Study design and ethics
This was a HIPAA compliant retrospective analysis of 9 patients with acute intermediate-high and high-risk PE for patients with concurrent PFO from two hospital centers affiliated with Yale Medicine from December 2018 to November 2019. This was an investigator-initiated, non-sponsored study, designed to assess the immediate and short-term follow-up outcomes after PA mechanical thrombectomy using the Inari FlowTriever system in patients. This study received an institutional review board (IRB) approval from the Yale School of Medicine implemented in compliance with the Health Insurance Portability and Accountability Act (IRB ID: 2000025511). Obtaining written consent was waived by the IRB committee.
Study population
All patients within the designated timeframe who were diagnosed with acute intermediate- or high-risk PE, and treated with mechanical thrombectomy using the Inari FlowTriever System were evaluated for concurrent diagnosis of PFO with preprocedural echocardiography.
Patient pulmonary embolism classification as high-risk, intermediate-risk, and low-risk PE were based on the 2011 American Heart Association’s (AHA) Scientific Statement for venous thromboembolism management (Jaff et al., 2011). Intermediate-risk patients were further classified as intermediate-high-risk if hemodynamically stable (Mirambeaux et al., 2019), but showing positive simplified Pulmonary Embolism Severity Index, concomitant echocardiographic RV dysfunction, and positive cardiac troponin. All patients were on anticoagulation without evidence of improvement while deteriorating.
Imaging
Bedside transthoracic echocardiography was performed on patients by a cardiology fellow or emergency medicine attending with ultrasound training.
Pretreatment CT angiogram of chest was routinely performed for all patients before calling for our institute’s pulmonary embolism response team (PERT) team. A 64 multi–detector row CT scanner (LightSpeed16; GE Medical Systems, Milwaukee, Wisconsin) was used for dynamic CT. Based on PE protocol, PE was defined as any filling defect observed in at least 1 main or lobar pulmonary artery on CT angiogram.
Gray scale, color and spectral Doppler examination of the bilateral lower extremities were performed including the external iliac vein, common femoral vein, deep femoral vein, femoral vein, popliteal vein, tibioperoneal trifurcation, posterior tibial, and peroneal veins. A Philips Ultrasound machine, Model iU22, (Philips Company, WA, USA) with a combination of linear 12 MHZ and curved 5MHZ transducers were used for these exams.
Mechanical Thrombectomy technique
Common femoral vein access was obtained for all 9 patients. A 6 French 100 cm long pigtail catheter was used to measure right atrial and ventricular pressures, perform pulmonary artery angiography, and measure pulmonary artery pressures. A 22 French Gore Dryseal sheath was placed at the access site to accommodate the FlowTriever System. The device is composed of the Triever20 (Fig. 1a) and the FlowTriever catheters (Fig. 1b) (Weinberg et al., 2016; Chauhan et al., 2017).
The 20 Fr/95 cm-long Triever20 (formerly known as the Aspiration Guide Catheter) was used for direct clot aspiration via a 60 cc self-locking syringe and was advanced over the guidewire into the right atrium and then to the pulmonary artery under fluoroscopy guidance. Next, suction was applied to retrieve clot from the targeted pulmonary artery, repeated 2 to 3 times. Repeat digital subtraction angiography was performed after clot retrieval to determine the amount of residual clot within the targeted pulmonary artery and demonstrate restoration of blood flow to the distal branches. Repeat PA pressures were measured after the final thrombectomy was complete to assess improvement. In patients with demonstrated deep venous thrombosis in the lower extremity, a cavogram was subsequently performed to look for clot in the inferior vena cava (IVC). If necessary, an IVC filter was deployed in the infrarenal IVC under fluoroscopy. Figure 2 demonstrates an example of MT with visualization of catheter tip and clot.
Definition of technical and clinical success parameters
Procedure logs, patient demographic data, patient medical history, vital signs, imaging and laboratory variables were collected. Pre- and post-procedural symptoms, stability, pulmonary function, and electrocardiogram (EKG), echocardiographic and CT angiographic findings were documented. Patient outcomes, including major, immediate, or late procedure-related complications and bleeding events were recorded.
Technical success was defined as successful placement of FlowTriever system and initiation of aspiration thrombectomy. An acceptable reduction in thrombus burden was determined intra-procedurally by a minimum of two interventional radiologists on digital subtraction angiograms obtained before and after MT.
Clinical success was defined as meeting all of the following five endpoints: 1) stabilization of hemodynamic parameters (resolution of hemodynamic shock with systolic blood pressure > 90 mmHg without need for vasopressor support); 2) Improved O2 saturation; 3) improvement in pulmonary hypertension 4) Resolution of right sided heart strain; and 5) survival to hospital discharge.
Statistical analysis
Statistical analysis was performed using SPSS statistical software version 22.0 (IBM Co., Armonk, NY). Pearson’s chi-square test was used to determine patients’ baseline characteristics and clinical variables to determine predictors of adverse outcomes. Nonparametric Wilcox tests were used to compare the effect of mechanical thrombectomy on quantitative variables. A p-value less than 0.05 was considered significant.