Blood pressure measurement in the artery proximal and distal to an intra-arterial embolus during thrombolytic therapy

Modelling collateral flow and thrombus permeability during acute ischaemic stroke

The presence of collaterals and high thrombus permeability are associated with good functional outcomes after an acute ischaemic stroke. We aim to understand the combined effect of the collaterals and thrombus permeability on cerebral blood flow during an acute ischaemic stroke. A cerebral blood flow model including the leptomeningeal collateral circulation is used to simulate cerebral blood flow during an acute ischaemic stroke. The collateral circulation is varied to capture the collateral scores: absent, poor, moderate and good. Measurements of the transit time, void fraction and thrombus length in acute ischaemic stroke patients are used to estimate thrombus permeability. Estimated thrombus permeability ranges between 10^-7 and 10^-4 mm². Measured flow rates through the thrombus are small and the effect of a permeable thrombus on brain perfusion during stroke is small compared with the effect of collaterals. Our simulations suggest that the collaterals are a dominant factor in the resulting infarct volume after a stroke.

A Review of the Advancements in the in-vitro Modelling of Acute Ischemic Stroke and Its Treatment

In-vitro neurovascular models of large vessel occlusions (LVOs) causing acute ischemic stroke (AIS) are used extensively for pre-clinical testing of new treatment devices. They enable physicians and engineers to examine device performance and the response of the occlusion to further advance design solutions for current unmet clinical needs. These models also enable physicians to train on basic skills, to try out new devices and new procedural approaches, and for the stroke team to practice workflows together in the comfort of a controlled environment in a non-clinical setting. Removal of the occlusive clot in its entirety is the primary goal of the endovascular treatment of LVOs via mechanical thrombectomy (MT) and the medical treatment via thrombolysis. In MT, recanalization after just one pass is associated with better clinical outcomes than procedures that take multiple passes to achieve the same level of recanalization, commonly known as first pass effect (FPE). To achieve this, physicians and engineers are continually investigating new devices and treatment approaches. To distinguish between treatment devices in the pre-clinical setting, test models must also be optimized and expanded become more nuanced and to represent challenging patient cohorts that could be improved through new technology or better techniques. The aim of this paper is to provide a perspective review of the recent advancements in the in-vitro modeling of stroke and to outline how these models need to advance further in future. This review provides an overview of the various in-vitro models used for the modeling of AIS and compares the advantages and limitations of each. In-vitro models remain an extremely useful tool in the evaluation and design of treatment devices, and great strides have been made to improve replication of physiological conditions. However, further advancement is still required to represent the expanding indications for thrombectomy and thrombolysis, and the generation of new thrombectomy devices, to ensure that smaller treatment effects are captured.

Measuring the effect of thrombosis, thrombus maturation and thrombolysis on clot mechanical properties in an in-vitro model

Changes in acute ischemic stroke thrombi structure and composition may result in significant differences in treatment responsiveness. Ischemic stroke patients are often treated with a thrombolytic agent to dissolve thrombi, however these patients may subsequently undergo mechanical thrombectomy to remove the occlusive clot. We set out to determine if rt-PA thrombolysis treatment of blood clots changes their mechanical properties, which in turn may impact mechanical thrombectomy. Using a design-of-experiment approach, ovine clot analogues were prepared with varying composition and further exposed to different levels of compaction force to simulate the effect of arterial blood pressure. Finally, clots were treated with three r-tPA doses for different durations. Clot mass and mechanical behaviour was analysed to assess changes due to (i) Platelet driven contraction (ii) Compaction force and (iii) Thrombolysis. Clots that were exposed to r-tPA for longer duration showed significant reduction in clot mass (p < 0.001). Exposure time to r-tPA (p < 0.001) was shown to be an independent predictor of lower clot stiffness. A decrease in energy dissipation ratio during mechanical compression was associated with longer exposure time in r-tPA (p = 0.001) and a higher platelet concentration ratio (p = 0.018). The dose of r-tPA was not a significant factor in reducing clot mass or changing mechanical properties of the clots. Fibrinolysis reduces clot stiffness which may explain increased distal clot migration observed in patients treated with r-tPA and should be considered as a potential clot modification factor before mechanical thrombectomy.

Modelling the leptomeningeal collateral circulation during acute ischaemic stroke

A novel model of the leptomeningeal collateral circulation is created by combining data from multiple sources with statistical scaling laws. The extent of the collateral circulation is varied by defining a collateral vessel probability. Blood flow and pressure are simulated using a one-dimensional steady state blood flow model. The leptomeningeal collateral vessels provide significant flow during a stroke. The pressure drop over an occlusion predicted by the model ranges between 60 and 85 mmHg depending on the extent of the collateral circulation. The linear transport of contrast material was simulated in the circulatory network. The time delay of peak contrast over an occlusion is 3.3 s in the model, and 2.1 s (IQR 0.8-4.0 s) when measured in dynamic CTA data of acute ischaemic stroke patients. Modelling the leptomeningeal collateral circulation could lead to better estimates of infarct volume and patient outcome.

Quantification of pial collateral pressure in acute large vessel occlusion stroke: basic concept with patient outcomes

PURPOSE

Pial collateral perfusion to the ischemic penumbra plays a critical role in determining patient outcomes in acute stroke. We aimed to assess the validity and reliability of an intra-procedural technique for measuring and quantifying the pial collateral pressure (QPCP) to ischemic brain tissue during acute stroke secondary to LVO. QPCP measurements were correlated with standard computed tomography angiography (CTA) and digital subtraction angiography imaging assessments of pial collateral perfusion and outcomes after mechanical endovascular revascularization (MER).

METHODS

This prospective cohort study included 60 consecutive patients with middle cerebral artery (MCA)-M1 and proximal M2 occlusions. QPCP measurements were obtained during MER. The validity of QPCP measurements was evaluated using four widely accepted collateral grading scales. QPCP measurements were also analyzed as a predictor of patient outcomes utilizing National Institute of Health Stroke Scale reduction at 24 h and modified Rankin Scale (mRS) scores at 30 days.

RESULTS

QPCP measurements and QPCP ratio (QPCP/systemic mean arterial blood pressure) showed a statistically significant association with single-phase pretreatment CTA Maas and American Society of Interventional and Therapeutic Neuroradiology/Society of Interventional Radiology binary grading scales. Patient outcomes demonstrated for every 10-unit increase in QPCP, the odds of mRS 0-2 at 30 days increased by 76% (p = 0.019).

CONCLUSION

QPCP measurements related best with the pretreatment CTA Maas collateral grading scale but were more strongly associated with patient outcomes than any of the four widely accepted collateral grading scales. Greater QPCP was significantly associated with better overall patient outcomes as defined by mRS at 30 days.

Intra-arterial pulse wave analysis during thrombectomy for the assessment of collateral status - A feasibility study

Purpose

Knowledge of the collateralization of an occluded vessel is important for the risk-benefit analysis of difficult revascularization maneuvers during mechanical thrombectomy. If the territory behind a clot is well perfused, one could desist from performing a risky thrombectomy maneuver. The arterial pulse pressure curve may serve as an indicator for the collateralization of an occluded target vessel. We investigated the feasibility of arterial pulse measurements with a standard microcatheter.

Methods

We measured the intra-arterial blood pressure proximal and distal to the clot in 40 thrombectomy maneuvers in a porcine stroke model. We used a microcatheter (Trevo Pro 18, Stryker, Kalamazoo, CA, USA), a pressure transducer (MEMSCAP SP844), an AdInstruments Powerlab 16/35 workstation, and LabChart 8 Software (AdInstruments, Dunedin, New Zealand).

Results

Median arterial blood pressure proximal and distal to the clot was 96.0 mmHg (IQR, 23.8 mmHg) and 47.5 mmHg (IQR, 43.5 mmHg), respectively (p < .001). The median difference between systolic maximum and diastolic minimum proximal and distal to the clot decreased significantly from 1.8 mmHg (IQR, 3.6 mmHg) to 0.0 mmHg (IQR, 0.5 mmHg) (p < .001). There was loss of the curve in 26 of 40 cases and loss of pressure in 23 of 40 cases (p = .008). There was no significant correlation between vessel diameter and either loss of the pulse pressure curve (p = .20) or overall pressure loss (p = .31).

Conclusion

It is possible to measure the pulse pressure proximal and distal to the clot with a standard microcatheter used during mechanical thrombectomy.

Necessary Catheter Diameters for Mechanical Thrombectomy with ADAPT

BACKGROUND AND PURPOSE

Large-bore catheters allow mechanical thrombectomy in ischemic stroke by engaging and retrieving clots without additional devices (direct aspiration first-pass technique [ADAPT]). The purpose of this study was to establish a model for minimal catheter diameters needed for ADAPT.

MATERIALS AND METHODS

We established a theoretic model for the calculation of minimal catheter diameters needed for ADAPT. We then verified its validity in 28 ADAPT maneuvers in a porcine in vivo model. To account for different mechanical thrombectomy techniques, we factored in ADAPT with/without a hypothetic 0.021-inch microcatheter or 0.014-inch microwire inside the lumen of the aspiration catheter and aspiration with a 60-mL syringe versus an aspiration pump.

RESULTS

According to our calculations, catheters with an inner diameter of >0.040 inch and >0.064 inch, respectively, are needed to be effective in the middle cerebral artery (2.5-mm diameter) or in the internal carotid artery (4 mm) in an average patient. There was a significant correlation between predicted and actual thrombectomy results (P = .010). Our theoretic model had a positive and negative predictive value of 78% and 79%, respectively. Sensitivity and specificity were 88% and 64%, respectively.

CONCLUSIONS

Our theoretic model allows estimating the minimal catheter diameters needed for successful mechanical thrombectomy with ADAPT, as demonstrated by the good agreement with our animal experiments. Our model will be helpful to interventionalists in avoiding selecting catheters that are likely too small to be effective.

Computational fluid dynamics modeling of symptomatic intracranial atherosclerosis may predict risk of stroke recurrence

BACKGROUND

Patients with symptomatic intracranial atherosclerosis (ICAS) of ≥ 70% luminal stenosis are at high risk of stroke recurrence. We aimed to evaluate the relationships between hemodynamics of ICAS revealed by computational fluid dynamics (CFD) models and risk of stroke recurrence in this patient subset.

METHODS

Patients with a symptomatic ICAS lesion of 70-99% luminal stenosis were screened and enrolled in this study. CFD models were reconstructed based on baseline computed tomographic angiography (CTA) source images, to reveal hemodynamics of the qualifying symptomatic ICAS lesions. Change of pressures across a lesion was represented by the ratio of post- and pre-stenotic pressures. Change of shear strain rates (SSR) across a lesion was represented by the ratio of SSRs at the stenotic throat and proximal normal vessel segment, similar for the change of flow velocities. Patients were followed up for 1 year.

RESULTS

Overall, 32 patients (median age 65; 59.4% males) were recruited. The median pressure, SSR and velocity ratios for the ICAS lesions were 0.40 (-2.46-0.79), 4.5 (2.2-20.6), and 7.4 (5.2-12.5), respectively. SSR ratio (hazard ratio [HR] 1.027; 95% confidence interval [CI], 1.004-1.051; P = 0.023) and velocity ratio (HR 1.029; 95% CI, 1.002-1.056; P = 0.035) were significantly related to recurrent territorial ischemic stroke within 1 year by univariate Cox regression, respectively with the c-statistics of 0.776 (95% CI, 0.594-0.903; P = 0.014) and 0.776 (95% CI, 0.594-0.903; P = 0.002) in receiver operating characteristic analysis.

CONCLUSIONS

Hemodynamics of ICAS on CFD models reconstructed from routinely obtained CTA images may predict subsequent stroke recurrence in patients with a symptomatic ICAS lesion of 70-99% luminal stenosis.