Rapid Removal of Pulmonary Emboli and Subsequent Reversal of Right Ventricular Dysfunction Using the FlowTriever Retrieval/Aspiration System

Acute pulmonary embolism (PE) is a life-threatening condition with a broad spectrum of clinical manifestations. Mortality rates associated with PE reportedly exceed 15% in the first three months.^1,2 According to the Scientific Statement published by the American Heart Association, PE severity is defined based on a three-tier risk stratification scheme.³ At the highest risk level, massive PE characterizes patients presenting with sustained systemic hypotension, pulselessness, or persistent profound bradycardia. Submassive PE, the intermediate category, includes those with evidence of right ventricular (RV) dysfunction or myocardial necrosis, while maintaining systemic normotension. Minor PE represents a low risk level, identified in patients having minor symptoms, but no evidence of RV dysfunction.   

Patients with submassive PE are typically managed conservatively with anticoagulation; however, the presence of RV dysfunction has been demonstrated to predict poor outcomes, including increased mortality.^4–7 Catheter-based intervention is an emerging mode of therapy supported by evidence of safety and effectiveness with use of various techniques in the massive and submassive PE patient populations.^8,9 This report presents a case of a submassive PE patient treated with a novel catheter-based approach using the FlowTriever Retrieval/Aspiration System (Inari Medical), which is designed to mechanically remove emboli and restore blood flow in the pulmonary arteries.

Case Report

A 43-year-old male who underwent surgical repair of his right quadriceps tendon rupture three weeks prior presented to his primary care physician’s office with a three-day history of chest pain and dyspnea on exertion the evening before. He exhibited a normal electrocardiogram (EKG) and chest x-ray at the office, and was referred to the emergency department. At the hospital, he had a blood pressure of 119/75 mmHg, pulse rate of 93 bpm, respiratory rate of 21/min, temperature of 97.4˚F, and oxygen saturation of 95% on room air. Troponin level was slightly elevated at 0.052 ng/ml. Complete metabolic panel was unremarkable.

Computed tomography angiography (CTA) of the chest demonstrated a large saddle embolus with multiple bilateral lobar, segmental, and subsegmental pulmonary emboli, and right ventricular (RV) dilation with a right-ventricle-to-left-ventricle end-diastolic diameter (RV/LV) ratio of 1.2 (Figure 1). Cardiothoracic surgery was consulted for urgent revascularization therapy. Based on the patient hemodynamics and CTA findings, characterized as submassive PE, with no relevant contraindications, a catheter-based approach was chosen. The patient was admitted to the intensive care unit (ICU), where anticoagulant therapy was initiated. The risks and benefits of the treatment approach compared to conventional therapy with anticoagulation alone were discussed with the patient, who consented to proceed with the planned procedure. A subsequent transthoracic echocardiography demonstrated ejection fraction of 55-60%, abnormal relaxation of the left ventricle (LV) in diastole, mild concentric LV hypertrophy, systolic septal flattening consistent with RV pressure overload, abnormal relaxation of the ventricle in diastole, moderately dilation and reduced RV systolic function.    

The patient was taken to the hybrid suite and placed in a supine position. The anesthesia team administered intravenous (IV) sedation. Following prepping of his right groin, ultrasound was used to visualize the right femoral vein, which was then accessed percutaneously with a needle using the Seldinger technique. Over a .035-inch guidewire, a 5 French (Fr) pigtail catheter was advanced to the right atrium, RV, and then the pulmonary artery (PA). Pulmonary bilateral angiography was performed, which demonstrated poor perfusion in the pulmonary arterial system and thrombus consistent with the CTA findings. The .035-inch guidewire was exchanged for an Amplatz .035-inch Super Stiff wire (Boston Scientific), and the pigtail catheter and 6 Fr sheath were exchanged for a 22 Fr sheath to facilitate catheter-based thrombectomy with use of the FlowTriever. 

The FlowTriever System (Figure 2) consists of following components: 1) the Flowtriever Catheter (FTC); 2) the Aspiration Guide Catheter (AGC); and, 3) the Retraction Aspirator (RA). The FTC is a catheter with a coaxial shaft with three regularly spaced, self-expanding nitinol mesh wireforms at its distal section, deployable by retracting the outer delivery catheter. The wireforms are designed to occupy the diameter of the lumen and engage the thrombus circumferentially. Additionally, the wireforms are available in three size configurations to accommodate vessels from 6 mm to 18 mm in diameter. The AGC is a single lumen catheter with a proximal hemostatic valve and stopcock, equipped with a dilator compatible with a .035-inch guidewire. The RA is a user-controlled, hand-held device that integrates a lever-actuated aspiration syringe and a retraction mechanism to facilitate both FTC retraction and material evacuation through a tubing set connected to the stopcock of the AGC. 

The procedure begins with advancing the AGC over a guidewire to a position proximal to the treatment site, followed by placement of the FTC with its distal section beyond the AGC and over the targeted occlusive segment (Figure 3). Upon deploying the wireforms to engage the thrombus, the FTC is locked in position with its shaft and, together with the AGC, connected at its proximal end to the RA to form the complete system. Shifting the lever from position “2” to “1” (away from the patient) pulls the FTC with the wireforms back toward the AGC, while aspirating the blood and thrombotic material into the syringe. Shifting the lever back to position “2” (toward the patient) pumps the aspirant in the syringe through the tubing set into a waste bag. When needed, the AGC and FTC could be removed to expel material in the lumen. If necessary, steps to deploy the wireforms, and aspirate the blood and emboli could be repeated upon repositioning the AGC and FTC at another target area in the vessel. 

In the current case, an FTC in the large sized configuration (15-18 mm) was chosen based on PA diameter measurements. Over an Amplatz Super Stiff wire with a 7 cm floppy tip, the AGC and FTC were advanced into the proximal right PA to first target the saddle embolus. Wireform deployment followed by aspiration was performed, evacuating a significant amount of thrombus (Figure 4). Following this, a new set of AGC and FTC with a medium-sized configuration (11-14 mm) was chosen and advanced over the same wire to reach the distal right PA, where additional thrombotic material was removed. Completion angiography was performed, revealing substantially improved bilateral lung perfusion. The catheters, wires, and sheath were then removed. Manual pressure was applied to the puncture site to achieve hemostasis. The patient remained in stable condition throughout the procedure.

After the procedure, the patient returned to the ICU for one day and was transitioned on oral anticoagulants. Follow-up CTA demonstrated significantly decreased clot burden bilaterally, with resolution of the large, central saddle embolus (Figure 5). Persistent emboli within the distal pulmonary arteries extending into the lobar branches remained. RV dilation has resolved, achieving an RV/left ventricular (LV) ratio of 0.75. The patient recovered uneventfully and was discharged two days post-procedure. 

Discussion

Catheter-based intervention for acute PE is a growing area of research interest. Various techniques have been evaluated in recent studies that included both massive and submassive PE patients.^8–11 In a recently completed prospective registry of 101 patients, clinical success (defined as stabilization of hemodynamics, improvement in pulmonary hypertension, and resolution of RV strain) was observed in 85.7% of the study population, with no procedure-related complications.⁸ A meta-analysis of 35 studies with 594 patients provided earlier evidence, reporting a clinical success rate of 86.5% and a pooled risk of major and minor procedural complications of 2.4% and 7.9%, respectively.⁹ Among these two sets of data, mechanically driven techniques, such as pigtail fragmentation, aspiration, and embolectomy, were a common approach. The authors concluded that catheter-based therapy overall is relatively safe and effective.

The present case report introduces a novel catheter-based technique using the FlowTriever System, which could be considered a mechanically driven approach comparable to those evaluated in the above studies. It is designed to rapidly restore blood flow by means of a synergistic mechanism that retrieves the targeted thrombus and evacuates it from the pulmonary vasculature. A series of differently sized wireforms that appose to luminal surfaces when deployed allows effective thrombus engagement and removal in a population of PE patients with variable clot burden and vessel sizes. This circumvents potential limitations with techniques, such as pigtail fragmentation, which are nonspecific to vessel size. Additionally, clot removal by retrieval/aspiration reduces the risk for distal embolization. Moreover, aspirations are performed in a gentle and controlled manner, in contrast to selected power-driven high-pressure techniques, which have been reportedly associated with increased risk of severe complications.⁹

This case report also addresses patient selection for consideration of catheter interventions, particularly for submassive PE patients, who are typically managed conservatively. Though hemodynamically stable, they exhibit the presence of RV dysfunction, which has been widely investigated as a marker for poor outcomes. For example, RV dilation characterized by an echocardiographic RV/LV ratio exceeding 0.9 was shown to be an independent predictor for hospital mortality.⁴ Another study demonstrated that an RV/LV ratio measured on CT exceeding the same level significantly increased the risk for adverse events at 30 days.⁷ Evidence suggests that the extent to which the RV dilates increases with the rate of mortality.⁵ Furthermore, a long-term follow-up study demonstrates improvement in rates of mortality and recurrent venous thromboembolism events among patients who exhibited resolution of RV dysfunction prior to discharge, compared to those who did not.⁶ In the current case, the patient revealed not only a substantially dilated RV, but also evidence of reduced LV function and ejection fraction. These conditions could progress toward further impairment of LV function, leading to hypotension and eventually cardiac failure, if not treated promptly. With treatment using the FlowTriever System, the patient restored pulmonary hemodynamics and achieved prompt resolution of RV dilation (with RV ratio reduced from 1.2 to 0.75), thus mitigating the risk for deteriorative changes and adverse outcomes. Collectively, these findings support the need for consideration of advanced therapy among submassive PE patients. These patients have been the focus of recent studies, which demonstrated encouraging outcomes with another catheter-based modality.^10,11 

Conclusion

The current case report demonstrated that the FlowTriever System provided an effective means of removing emboli and reversing compromised hemodynamics without any complication in a submassive PE patient. This represents an advancement in catheter-based technologies for managing acute PE; however, prospective clinical trials are needed to determine the safety and efficacy of this technique across different patient populations, and evaluate its potential role in those who present with conditions that warrant an immediate intervention and/or with contraindications to IV thrombolysis.

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Disclosure: Dr. Engelhardt reports no conflicts of interest regarding the content herein.

Dr. Tod Engelhardt can be contacted at tengelha@ejgh.org.