A multi-asperity adhesive contact model for catheter and vascular artery contact in endovascular surgery.

Contact behaviors of medical devices, such as guidewires and catheters, are critical in endovascular surgeries. In this work, a new method to predict adhesive contact force between catheter and vascular artery is presented. Multi-asperity adhesion on the surface of vascular artery, deformation of asperity and deformation of vascular substrate are all considered. The single asperity behavior is described with Johnson-Kendall-Roberts (JKR) contact model. The multi-asperity behavior is based on Greenwood-Williamson (GW) asperity model. Vascular substrate is considered as elastic bulk substrate and its deformation is determined with Hertzian pressure from asperity on a circular region on the elastic half space. The model shows that the deformation of vascular substrate accounts for the majority of the total contact deformation and significantly affects the predicted contact force. The model is verified with published experimental data. The comparison shows that the model produces very accurate prediction of contact force between catheter and vascular artery when the contact force is compressive. Parametric analysis based on asperity topography is carried out. The analysis shows that the diameter of the circular region of the interface between asperity and vascular substrate has more significant effect on the estimation of contact force than the radius of asperity. Further validation of prediction accuracy of the model under experiment is needed.

Novel model of direct and indirect cost-benefit analysis of mechanical embolectomy over IV tPA for large vessel occlusions: a real-world dollar analysis based on improvements in mRS.

BACKGROUND: Ischemic strokes result in significant healthcare expenditures (direct costs) and loss of quality-adjusted life years (QALYs) (indirect costs). Interventional therapy has demonstrated improved functional outcomes in patients with large vessel occlusions (LVOs), which are likely to reduce the economic burden of strokes. OBJECTIVE: To develop a novel real-world dollar model to assess the direct and indirect cost-benefit of mechanical embolectomy compared with medical treatment with intravenous tissue plasminogen activator (IV tPA) based on shifts in modified Rankin scores (mRS). METHOD: A cost model was developed including multiple parameters to account for both direct and indirect stroke costs. These were adjusted based upon functional outcome (mRS). The model compared IV tPA with mechanical embolectomy to assess the costs and benefits of both therapies. Direct stroke-related costs included hospitalization, inpatient and outpatient rehabilitation, home care, skilled nursing facilities, and long-term care facility costs. Indirect costs included years of life expectancy lost and lost QALYs. Values for the model cost parameters were derived from numerous resources and functional outcomes were derived from the MR CLEAN study as a reflective sample of LVOs. Direct and indirect costs and benefits for the two treatments were assessed using Microsoft Excel 2013. RESULTS: This cost-benefit model found a cost-benefit of mechanical embolectomy over IV tPA of $163 624.27 per patient and the cost benefit for 50 000 patients on an annual basis is $8 181 213 653.77. CONCLUSIONS: If applied widely within the USA, mechanical embolectomy will significantly reduce the direct and indirect financial burden of stroke ($8 billion/50 000 patients).

Endovascular external carotid artery occlusion for brain selective targeting: a cerebrovascular swine model.

BACKGROUND: The choice of an animal model for cerebrovascular research is often determined by the disease subtype to be studied (e.g. ischemic stroke, hemorrhage, trauma), as well as the nature of the intervention to be tested (i.e. medical device or pharmaceutical). Many initial studies are performed in smaller animals, as they are cost-effective and their encephalic vasculature closely models that of humans. Non-human primates are also utilized when confirmation or validation is required on higher levels and to test larger devices. However, working with primates is complex and expensive. Intermediate sized animal models, such as swine and sheep, may represent a valuable compromise. Their cerebrovascular anatomy, however, comes with challenges because of the natural higher external carotid artery perfusion and the existence of a rete mirabile. We describe a modification to the traditional swine cerebrovascular model that significantly enhances selective brain hemispheric perfusion, limiting external carotid perfusion and dilution. RESULTS: We investigated whether unilateral endovascular coil-embolization of external carotid artery branches in swine would lead to increased brain perfusion, altering cerebral circulation so that it more closely models human cerebral circulation. Equal amounts of approximately 4 °C cold saline were injected in 6 Yorkshire pigs into the ipsilateral common carotid artery before and after embolization. Hemispheric temperature changes from pre- and post-embolization were obtained as a measure of brain perfusion and averaged and compared using non-parametric statistical tests (Wilcoxon signed rank test, Mann-Whitney U Test). Graphs were plotted with absolute changes in hemispheric temperature over time to determine peak temperature drop (PTD) and corresponding time to peak (TTP) following the cold bolus injection. There was a 288 ± 90% increase in ipsilateral brain cooling after embolization indicating improved selective blood flow to the brain due to this vascular modification. CONCLUSION: We have developed an effective, selective vascular brain model in swine that may be useful as a practical and cost-reducing intermediate step for evaluating target dose-responses for central nervous system drugs and brain selective interventions, such as local hypothermia.

Feasibility of near-infrared spectroscopic tomography for intraoperative functional cerebral monitoring: a primate study.

OBJECTIVE: The wide-ranging manipulations to the cardiovascular system that frequently occur during cardiac surgery can expose the brain to variations in its blood supply that could prove deleterious. As a first step to developing a resource suitable for monitoring such changes, we detected the hemodynamic events induced in the brain of a primate model, using high-density near-infrared spectroscopy combined with tomographic reconstruction methods and validated the findings using established radiologic and histologic techniques. METHODS: Continuous monitoring of the relative changes in the components of the cerebral hemoglobin signal was performed using high-density near-infrared spectroscopy (270 source-detector channel array) in anesthetized bonnet macaques with the brain exposed to induced ischemia and other acute events. A comparative analysis (exact binomial test) applied to reconstructed 3-dimensional images before and after the events and between cerebral hemispheres, combined with postprocedure magnetic resonance imaging, and postmortem histopathologic examination of the macaques' brains was performed to document and validate the spatial features revealed by the optical findings. RESULTS: Relative changes in the measured and calculated components of the hemoglobin signal, in response to the performed manipulations, revealed substantial concurrence among the reconstructed 3-dimensional images, magnetic resonance imaging of the macaques' brains, and postmortem histopathologic examination findings. Concurrence was seen when the manipulated hemoglobin concentration and associated oxygenation levels were either increased or decreased, and whether they were bilateral or restricted to a specified hemisphere. CONCLUSIONS: Continuous near-infrared spectroscopy tomography has been shown to accurately capture and localize cerebral ischemia, vasodilatation, and hemorrhage in primates in real time. These findings are directly applicable to clinical intraoperative functional cerebral monitoring.

Complications of modern diagnostic cerebral angiography in an academic medical center.

PURPOSE: Catheter cerebral angiography and noninvasive cerebral imaging have steadily improved in the past several decades. Now, catheter angiography is frequently reserved for treatment planning. To remain relevant as a diagnostic modality, catheter angiography must be safe, even in critically ill patients. The present report describes the complication rate of catheter cerebral angiography performed by neurointerventional specialists at an academic medical center. MATERIALS AND METHODS: From July 2001 through June 2007, 3,636 diagnostic catheter cerebral angiograms were obtained at a large academic institution. Complication data were prospectively acquired according to institutional policy and New York Patient Occurrence Reporting and Tracking System criteria. Data collected included patient age, sex, indication for the procedure, operator, and nature of adverse event, including need for treatment. Clinical predictors of complications were evaluated with logistic regression. RESULTS: Among 3,636 diagnostic cerebral angiograms obtained in 6 years, there were 11 clinical complications (0.30%). One patient (0.03%) had magnetic resonance imaging-detected stroke with no apparent clinical deterioration. Iatrogenic dissections were seen in five arteries (0.14%). No patient developed neurologic symptoms. Nonneurologic complications occurred in five patients (0.14%) who had arteriotomy site-related complications: one femoral abscess, two occlusions of the femoral artery with leg ischemia requiring surgical revascularization, one dissection with pseudoaneurysm formation requiring percutaneous thrombin injection, and one retroperitoneal hemorrhage requiring transfusion. Three of these patients were treated with an arterial closure device. Age greater than 65 years was associated with development of complications (P = .03). CONCLUSIONS: Modern catheter cerebral angiography performed by neurointerventionalists is associated with a low complication rate of 0.30%, even in a highly complex patient population.

External carotid arterial injury.

Carotid vascular trauma has high mortality. The two primary causes of death are associated head injury and vascular injuries that cause exsanguination or stroke. In the past two decades interventional radiology, i.e. techniques of transcatheter embolisation, has become a vital component of the care of these cases. External carotid artery injuries are complex and are often inaccessible causes of exsanguinating haemorrhage. Transcatheter techniques have been shown to be highly effective in controlling this haemorrhage. An overview of injuries of the external carotid artery and its branches is presented.

Major neurologic improvement following endovascular recanalization therapy for acute ischemic stroke.

BACKGROUND: We aimed to identify the rate of major neurologic improvement (MNI) at 24 h following endovascular recanalization therapy (ERT) for acute ischemic stroke and its association with short-term outcome. METHODS: We retrospectively reviewed consecutive acute ischemic stroke patients presenting to our institution over 4 years and undergoing ERT. Angiograms were independently reviewed. Data on demographics, medical history, initial NIHSS score, 24-hour NIHSS score, site of acute vascular lesion, pre- and posttreatment Thrombolysis in Myocardial Infarction scores, symptomatic intracerebral hemorrhage (within 36 h of intervention that was associated with a 4-point decline in NIHSS score) and discharge disposition were collected. We used logistic regression analysis to identify predictors of MNI (defined as >or=8-point improvement in NIHSS or a score of 0-1 at 24 h) and favorable discharge status (defined as home or acute rehabilitation). RESULTS: Sixty-eight patients were included (median age = 71 years, 60% women, median NIHSS score = 19.5, anterior circulation = 75%). The modes of ERT were pharmacologic only (28%), mechanical only (35%) and multimodal therapy (37%). Thrombolysis in Myocardial Infarction 2 or 3 recanalization was achieved in 64.7% (mechanical only 46%, pharmacologic only 63% and multimodal 84%). The outcomes were: symptomatic intracerebral hemorrhage (11.8%), MNI (26.5%) and favorable discharge (41.2%). Age (OR = 0.93, p = 0.003) and cardioembolic stroke subtype (OR = 6.0, p = 0.018) were independent predictors of MNI. MNI was a strong predictor of favorable discharge status (OR = 46.4, p < 0.001). CONCLUSIONS: Despite initial stroke severity, MNI occurred in over one fourth of the patients and independently and strongly predicted favorable discharge outcome.

Endovascular recanalization therapy in acute ischemic stroke.

BACKGROUND AND PURPOSE: To assess the outcome in acute ischemic stroke patients not eligible for systemic thrombolysis (outside the 3-hour time window, after surgery, or on anticoagulant) undergoing endovascular recanalization therapy (ERT) at the Columbia University Medical Center (CUMC) and to determine US nationwide usage and outcome of ERT in acute ischemic stroke. METHODS: Patients treated at CUMC from 2001 to 2004 and the Nationwide Inpatient Sample (NIS) comprising 20% of all admissions in the United States from 1999 to 2002 were analyzed retrospectively. RESULTS: Thirty-one patients underwent ERT. Mean age was 68+/-14 years, 68% were female, and 45% nonwhite (occlusion sites: internal carotid artery 29%; middle cerebral artery 39%; posterior circulation 32%). Pharmacological or mechanical ERT was initiated beyond 3 hours after symptom onset (median time 4.4 hours) in 61%, 29% had surgery, and 39% were on anticoagulant medication. At discharge, 32% had modified Rankin Scale scores of 0 to 2 (52% discharged home or to rehabilitation facilities); overall mortality was 29%, of which 19% were fatal intracerebral hemorrhages. From the NIS cohort, 477 patients (0.17% of all strokes and 14% of all thrombolysis cases) underwent ERT. Fifteen percent died, and approximately 50% were discharged home or to rehabilitation facilities. Intracerebral hemorrhage occurred in 6%. Fewer good outcomes of the CUMC cohort may be explained by more unfavorable premorbid patient characteristics compared with the NIS cohort. CONCLUSIONS: Despite significant variability in patient characteristics and treatment methods among 2 sources of data analyzed, ERT in stroke patients not eligible for intravenous thrombolysis appears to be a relatively safe and effective treatment alternative that is being used increasingly nationwide.

Real-time magnetic resonance imaging for interventional neuroradiological procedures.

Over the last two decades, interventional neuroradiologists have developed powerful techniques for the treatment of cerebrovascular disorders and brain tumors. Current interventional neuroradiological procedures are performed under X-ray fluoroscopy, which has allowed for high temporal and spatial resolution. However, these imaging techniques do not provide the treating physician with vital anatomic and functional information regarding vessel walls and the surrounding brain tissue. Better visualization of vessel structures and real-time information about the state of perfusion and metabolism of the surrounding brain tissue (real-time magnetic resonance arteriography, diffusion and perfusion-weighted imaging, apparent diffusion coefficient maps) would enhance safety and efficacy of neuroendovascular procedures available currently. Recent advances in magnetic resonance hardware and software have permitted significant enhancements in temporal and spatial resolution, which have resulted in the capability of visualizing anatomic structures with real-time fluoroscopy and angiography. This review outlines how real-time magnetic resonance procedures may replace conventional X-ray fluoroscopy in diagnostic and interventional neuroradiology during the next decade.

Histopathological evaluation of middle cerebral artery after percutaneous intracranial transluminal angioplasty.

BACKGROUND: Intracranial atherosclerosis accounts for 8% to 10% of all ischemic strokes, and intracranial angioplasty is increasingly performed to treat stenotic lesions. We report an autopsy case and discuss the effects of intracranial angioplasty for atherosclerotic arteries. CASE DESCRIPTION: A 77-year-old patient died 9 days after angioplasty of the left middle cerebral artery as a result of cardiorespiratory failure. The patient was anticoagulated before, during, and after the procedure with heparin, aspirin, and clopidogrel. At the site of angioplasty, the densely fibrotic eccentric plaque was displaced from the adjacent media into the lumen, distorting it and forming elongated projections. No local thrombosis, plaque compression, or inflammation was observed. Additionally, an intramural hemorrhage extended from the site of angioplasty into the stenotic proximal inferior division of the left middle cerebral artery. CONCLUSIONS: Histopathological findings after intracranial angioplasty parallel those in other arterial territories. The implications of these pathological findings on the medical and endovascular treatment of intracranial atherosclerosis are discussed.

The acute cerebrovascular effects of intracarotid adenosine in nonhuman primates.

UNLABELLED: In this study we sought to determine the acute cerebrovascular effects of intracarotid adenosine by using real-time cerebral blood flow (CBF) measurements in nonhuman primates. The internal carotid arteries of healthy anesthetized baboons were transfemorally cannulated. Changes in CBF were continuously measured at baseline and with 6 increasing doses of adenosine (0.002 to 1.5 mg/min) by use of an intraparenchymal thermal diffusion (TD) probe. Each infusion lasted 5 min. At baseline and at the largest dose of adenosine, CBF was also determined by the intraarterial (133)Xe technique. TD measurements revealed a dose-dependent increase in CBF from 32 +/- 6 mL x l00 g(-1) x min(-1) at baseline to 90 +/- 38 mL x l00 g(-1) x min(-1) with the largest dose of adenosine (n = 5; P < 0.0001). A similar magnitude of increase in CBF was also observed with (133)Xe CBF measurements. No significant increases in intracranial pressure or adverse systemic hemodynamic side effects were observed during adenosine infusion. The increase in CBF after adenosine lasted only for the duration of drug infusion. In conclusion, the transient cerebrovascular effects of intracarotid adenosine make it suitable for a trial of intraarterial vasodilator therapy and for controlled manipulation of cerebrovascular resistance. IMPLICATIONS: Using a real-time cerebral blood flow (CBF) measurement technique, we evaluated the acute cerebrovascular effects of intracarotid adenosine in anesthetized baboons. The increase in CBF lasted only for the duration of the adenosine infusion. Adenosine might be a suitable drug for trial as an intraarterial vasodilator for the treatment of cerebral vasospasm.

Preliminary experience with endovascular reconstruction for the management of carotid blowout syndrome.

BACKGROUND AND PURPOSE: Permanent balloon occlusion (PBO) of the carotid artery has been previously shown to be an effective means to treat carotid blowout syndrome (CBS). However, despite the effectiveness of this endovascular technique, concern remains regarding its potential for producing delayed cerebral ischemic complications in 15% to 20% of patients. This significant limitation of carotid PBO led our group to evaluate an alternative management strategy, consisting of endovascular reconstruction of the carotid artery (ERCA) in patients thought to be at particularly high risk for carotid occlusion (ie, provocative balloon test occlusion, angiographic documented incomplete circle of Willis, or contralateral carotid artery occlusion). METHODS: We reviewed all cases of CBS referred to our service, in which ERCA was chosen as a management strategy for patients thought to be at high risk for PBO, based on previously defined criteria. RESULTS: Sixteen carotid blowout events occurred in 12 patients with CBS who were deemed to be at high risk for cerebral ischemic complications, which were managed with ERCA by using a variety of stent devices and techniques. Adjunctive embolization of carotid pseudoaneurysms was performed in five of these patients by using platinum coils or acrylic glue. Hemostasis was achieved in all cases, although one patient with traumatic CBS and three patients with aggressive head and neck cancer-related CBS, required retreatment with ERCA. Recurrent CBS rates were similar to those reported in other studies using PBO. Overall, no treatment-related strokes or deaths occurred. CONCLUSION: CBS managed with ERCA can be performed safely and with efficacy of outcomes at least equivalent to those previously reported in association with conventional carotid PBO, therefore representing an excellent alternative endovascular technique for patients who are at increased risk of stroke after PBO.

Conducting stroke research with an exception from the requirement for informed consent.

BACKGROUND: Obtaining viable informed consent from stroke patients for participation in clinical trials of acute stroke therapies is often problematic because of patients' neurological deficits. Furthermore, obtaining permission from surrogates is often not possible or not legally permissible. SUMMARY OF REVIEW: In 1996 the Food and Drug Administration and Department of Health and Human Services published regulations that allow investigators to conduct emergency research without patient consent under a narrowly defined set of circumstances. We review requirements of these regulations, paying particular attention to how they may be applied in a clinical trial of an acute stroke therapy. CONCLUSIONS: Acute stroke researchers should consider conducting clinical trials with an exception from the informed consent requirement permitted by this law.

Intra-arterial 133Xe measurements suggest a dose-dependent increase in cerebral blood flow during intracarotid infusion of adenosine in nonhuman primates.

Intra-arterial vasodilators, such as papaverine, have been used to treat cerebrovascular insufficiency. The short biologic half-life, and the vasodilating and neuroprotective properties of adenosine could be useful during the treatment of cerebral ischemia. However, in human subjects a proposed intracarotid dose of 1 mg/min adenosine was ineffective in augmenting cerebral blood flow (CBF). The object of this experiment was to determine the dose-CBF response characteristics of intracarotid adenosine in nonhuman primates. Studies were conducted on five male baboons under isoflurane anesthesia. After transfemoral internal carotid artery cannulation, changes in CBF (intra-arterial 133Xe technique) were determined after intracarotid infusion of saline and three increasing doses of adenosine (0.5, 1.0, and 1.5 mg/min). Each infusion lasted 5 minutes. Data (mean +/- standard deviation) were analyzed by repeated-measure analysis of variance and the post hoc Tukey test. Intracarotid adenosine (0.5, 1.0, and 1.5 mg/min) resulted in a dose-dependent increase in CBF from 22.6 +/- 4 mL/100 g/min at baseline to 50 +/- 15, 65 +/- 22, and 83 +/- 31 mL/100 g/min respectively (n = 5, P < .05 each). No adverse hemodynamic side effects were noted, and animals recovered promptly from anesthesia. The authors conclude that intracarotid adenosine in the range of 0.5 to 1.5 mg/min results in a robust increase in CBF. Based on body weight, intracarotid adenosine in a dose range of 2.5 to 7.5 mg/min may be required to augment CBF in human subjects.

Peripheral aneurysms of the lateral posterior choroidal artery: clinical presentation and endovascular treatment: report of two cases.

OBJECTIVE AND IMPORTANCE: To describe the clinical presentation and endovascular management of peripheral aneurysms of the lateral posterior choroidal artery. Aneurysms in this location are exceptionally rare and optimal treatment may be difficult. CLINICAL PRESENTATION: Two patients with peripheral aneurysms of the distal portion of the lateral posterior choroidal artery presented with headaches from extensive intraventricular hemorrhage. INTERVENTION: Endovascular surgical therapy by use of superselective n-butylcyanoacrylate embolization of the aneurysm and adjacent distal parent artery was successful in both patients. CONCLUSION: Patients with peripheral aneurysms of the lateral posterior choroidal artery usually present with intraventricular hemorrhage. They may be difficult to treat by open surgical techniques owing to their intraventricular location and the frequent inability to preserve the parent artery by aneurysm clipping. Instead, it is typical that either proximal parent artery occlusion or aneurysm trapping must be used. An equivalent endovascular surgical technique may be an attractive alternative method of management.

In nonhuman primates intracarotid adenosine, but not sodium nitroprusside, increases cerebral blood flow.

UNLABELLED: Intracarotid infusion of short-acting vasodilators, such as adenosine and nitroprusside, in doses that lack significant systemic side effects, may permit controlled manipulation of cerebrovascular resistance. In this experiment we assessed changes in cerebral blood flow (CBF) after intracarotid infusion of nitroprusside and adenosine. The study was conducted on six adult baboons under isoflurane anesthesia and controlled ventilation. Intracarotid drug infusion protocol avoided hypotension during nitroprusside infusion and tested for autoregulatory vasoconstriction. CBF (intraarterial (133)Xe technique) was measured four times during infusions of 1) intracarotid saline, 2) IV phenylephrine (0.2 microg x kg(-1) x min(-1)) aimed to increase mean arterial pressure by 10-15 mm Hg, 3) IV phenylephrine and intracarotid nitroprusside (0.5 microg x kg(-1) x min(-1)), and 4) intracarotid adenosine (1 mg/min). IV phenylephrine increased mean arterial pressure (69 +/- 8 to 91 +/- 9 mm Hg, P < 0.0001, n = 6), and concurrent infusion of intracarotid nitroprusside reversed this effect. However, compared with baseline, CBF did not change with IV phenylephrine or with concurrent infusion of IV phenylephrine and intracarotid nitroprusside. Intracarotid adenosine profoundly increased CBF (from 29 +/- 8 to 75 +/- 32 mL x 100 g(-1) x min(-1); P < 0.0001). In nonhuman primates, intracarotid adenosine increases CBF in doses that lack significant systemic side effects, whereas intracarotid nitroprusside has no effect. Intracarotid adenosine may be useful for manipulating cerebrovascular resistance and augmenting CBF during cerebral ischemia. IMPLICATIONS: Intraarterial (133)Xe cerebral blood flow (CBF) measurements suggest that intracarotid adenosine, in a dose that lacks significant systemic side effects, profoundly increases CBF, whereas nitroprusside has no effect.(5-12)