Failure modes and effects analysis of mechanical thrombectomy for stroke discovered in human brains

Abstract

OBJECTIVE Despite advancement of thrombectomy technologies for large-vessel occlusion (LVO) stroke and increased user experience, complete recanalization rates linger around 50%, and one-third of patients who have undergone successful recanalization still experience poor neurological outcomes. To enhance the understanding of the biomechanics and failure modes, the authors conducted an experimental analysis of the interaction of emboli/artery/devices in the first human brain test platform for LVO stroke described to date. METHODS In 12 fresh human brains, 105 LVOs were recreated by embolizing engineered emboli analogs and recanalization was attempted using aspiration catheters and/or stent retrievers. The complex mechanical interaction between diverse emboli (elastic, stiff, and fragment prone), arteries (anterior and posterior circulation), and thrombectomy devices were observed, analyzed, and categorized. The authors systematically evaluated the recanalization process through failure modes and effects analysis, and they identified where and how thrombectomy devices fail and the impact of device failure. RESULTS The first-pass effect (34%), successful (71%), and complete (60%) recanalization rates in this model were consistent with those in the literature. Failure mode analysis of 184 passes with thrombectomy devices revealed the following. 1) Devices loaded the emboli with tensile forces leading to elongation and intravascular fragmentation. 2) In the presence of anterograde flow, small fragments embolize to the microcirculation and large fragments result in recurrent vessel occlusion. 3) Multiple passes are required due to recurrent (15%) and residual (73%) occlusions, or both (12%). 4) Residual emboli remained in small branching and perforating arteries in cases of alleged complete recanalization (28%). 5) Vacuum caused arterial collapse at physiological pressures (27%). 6) Device withdrawal caused arterial traction (41%), and severe traction provoked avulsion of perforating and small branching arteries. CONCLUSIONS Biomechanically superior thrombectomy technologies should prevent unrestrained tensional load on emboli, minimize intraluminal embolus fragmentation and release, improve device/embolus integration, recanalize small branching and perforating arteries, prevent arterial collapse, and minimize traction.

Arterial Collapse during Thrombectomy for Stroke: Clinical Evidence and Experimental Findings in Human Brains and In Vivo Models

“…Such a failure mechanism has been reported in ex vivo human brains. 6 It has also been reported that the incidence rate of symptomatic intracranial hemorrhage was .3 times higher for M2 occlusions than for M1 occlusions. 13 Our findings reveal that thrombectomy in the M2 branches results in more frequent and severe collapse and could, therefore, lead to microvascular avulsions during arterial traction.…”

“…To mechanistically validate the in vivo observations and to better understand the impact of different variables in the likelihood of arterial collapse by an experimental design, we used a validated human brain model. 6,7 Unlike the other models using rigid or semirigid arterial phantoms, [9][10][11] this validated model uses fresh human cerebral vessels (ie, flexible and collapsible arteries) and can reproduce different physiologic hemodynamic conditions. On connection of the catheter to the vacuum, we frequently observed collapse.…”

“…The whole human brain model used in this study has been previously described. 6,7 After institutional approval, fresh adult brains were harvested during research-consented postmortem examinations within 24 hours of death. Extra effort was made to preserve the circle of Willis and minimize damage to perforating arteries.…”

A Thrombectomy Model Based on Ex Vivo Whole Human Brains

“…3 Residual occlusion in small branching and perforating arteries is believed to be one of the reasons for poor neurologic outcome despite apparently "complete" recanalization, and this model may be of benefit to better characterize this problem and develop solutions. 14 Second, the human brain model provides a realistic mechanical response of the arteries to the mechanical load of devices. This is critical to accurately test arterial deformation, stretching, collapse under vacuum, and even arterial injury such as perforation.…”

“…In addition, the realistic mechanical properties of the vessel wall make this model unique to reveal failure modes of device-artery interaction such as vessel traction and vessel collapse as shown previously. 14 Pulling back the catheter with weak clot-catheter integration results in residual occlusions or iatrogenic embolization and is likely the main cause of low first-pass recanalization. We think that future aspiration technologies should aim to ingest clots in situ, proximal-to-distal, and at low vacuum power to prevent vessel collapse.…”