Kallmes, David F.

Background Expansion of the endovascular and surgical workforce in the USA might lead to carotid revascularization procedures being carried out at low volume centers. Objective To evaluate trends in the treatment of carotid stenosis at high volume centers in the USA and compare outcomes by hospital volume. Methods Using the Nationwide Inpatient Sample, we evaluated trends in the proportion of carotid revascularization procedures performed at high volume centers in the USA from 2005 to 2011. High volume was defined as combined endarterectomy/stenting volume ≥130 patients/year, carotid endarterectomy volume ≥117 cases/year and carotid stenting volume ≥38 cases/year. In-hospital mortality, discharge to a long-term facility, intracranial hemorrhage, and postoperative stroke rates were compared between high and low volume centers. Results A total of 181 972 patients were included in this study. Overall, 63 442 patients (34.9%) were treated at high volume centers. The proportion of patients treated at high volume carotid revascularization centers decreased from 38.3% in 2005–2006 to 30.2% in 2010–2011. The proportion of patients treated at high volume centers decreased from 35.7% to 30.0% for carotid endarterectomy (p<0.0001) and 45.2% to 35.1% for carotid stenting. Patients treated at low volume centers had significantly higher rates of discharge to a long-term facility than high volume center patients (6.3% vs 5.0%, p<0.0001). The same was true for endarterectomy patients (6.0% vs 4.7%, p<0.0001) and stenting patients (8.3% vs 6.5%, p<0.0001). Conclusions A trend toward a lower proportion of patients with carotid stenosis being treated in high volume centers from 2005 to 2011 is concerning as these high volume centers had lower complication rates.

Hemodynamic factors are thought to play an important role in the initiation, growth, and rupture of cerebral aneurysms. In-vitro studies have demonstrated a correlation between the magnitude and distribution of wall shear stress (WSS) and biological response of both endothelial cells and smooth muscle cells [1–3]. In elastase induced saccular aneurysms, low WSS (below 0.5 Pa) was found to have a correlation with altered expression of biological markers [4]. Localized regions of rapid aneurysm growth in-vivo have been shown to be associated with regions where WSS is below a critical value of 0.1 Pa [5]. Further, aspect ratio (AR), the ratio of the maximum diameter of the aneurysm to the width of the aneurysm neck, has been correlated with elevated risk of rupture [6]. The purpose of the current study is to explore the possibility of creating elastase induced aneurysms in rabbits with a range of aspect ratios (ratio of aneurysm height/neck) and evaluate the existence of a correlation between aspect ratio and WSS distribution. Aneurysms with ARs from 0.98 to 2.8 were created at the origin of the right common carotid artery (n = 30). Qualitative differences in WSS distribution were found in the high AR aneurysms (HARA) (AR>1.6) and low AR aneurysms (LARA) (AR<1.6) [7].

Flow diversion treatment of cerebral aneurysms has increasingly been considered, especially for large complex aneurysms with wide necks that are difficult to treat with coils of by clipping. However, the relationship between the hemodynamic environment created immediately after implantation of flow diverters (FD) and the subsequent aneurysm occlusion is poorly understood [1].

Since treatment of cerebral aneurysms with flow diverters (FD) has gained much attention in recent years, it is important to understand what is the effect of these devices on the flow through arteries jailed or crossed by these devices [1].

We present a quantified description of the fluid flow and a novel flowline-based meshing technique to create adaptive grids for Computational Fluid Dynamics (CFD) simulations in patient-specific intracranial aneurysms. The adaptive grid density is obtained such that it captures the fine geometrical details of the flow with high grid density, while smoother flow characteristics are calculated with a coarser grid density. The correlation between the topological characteristics of the flow and the element size of the adaptive grid results in a practical mathematical formula for calculating the element size using only one uniform base mesh and a user defined implementation in CFD post processors.

Background and Purpose— Angiographic revascularization grading after intra-arterial stroke therapy is limited by poor standardization, making it unclear which scale is optimal for predicting outcome. Using recently standardized criteria, we sought to compare the prognostic performance of 2 commonly used reperfusion scales. Methods— Inclusion criteria for this multicenter retrospective study were acute ischemic stroke attributable to middle cerebral artery M1 occlusion, intra-arterial therapy, and 90-day modified Rankin scale score. Post–intra-arterial therapy reperfusion was graded using the Thrombolysis in Myocardial Infarction (TIMI) and Modified Thrombolysis in Cerebral Infarction (mTICI) scales. The scales were compared for prediction of clinical outcome using receiver-operating characteristic analysis. Results— Of 308 patients, mean age was 65 years, and median National Institutes of Health Stroke Scale score was 17. The mean time from stroke onset to groin puncture was 305 minutes. There was no difference in the time to treatment between patients grouped by final TIMI (ie, 0 versus 1 versus 2 versus 3) or mTICI grades (ie, 0 versus 1 versus 2a versus 2b versus 3). Good outcome (modified Rankin scale, 0–2) was achieved in 32.5% of patients, and mortality rate was 25.3% at 90 days. There was a 6.3% rate of parenchymal hematoma type 2. In receiver-operating characteristic analysis, mTICI was superior to TIMI for predicting 90-day modified Rankin scale 0 to 2 (c-statistic: 0.74 versus 0.68; P <0.0001). The optimal threshold for identifying a good outcome was mTICI 2b to 3 (sensitivity 78.0%; specificity 66.1%). Conclusions— mTICI is superior to TIMI for predicting clinical outcome after intra-arterial therapy. mTICI 2b to 3 is the optimal biomarker for procedural success.

The Modeling and Analysis group in the Division of Engineering at Mayo Clinic, Rochester works in the area of numerical modeling and experimental validation of cerebral aneurysms. In our modeling we use patient-specific geometries from imaging studies provided by Dr. Kallmes. The CFD analysis is performed with commercial packages Mimics (Materialise, Leuven, Belgium), for segmentation and ANSYS (ANSYS Inc. Canonsburg, PA) for meshing, simulation and post-processing. The experiments are conducted using a tomographic Particle Image Velocimetry system from LaVision Inc. The group is led by Dan Dragomir-Daescu, PhD and David F. Kallmes, MD and consists of two postdoctoral fellows and three engineers. For this project, CFD simulations were performed by postdoctoral fellow Simona Hodis, using the finite volume based solver Fluent.

An intracranial aneurysm (IA) is a pathological condition of cerebral arteries characterized by local enlargements of the arterial wall, typically into a saccular shape. Rupture of the aneurysm sac can result in devastating cerebral hemorrhage. Hemodynamic factors are believed to play an important role in initiation, development and rupture of IAs [1–3]. However, the coupling between hemodynamics and aneurysm pathophysiology is complex and remains poorly understood. Patient specific diagnostics regarding risk of rupture can be substantially advanced by improving our understanding of the in-vivo response of the aneurysm wall to intra-saccular hemodynamic stresses. A mechanism for fundamental studies of the impact of chronically altered WSS on the intact vascular wall is provided by animal models. However, cerebral aneurysms have not been shown to occur naturally in animals. Thus, a number of animal models have been created for studying aneurysm pathogenesis including those in mice, rats, rabbits, canines, swine and primates. To make meaningful use of these models, it is important to evaluate their relevance to human biomechanics and pathophysiology.

Background and Purpose— Reversal of anticoagulation with protamine might predispose to a higher risk of stroke in patients with carotid stenting. We evaluated a national, multihospital patient database to examine the risk of stroke in patients with carotid stenting receiving protamine compared with those who did not. Methods— The Premier Perspective database was used to identify patients who were electively hospitalized for carotid stenting from 2006 through 2011. The incidence of in-hospital mortality and morbidity was compared between patients who did and did not receive protamine after propensity score adjustment via 1:1 matching to reduce selection bias. Results— Of 6664 patients with carotid stenting treated at 193 hospitals, 556 (8%) received protamine on the day of the procedure. After matching by propensity score, patients who received protamine had a similar likelihood of stroke or transient ischemic attack ( P =0.77), in-hospital mortality ( P =0.12), discharge to long-term care ( P =0.15), and access site complications ( P =0.90) as compared with patients who did not receive protamine. Conclusions— Protamine administration is not associated with additional risk of adverse events after carotid stenting.