Collateral Blood Flow and Ischemic Core Growth

Cerebral blood volume index in the era of thrombectomy-treated large and medium vessel ischemic strokes

The cerebral blood volume index (CBV index) is a perfusion-based marker of collateral status. Several real-world data analyses from observational stroke cohorts have established relationships between this parameter and a range of favorable and unfavorable stroke outcomes. In this review, an overview is provided of the CBV index, within the context of thrombectomy-treated large vessel and medium vessel occlusion ischemic strokes. The current literature is summarized describing the CBV index and its association with a variety of efficacy, safety, and clinical outcome measures during the thrombectomy course and post-treatment recovery in both large vessel occlusion and medium vessel occlusion strokes. The range of CBV index value thresholds that have been identified and are able to differentiate between favorable and unfavorable outcomes across different clinical scenarios are summarized. This review underscores the need for additional analyses to further explore the CBV index in other clinical outcome contexts and for future prospective studies to validate the CBV index in thrombectomy-treated large vessel and medium vessel occlusion strokes, especially with increasing use of thrombectomy for treating medium vessel occlusions.

The number of recanalization attempts, procedure time and endovascular therapy outcomes in acute large core stroke patients

INTRODUCTION

Landmark thrombectomy trials demonstrated improved functional outcomes after endovascular therapy (EVT) for large core strokes (LCSs). This study explored the impact of recanalization attempts and procedure time (PT) on outcomes in LCS patients.

PATIENTS AND METHODS

This was a retrospective study of patients with LCSs who underwent EVT from a prospective multicentre cohort. LCS was defined as an Alberta Stroke Program Early Computed Tomography Score of 0 to 5. Patients were divided into 6 groups (unsuccessful reperfusion [modified Thrombolysis in Cerebral Infarction Scale (mTICI) 0-2a] and successful reperfusion [mTICI, 2b/3]) after 1, 2, 3, 4, or >4 attempts. The primary outcome was a favorable 90-day mRS score of 0-3. Secondary outcomes included mRS 0-4, 90-day mortality, and 48-hour rates of symptomatic (sICH) and any intracranial hemorrhage (aICH).

RESULTS

A total of 447 patients were analysed. 388 with successful reperfusion, 59 without.Successful reperfusion during the first 3 passes increased the odds of favourable functional outcomes [attempt 1: aOR, 4.454 (1.723-11.514),p=0.002; 2: aOR, 3.762 (1.437-9.847),p=0.07; or 3: aOR, 3.619 (1.254-10.440),p=0.017] and decreased mortality at 90 days [(attempt 1: aOR, 0.336 (0.155-0.727),p=0.006; 2: aOR, 0.346 (0.160-0.746),p=0.007; or 3: aOR, 0.395 (0.164-0.953),p=0.039]. A shorter PT increased the odds of a favourable functional outcome [aOR, 0.991 (0.985-0.997),p=0.002]. PT may reduce the association between the number of attempts and patient outcomes. No associations were found between the number of attempts and sICH or aICH, whereas there was an increasing trend in the proportion of aICH or sICH when the number of attempts was more than two.

CONCLUSION

In patients with LCSs who underwent EVT, successful reperfusion within the first 3 attempts and a shorter PT were associated with favourable functional outcomes. However, the effect size of the association between the number of attempts and clinical outcomes may gradually decrease with extension of the PT.

Chronic hypertension alters the relationship between collateral blood flow cortical cerebral blood flow, and brain tissue oxygenation

This study measured the relationship between pial collateral (leptomeningeal anastomoses, LMA) flow, intraparenchymal cortical cerebral blood flow (cCBF) and brain tissue oxygenation (btO2) during acute ischemic stroke to investigate how pial flow translates to downstream cCBF and btO2 and examined how this relationship is altered in hypertension. Proximal transient middle cerebral artery occlusion (tMCAO) was performed in male Wistar (n = 8/group) and Spontaneously Hypertensive Rats (SHR, n = 8/group). A combination laser Doppler-oxygen probe was placed within the expected cortical peri-infarct in addition to a surface laser doppler probe which measured LMA flow. Phenylephrine (PE) was infused 30 minutes into tMCAO to increase blood pressure (BP) by 30% for 10 minutes and assessed CBF autoregulation. During the initial 30-minute period of tMCAO, btO2 and cCBF were lower in SHR compared to Wistar rats (btO2: 11.5 ± 10.5 vs 17.5 ± 10.8 mmHg and cCBF: -29.7 ± 23.3% vs -17.8 ± 41.9%); however, LMA flow was similar between groups. The relationship between LMA flow, cCBF and btO2 were interdependent in Wistar rats. However, this relationship was disrupted in SHR rats and partially restored by induced hypertension. This study provides evidence that cCBF and btO2 were diminished during tMCAO in chronic hypertension, and that induced hypertension was beneficial regardless of hypertensive status.

In vitro modelling of the neurovascular unit for ischemic stroke research: Emphasis on human cell applications and 3D model design

Ischemic stroke has garnered global medical attention as one of the most serious cerebrovascular diseases. The mechanisms involved in both the development and recovery phases of ischemic stroke are complex, involving intricate interactions among different types of cells, each with its own unique functions. To better understand the possible pathogenesis, neurovascular unit (NVU), a concept comprising neurons, endothelial cells, mural cells, glial cells, and extracellular matrix components, has been used in analysing various brain diseases, particularly in ischemic stroke, aiming to depict the interactions between cerebral vasculature and neural cells. While in vivo models often face limitations in terms of reproducibility and the ability to precisely mimic human pathophysiology, it is now important to establish in vitro NVU models for ischemic stroke research. In order to accurately portray the pathological processes occurring within the brain, a diverse array of NVU 2D and 3D in vitro models, each possessing unique characteristics and advantages, have been meticulously developed. This review presents a comprehensive overview of recent advancements in in vitro models specifically tailored for investigating ischemic stroke. Through a systematic categorization of these developments, we elucidate the intricate links between NVU components and the pathogenesis of ischemic stroke. Furthermore, we explore the distinct advantages offered by innovative NVU models, notably 3D models, which closely emulate in vivo conditions. Additionally, an examination of current therapeutic modalities for ischemic stroke developed utilizing in vitro NVU models is provided. Serving as a valuable reference, this review aids in the design and implementation of effective in vitro models for ischemic stroke research.

Hypoperfusion Intensity Ratio and Hemorrhagic Transformation in Patients with Successful Recanalization after Thrombectomy

BACKGROUND AND PURPOSE

Hemorrhagic transformation remains a potentially devastating complication of acute ischemic stroke. We aimed to evaluate whether the hypoperfusion intensity ratio, a parameter derived from CT perfusion imaging, is associated with the development of hemorrhagic transformation in patients with anterior large-artery occlusion who had undergone thrombectomy.

MATERIALS AND METHODS

We retrospectively reviewed data from patients with consecutive acute ischemic strokes who had achieved successful recanalization (Thrombolysis in Cerebral Infarction score ≥2b) between January 2020 and December 2023. HIR was defined as the ratio of the volume of lesions with a time-to-maximum (Tmax) >6 seconds to those with a Tmax >10 second delay. The primary outcome, based on the European Cooperative Acute Stroke Study, was hemorrhagic transformation, diagnosed by follow-up imaging assessment in 24-hour windows, and radiologically classified as hemorrhagic infarction and parenchymal hematoma. The secondary outcome was a 3-month mRS score of ≥3.

RESULTS

Among 168 patients, 35 of 168 developed hemorrhagic transformation; 14 of 168 developed hemorrhagic infarction, and 21 of 168 developed parenchymal hematoma PH. After adjusting the latent covariates, increased hypoperfusion intensity ratio (per 0.1, adjusted OR [aOR] 1.68, 95% CI 1.26-2.25), ASPECTS (aOR 0.44, 95% CI 0.27-0.72), onset-to-puncture (aOR 1.01, 95% CI 1.00-1.02), and cardioembolism (aOR 5.6, 95% CI 1.59-19.7) were associated with hemorrhagic transformation in multivariable regression. The receiver operating characteristic curve indicated that hypoperfusion intensity ratio can predict hemorrhagic transformation accurately (area under the curve = 0.81; 95% CI, 0.738-0.882; P < .001) and predict parenchymal hematoma (area under the curve = 0.801; 95% CI, 0.727-0.875; P < .001).

CONCLUSIONS

Upon admission, hypoperfusion intensity ratio, an imaging parameter, predicted hemorrhagic transformation after reperfusion therapy in this patient population.

CT perfusion for predicting intracranial atherosclerotic middle cerebral artery occlusion

Backgrounds and purpose

Identifying the underlying cause of acute middle cerebral artery occlusion (MCAO) as intracranial atherosclerotic stenosis (ICAS) or embolism is essential for determining the optimal treatment strategy before endovascular thrombectomy. We aimed to evaluate whether baseline computed tomography perfusion (CTP) characteristics could differentiate ICAS-related MCAO from embolic MCAO.

Methods

We conducted a retrospective analysis of the clinical and baseline CTP data from patients who underwent endovascular thrombectomy for acute MCAO between January 2018 and December 2022. Core volume growth rate was defined as core volume on CTP divided by onset to CTP time. Multivariate logistic analysis was utilized to identify independent predictors for ICAS-related acute MCAO, and the diagnostic performance of these predictors was evaluated using receiver operating characteristic curve analysis.

Results

Among the 97 patients included (median age, 71 years; 60% male), 31 (32%) were diagnosed with ICAS-related MCAO, and 66 (68%) had embolism-related MCAO. The ICAS group was younger (p = 0.002), had a higher proportion of males (p = 0.04) and smokers (p = 0.001), a lower prevalence of atrial fibrillation (AF) (p < 0.001), lower NIHSS score at admission (p = 0.04), smaller core volume (p < 0.001), slower core volume growth rate (p < 0.001), and more frequent core located deep in the brain (p < 0.001) compared to the embolism group. Multivariate logistic analysis identified core volume growth rate (aOR 0.46, 95% CI 0.26-0.83, p = 0.01) as an independent predictor of ICAS-related MCAO. A cutoff value of 2.5 mL/h for core volume growth rate in predicting ICAS-related MCAO was determined from the receiver operating characteristic curve analysis, with a sensitivity of 81%, specificity of 80%, positive predictive value of 66%, and negative predictive value of 90%.

Conclusion

Slow core volume growth rate identified on baseline CTP can predict ICAS-related MCAO. Further prospective studies are warranted to confirm and validate these findings.

Remote Ischemic Conditioning Enhances Collateral Circulation Through Leptomeningeal Anastomosis and Diminishes Early Ischemic Lesions and Infarct Volume in Middle Cerebral Artery Occlusion

Remote ischemic conditioning (RIC) has attracted much attention as a protective strategy for the heart and brain, although the underlying mechanisms remain unclear. We hypothesized that RIC enhances collateral circulation during cerebral ischemia through endothelial function and mitigates both early ischemic change and final infarct volume. We tested the RIC and sham procedure 30 min after permanent middle cerebral artery occlusion (MCAO) in male mice. Collateral circulation was examined during the procedure with 2D color-coded ultrasound imaging. Immediately after four cycles of RIC, early ischemic lesions on magnetic resonance imaging (MRI), diffusion-weighted imaging (DWI), and development of pial collateral vessels were examined. The neurological signs and infarct volume with TTC were examined until 48 h after daily RIC. As compared with sham procedure, RIC enhanced collateral circulation, diminished early ischemic lesions, enlarged pial collaterals, and mitigated infarct volume. Next, we examined the effect of inhibitor of nitric oxide synthase (NOS) and Akt on the beneficial effect of RIC in MCAO. Both allosteric Akt inhibitor, 8-[4-(1-Aminocyclobutyl)phenyl]-9-phenyl[1,2,4]triazolo[3,4-f][1,6]naphthyridin-3(2H)-one (MK2206), and two NOS inhibitors, N5-(1-Iminoethyl)-L-ornithine dihydrochloride (L-NIO) and NG-Nitro-L-arginine methyl ester hydrochloride (L-NAME), counteracted the beneficial effect of RIC on collateral circulation, early lesions, pial anastomosis, and infarct volume. In permanent MCAO, RIC could enhance collateral circulation through leptomeningeal anastomosis with Akt-eNOS pathway and diminish early lesion and final infarct volume.

Blood Oxygenation Level-Dependent Cerebrovascular Reactivity-Derived Steal Phenomenon May Indicate Tissue Reperfusion Failure After Successful Endovascular Thrombectomy

In acute ischemic stroke due to large-vessel occlusion (LVO), the clinical outcome after endovascular thrombectomy (EVT) is influenced by the extent of autoregulatory hemodynamic impairment, which can be derived from blood oxygenation level-dependent cerebrovascular reactivity (BOLD-CVR). BOLD-CVR imaging identifies brain areas influenced by hemodynamic steal. We sought to investigate the presence of steal phenomenon and its relationship to DWI lesions and clinical deficit in the acute phase of ischemic stroke following successful vessel recanalization.From the prospective longitudinal IMPreST (Interplay of Microcirculation and Plasticity after ischemic Stroke) cohort study, patients with acute ischemic unilateral LVO stroke of the anterior circulation with successful endovascular thrombectomy (EVT; mTICI scale ≥ 2b) and subsequent BOLD-CVR examination were included for this analysis. We analyzed the spatial correlation between brain areas exhibiting BOLD-CVR-associated steal phenomenon and DWI infarct lesion as well as the relationship between steal phenomenon and NIHSS score at hospital discharge.Included patients (n = 21) exhibited steal phenomenon to different extents, whereas there was only a partial spatial overlap with the DWI lesion (median 19%; IQR, 8-59). The volume of steal phenomenon outside the DWI lesion showed a positive correlation with overall DWI lesion volume and was a significant predictor for the NIHSS score at hospital discharge.Patients with acute ischemic unilateral LVO stroke exhibited hemodynamic steal identified by BOLD-CVR after successful EVT. Steal volume was associated with DWI infarct lesion size and with poor clinical outcome at hospital discharge. BOLD-CVR may further aid in better understanding persisting hemodynamic impairment following reperfusion therapy.

CT perfusion extended window ischemic core estimation: Bayesian algorithm versus oscillation index singular value decomposition

BACKGROUND AND PURPOSE

Ischemic core estimation by CT perfusion (CTp) is a diagnostic challenge, mainly because of the intrinsic noise associated with perfusion data. However, an accurate and reliable quantification of the ischemic core is critical in the selection of patients for reperfusion therapies. Our study aimed at assessing the diagnostic accuracy of two different CTp postprocessing algorithms, that is, the Bayesian Method and the oscillation index singular value decomposition (oSVD).

METHODS

All the consecutive stroke patients studied in the extended time window (>4.5 hours from stroke onset) by CTp and diffusion-weighted imaging (DWI), between October 2019 and December 2021, were enrolled. The agreement between both algorithms and DWI was assessed by the Bland-Altman plot, Wilcoxon signed-rank test, Spearman's rank correlation coefficient, and the intraclass correlation coefficient (ICC).

RESULTS

Twenty-four patients were enrolled (average age: 72 ± 15 years). The average National Institutes of Health Stroke Scale was 14.42 ± 6.75, the median Alberta Stroke Program Early CT score was 8.50 (interquartile range [IQR] = 7.75-9), and median time from stroke onset to neuroimaging was 7.5 hours (IQR = 6.5-8). There was an excellent correlation between DWI and oSVD (ρ = .87, p-value < .001) and DWI and Bayesian algorithm (ρ = .94, p-value < .001). There was a stronger ICC between DWI and Bayesian algorithm (.97, 95% confidence interval [CI]: .92-.99, p-value < .001) than between DWI and oSVD (.59, 95% CI: .26-.8, p-value < .001).

DISCUSSION

The agreement between Bayesian algorithm and DWI was greater than between oSVD and DWI in the extended window. The more accurate estimation of the ischemic core offered by the Bayesian algorithm may well play a critical role in the accurate selection of patients for reperfusion therapies.

Collateral Flow: Prolonging the Ischemic Penumbra

This editorial serves as an introduction to the Special Issue on Collateral Flow: Prolonging the Ischemic Penumbra