Basic and Translational Research in Cardiac Repair and Regeneration: JACC State-of-the-Art Review

This paper aims to provide an important update on the recent preclinical and clinical trials using cell therapy strategies and engineered heart tissues for the treatment of postinfarction left ventricular remodeling and heart failure. In addition to the authors’ own works and opinions on the roadblocks of the field, they discuss novel approaches for cardiac remuscularization via the activation of proliferative mechanisms in resident cardiomyocytes or direct reprogramming of somatic cells into cardiomyocytes. This paper’s main mindset is to present current and future strategies in light of their implications for the design of future patient trials with the ultimate objective of facilitating the translation of discoveries in regenerative myocardial therapies to the clinic.

Multiple pipeline embolization devices improves aneurysm occlusion without increasing morbidity: A single center experience of 140 cases

INTRODUCTION

Rates of aneurysm occlusion with the pipeline embolization device (PED) has varied widely in the literature from 55.7% to 93.3% at 6 months, which may reflect a difference in technique including sizing and number of devices used.

METHODS

140 cases at our institution were retrospectively reviewed, and aneurysms treated with a single PED vs. multiple were compared.

RESULTS

Complete aneurysm occlusion was achieved in 86.9% at 6 months, 91.8% at 1 year, and 97.6% at longest follow-up. Retreatment with an additional device was required in 7 (5.1%). Major and minor complication rate within 30 days was 1.4% and 5.0%, and at greater than 30 days was 0.8% and 3.1%. Patients treated with multiple PEDs had significantly higher rates of aneurysm occlusion at 6 months (92.9% vs. 75.6%, p = 0.017) and 12 months (98.4% vs. 81.1%, p = 0.014), with no difference in complications. The two groups were similar aside from a higher number of ophthalmic and paraophthalmic aneurysms treated with multiple PEDs (23.4% vs. 6.5%, p = 0.004; and 35.1% vs. 17.4%, p = 0.020), and more posterior communicating artery and recurrent aneurysms treated with a single PED (28.3% vs. 3.2%, p = 0.001; 23.9% vs. 8.5%, p = 0.031). The use of multiple PEDs was found to be an independent predictor of aneurysm occlusion in a multivariate analysis (p = 0.015).

CONCLUSIONS

The use of multiple PEDs for intracranial aneurysms leads to significantly higher occlusion rates without added morbidity. This benefit is particularly appropriate for ophthalmic segment aneurysms, while more distal segments with eloquent perforating branches should be managed with caution.

Future Directions of Flow Diverter Therapy

The treatment of intracranial aneurysms has undergone a few very significant paradigm shifts in its history. Needless to say, microsurgery and surgical clipping served as the initial basis for successful treatment of these lesions. The pursuit of endovascular therapy subsequently arose from the desire to reduce the invasiveness of therapy. While the first breakthrough arose with Guido Guglielmi's invention of the detachable platinum coil, commercialized flow diverter therapy represents a disruptive therapy with a completely different paradigm for aneurysmal obliteration. This has not only altered the distribution of aneurysmal management strategies, but also opened the gateway to the treatment of previously inoperable lesions. With the basic flow diverter stent technology now considered an integral part of the neurointerventional armamentarium, we now consider what may lay in the future - including potential directions for research with regards to case selection; the location and type of aneurysms which may become routinely treatable; and modifications to the flow diverter, which may increase its utility and safety in terms of size, structural design, and surface modifications.

Safety and Efficacy of Bilateral Flow Diversion for Treatment of Anterior Circulation Cerebral Aneurysms

BACKGROUND

Nearly 20% of individuals with an aneurysm will have multiple aneurysms-these individuals are at increased risk of subarachnoid hemorrhage. Treatment of bilateral aneurysms with flow diverters (FDs), or Pipeline embolization device, has not yet been established as an effective therapy. We evaluated the safety and efficacy of a 2-stage treatment of bilateral aneurysms with Pipeline embolization devices placed 6 months apart.

METHODS

We performed a retrospective review to analyze the clinical and angiographic outcomes of 16 individuals with bilateral aneurysms treated with 2-stage flow diversion at a tertiary referral center from January 2010 to July 2018.

RESULTS

Of the 16 patients with 33 aneurysms treated with bilateral flow diversion, 1 had 2 aneurysms treated with a single FD on the contralateral side. The aneurysms treated were ophthalmic, superior hypophyseal, posterior communicating, or cavernous segment aneurysms, with an average size of 6.5 mm. No major complications, such as in-stent stenosis, thromboembolic events, distal intraparenchymal hemorrhage, rerupture, stent migration, or neurological death, were recorded. All the patients had good functional outcomes. At the 24-month follow-up examination, 81% of aneurysms showed complete occlusion. No aneurysm required repeat treatment.

CONCLUSIONS

The results from the present study have demonstrated that 2-stage treatment of bilateral aneurysms with FDs is both safe and efficacious. The timing of contralateral FD stent placement is critical. We found that 6 months allows for adequate neurological recovery and stent endothelialization.

Bone marrow-derived mononuclear cell seeded bioresorbable vascular graft improves acute graft patency by inhibiting thrombus formation via platelet adhesion

Background:

Acute thrombosis is a crucial cause of bioresorbable vascular graft (BVG) failure. Bone marrow-derived mononuclear cell (BM-MNC)-seeded BVGs demonstrated high graft patency, however, the effect of seeded BM-MNCs against thrombosis remains to be elucidated. Thus, we evaluated an antithrombotic effect of BM-MNC-seeding and utilized platelet-depletion mouse models to evaluate the contribution of platelets to acute thrombosis of BVGs.

Methods and results:

BVGs were composed of poly (glycolic acid) mesh sealed with poly (l-lactideco-ε-caprolactone). BM-MNC-seeded BVGs and unseeded BVGs were implanted to wild type C57BL/6 mice (n = 10/group) as inferior vena cava interposition conduits. To evaluate platelet effect on acute thrombosis, c-Mpl^–/– mice and Pf4-Cre⁺; iDTR mice with decreased platelet number were also implanted with unseeded BVGs (n = 10/group). BVG patency was evaluated at 2, 4, and 8 weeks by ultrasound. BM-MNC-seeded BVGs demonstrated a significantly higher patency rate than unseeded BVGs during the acute phase (2-week, 90% vs 30%, p = .020), and patency rates of these grafts were sustained until week 8. Similar to BM-MNC-seeded BVGs, C-Mpl^−/− and Pf4-Cre⁺; iDTR mice also showed favorable graft patency (2-week, 90% and 80%, respectively) during the acute phase. However, the patency rate of Pf4-Cre⁺; iDTR mice decreased gradually after DTR treatment as platelet number recovered to baseline. An in vitro study revealed BM-MNC-seeding significantly inhibited platelet adhesion to BVGs compared to unseeded BVGs, (1.75 ± 0.45 vs 8.69 ± 0.68 × 10³ platelets/mm², p < .001).

Conclusions:

BM-MNC-seeding and the reduction in platelet number prevented BVG thrombosis and improved BVG patency, and those results might be caused by inhibiting platelet adhesion to the BVG.

[Modern polyurethanes in cardiovascular surgery]

Currently, there is great clinical demand for synthetic tissue-engineered cardiovascular prostheses with good long-term patency. Polyurethanes belong to the class of polymers with excellent bio- and hemocompatibility. They are known to possess good mechanical properties, but are prone to processes of degradation in conditions of functioning in living organisms. Attempts at solving this problem have resulted in the development of various new subclasses of polyurethanes such as thermoplastic polyether polyurethanes, polyurethanes with a silicone segment, polycarbonate polyurethanes and nanocomposite polyurethanes. This was accompanied and followed by offering a series of new technologies of production of implantable medical devices such as vascular grafts, heart valves and others. In the presented review, we discuss biological and mechanical properties of modern subclasses of polyurethanes, as well as modern methods of manufacturing implantable medical devices made of polyurethanes, especially small-diameter vascular prostheses.

Contrasting biofunctionalization strategies for the enhanced endothelialization of biodegradable vascular grafts

Surface modification of biodegradable vascular grafts is an important strategy to improve the in situ endothelialization of tissue engineered vascular grafts (TEVGs) and prevent major complications associated with current synthetic grafts. Important strategies for improving endothelialization include increasing endothelial cell mobilization and increased endothelial cell capture through biofunctionalization of TEVGs. The objective of this study was to assess two biofunctionalization strategies for improving endothelialization of biodegradable polyester vascular grafts. These techniques consisted of cross-linking heparin to graft surfaces to immobilize vascular endothelial growth factor (VEGF) or antibodies against CD34 (anti-CD34Ab). To this end, heparin, VEGF, and anti-CD34Ab attachment and quantification assays confirmed the efficacy of the modification strategy. Cell attachment and proliferation on these groups were compared to unmodified grafts in vitro and in vivo. To assess in vivo graft functionality, the grafts were implanted as inferior vena cava interpositional conduits in mice. Modified vascular grafts displayed increased endothelial cell attachment and activity in vivo, according to microscopy techniques, histological results, and eNOS expression. Inner lumen diameter of the modified grafts was also better maintained than controls. Overall, while both functionalized grafts outperformed the unmodified control, grafts modified with anti-CD34Ab appeared to yield the most improved results compared to VEGF-loaded grafts.

Technological advances in nanoscale biomaterials: the future of synthetic vascular graft design

Currently, autologous veins are the first choice for patients in need of bypass grafting materials. However, due to either pre-existing conditions or previous bypass surgery, some patients lack the necessary amount of host tissue for such procedures. Unfortunately, current synthetic vascular grafts of less than 6 mm in diameter have been plagued by a variety of problems. For this reason, there has been significant research aimed at finding more suitable small-diameter vascular graft materials. In order to improve vascular cell functions on such synthetic materials, several techniques are currently under development that attempt to mimic the natural nanometer architecture of the vascular basement membrane. This review presents several processes including colloidal lithography, chemical etching, electrospinning and solid free-form fabrication that could play a role in the future of vascular nanostructured biomaterial development.

Degradable, drug-eluting stents: a new frontier for the treatment of coronary artery disease

This article reviews the clinical use of stents in the treatment of coronary artery disease and the rationale for the use of degradable, drug-eluting polymer stents. The authors note the challenges of using off-the-shelf polymers for the development of degradable stents, as well as the interplay between polymer properties and a functional stent design. Drug-eluting metal stents are the most significant advancement in the treatment of coronary artery disease, and have significantly reduced the occurrence of in-stent restenosis after placement. Some regard drug-eluting metal stents as the final technologic advancement in the treatment of coronary artery disease, others consider the future development of degradable, drug-eluting stents as the next logical step.

[Professor Iosif Khaimovich Rabkin and his priorities in roentgenoendovascular surgery]

The article is dedicated to outstanding Soviet and Russian interventional radiologist, Professor I. Kh. Rabkin and his priorities in the development of roentgenoendovascular methods of diagnosis and treatment of arterial and venous diseases. Virtually simultaneously with American surgeons, I. Kh. Rabkin not only worked out anew method of intravascular stenting of arteries with spirals made of shape-memory metal ( nitinol) but was the first in the world who in 1984 successfully stented the external iliac artery in a 56-year-old male patient with stage IV limb ischaemia.

[Stages of development of surgical treatment for insufficiency of venous valves of lower limbs]

Insufficiency of the valvular apparatus of the lower-limb veins is one of the main causes of the development of chronic venous insufficiency. This disease is commonly prevalent in developed countries including Russia and is an urgent and socially significant problem. Insufficiency of the venous valves may be corrected by a wide variety of approaches and methods however they all are not universal or have low efficacy and in some cases cannot be applied at all. This article is dedicated to the review of the existing methods of surgical correction of valvular insufficiency of lower-limb veins, as well as a review of the studies of the most promising trend of this problem, i.e. prosthetic repair of venous valves.

Current endovascular treatment of infrarenal abdominal aortic aneurysms and future directions

The paradigm in elective surgical management of infrarenal abdominal aortic aneurysms (AAAs) has quickly shifted from major open surgical repairs to less invasive, endovascular procedures. In the last few years, there have been numerous advancements to commercially available devices making the endovascular approach more attractive and efficacious. This review serves to detail the similarities, differences, advantages, and disadvantages of currently available endovascular stent-grafts as well as preview future and emerging technologies in endovascular aortic therapies.

[Coronary intervention. 2012 update]

In-stent restenosis and stent thrombosis are still the main topics of any update on coronary intervention. One of the challenging issues in the past year lay in answering the question of whether the data on first-generation drug-eluting stents are still relevant in the light of newer stent designs and drugs. Other issues include new strategies in antiplatelet therapy, treatment of in-stent restenosis, particularly drug-eluting stent restenosis, treatment of multivessel and left-main disease, as well as the latest developments in bioresorbable polymers and "scaffolds". In the light of demographic changes, the main challenge for the interventional community is to build an evidence base for the adequate treatment of elderly patients in order to resolve uncertainties in the treatment of this challenging patient group.

Stent evolution for peripheral arterial disease

Endovascular treatment and stent implantation for peripheral arterial disease have been proposed for over 20 years. However, the first experiments with stainless stents were relatively disappointing. The first improvement consisted in the introduction of nitinol self-expanding stents. This technology allowed an initial improvement of clinical performances, but the first generation of nitinol stents demonstrated a relatively high rate of fractures. Better knowledge of arterial biomechanics and advances in technology allowed to propose a second generation of nitinol stents with improved flexibility, which decreased the rates of fracture. In-stent restenosis related to neointimal hyperplasia has also led to the development of new concepts to improve patency rates after stenting: drug-eluting stents (coated-stents), biodegradable stents, and covered stents. These technologies will help to treat more complex lesions in the future, but we are still waiting for results of ongoing studies.

[Comparative characteristics of new PTFE vascular patches in experiment]

Presented herein are the findings of a comparative experimental study of 64 novel patches made of porous polytctrafluoroethylene (PTFE). The PTFE explants with various number of technological layers were examined both in vitro and in vivo. The authors performed plasty of the canine aorta with explants followed by morphological assessment of the tissues with PTFE at various terms of follow up. Based on the results obtained during intraoperative assessment of the patches' properties and histological examination thereof, we selected better patches for plasty of the aorta and major arteries to be implemented into clinical practice.

Update on endovascular management of infrarenal abdominal aortic aneurysms in 2010; what has come and gone

The past few decades have seen a very rapid change in the manner in which infrarenal aortic disease is diagnosed and dealt with. The approach has changed from open, large incision surgery with long and complicated postoperative courses to minimally invasive techniques in which the patient can go home the next day. A large number of devices have come and gone, and techniques to deal with aortic problems are ever changing. We have reviewed the past, current, and future technology to help make the treatment options more clear.

The culture of vascular access cannulation among nurses in a chronic hemodialysis unit

The native arteriovenous fistula (AVF) is the vascular access of choice for patients on chronic hemodialysis (HD) because of its longevity and lower complication rate. Yet from 2001 to 2004 in Canada, there has been a notable increase in both incident and prevalent central venous catheter (CVC) use with a corresponding decrease in AVF use over the same time period (Moist, Trpeski, Na, & Lok, 2008). A similar trend has been found in other countries (Moist, Chang, Polkinghorne, & McDonald, 2007). There are a number of contributing factors to low AVF use in patients on chronic hemodialysis. While some of these factors may be patient-related, nursing interventions specific to cannulation may be a contributor. To date, little is known about HD nurses' attitudes and experiences regarding cannulation. The purpose of this study was to describe the culture and everyday practices of vascular access cannulation of the AVF from the perspective of the HD nurse. An ethnographic research design was employed, utilizing qualitative methods. Ten HD nurses were interviewed using a semi-structured interview tool, and a number of themes were generated from the interviews. One overarching theme of "perpetual novice" was evident, acknowledging the failure to transition from novice to expert cannulator despite working in HD for a number of years. Other common themes that emerged from the interviews were a) the lack of fistulas, b) the fistula as a "hard sell" to patients, c) the skill of cannulation, and d) the assembly-line approach to care. As a result of a number of factors, HD nurses were unable to acquire the skills necessary to become an expert cannulator. Moreover, the decrease in opportunities to practise cannulation has resulted in wide variation in skill level among HD nurses. To improve cannulation skills and achieve successful cannulation of AV fistulas, HD nurses identified a number of educational strategies that should take place. They also identified the need for an improved documentation system in order to track cannulation-related problems. Results of this study may be helpful in understanding the culture of cannulation in a chronic HD unit and in directing future educational, supportive, and practice interventions for HD nurses.

The evolution of tissue engineered vascular grafts: from research to clinical practice

There is a considerable need for alternatives to the autologous vein and artery tissues used for vascular reconstructive surgeries such as CABG, lower limb bypass, arteriovenous shunts and repair of congenital defects of the pulmonary outflow tract. So far, synthetic materials have not matched the efficacy of native tissues, particularly small diameter applications. We have developed a completely autologous approach called sheet based tissue engineering.

Living heart valve and small-diameter artery substitutes--an emerging field for intellectual property development

Cardiovascular diseases, such as heart valve dysfunction and coronary artery stenosis, are next to cancer the leading cause of death in the US. Treatments involve replacement of the heart valve or bypassing the obstructed coronary artery with a small-diameter vascular graft. The major limitation of currently used replacements is their inability to grow, adapt and repair in the patient. Considering the increasing age of the population and the subsequent increase in cardiovascular disease incidence, efforts to improve existing replacements and unraveling novel types of replacements are of paramount importance. Cardiovascular tissue engineering represents a rapid evolving field of research, providing living heart valve and small-diameter vascular substitutes with the ability to grow, adapt and repair after implantation. Various tissue engineering approaches are being employed, based on in vivo and/or in vitro tissue formation. This review provides an overview of the current heart valve and small-diameter vascular replacements and presents the status and future developments within the various tissue engineering approaches. The potential of tissue engineering for the development of living heart valve and small-diameter vascular substitutes is reflected in the numerous patents related to this emerging field of research.

Engineering blood vessels by gene and cell therapy

Cardiovascular-related syndromes are the leading cause of morbidity and mortality worldwide. Arterial narrowing and blockage due to atherosclerosis cause reduced blood flow to the brain, heart and legs. Bypass surgery to improve blood flow to the heart and legs in these patients is performed in hundreds of thousands of patients every year. Autologous grafts, such as the internal thoracic artery and saphenous vein, are used in most patients, but in a significant number of patients such grafts are not available and synthetic grafts are used. Synthetic grafts have higher failure rates than autologous grafts due to thrombosis and scar formation within graft lumen. Cell and gene therapy combined with tissue engineering hold a great promise to provide grafts that will be biocompatible and durable. This review describes the field of vascular grafts in the context of tissue engineering using cell and gene therapies.

Absorbierbare Stents

Coronary stent implantation started in Germany 20 years ago. In the beginning, the progress was very slow and accelerated 10 years later. Meanwhile, coronary stent implantation is a standard procedure in interventional cardiology. From the beginning of permanent stent implantation, research started to provide temporary stenting of coronary arteries, first with catheter-based systems, later with stent-alone technology. Stents were produced from polymers or metal. The first polymer stent implantation failed except the Igaki-Tamai stent in Japan. Newly developed absorbable polymer stents seem to be very promising, as intravascular ultrasound (IVUS) and optical coherence tomography have demonstrated. Temporary metal stents were developed based on iron and magnesium. Currently, the iron stent is tested in peripheral arteries. The absorbable magnesium stent (Biotronik, Berlin, Germany) was tested in peripheral arteries below the knee and meanwhile in the multicenter international PROGRESS-AMS (Clinical Performance and Angiographic Results of Coronary Stenting with Absorbable Metal Stents) study. The first magnesium stent implantation was performed on July 30, 2004 after extended experimental testing in Essen. The magnesium stent behaved like a bare-metal stent with low recoil of 5-7%. The stent struts were absorbed when tested with IVUS. Stent struts were not visible by fluoroscopy or computed tomography (CT) as well as magnetic resonance imaging (MRI). That means, that the magnesium stent is invisible and therefore CT and MRI can be used for imaging of interventions. Only using micro-CT the stent struts were visible. The absorption process could be demonstrated in a patient 18 days after implantation due to suspected acute coronary syndrome, which was excluded. IVUS showed a nice open lumen. Stent struts were no longer visible, but replaced by tissue indicating the previous stent location. Coronary angiography after 4 months showed an ischemia-driven target lesion revascularization rate of 23.8% which was below the 30% cut point of the study protocol. No myocardial Q wave infarction or death were reported. The primary endpoint was reached. During the follow-up period, vasomotion was tested in some of the patients. The proof of principle was confirmed: restoration of vasomotion during acetylcholine testing. The development of the absorbable magnesium stent, which was pushed forward by B. Heublein, Hanover, Germany, has been successful and opens new possibilities for treatment of coronary arteries. Permanent foreign-body implantation is avoided allowing further revascularization procedures in the future, bypass grafting, and restoration of vasomotion. Even prophylactic stenting in nonsignificant stenosis, like vulnerable lesions, may become a regular procedure. Noninvasive coronary imaging by CT and MRI is now possible. Stenting of children and in peripheral arteries may become a standard procedure. Currently, the degradation process of the magnesium stent has to be prolonged, and the neointima proliferation rate has to be reduced so that the DREAM (Drug-Eluting Absorbable Magnesium Stent) concept of Ron Waksman, Washington, DC, USA, can be realized.

Endovascular management of intracranial aneurysms: current experience and future advances

OBJECTIVE

The past 15 years have seen a revolution in the treatment of intracranial aneurysms. Endovascular technology has evolved rapidly since the Food and Drug Administration approval of Guglielmi detachable coils in 1995, which now allows successful treatment of most aneurysms. The authors provide a review of their 11-year experience at Jefferson Hospital for Neuroscience with endovascular embolization of intracranial aneurysms and discuss clinical trial outcomes and future directions of this treatment method.

METHODS

The authors reviewed the clinical and angiographic outcomes for 1307 patients undergoing endovascular treatment of intracranial aneurysms. Their analysis focuses on posterior circulation and middle cerebral artery aneurysms, as well as cases of stent-assisted coil embolization. They review their procedural protocol and patient selection criteria for endovascular management.

RESULTS

Several large clinical trials have demonstrated the safety and efficacy of endovascular treatment of intracranial aneurysms. The International Subarachnoid Aneurysm Trial provides Level I evidence demonstrating a significant reduction in disability or death with endovascular treatment compared with surgical clipping. The most common procedural complications include intraprocedural rupture and thromboembolic events; avoidance strategies are also discussed. Vasospasm after subarachnoid hemorrhage causes neurological morbidity and mortality and can be successfully managed by early recognition and interventional treatment with angioplasty, pharmacologic agents, or both.

CONCLUSION

Long-term studies evaluating experience with aneurysm coil embolization during the past decade indicate that this is a safe and durable treatment method. The introduction of stent-assist techniques has improved the management of wide-neck aneurysms. Future technology developments will likely improve the durability of endovascular treatment further by delivering bioactive agents that promote aneurysm thrombosis beyond the coil mass alone. It is clear that endovascular therapy of both ruptured and unruptured aneurysms is becoming a mainstay of practice in this patient population. Although not replacing open surgery, the continued improvements have allowed aneurysms that previously were amenable only to open clip ligation to be treated safely with durable long-term outcomes.

Recent steps toward a reconstructive endovascular solution for the orphaned, complex-neck aneurysm

OBJECTIVE

The purposes of this article are to summarize recent developments and concerns in endovascular aneurysm therapy leading to the adjunctive use of endoluminal devices, to review the published literature on stent-supported coil embolization of cerebral aneurysms, and to describe our experience with this technique in a limited subgroup of problematic complex aneurysms over a medium-term follow-up period.

METHODS

Between January 2003 and June 2004, 28 individuals among 157 patients with cerebral aneurysms we evaluated were identified as harboring aneurysms with exceptionally broad necks. Out of these 28 patients, 16 were treated with a combination of stents and detachable coils, preserving the parent artery. Recorded data included patient demographics, the clinical presentation, aneurysm location and characteristics, procedural details, and clinical and angiographic outcome.

RESULTS

Over an 18-month period, 16 patients with large cerebral aneurysms additionally characterized by neck sizes between 7 and 14 mm were treated, using combined coil embolization of the aneurysm with stent reconstruction of the aneurysm neck. Thirteen out of the 16 aneurysms were occluded at angiographic reevaluation between 11 and 24 months (mean angiographic follow-up, 17.5 mo). There were no treatment-related deaths or clinically evident neurological complications. Thirteen patients experienced excellent clinical outcomes, with good outcomes in two patients and a poor visual outcome in one patient (mean clinical follow-up, 29 mo). A single technical complication occurred, involving transient nonocclusive stent-associated thrombus, which was treated uneventfully with abciximab.

CONCLUSION

Stent-supported coil embolization of large, complex-neck cerebral aneurysms seems to provide superior medium-term anatomic reconstruction of the parent artery compared with historic series of aneurysms treated exclusively with endosaccular coils. In the near future, increasingly sophisticated endoluminal devices offering higher coverage of the neck defect will likely enable more definitive endovascular treatment of complex cerebral aneurysms and further expand our ability to manipulate the vascular biology of the parent artery.

The role of neuroendovascular therapy for the treatment of brain arteriovenous malformations

Neuroendovascular embolization represents a critical component of the multidisciplinary management of cerebral arteriovenous malformations. Safe and effective embolization may be performed only in the context of a well-designed, rational treatment plan that is fundamentally based on a clear understanding of the natural history of the lesion, as well as the cumulative risks of multimodality treatment. This article outlines the role of neuroendovascular embolization in arteriovenous malformation therapy with a specific emphasis on decision making in the context of formulating a treatment plan. The authors also provide a summary of the available embolic agents and their technical application, potential intraprocedural and periprocedural complications, and postprocedural management.

Therapy of brain arteriovenous malformations: multimodality treatment from a balanced standpoint

The three therapeutic modalities for arteriovenous malformation (AVM) treatment (surgery, embolization, and radiotherapy) developed in the past years with specific tools, each tool with its own qualities. Soon after the implementation of embolization for treatment of AVMs, this technique was used in combination with microsurgery; since the development of radiosurgery, treatment algorithms combining embolization with surgery and eventual subsequent radiosurgery, embolization with radiosurgery, or surgery with subsequent radiosurgery have been reported. These different combinations have been in use under the term multimodality treatment for many years, but the algorithms regarding the combination of tools, which tool has priority, and how the risk levels of each tool are assessed shows great variability among institutions. Centers with a surgical background see embolization as a technique to increase surgical feasibility and radiosurgery as a tool to complete subtotal AVM excision. Institutions with an endovascular background embolize AVMs with the aim of maximal occlusion rates and view surgery or radiosurgery as a technique to be used if the goal of total endovascular occlusion cannot be achieved. Radiosurgeons receive patients after incomplete embolization or surgical extirpation or a combination of both.

Endothelial progenitor cell-seeded grafts: rash and risky

The patency of prosthetic vascular grafts is impaired by intimal hyperplasia (IH) near the anastomotic regions. The absence of a functional endothelial monolayer on the prosthetic grafts is an important stimulus for IH. To improve the outcome of synthetic vascular bypass surgery, cell seeding is a promising concept that has been extensively investigated and is still evolving. In the present paper, the concept of prosthetic graft cell seeding is discussed, with emphasis on its newest era: seeding with endothelial progenitor cells. Although experimental studies on prosthetic graft seeding using endothelial progenitor cells have shown excellent results on graft endothelialization, none of these studies reported favourable effects on the more clinically relevant end points such as IH or graft patency.

Giant Cerebral Aneurysms: Endovascular Challenges

OBJECTIVE:

Giant (≥25 mm in diameter) cerebral aneurysms have a poor natural history, with high risks of subarachnoid hemorrhage or progressive disability or death caused by mass effect or stroke. Surgical treatment may be effective but carries a high burden of morbidity and mortality. Thus, attempts at endovascular solutions to these complex lesions have been developed to offer therapy at reduced risk.

METHODS:

The authors reviewed their clinical experience and the current body of literature concerning giant cerebral aneurysms and present their perspective on the current state of the art in endovascular therapy for these aneurysms. A variety of techniques are described that can be used in an attempt to provide a solution to the wide variety of clinical dilemmas associated with the management of these difficult lesions. Preprocedural planning and periprocedural considerations are discussed briefly. The use of intracranial balloons and stents are described in conjunction with the use of detachable platinum coils. The developing concept of using stents alone to treat aneurysms is discussed. Alternative methods of treating giant aneurysms are discussed.

RESULTS:

Current endovascular approaches, when properly selected and applied, can provide lower-risk therapies than conventional microsurgical approaches for patients harboring giant cerebral aneurysms. However, endovascular approaches do not, at present, provide results that are as durable as current surgical techniques for giant cerebral aneurysms.

CONCLUSION:

Treatment of giant cerebral aneurysms via endovascular therapeutics requires the interventionist to possess an extensive armamentarium. Meticulous preprocedure evaluation, patient selection, and execution of the treatment plan enable safe and effective management. Current therapies do not provide an ideal solution for every patient, so one must consider creative and evolving solutions to these difficult clinical challenges. The procedural morbidity of open surgery versus the decreased durability of current endovascular techniques must be assessed carefully.

Giant Intracranial Aneurysms: Endovascular Challenges

THE TREATMENT OF giant aneurysms remains a formidable challenge for endovascular and surgical strategies. The use of endovascular techniques in a deconstructive (e.g., parent vessel occlusion) and reconstructive (e.g., stent coiling) methodology is reviewed. The results of endovascular coiling as a primary therapy for giant aneurysm occlusion have been disappointing. Hunterian strategies have had more success in published series, but recent developments in coil, glue, and stent technology show great promise in allowing parent vessel reconstruction as a primary endovascular target, with acceptable morbidity, mortality, and durability. A literature review of giant aneurysm endovascular treatment strategies was undertaken after 1994, when Guglielmi detachable coils were approved by the Food and Drug Administration. Where possible, follow-up, durability, and occlusion rates are also reviewed.

Challenges in the Endovascular Treatment of Giant Intracranial Aneurysms

OBJECTIVE:

Giant intracranial aneurysms present unique therapeutic intricacies. The purpose of this study was to evaluate the anatomic and hemodynamic characteristics of these lesions and the current endovascular and combined surgical and endovascular techniques available for their treatment.

METHODS:

A review of the literature and the personal experiences of the authors with endovascular treatment of giant aneurysms are presented. This review included anatomic and hemodynamic features and analysis of the diverse endovascular techniques that have been reported for the management of these aneurysms.

RESULTS:

Anatomic features that create particular challenges in the therapeutic approach of giant aneurysms include size, shape (saccular, fusiform, serpentine), neck dimensions, branch involvement, intraluminal thrombosis, and location. Hemodynamic characteristics that affect endovascular treatment are lateral or terminal aneurysm type of flow and embolic material placement (inflow versus outflow aneurysmal region). The current endovascular therapeutic approaches include parent artery occlusion, trapping, endosaccular embolization with or without adjunctive techniques such as balloon-assisted or stent placement, and combined surgical and endovascular approaches, mainly with surgical revascularization and endovascular occlusion.

CONCLUSION:

Although there are a wide variety of endovascular therapeutic options for the treatment of giant intracranial aneurysms, none of the current techniques is completely successful and free of complications in the management of these complex lesions. A detailed and individualized analysis of each case in conjunction with sufficient understanding of the anatomy and hemodynamics of a particular aneurysm should guide the therapeutic decision. Further research advances will assist in elucidating the factors predisposing to genesis, progression, and aggressive clinical manifestations of these giant lesions.

Endovascular Management of Cerebral Vasospasm

CEREBRAL VASOSPASM REMAINS a leading cause of death and disability in patients with ruptured cerebral aneurysms. The development of endovascular intervention in the past two decades has shown promising results in the treatment of vasospasm. Endovascular techniques that have been used in humans include intra-arterial infusion of vasorelaxants and direct mechanical dilation with transluminal balloon angioplasty. This article reviews the current indications and role of endovascular therapy in the management of cerebral vasospasm, its clinical significance, and potential future therapies.

Evolution and Future of Preclinical Testing for Endovascular Grafts

The preclinical testing of endovascular grafts has evolved significantly since the creation and early testing of these devices; however, there are continued limitations in using preclinical testing to predict clinical performance. Early testing was conducted in the absence of standards and guidance specific to endovascular grafts, and references available for vascular grafts and stents did not adequately account for the complexity of endovascular graft systems. Failure of early-generation devices suggested that the testing being conducted was inadequate and that there was a lack of understanding of the in vivo environment. These concerns led to several efforts to improve preclinical testing. The Food and Drug Administration (FDA) sponsored a workshop to discuss the limitations inherent in testing of endovascular grafts, and an ISO standard for endovascular grafts was developed. Publication of the standard in 2003 succeeded in standardizing testing and reporting across device manufacturers; however, several clinical failure modes, such as migration and stent fractures, continued to be unpredicted by current preclinical testing. This, coupled with knowledge gained from additional clinical experience, led the FDA to hold a second workshop to discuss the benefits and limitations of current testing and propose future testing that may better predict device performance. This workshop was successful in accurately describing past testing, determining what has been learned, identifying issues that have not been adequately addressed, proposing modifications to address these limitations, and discussing how the proposed modifications should be implemented. While significant progress has been made in endovascular graft testing, continued collaboration among industry, academia, regulators, and clinicians will provide continued improvement in the predictability of device performance.

The Valiant thoracic endograft

Thoracic aortic pathology is common, but conventional surgery carries with it a significant risk of mortality and morbidity due to thoracotomy, extensive surgical dissection, partial left lung collapse, proximal aortic cross-clamping and blood loss necessary for open thoracic aortic replacement. Endovascular techniques have the potential to remove much of this harm. However, endograft delivery to the thoracic aorta brings its own challenges; the graft and delivery system must be conformable to follow the aortic arch, flexible to track through tortuous calcified vessels, of low profile for access through the iliac arteries, and deploy accurately and with minimal force to avoid accidental side branch occlusion. The endoprosthesis must also prove to be durable. This paper reviews current indications for thoracic aortic stent grafts and the properties of an ideal endograft for deployment in the arch and descending aorta. The Medtronic Valiant TM endoprosthesis with Xcelerant TM Delivery System is a third-generation system designed specifically for the treatment of a range of thoracic aortic pathologies, including but not exclusively, aneurysms and dissections. The design of the Valiant endoprosthesis and delivery system are described in detail, and compared to the second-generation Talent system. Our early experience of using Valiant in 28 patients with a range of pathologies is described. The graft achieved an initial technical success in 93% and was easy to position and deploy. Long-term data is now required; the Virtue Registry is a prospective multicenter European registry collecting clinical and health economics data on Valiant in the management of aortic dissections.

Transrenal fixation of aortic stent-grafts: current status and future directions

Aortic stent-graft repair has been widely used in clinical practice for more than a decade, achieving satisfactory results compared to open surgical techniques. Transrenal fixation of stent-grafts is designed to obtain secure fixation of the proximal end of the stent-graft to avoid graft migration and to prevent type I endoleak. Unlike infrarenal deployment of stent-grafts, transrenal fixation takes advantage of the relative stability of the suprarenal aorta as a landing zone for the uncovered struts of the proximal stent. These transostial wires have sparked concern about the patency of the renal arteries, interference with renal blood flow, and effects on renal function. Although short to midterm results with suprarenal stent-grafts have not shown significant changes in renal function, long-term effects of this technique are still not fully understood. This review will explore the current status of transrenal fixation of aortic stent-grafts, potential risks of stent struts relative to the renal ostium, alternative methods to preserve blood flow to the renal arteries, and future directions or developments in stent-graft design to prevent myointimal proliferation around the stent struts.

Past, Present, and Future Endograft Devices

Since the original descriptions of endovascular grafts for treatment of aneurysms, a number of devices and approaches have been developed. The following is a discussion summarizing the number of devices which have been developed and used in patients, as well as chosen the directions of this technology. The diversity of approach from an engineering and materials point of view speaks of the fact that opportunity exists for continued development in the future.

Overview of success of EVAR: Progress to date

Endovascular aneurysm repair (EVAR) of abdominal aortic aneurysms has been challenged by a number of groups, and the shortcomings of this procedure have been documented in the scientific literature. However, patients and physicians continue to pursue this procedure as a viable means of treating abdominal aortic aneurysms. Both device evolution and advancement of technical skills have led to dramatic improvements in the outcomes of EVAR within the last decade. These improvements and accomplishments have also been chronicled in the literature. This review looks at the successes of EVAR, based on both US Food and Drug Administration trials and independent studies comparing conventional open repair and endovascular repair.

Engineering of bypass conduits to improve patency

For patients with severe coronary artery and distal peripheral vascular disease not amenable to angioplasty and lacking sufficient autologous vessels there is a pressing need for improvements to current surgical bypass options. It has been decades since any real progress in bypass material has reached mainstream surgical practice. This review looks at possible remedies to this situation. Options considered are methods to reduce prosthetic graft thrombogenicity, including endothelial cell seeding and developments of new prosthetic materials. The promise of tissue-engineered blood vessels is examined with a specific look at how peptides can improve cell adhesion to scaffolds.

Substituts vasculaires

Performed since the 1950s, vascular grafting has opened modern era of vascular surgery. Autologous venous grafts are of first choice for revascularisation of small arteries. Synthetic grafts are mainly modelled using microporous polytetrafluoroethylene or terephtalate polyethylene. These prosthesis are mainly used for revascularization of medium and large size arteries.

Advances in vascular tissue engineering

Coronary and peripheral artery bypass grafting is commonly used to relieve the symptoms of vascular deficiencies, but the supply of autologous artery or vein may not be sufficient or suitable for multiple bypass or repeat procedures, necessitating the use of other materials. Synthetic materials are suitable for large bore arteries but often thrombose when used in smaller arteries. Suitable replacement grafts must have appropriate characteristics, including resistance to infection, low immunogenicity and good biocompatability and thromboresistance, with appropriate mechanical and physiological properties and cheap and fast manufacture. Current avenues of graft development include coating synthetic grafts with either biological chemicals or cells with anticoagulatory properties. Matrix templates or acellular tubes of extracellular matrix (such as collagen) may be coated or infiltrated with cultured cells. Once placed into the artery, these grafts may become colonised by host cells and gain many of the properties of normal artery. "Tissue-engineered blood vessels" may also be formed from layers of human vascular cells grown in culture. These engineered vessels have many of the characteristics of arteries formed in vivo. "Artificial arteries" may be also be derived from peritoneal granulation tissue in body "bioreactors" by adapting the body's natural wound healing response to produce a hollow tube.

Biomaterials in the development and future of vascular grafts

Recent developments in the field of tissue engineering have re-invigorated the quest for more suitable biomaterials that are applicable to novel cardiovascular devices, including small-diameter vascular grafts. This review covers both commercially available and relevant newly developed experimental materials, including elastic polymers (polyurethane), the biodegradable and bioresorbable materials, and the naturally occurring materials, focusing on their potential applications in the development of future vascular substitutes.

Synthetic vascular prostheses

Polyethyleneterephthalate (PET), and to a lesser extent Teflon have become the major synthetic grafting material. Unlike nylon, Ivalon, and Vinyon-N which lose their tensile strength after implantation, PET and Teflon remain essentially unchanged even after long periods. TRICOMED S.A. produces the family of the knitted vascular implants Dallon made from PET fibres including: Dallon, Dallon H, Tricogel. Both Dallon and Dallon H are manufactured in a form of double (external and internal) velour surface using multifilament yarn and having optimal graft design (a variety of sizes and lengths). The velour surface gives the surface a velvety, plush texture, which improves tissue in--growth. Moreover, Dallon H is a unique vascular prostheses showing the increase in the blood susceptibility that is useful for 4 times less blood demand during preclotting as compared with standard prosthesis. Tricogel graft is made of thin-wall prostheses sealed with the porcine gelatin that provides intraoperative tightness (without preclotting) and the optimal healing process. Hydrophilic behavior of the graft is observed as an instant moistening of the surface with patient's blood and as sweating. The blood stream does not dissolve nor washes away the gelatin but causes the gelatin film to swell, which makes a better tightness. The work will describe the properties of manmade vascular grafts as well as their applications in the vascular surgery.