2 L/min/m². **In patients with depressed cardiac index at baseline. ICU: intensive care unit; LOS: length of stay; PA: pulmonary artery; PE: pulmonary embolism; RV: right ventricle

Figure 3. Multiple linear regression models of absolute reduction in mean PAP and dyspnoea score.

A) Multiple linear regression was performed to identify baseline characteristics associated with absolute reduction in mPAP measured immediately prior to and following thrombectomy. B) Multiple linear regression was performed to identify baseline characteristics associated with absolute reduction in self-reported mMRC dyspnoea score measured at baseline and 48 hours post-procedure. BMI: body mass index; BPM: beats per minute; CI: confidence interval; DVT: deep vein thrombosis; LV: left ventricle; mMRC: modified Medical Research Council; mPAP: mean pulmonary artery pressure; PAP: pulmonary artery pressure; PE: pulmonary embolism; PH: pulmonary hypertension; RV: right ventricle