Beyond Acute PE: Removal of Chronic Thrombus with Catheter-Directed Mechanical Pulmonary Thrombectomy

Learning Objectives: 1. Review current guidelines and literature of treatment of pulmonary emboli.

2. Describe the pathogenesis and chronological transformation of thrombus.

3. Discuss the potential future role of mechanical thrombectomy in the treatment of chronic pulmonary emboli.

Background: Catheter-directed pulmonary mechanical thrombectomy has emerged in recent years as an effective and safe therapy for intermediate-risk acute pulmonary embolism (PE). The technique has demonstrated comparable reduction in right heart strain compared to catheter-directed thrombolysis as well as lower rates of major bleeding events compared to both catheter-directed and systemic thrombolysis. However, robust research directly comparing various PE treatments is largely lacking. Among potentially important yet largely unexplored difference is the relative effectiveness of mechanical thrombectomy in removing nonacute thrombus when compared to other therapies.

Histologically, thrombus undergoes chronological, structural transformation through multiple stages. This is largely related to changes in numerous factors at the cellular level including fibrin, pro-collagen, collagen IV and other cellular components. This structural transformation represents a continuous spectrum; all stages are thought to be simultaneously present to varying degrees within any given thrombus. And thus, given this heterogeneity, the effectiveness of thrombolysis and anticoagulation is thought to be inherently limited.

Clinical Findings/Procedure Details: Histopathologic analysis was performed on clot specimens from 7 patients that underwent catheter-directed mechanical pulmonary thrombectomy for acute, intermediate-risk PE at a single institution. All procedures were performed by an Interventional Radiologist and histopathologic analysis was performed by a Clinical Pathologist. To date, preliminary histopathologic analyses demonstrate evidence of late-stage thrombus at the cellular level within the aspirate.

Conclusion and/or Teaching Points: Our observational study thus far demonstrates evidence of late-stage thrombus within aspirate from pulmonary mechanical thrombectomy. This finding raises the question of whether mechanical thrombectomy treatment for PE might be of better therapeutic value compared to other therapies. Studies comparing the long-term outcomes of mechanical thrombectomy versus other therapies for PE are of significant need. We plan to continue assessing our growing cohort for features of chronicity within aspirated clot from mechanical thrombectomy for PE.