Coronary intimal proliferation after balloon injury and stenting in swine: an animal model of restenosis

Therapeutic potential of active stent coating

Various clinical studies have shown the superiority of stent implantation as compared to conventional balloon angioplasty for the treatment of significant coronary stenosis. However, restenosis remains a major drawback of this interventional technique. Against the background of this serious problem, the concept of stent coating has been developed. In general, coatings can be classified into two types: passive coatings, which only serve as a barrier between the stainless steel, and the tissue and active coatings, which directly interfere with the process of intima proliferation. At this moment, primarily immunosuppressive and cytostatic substances are used as active coatings. Large randomised studies have shown that this novel concept can be successfully implemented into clinical practice. Beside these promising results, studies also revealed potential risks of this new approach. Not only the dosage of the drug but also an optimised kinetic of drug release seem to be essential in preventing restenosis. As with most drugs, the inhibition of neointima proliferation is not restricted to vascular smooth muscle cells but also affects the process of re-endothelialisation, thus we may face a new pitfall of late-stent thrombosis. Although this technique may harbour potential risks, the introduction of stent coating has the potential to dramatically reduce the incidence of restenosis and an exciting chapter in the field of cardiology has been opened.

Direct coronary stenting versus predilatation followed by stent placement

Direct stenting without antecedent dilatation may reduce procedural time, costs, and radiation exposure, and may result in less vessel injury. The purpose of this investigation was to compare immediate and long-term clinical and angiographic outcomes of direct stenting with stent placement after initial balloon dilation. Three hundred thirty-five symptomatic patients with single or multiple coronary lesions (diameter reduction 60% to 95%) of < or =30 mm length and with a vessel diameter of 2.5 to 4.0 mm were randomized either to direct stenting (group A, n = 171) or stenting after predilation (group B, n = 164). Patients with vessels with excessive calcification, severe proximal tortuosity, or occlusion were excluded. All patients were asked to return for routine repeat angiography at 6 months, irrespective of symptoms. Feasibility of direct stenting was 95% in group A, with 5% requiring crossover to predilation. Successful stent placement after predilation was performed in all 164 patients in group B. Direct stenting was associated with less procedural duration (group A 42.1 +/- 18.7 minutes vs group B 51.5 +/- 23.8 minutes, p = 0.004), radiation exposure time (group A 10.3 +/- 7.7 minutes vs group B 12.5 +/- 6.4 minutes, p = 0.002), amount of contrast dye used (group A 163 +/- 69 ml vs group B 197 +/- 84 ml, p <0.0001), and lower procedural costs (group A 845 +/- 167 vs group B 1,064 +/- 175, p <0.0001). Immediate angiographic results and in-hospital clinical outcomes (death, Q-wave myocardial infarction, repeat revascularization) were not significantly different between both strategies. However, at 6-month follow-up, direct stenting was associated with a lower angiographic restenosis (group A 20% vs group B 31%, p = 0.048) and target lesion revascularization rates (group A 18% vs group B 28%; p = 0.03). This study demonstrates the feasibility, safety, and outcomes of direct stenting in eligible coronary lesions. In appropriately selected cases, direct stenting has a lower rate of angiographic restenosis up to 6 months after the procedure, resulting in fewer coronary reinterventions compared with the conventional strategy of stenting with antecedent dilatation.

Neointima in coronary stent does not increase during over 1-year in non-restenosed lesion at 6 months follow-up: serial volumetric intravascular ultrasound study

The long-term outcomes of coronary artery stenting have been determined by coronary angiography only with has the limitation of determining stent expansion and neointimal proliferation at long-term follow-up. Volumetric intravascular analysis has the potential to evaluate the morphology and distribution of neointima longitudinally after coronary artery stenting. We used three-dimensional intravascular ultrasound (3-D IVUS) to evaluate serial changes in stent and neointimal volumes for over 1-year in 9 patients who did not exhibit angiographic restenosis at 6-month follow-up. Volumetric analysis by a validated Netra 3-D IVUS system was performed pre- and post-intervention, at 6-month follow-up (FU1), and at over one-year follow-up (FU2). Lumen volume in the stented lesions increased significantly after intervention, and the increase persisted until FU2. There were no significant changes in stent volume between just after stent implantation and at FU2. Neointimal volume within the stents did not change from FUI to FU2 (FU1; 38.4 +/- 9.0 mm3 vs FU2; 33.8 +/- 10.3 mm3). In 33% (3/9) of all lesions, neointimal volume increased between from 6-months to over 1-year after stent implantation. Neointimal distribution after stenting seemed to be almost equal and unrelated to the plaque burden at pre-intervention. Neointimal volume within the stents did not increase and stent volume did not change over the 1st-year in patients who did not exhibit angiographic restenosis at 6-months.

A novel measurement technique to assess the effects of coronary brachytherapy in clinical trials

This paper presents a novel measurement technique to assess the effects of coronary brachytherapy. This new technique is based upon the conventional quantitative coronary analysis (QCA) technique, which is accepted worldwide as an accurate and reliable analysis tool for clinical trials. This paper provides the definitions and main issues important for correct brachytherapy analysis. Based on these definitions, this novel technique is implemented as an extension of conventional QCA software, as a multisegmental analysis tool. It allows to follow the influence of radiation on restenosis, and the mutual relation between intervention devices. A pilot interobserver study was performed to assess the reliability and reproducibility of the brachytherapy analysis tool, using 15 patient cases. The validation results show that the segment lengths, minimum lumen diameter, and reference diameters of the user-defined and derived (sub)segments can be assessed reproducible. However, these good results can only be obtained, when strict and extensive image acquisition and image analysis protocols are followed. From this pilot validation study presented in this paper and only based on a small number of patients, we may conclude that the software can be applied to clinical trials.

Rat carotid artery dilation by PTCA balloon catheter induces neointima formation in presence of IEL rupture

The best animal angioplasty model is the porcine model, which is expensive and not available in all laboratories. The aim of this study was to describe a new rat model of angioplasty. An injury was induced with the use of a standard percutaneous transluminal coronary angioplasty (PTCA) 1.5-mm balloon catheter. The neointimal tissue, arterial dimensions, and the injury index were assessed following angioplasty. Ki-67 expression was detected to evaluate cell turnover after balloon angioplasty. In contrast with the standard Clowes model, a significant neointimal formation was detected only in the presence of ruptured internal elastic lamina (IEL). A positive correlation between the percentage of ruptured IEL and the amount of neointimal tissue was also demonstrated. The percentage of IEL fracture correlates with the proliferation index by anti-Ki-67 immunolabeling 7 and 14 days after the angioplasty. Significant arterial negative remodeling was observed following PTCA balloon dilation. In conclusion, our inexpensive animal model of restenosis after angioplasty may have great relevance toward a better understanding of the mechanisms and toward assessment of new therapeutical strategies for this phenomenon.

Coronary artery brachytherapy

Coronary artery disease is the leading cause of mortality in the West with over 1.2 million angioplasties performed annually. Despite the introduction of stents, restenosis occurs in 30-40% of vessels, which until recently has only been treated effectively by coronary artery bypass surgery. Coronary artery brachytherapy appears to provide an alternative, less invasive remedy. The mechanisms of restenosis and how these are inhibited by radiation are described here. The practicalities of radiation delivery and the history of the development of intravascular radiation as an effective clinical tool are outlined. Finally, the pitfalls of the current technology and the areas in which future research must be targeted for the field to develop are discussed.

The influence of diabetes mellitus on late clinical outcomes following coronary stent implantation

Diabetic patients have a higher restenosis rate and late morbidity following balloon angioplasty. However, the increased risk of restenosis after coronary stent implantation in diabetic patients is controversial. We compared the quantitative coronary angiographic (QCA) variables between 42 diabetic patients and 71 non-diabetic patients undergoing coronary stent implantation and for 6 months follow-up. Pre-procedural variables were identical in the diabetic and non-diabetic patients. The stent-artery ratio was lower (1.07+/-0.13 vs. 1.13+/-0.13, P=0.020), and acute gain after coronary stenting was lower (1.58+/-0.53 vs. 1.77+/-0.48, P=0.049) in the diabetic patients than in the non-diabetic patients. However, the late lumen loss (0.42+/-0.64 vs. 0.49+/-0.69), loss index (0.28+/-0.49 vs. 0.28+/-0.45), restenosis rate (19 vs. 23%) and target lesion revascularization rate (17 vs. 18%) after 6 months were identical in the diabetic and non-diabetic patients. These results suggest that diabetes itself does not increase stent restenosis.

Acute coronary syndrome is a common clinical presentation of in-stent restenosis

Coronary stents have been the major advancement in percutaneous coronary intervention in the last decade and are used in 60% to 80% of patients. However, in-stent restenosis continues to be a problem, occurring in 20% to 30% of cases. The clinical presentation of patients who develop restenosis after stenting has not been well characterized. In this study we compared the clinical presentation of in-stent restenosis with that of restenosis without stenting. Of 739 patients who underwent percutaneous coronary intervention and had repeat catheterization between October 1, 1997, and June 30, 2000, 262 consecutive patients with recurrent ischemia and restenosis were identified: 191 patients with (group A) and 71 without (Group B) stenting. Patients who underwent interventions in bypass grafts and those who developed early acute stent thrombosis were excluded from the study. Recurrent clinical ischemia occurred at a mean of 5.5 months in group A and 6.5 months in group B (p = 0.24). Rest angina (Braunwald class II and III) was more frequent in group A (48% vs 32%, p = 0.032). Acute coronary syndromes, the combination of rest angina, and acute myocardial infarction were also more frequent in group A (68% vs 46%, p = 0.03). Patients in group A were more likely to have angiographically visible thrombus than those in group B (9% vs 0%, p = 0.02). Thus, acute coronary syndromes are a common clinical presentation of restenosis among patients whose follow-up angiogram is obtained for clinical reasons, and occur more frequently in patients with in-stent restenosis than in those with restenosis without stenting.

Decoy oligodeoxynucleotide against activator protein-1 reduces neointimal proliferation after coronary angioplasty in hypercholesterolemic minipigs

OBJECTIVES

We sought to demonstrate, in an appropriate animal model, that co-medication with a transcription factor-blocking agent limits restenosis after percutaneous transluminal coronary angioplasty (PTCA).

BACKGROUND

Enhanced synthesis in the vessel wall of endothelin-1 (ET-1), a powerful co-mitogen for vascular smooth muscle cells, appears to be one mechanism that promotes restenosis after PTCA. Deformation-induced expression of prepro-ET-1 is governed by the transcription factor, activator protein-1 (AP-1).

METHODS

An anti-AP-1 decoy oligodeoxynucleotide (dODN) strategy was devised in which the dODN-containing solution (20 nmol) was administered locally through a Dispatch catheter into the coronary arteries of hypercholesterolemic minipigs at the time of PTCA (AVE-GFX stent).

RESULTS

Treatment with an AP-1 dODN, mimicking the consensus binding site of the transcription factor, significantly reduced neointimal formation in the coronary arteries of hypercholesterolemic minipigs (n = 10 to 12), compared with vehicle-treated coronary arteries, after four weeks of follow-up (neointimal area 2.64 +/- 0.33 vs. 4.81 +/- 1.04 mm(2) [mean +/- SEM]; p < 0.05). This effect was maintained after eight weeks (neointimal area 2.04 +/- 0.22 mm(2); n = 3) and correlated with a reduction in both nuclear translocation of AP-1 and ET-1 synthesis in the vessel wall 48 h after PTCA (n = 4). In contrast, an AP-1 mutant dODN, to which the transcription factor does not bind, showed no effect on neointimal formation at either time point (n = 3 to 7). Moreover, a consensus dODN directed against CCAAT/enhancer binding protein (C/EBP), another deformation-sensitive transcription factor, did not significantly affect neointimal formation after four weeks (n = 3).

CONCLUSIONS

These findings demonstrate the feasibility, efficacy and specificity of the anti-AP-1 dODN approach to the treatment of restenosis, which principally but not exclusively targets deformation-induced ET-1 synthesis in the vessel wall. Provided that these findings can be extrapolated to the situation of patients with coronary artery disease, the observed extent of the inhibitory effect of the AP-1 dODN treatment suggests that this co-medication may greatly reduce the incidence of in-stent restenosis.

New stent design for autologous venous graft-covered stent preparation: first human application for sealing of a coronary aneurysm

In this case report, we present the first clinical application of a new stent design for autologous venous graft-covered stent preparation. This stent consists of a main body, resembling the configuration of conventional stents, and two connecting arms at the edges of the stent for the stabilization of the venous graft on the external surface of the stent. This new stent design was applied in a patient with an aneurysm in a stented segment in the right coronary artery. The immediate and long-term angiographic evaluation after the covered stent implantation showed complete sealing of the aneurysm without restenosis.

Rationale for coronary artery radiation therapy

Within the past decade, focus on radiation to prevent restenosis has moved from a concept developed in the animal laboratory to a clinical treatment. The initial evaluation of coronary artery radiation therapy focused on changes in the function of the artery or lesion formation following overstretch balloon injury in pigs. A number of concepts emerged from this work: (1) radiation inhibits neointima formation in a dose-dependent fashion, (2) radiation prevents negative remodeling, (3) radiation does not reverse established injury, (4) low dose irradiation in an injured area may be injurious, (5) radiation is a useful adjunct to stenting, (6) benefits of radiation in animal models at 6 months are less pronounced than at 1 month, (7) radiation delays healing, (8) permanent stents and radiation delivered from external sources may have very different effects on restenosis, and (9) radiation interferes with vessel wall function. More recent studies of irradiation have looked at the molecular biological effects of radiation in hopes of understanding how this therapy works, and how it may be improved. This article attempts to summarize the known animal and cellular work on radiation in preventing restenosis.

Neointima formation after stent implantation in an experimental model of restenosis: polytetrafluoroethylene-covered versus uncovered stainless steel stents

The aim of the study was to assess whether stents covered with a membrane of polytetrafluoroethylene spanned over the mashes of a sandwich-configured double stent (n = 15) prevent migration of smooth muscle cells through stent spaces, leading to less neointima formation compared with uncovered stainless steel stents (n = 14) in iliac arteries of male Chinchilla Bastard rabbits (n = 18). Lumen stenosis was assessed by quantitative angiography immediately before the animals were killed 5 weeks after stent deployment. Neointima formation was quantified by histomorphometric analysis. There were large regional and individual differences in neointima formation, leading locally to a significantly higher degree of stenosis in covered stents (histologically, 76.0 +/- 13.7 vs. 62.9 +/- 12.9%; angiographically, 33.5 +/- 21.1 vs. 7.8 +/- 8.8%) compared with uncovered stents, though mean neointimal and lumen area values were not significantly different. In conclusion, polytetrafluoroethylene-covered stents do not prevent neointima formation compared with uncovered stents. Although the membrane reduces local smooth muscle cell migration, the neointima hyperplasia at the proximal and distal ends of a covered stent stimulates migration along its longitudinal axis. In this stent-restenosis model, regional and individual proliferation processes and not the membrane-covering strut-to-strut distances determine lumen restenosis.

Perivascular responses after angioplasty which may contribute to postangioplasty restenosis: a role for circulating myofibroblast precursors?

These studies suggest that the adventitia may play a role in vascular lesion formation after balloon overstretch injury of pig coronary arteries by contributing to the cellular mass of the neointima and the synthesis of growth factors. In addition, the adventitia may contribute to vascular remodeling and constriction of the external elastic lamina through accumulation of myofibroblasts containing alpha smooth muscle actin in the adventitia surrounding the injury site. Inhibition of myofibroblast proliferation and/or recruitment by intravascular brachytherapy positively affects vascular remodeling through its action on adventitial cells. Inflammation is a major event associated with balloon angioplasty, resulting in the sequential recruitment of neutrophils (2-24 hours) and monocyte/macrophages (24-72 hours) predominantly into the adventitia surrounding the injury site. It is hypothesized that inflammatory cells release cytokines and/or increase the production of superoxides which stimulate the proliferation and recruitment of adventitial myofibroblasts. Inflammatory and proliferative responses were not confined to the local adventitia but were found extending as far as 1-3 mm away from the injured vessel in the distal perivascular tissues. Studies were performed to examine the expression of genes associated with cell migration at early times after injury in an attempt to determine the source of the adventitial myofibroblasts. Expression of genes involved in cell migration including MMP-2, MMP-9, and tenascin was found as early as 2 hours following angioplasty in the intramyocardial, pericardial, and adipose tissue fibroblasts. While these studies suggest that local tissue was the source of the myofibroblasts recruited to the injury site, we have been unable to confirm this finding by direct fluorescent labeling of adventitial cells. Recent work from our laboratory suggests that myofibroblast precursors may be isolated from buffy coat preparations from peripheral blood. These results lead us to hypothesize that stem cells that differentiate into myofibroblasts may be recruited in early inflammatory infiltrates in the adventitia. Clearly, additional work will have to be directed at a more detailed examination of the response of adventitial and other perivascular cells and tissues to balloon injury to determine their sources and their role in regulating vascular lesion development.

High-dose external beam irradiation inhibits neointima formation in stented pig coronary arteries

PURPOSE

To evaluate high-dose external beam irradiation (EBRT) in a pig coronary stent preparation because low and intermediate-dose EBRT failed to show inhibition of neointima formation in stented animal models.

METHODS AND MATERIALS

Thirty-five stents were implanted in the coronary arteries of 17 pigs. Seven pigs were exposed to a single dose of 21 Gy EBRT immediately after stenting. Ten stented, nonirradiated pigs served as controls. After 4 weeks, the study arteries and myocardium were examined by light and scanning electron microscopy.

RESULTS

Compared with controls, 21 Gy EBRT resulted in a larger lumen area (7.57 +/- 1.67 mm2 vs. 4.00 +/- 1.63 mm2, p <0.001), a smaller neointima area (0.47 +/- 0.43 mm2 vs. 3.36 +/- 2.26 mm2, p <0.001) and a smaller maximal intimal thickness (0.16 +/- 0.09 mm vs. 0.68 +/- 0.31 mm, p <0.001). Unresorbed intramural hemorrhages and adherent mural thrombi were present in the irradiated vessels, which also showed incomplete re-endothelialization. The irradiated hearts demonstrated diffuse interstitial and perivascular inflammation and fibrosis.

CONCLUSIONS

EBRT at 21 Gy to the entire heart significantly inhibited neointima formation in stented pig coronary arteries but also resulted in incomplete re-endothelialization, myocardial inflammation, and fibrosis. Improvements in localization and delivery techniques are required to allow clinical implementation of this technique.

Coronary artery endothelial protection after local delivery of 17beta-estradiol during balloon angioplasty in a porcine model: a potential new pharmacologic approach to improve endothelial function

OBJECTIVES

The goal of this research was to study the effect of locally delivered 17beta-estradiol (17beta-E) during angioplasty on endothelial function after percutaneous transluminal coronary angioplasty (PTCA) at four weeks.

BACKGROUND

The endothelium plays a major role in the structural and functional integrity of coronary arteries and is damaged by PTCA.

METHODS

Juvenile swine were subjected to PTCA, after which each artery was randomly-assigned to 600-microg 17beta-E delivered locally, an equal volume of vehicle (V) or PTCA alone. After four weeks, the improvement in endothelial function was assessed by angiography using intracoronary acetylcholine (Ach) infusion and by immunohistochemistry.

RESULTS

At 10(-5) mol/l and 10(-4) mol/l Ach, significant vasoconstriction was noted in arteries treated with PTCA alone (p < 0.01 and p < 0.0001, respectively) and with PTCA plus V (p < 0.02 and p < 0.001, respectively). No significant vasoconstrictive response to Ach was observed in arteries treated with PTCA plus 17beta-E. Immunohistochemistry of vessels four weeks after PTCA revealed enhanced re-endothelialization (p < 0.0005) and endothelial nitric-oxide synthase (eNOS) expression (p < 0.0005) in PTCA plus 17beta-E-treated arteries compared with the other two treatment groups. Arteries treated with 17beta-E showed significantly lower neointima formation, which correlated inversely with the extent of re-endothelialization and eNOS expression.

CONCLUSIONS

Locally delivered 17beta-E significantly enhances re-endothelialization and endothelial function after PTCA, possibly by improving the expression of eNOS. Since endothelial dysfunction can promote both restenosis and coronary spasm, local 17beta-E administration is a promising new approach to improve long-term results after PTCA.

An iron-binding exochelin prevents restenosis due to coronary artery balloon injury in a porcine model

Background- Vascular smooth muscle cell (VSMC) proliferation is a critical factor in the neointima formation that causes restenosis after coronary angioplasty (PTCA). Desferri-exochelin 772SM (D-EXO), a highly diffusible, lipophilic iron chelator secreted by Mycobacterium tuberculosis, inhibits proliferation of VSMCs in culture. We hypothesized that treatment with D-EXO would inhibit neointima formation in balloon-injured vessels in vivo. Methods and Results- We subjected 24 pigs to overstretch coronary artery injury with standard PTCA balloons and then administered intramural injections of either D-EXO (n=14) or vehicle (n=10) through an Infiltrator catheter. Treatments were randomized, and the investigators were blinded with regard to treatment group until data analysis was completed. One month later, we euthanized the pigs, excised the injured coronary segments, made multiple sections of each segment, and identified the site of maximal neointima formation. An injury score based on the degree of disruption of the internal or external elastic lamina or media was assigned. D-EXO reduced stenosis index (neointima area divided by the area within the internal elastic lamina), adjusted for injury score, by 47%. Neointima thickness was also reduced. Conclusions- D-EXO, injected intramurally, substantially inhibited formation of neointima in a porcine vascular injury model.

Stent coating with titanium-nitride-oxide for reduction of neointimal hyperplasia

BACKGROUND

Coronary stents prevent constrictive arterial remodeling but stimulate neointimal hyperplasia. Stainless steel induces a metallic foreign body reaction, which is absent for titanium. The hypothesis of the present study was that titanium renders the stent surface biologically inert, with reduced platelet and fibrinogen binding.

METHODS AND RESULTS

Twelve pigs were instrumented with a stainless steel and 2 titanium-nitride-oxide-coated stents (TiNOX 1, ceramic; TiNOX 2, metallic). Animals were restudied after 6 weeks. Histological specimens of stented segments were analyzed by digital morphometry. Platelet adhesion and fibrinogen binding studies were performed in the perfusion chamber. Under in vitro conditions, TiNOX 1 showed reduced platelet adhesion (65+/-3%) compared with TiNOX 2 (72+/-5%; P<0.05) and stainless steel (71+/-4%; P<0.05). Platelet adhesion 48 hours after incubation with human plasma, however, was not different between TiNOX 1 (17+/-3%) and 2 (15+/-3%) but was significantly higher with stainless steel (23+/-2%; P<0.05). Fibrinogen binding was significantly reduced with TiNOX 2 (54+/-3%) compared with TiNOX 1 (82+/-4%, P<0.05) or stainless steel (100%, P<0.05). Histomorphometry revealed a significantly larger neointimal area in stainless steel (2.61+/-1.12 mm(2)) than in TiNOX 1-coated (1.47+/-0.84 mm(2), P<0.02) or TiNOX 2-coated (1.39+/-0.93 mm(2), P<0.02) stents. The reductions were 44% and 47%, respectively.

CONCLUSIONS

TiNOX coating significantly reduces neointimal hyperplasia in stainless steel stents. The antiproliferative effect was similar for both TiNOX coatings, suggesting that the electrochemical properties are more important for attenuation of neointimal proliferation than the observed differences in platelet adhesion and fibrinogen binding.

Mechanisms of angioplasty and stent restenosis: implications for design of rational therapy

Restenosis after angioplasty or stenting remains the major limitation of both procedures. A vast array of drug therapies has been used to prevent restenosis, but they have proven to be predominantly unsuccessful. Recent trends in drug therapy have attempted to refine the molecular and biological targets of therapy, based on the assumption that a single biological process or molecule is critical to restenosis. In contrast, both stenting and brachytherapy, which are highly nonspecific, can successfully reduce restenosis after angioplasty or stenting, respectively. This review examines the biology of both angioplasty and stent stenosis, focussing on human studies. We also review the landmark human trials that have definitively proven successful therapies, such as stenting and brachytherapy. We suggest that the successful trials of stenting and brachytherapy and the failure of other treatments have highlighted the shortcomings of conventional animal models of arterial intervention, and gaps in our knowledge of human disease. In contrast to arguments advocating gene therapy, these studies suggest that the most likely successful drug therapy will have a wide therapeutic range, targeting as many of the components or biological processes contributing to restenosis as possible.

Pressure rinsing of coronary stents immediately before implantation reduces inflammation and neointimal hyperplasia

OBJECTIVES

This study evaluates whether rinsing stents with high pressure immediately before implantation minimizes stent-induced inflammation and neointimal formation.

BACKGROUND

Several reports indicate that manual stent manipulation before implantation results in foreign body contamination and increased neointimal hyperplasia.

METHODS

A stent-cleaning chamber was developed to rinse stents at a sustained hydrodynamic pressure of 4 atm for 10 s. Commercial pre-mounted stents were examined with different levels of manipulation: 1) untouched stents: no stent manipulation before implantation; 2) handled stents: manual stent re-crimping on the balloon; 3) rinsed stents: pressure-rinsed with the stent-cleaning chamber. In vitro surface analysis was evaluated by scanning electron microscopy. Neointimal hyperplasia and inflammation around stent struts were also assessed in the pig in-stent restenosis model.

RESULTS

In vitro analysis revealed fewer contaminants on rinsed stents compared with untouched (p = 0.01) and handled stents (p < 0.001). In vivo, neointimal thickness, neointimal area and vessel percent stenosis were significantly reduced in rinsed, compared with not-rinsed, stents (p = 0.002, p = 0.007, p = 0.008 respectively). In addition, a significant reduction in the inflammatory infiltrate around struts was observed in untouched, compared with handled, stents (p = 0.04) and in rinsed, compared with not-rinsed, stents (p < 0.001). Regression analysis accounting for injury and neointimal thickness showed significant differences in slopes between "handled + not-rinsed" and "handled + rinsed" stents (p = 0.004), and between "untouched + not-rinsed" and "untouched + rinsed stents" (p = 0.037).

CONCLUSIONS

Rinsing stents under high pressure immediately before coronary implantation results in less inflammation around struts and thinner neointima at 28 days in this pig model.

Improved reproducibility of intravascular ultrasound assessment of coronary in-stent neointima with the use of an echogenic contrast agent

The present study evaluated a new technique that has the potential to improve the border detection of in-stent neointima using an echogenic contrast agent during intravascular ultrasound (IVUS). To confirm the reproducibility of IVUS imaging for measuring the cross-sectional in-stent neointima area, inter- and intra-observer variability and correlation were determined. Conventional IVUS (plain IVUS) and IVUS using a contrast agent (contrast IVUS) were performed in 24 subjects 6.5+/-1.5 months after undergoing a Palmaz-Schatz coronary stent implant. Conventional IVUS delineated completely the in-stent neointima in 6 subjects (25%). In the remaining 18 subjects (75%), delineation of the neointima was incomplete despite the use of various combinations of imaging conditions (eg, transmission, compress, post-process). With contrast IVUS, the boundary of the neointima, and therefore the neointima area, was clearly distinguishable, and this resulted in complete delineation of the neointima in all 24 subjects. With a contrast agent, inter- and intra-observer variability significantly decreased (0.94+/-0.69mm2 conventional IVUS vs 0.37+/-0.40mm2 contrast IVUS, p<0.001; 0.69+/-0.56mm2 conventional IVUS vs 0.07+/-0.10mm2 contrast IVUS, p<0.0001; respectively). Thus, contrast IVUS provides a reproducible method for the quantitative analysis of in-stent neointima with excellent inter- and intra-observer correlation.

A novel 32P deployable balloon system inhibits formation of neointima in porcine coronary arteries after balloon-overstretching injury

BACKGROUND

Intracoronary radiation has shown the potential to reduce formation of neointima in porcine models of restenosis.

OBJECTIVE

To investigate the feasibility, safety, and efficacy of a new 'deployable-balloon' device with radioisotope 32P integrated into the balloon material.

METHODS

Ten swine were subjected to balloon-overstretching injury in 20 coronary arteries and were randomly allocated to receive a radiation dose of 0, 15, or 20Gy prescribed to 1 mm from the surface of the radioactive balloon material. The animals were killed 4 weeks after the procedure. Their coronaries were perfusion fixed and stained. Vessel parameters (area of intima and length of fracture) and area of thrombus area were analyzed by computer-aided histomorphometry.

RESULTS

Radiation treatment with the new 32P balloon device was performed without complications. The lengts of fracture for the three groups were similar (NS). Formation of neointima after balloon injury was less in members of the radiated groups than it was in controls (area of intima/length of fracture was 0.70 +/-0.12 mm for controls, 0.08+/-0.13mm with 15 Gy, and 0.07+/-0.17 mm with 20 Gy; P < 0.001). Vessels treated with 20 Gy had a greater total area of thrombus (0.00+/-0.00 versus 0.51+/-0.98 mm2, P< 0.01).

CONCLUSIONS

Intracoronary radiation therapy using a new 32P deployable-balloon system is feasible and safe. A radiation dose of 15 Gy was sufficient to inhibit neointimal response in the porcine coronary-balloon-injury model.

Long-term vessel response to a self-expanding coronary stent: a serial volumetric intravascular ultrasound analysis from the ASSURE Trial.A Stent vs. Stent Ultrasound Remodeling Evaluation

OBJECTIVES

We sought to investigate the in vivo mechanical properties of a new self-expanding coronary stent (RADIUS) and, particularly, the subsequent vessel response over time.

BACKGROUND

Preclinical studies have suggested that self-expanding stents may produce less vessel wall injury at initial deployment, leading to larger follow-up lumens than with balloon-expandable stents. However, the influence of the chronic stimulus from self-expanding stents on the vessel wall remains unknown.

METHODS

Sixty-two patients were randomly assigned to either the RADIUS self-expanding stent group (n = 32) or the Palmaz-Schatz balloon-expandable stent group (n = 30). Intravascular ultrasound was performed after stent deployment and at six-month follow-up.

RESULTS

At follow-up, the RADIUS stents had increased 23.6% in overall volume, while the Palmaz-Schatz stents had remained unchanged. Due to the greater mean neointimal area (3.0 +/- 1.7 mm2 vs. 1.9 +/- 1.2 mm2, p = 0.02) in the RADIUS group, no significant difference in net late lumen loss was observed between the two groups. On the other hand, analysis at the peristent margins demonstrated that mean late loss was significantly smaller in the RADIUS group than it was in the Palmaz-Schatz group (0.1 +/- 2.1 mm2 vs. 1.9 +/- 2.4 mm2, p = 0.02).

CONCLUSIONS

Serial volumetric IVUS revealed that the RADIUS stents continued to enlarge during the follow-up period. In this stent implantation protocol, this expansion was accompanied by a greater amount of neointima than the Palmaz-Schatz stents, resulting in similar late lumen loss in both configurations. In the peristent margins, however, late lumen loss was minimized with the RADIUS stents.

Differential remodeling after balloon overstretch injury and either beta- or gamma-intracoronary radiation of porcine coronary arteries

BACKGROUND

Restenosis is a consequence of both neointimal hyperplasia and vessel remodeling. Prior studies have shown that intracoronary radiation (IR) prevents neointima accumulation, but its contribution to vessel remodeling is unknown. The purpose of this study was to evaluate the effect of IR on differential vascular remodeling after balloon angioplasty in porcine coronary arteries.

METHODS

A total of 20 juvenile swine (30 coronary arteries) were subjected to overstretch balloon injury (BI) followed by IR with either beta- or gamma-radiation ((90)Y or (192)Ir). After 2 weeks following treatment, serial tissue sections were perfusion fixed and stained by hematoxylin and eosin (H&E), Verhoeff von Giesson (VVG), or Masson Trichrome. Adventitial area (AA), lumen area (LA), vessel area (VA), intimal area (IA), and IA corrected for medial fracture length (IA/FL) were quantified by digital image analysis. The vessel circumference was divided into two regions containing (1) the undisrupted region (UReg) with the undisrupted arc of media and internal elastic lamina (IEL) and (2) the disrupted region (DReg) with the disrupted arc between the medial tears. Quantitative regional analysis was performed by (1) measuring the IEL to define the UReg, (2) calculating the area of the UReg with the perimeter value derived from measurement of the IEL, and (3) calculating the DReg as follows: LA+IA-UReg. Immunohistochemical smooth muscle cell alpha-actin and Masson Trichrome were quantified by digital image analysis.

RESULTS

The IA/FL was significantly smaller following treatment with (90)Y or (192)Ir vs. control (P<.01). A smaller AA was obtained following IR with both beta- and gamma-sources vs. control (P<.01). The UReg calculation was smaller in the irradiated arteries as compared to control (beta: 2.3+/-0.4 mm(2), gamma: 2.1+/-0.5 mm(2), P<.01 vs. control; control: 3.6+/-0.7 mm(2)). In contrast, the DReg was increased following IR, as demonstrated by the FL and the calculated area of the injured segment (control: 2.7+/-0.5 mm(2); beta: 5.5+/-1.1 mm(2), gamma: 5.5+/-1.1 mm(2), P<.01 vs. control). Adventitial alpha-actin positive cell density (CD) was decreased after IR; however, the collagen density was similar. In contrast, the neointimal collagen density in the injured segment was significantly decreased following IR.

CONCLUSION

We consider that the global arterial remodeling after IR is a heterogeneous process that includes the absence of retraction in an UReg and a positive remodeling in the DReg as shown in the porcine coronary model. These changes in adventitia and neointima appear to contribute to differential vascular remodeling caused by IR in injured vessels.

Coagulation and complement activation

The purpose of this investigation was to assess the effect of heparin coating of a new stent construction (Stent Graft, Jomed Implantate GmbH, Germany) on platelet and coagulation activity.

METHODS

Stent grafts with an ePTFE membrane interfoliated between two stents were deployed in tubings to form Chandler loops. Fresh human blood with a low concentration of heparin was rotated for 1 h, then collected and used for measurements of platelet number, thrombin-antithrombin complex (TAT), CD11b, C3a and C5b-9. There were five study groups: Group 1, conventional unmodified stents (n = 8); Group 2, untreated stent grafts (n = 8); Group 3, heparin-coated stents and untreated membrane (n = 7); Group 4, heparin-coated stents and membrane (n = 8); Group 5, heparin-coated PVC tubings with no stents (n = 8).

RESULTS

There was a significant drop in platelet count, increase in TAT-values and CD11b expression in Groups 1-3 but not in Group 4 compared to Group 5. Examination by scanning electron microscopy revealed extensive activation on non-modified stents but almost no deposition of thrombotic material on heparin-modified stent grafts.

CONCLUSIONS

With unmodified stents and membrane there were signs of significant activation of platelets and coagulation. In contrast, the heparin-coated stent graft induced much less alterations, indicating improved blood compatibility.

Effect of preintervention plaque burden on subsequent intimal hyperplasia in stented coronary artery lesions

We sought to determine if axial and circumferential distribution of plaque before stenting determines the axial and circumferential distribution of subsequent intimal hyperplasia (IH). We studied 22 patients with a single Palmaz-Schatz stent implanted in a native coronary artery, who underwent intravascular ultrasound (IVUS) imaging before intervention, after stenting, and at 6-month follow-up. For each lesion, 7 locations were analyzed: proximal and distal reference, proximal and distal edge of the stent, proximal and distal location within the body of the stent, and the articulation. Pre- and postintervention and follow-up image slices were precisely aligned and analyzed for pre- and postintervention plaque area and follow-up IH area and thickness. The location of maximal IH area was at or adjacent to the location of maximal preintervention plaque in 17 of 22 of the patients (77%). Similiarly, the circumferential distribution of IH at follow-up paralleled the eccentricity pattern of the native plaque burden in 69% (24 of 35 slices). Using multivariant analysis, the strongest predictor of IH was preintervention plaque area (p = 0.001). IH accumulates axially and circumferentially preferentially at the site of maximal preintervention plaque.

Local delivery of 17-beta-estradiol decreases neointimal hyperplasia after coronary angioplasty in a porcine model

BACKGROUND

Neointimal hyperplasia is an important mechanism of restenosis after percutaneous transluminal coronary angioplasty (PTCA). Systemically administered estrogen is known to inhibit neointimal formation after arterial injury.

OBJECTIVES

We sought to assess the efficacy of locally delivered 17-beta-estradiol (BE) in inhibiting neointimal hyperplasia after PTCA.

METHODS

Eighteen juvenile farm pigs were studied. Coronary angioplasty was performed in all three coronary arteries of each animal. After PTCA, each coronary artery in each pig was randomized to receive either local delivery of 600 microg BE, vehicle alone or PTCA only. Twelve animals were euthanized at 28 days for morphometric analysis, and four animals were euthanized at seven days for immunohistochemical analysis of vascular smooth muscle cell (SMC) proliferative activity. Two animals died a few days after PTCA and were excluded.

RESULTS

On morphometric study, the arterial segments treated with BE demonstrated significantly less neointimal proliferation. Arteries treated with BE had reductions in several indexes of restenosis compared with arteries treated with vehicle alone or PTCA only: neointimal area (0.4+/-0.09 mm2 for BE vs. 1.14+/-0.33 mm2 for vehicle alone vs. 0.88+/-0.2 mm2 for PTCA only, p<0.05), percent neointima (12.16+/-2.57% vs. 25.46+/-4.73% vs. 23.02+/-3.97%, p<0.025), neointima/media area (0.59+/-0.14 vs. 1.75+/-0.41 vs. 1.67+/-0.43, p<0.01) and restenotic index (1.3+/-0.14 vs. 2.42+/-0.22 vs. 2.4+/-0.23, p<0.005). Immunohistochemistry showed decreased SMC proliferative activity in BE-treated arteries compared with the other two treatment groups (p<0.05).

CONCLUSIONS

Local delivery of BE significantly decreases neointimal hyperplasia after PTCA in pigs, probably by the inhibition of SMC proliferation.

Relation between vascular morphologic changes during stent implantation and the magnitude of in-stent neointimal hyperplasia

Intimal hyperplasia usually occurs after balloon overstretch injury or wire coil stimuli to coronary arteries. We examined whether the degree of vessel wall stretch during coronary stent placement could predict the amount of in-stent neointimal hyperplasia after a 6-month follow-up. Serial (preintervention, postballooning, poststent implantation, and a follow-up after 6 months) intravascular ultrasound (IVUS) was used to study 457 consecutive cross-sectional areas in 28 patients. IVUS imaging, using a motorized pullback system at 0.5 mm/s, allowed 1-mm axial increment measurements of the total vascular, stent, and lumen cross-sectional areas. The mean total vascular area changed from 10.89 +/- 2.50 mm2 before to 11.27 +/- 2.49 mm2 after ballooning, to 12.80 +/- 2.59 mm2 after stenting, and to 12.58 +/- 2.41 mm2 at follow-up (p < 0.0001). The mean lumen area changed from 3.36 +/- 1.95 mm2 before to 4.21 +/- 1.65 mm2 after ballooning, to 5.16 +/- 1.09 mm2 after stenting, and to 3.57 +/- 1.23 mm2 at follow-up (p < 0.0001). The mean stent area decreased from 5.25 +/- 1.17 mm2 after stenting to 5.09 +/- 0.90 mm2 at follow-up (p < 0.0001). Stepwise logistic regression analysis showed that delta total vascular area (after stent implantation - before intervention) was a strong predictor of the amount of intimal hyperplasia (r = 0.57, p < 0.0001). Vascular overstretch caused by the stenting procedure promotes intimal hyperplasia in proportion to the degree of sectional vascular stretch.

Vascular repair after balloon overstretch injury in porcine model effects of intracoronary radiation

OBJECTIVES

The purpose of this study was to evaluate the effect of IR on thrombus formation and dissection repair following overstretch balloon injury in porcine coronary arteries.

BACKGROUND

Exposure of blood to the injured arterial wall after percutaneous transluminal coronary angioplasty (PTCA) induces thrombus formation and inflammation in the dissection plane. Neointima formation is related to smooth muscle cell (SMC) proliferation and migration into the preformed thrombus. Intracoronary radiation (IR) with doses of 10 to 25 Gy using either beta or gamma emitters can prevent neointima accumulation by reducing SMC proliferation. However, there are some indications that IR may delay the process of dissection repair after PTCA. The purpose of this study was to evaluate the effect of IR on thrombus formation and dissection repair after overstretch balloon injury in porcine coronary arteries.

METHODS

Forty porcine coronaries were injured by balloon overstretch followed by either 0 or 18 Gy of 90Y prescribed to 1.2 mm from the balloon center. The animals were euthanized 14 days after treatment, and intimal area (IA) and IA corrected for medial fracture length (IA/FL) were quantified by digital image analysis. Dissections were quantified by tracing the length, thickness and area behind the dissection flap. The rate of dissections was calculated for each group. Thrombi were identified and designated as intraluminal thrombus or thrombus within dissection planes (mural thrombus), and area measurements were obtained.

RESULTS

The irradiated group showed a significant reduction of IA/FL (0.55 +/- 0.29 vs. 0.05 +/- 0.09; p < 0.001). No difference was observed in the rate of dissection between control and irradiated arteries (77% vs. 88%, respectively). The control group showed a smaller dissection area (0.19 +/- 0.28 mm2 vs. 0.32 +/- 0.29 mm2; p < 0.05) with smaller mural thrombi (0.03 +/-0.01 mm2 vs. 0.29 +/- 0.30 mm2; p < 0.001). A strong correlation between dissection area and neointima area was observed only in the control group (R2 = 0.474; p < 0.003; alpha0.05 = 0.862). A positive correlation between mural thrombus and dissection area was observed only in the irradiated group (R2 = 0.889; p < 0.001; alpha0.05 = 1.00).

CONCLUSIONS

These results suggest that the dissection area may be a useful parameter by which to quantify the extent of injury and repair after IR and may indicate an incomplete healing process after IR at this time point.

Anti-restenotic effect of copper-62 liquid-filled balloon in porcine coronary arteries: novel use of a short half-life positron emitter

PURPOSE

To determine the efficacy of the use of copper-62, a positron emitter with a half-life of 9.7 minutes, as an intracoronary brachytherapy (IRBT) source in the prevention of neointima formation (NF) following overstretch balloon injury (BI) in the porcine model.

METHODS AND MATERIALS

Sixteen swine were treated after BI to their left anterior descending (LAD), left circumflex (LCX), and/or right coronary artery (RCA). Twelve of the injured arteries received placebo and 10 received 25 Gy, delivered to 0.5 mm from the surface of the treatment balloon filled with liquid (62)Cu. Dosimetry was based on Monte Carlo calculations. Two weeks after treatment, the animals were sacrificed, and the treated coronaries were perfusion-fixed and stained. Intimal area (IA) and medial fracture length (FL) were analyzed by computer-aided histomorphometry.

RESULTS

The ((62)Zn/(62)Cu) generator, together with a rapid concentration process, was successful in delivering the short-lived (62)Cu at the high concentration required for intravascular brachytherapy (IVBT). The fracture length in the two groups was similar (2.10 +/- 0.57; 2.02 +/- 0.77; p = NS). Arteries studied showed significant reduction in NF (IA: 0.23 +/- 0.47 mm(2) vs. 1.08 +/- 0.57 mm(2); p < 0.01. IA/FL = 0.09 +/- 0.17 mm vs. 0.51 +/- 0.21 mm; p < 0.01).

CONCLUSIONS

This study demonstrated that use of liquid (62)Cu as an IVBT source is safe and feasible. All 16 swine tolerated the treatment well with no radiation-induced side effects or symptoms throughout the 2-week period. The isotope delivered the dose necessary to inhibit NF in the porcine coronary BI model.

Irradiation and postangioplasty restenosis: a recent overview

One of the most intriguing developments in recent years towards prevention of restenosis after angioplasty is the use of ionizing radiation. The background for the use of radiation treatment for this application is sound, since radiation is used not only to treat malignant cancerous growths but also is used for treatment of benign hyperplastic disorders such as post-surgical keloid formation and recurrence of pterygium after surgical removal. Restenosis can be considered a form of overexuberant wound healing triggered by angioplasty. Ionizing radiation inhibits serum-stimulated proliferation of many cell types including fibroblasts and smooth muscle cells in vitro and also suppresses the synthesis of collagen by cultured fibroblasts. Liermann who showed inhibition of post-stent restenosis first used ionizing radiation for restenosis prevention clinically in iliac and iliofemoral arteries. Subsequently, extensive animal studies in various restenosis models have shown a profound inhibitory effect of catheter-based radiation (endovascular brachytherapy) on neointima formation and overall vessel shrinkage (negative remodeling). Based on these results clinical trials have been initiated with several types of devices and isotopes. Among these are 192Ir, 32P, 90Y, 90Sr/Y and 188Re. Additionally, radioactive stents have been developed; devices for clinical use are made radioactive at the microCi level by surface implantation of 32P ions. Results from early clinical trials are encouraging and brachytherapy appears safe for clinical use and at an appropriate dose, may be highly effective for restenosis prevention.

The effects of uncontrolled hyperglycemia on thrombosis and formation of neointima after coronary stent placement in a novel diabetic porcine model of restenosis

BACKGROUND

Results of recent clinical studies suggest that patients with diabetes mellitus have a higher than normal rate of restenosis after percutaneous transluminal coronary angioplasty or coronary stenting. The mechanism for this exaggerated neointimal response is not known.

OBJECTIVES

To determine the technical feasibility of a model of in-stent restenosis in swine with streptozotocin-induced hyperglycemia and to compare the late arterial responses to injury induced by placement of oversized coronary stents in diabetic and nondiabetic animals.

METHODS

Eighteen 25-40 kg castrated male or intact female Yucatan miniature swine aged 6 months were obtained from a commercial supplier. Twelve of the miniature swine were randomly selected for intravenous treatment with 125 mg/kg streptozotocin to induce a hyperglycemic state. Twelve weeks after treatment, all animals underwent placement of oversized balloon-expandable stainless steel stents in the coronary arteries. After 28 days, histomorphometric analysis of the stented coronary arteries to determine the neointimal responses for the diabetic and nondiabetic animals was completed.

RESULTS

Sudden death due to stent thrombosis occurred for five of 11 (45%) of the diabetic animals and none of the age-matched nondiabetic control animals (P=0.05). For histology after 28 days, the neointimal response was correlated to the extent of arterial injury for the diabetic (r=0.79, P < 0.0001) and nondiabetic (r=0.86, P < 0.0001) animals. The surviving diabetic animals had areas of neointimal (1.67 +/- 0.74 mm2) and percentages of in-stent stenosis (28 +/- 14) similar to those of the nondiabetic swine (1.36 +/- 0.40 mm2, P=0.26; 22 +/- 6, P=0.17). Multiple regression analysis also demonstrated that arterial injury (P < 0.0001) alone, not hyperglycemia (P=0.237), was independently correlated to formation of neointima.

CONCLUSIONS

Uncontrolled hyperglycemia results in greater than normal thrombosis after coronary-stent placement in swine with streptozotocin-induced diabetes. These data suggest that greater than normal early formation of thrombus rather than proliferation of smooth muscle cells contributes to restenosis after coronary stenting in patients with diabetes mellitus.

The comparative pathobiology of atherosclerosis and restenosis

Percutaneous coronary interventions (PCIs) play an increasingly important role in the management of patients with coronary artery disease. However, these important procedures are complicated by restenosis in a sizeable number of patients. The pathobiology of atherosclerosis comprises a complex interaction among lipids, the endothelium, circulating and tissue inflammatory cells, platelets, and vascular smooth muscle cells. The superimposition of the mechanical and cellular consequences of PCIs on the abnormal substrate of atherosclerosis leads to a characteristic and distinct pathobiology that initiates and perpetuates restenosis. A clear understanding of the significant differences between atherosclerosis and restenosis will provide a rational basis for developing treatment plans that always address both problems. This article reviews and contrasts the pathobiology of atherosclerosis and restenosis and compares the mechanisms and time-course of these distinct entities.

Initial and 6-month results of biodegradable poly-l-lactic acid coronary stents in humans

BACKGROUND

Although metallic stents are effective in preventing acute occlusion and reducing late restenosis after coronary angioplasty, many concerns still remain. Compared with metallic stents, poly-l-lactic acid (PLLA) stents are biodegradable and can deliver drugs locally. The aim of this study was to evaluate the feasibility, safety, and efficacy of the PLLA stent.

METHODS AND RESULTS

Fifteen patients electively underwent PLLA Igaki-Tamai stent implantation for coronary artery stenoses. The Igaki-Tamai stent is made of a PLLA monopolymer, has a thickness of 0.17 mm, and has a zigzag helical coil pattern. A balloon-expandable covered sheath system was used, and the stent expanded by itself to its original size with an adequate temperature. A total of 25 stents were successfully implanted in 19 lesions in 15 patients, and angiographic success was achieved in all procedures. No stent thrombosis and no major cardiac event occurred within 30 days. Coronary angiography and intravascular ultrasound were serially performed 1 day, 3 months, and 6 months after the procedure. Angiographically, both the restenosis rate and target lesion revascularization rate per lesion were 10.5%; the rates per patient were 6.7% at 6 months. Intravascular ultrasound findings revealed no significant stent recoil at 1 day, and they revealed stent expansion at follow-up. No major cardiac event, except for repeat angioplasty, developed within 6 months.

CONCLUSIONS

Our preliminary experience suggests that coronary PLLA biodegradable stents are feasible, safe, and effective in humans. Long-term follow-up with more patients will be required to validate the long-term efficacy of PLLA stents.

Percutaneous delivery of a heparin-impregnated collagen stent-graft in a porcine model of atherosclerotic disease

RATIONALE AND OBJECTIVES

To develop collagen stent-grafts impregnated with heparin to improve the biocompatibility of endovascular stents and to design a percutaneous delivery system for graft deployment in a swine model.

METHODS

Heparin-impregnated collagen stent-grafts were deployed, and follow-up angiograms were obtained every 15 minutes for 90 minutes to assess acute thromboses and again at 2 and 4 weeks afterward to assess patency. If stenosis or occlusion was detected at the 2-week evaluation, guidewire passage across the lesion was attempted and angioplasty was performed. If stenosis or occlusion was present at the 4-week evaluation, only guidewire passage was attempted; thereafter, the animals were killed and the stent-grafts were harvested and reviewed by a vascular pathologist.

RESULTS

Group A represents a feasibility study to optimize the deployment method applied in groups B and C. Fifteen of 17 stent-grafts were successfully deployed using this method. In group B, 89% of grafts were successfully deployed; 12% were patent at 2 weeks and none at 4 weeks. In group C, a 10-minute inflation time was added to the deployment procedure; 88% of grafts were successfully deployed and 28% were patent at 2 weeks and 14% at 4 weeks. Extensive luminal thrombosis and myointimal hyperplasia were present in every case.

CONCLUSIONS

A method was developed for percutaneous implantation of collagen stent-grafts into peripheral vessels. The heparin-impregnated grafts did not prevent vessel restenosis. Modification of the graft-processing technique may improve patency.

Short wave ultraviolet laser energy in porcine coronary arteries: medial cell death and neointimal formation

BACKGROUND AND OBJECTIVE

Smooth muscle cell migration and proliferation from arterial media into the neointima are major factors in the restenosis process following coronary angioplasty. Because short wave ultraviolet (UV) radiation is cytotoxic for rat carotid artery smooth muscle cells, the aims of this study were to determine the effects of short wave UV irradiation on normal pig coronary arteries and to evaluate the efficacy of UV laser energy for reducing neointimal hyperplasia (NI).

STUDY DESIGN/MATERIALS AND METHODS

In 13 pigs fed a normal diet, 37 coronary arteries were studied. UV laser light (275 nm) was applied in escalating doses from 0-16,353 mJ/cm2 via fiberoptic through a 20 mm PTCA balloon catheter. The pigs were euthanized at 21 days and histologic analysis performed. Arterial media was rendered acellular (ACM) in 20 of 33 irradiated coronary arteries (61%). The minimum UV energy density inducing ACM was 1348 mJ/cm2. The fraction of acellular media to internal elastic lamina length (ACM/IEL) was 0.79 +/- 0.29.

RESULTS

No statistically significant difference was found between NI thickness at normal media sites (NM) vs. ACM sites (0.17 +/- 0.14 mm vs. 0.16 +/- 0.17 mm). No correlation was found between UV dose and NI formation (r = 0.307, P = 0.08).

CONCLUSION

Short wave UV irradiation induces ACM in normal porcine coronary arteries. Induction of acellular media is not associated with a reduction of NI formation in this porcine coronary model.

Perlecan is required to inhibit thrombosis after deep vascular injury and contributes to endothelial cell-mediated inhibition of intimal hyperplasia

Perlecan, a heparan sulfate proteoglycan, has been suggested to be critical for regulation of vascular repair. We generated clones of endothelial cells expressing an antisense vector targeting domain III of perlecan. Transfected cells produced significantly less perlecan than parent cells and showed a reduced ability to inhibit the binding and mitogenic activity of fibroblast growth factor-2 in vascular smooth muscle cells. Endothelial cells were seeded onto three-dimensional polymeric matrices and implanted adjacent to porcine carotid arteries subjected to deep injury. Although the parent endothelial cells prevented occlusive thrombosis, perlecan-deficient cells were completely ineffective. The ability of endothelial cells to inhibit intimal hyperplasia, however, was abrogated only in part by perlecan suppression. The differential regulation by perlecan of these different aspects of vascular repair may explain why control of clinical clot formation does not lead to full control of intimal hyperplasia. Thus the use of genetically modified tissue-engineered cells provides a new approach for dissecting the role of specific factors within the complex environment of the blood vessel wall.

Elastic recoil of coronary stents: a comparative analysis

Minimum elastic recoil (ER) has became an essential feature of new coronary stents when deployed in artheromatous lesions of various morphologies. The ER of coronary stent might be an important component of 6-month restenosis rate by minimizing the luminal loss. We evaluated the intrinsic ER of 23 coronary stents with a mechanical test bench. The amount of ER for one size of stent (3.0 mm) was quantified using a 3D optical contactless machine (Smartscope MVP, Rochester, NY). The stents were expanded on their own balloon for the precrimped stents; the uncrimped stents were expended using identical 3.0-mm balloons. Two types of measurements were done without exterior stress and with a 0.2-bar exterior stress, directly on the stent at the end of balloon expansion, immediately after balloon deflation, and then 30 min, 60 min, and 120 min after. ER ranged from 1.54%+/-0.81% (Bestent BES 15) to 16.51%+/-2.89% (Paragon stent) without stress (P<0.01) and from 2.35%+/-1.14% (Bestent BES 15) to 18.34%+/-2.41% (Cook GR2) under 0.2-bar pressure (P<0.0001). Furthermore, there was a significant reduction between the mean result of tubular stents (TS) and coil stents (CS). The results of in vitro mechanical tests may confirm strongly the interest of a minimum ER in the prevention of the 6-month restenosis.

The mechanisms of coronary restenosis: insights from experimental models

Since its introduction into clinical practice, more than 20 years ago, percutaneous transluminal coronary angioplasty (PTCA) has proven to be an effective, minimally invasive alternative to coronary artery bypass grafting (CABG). During this time there have been great improvements in the design of balloon catheters, operative procedures and adjuvant drug therapy, and this has resulted in low rates of primary failure and short-term complications. However, the potential benefits of angioplasty are diminished by the high rate of recurrent disease. Up to 40% of patients undergoing angioplasty develop clinically significant restenosis within a year of the procedure. Although the deployment of endovascular stents at the time of angioplasty improves the short-term outcome, 'in-stent' stenosis remains an enduring problem. In order to gain an insight into the mechanisms of restenosis, several experimental models of angioplasty have been developed. These have been used together with the tools provided by recent advances in molecular biology and catheter design to investigate restenosis in detail. It is now possible to deliver highly specific molecular antagonists, such as antisense gene sequences, to the site of injury. The knowledge provided by these studies may ultimately lead to novel forms of intervention. The present review is a synopsis of our current understanding of the pathological mechanisms of restenosis.

Inhibition of neointima formation by tranilast in pig coronary arteries after balloon angioplasty and stent implantation

OBJECTIVES

We evaluated the effect of orally administered tranilast, N-(3,4-dimethoxycinnamoyl) anthranilic acid, on histologic and histomorphometric changes after angioplasty or stent implantation in pig coronary arteries.

BACKGROUND

Tranilast, which has antikeloid and antiallergic properties and therefore may modulate the fibrotic and inflammatory tissue responses to angioplasty and stenting, has been shown to inhibit angiographic restenosis in small clinical trials. However, its effect on histomorphometric changes in coronary arteries after angioplasty and stenting is unknown.

METHODS

Following initial pharmacokinetic studies in two pigs to determine desirable plasma levels of orally administered tranilast, 36 crossbred juvenile pigs were randomized to placebo or tranilast before undergoing balloon angioplasty in both the left anterior descending and left circumflex plus stent implantation in the right coronary artery. Oral tranilast was administered at 3 g/day starting 3 days before coronary injury and continued for 28 days until euthanasia. Injured vessels were harvested and sections analyzed by computer-assisted microscopic planimetry.

RESULTS

In balloon-injured vessels, tranilast was associated with a 37% reduction in neointimal area normalized to fracture length (0.47 +/- 0.01 vs. 0.74 +/- 0.03 mm; p < 0.001) and a 23% reduction in adventitial area normalized to vessel size (0.43 +/- 0.02 vs. 0.56 +/- 0.03; p = 0.003). In stented arteries, neointimal area normalized to injury score was 32% lower in the tranilast-treated group compared to control (1.94 +/- 0.17 vs. 2.86 +/- 0.29; p = 0.01).

CONCLUSIONS

In pig coronary arteries, tranilast was associated with a reduction in neointima formation and adventitial reaction after balloon injury. In stented vessels, tranilast was associated with a reduction in neointima formation normalized to injury score.

Local adenovirus-mediated transfer of C-type natriuretic peptide suppresses vascular remodeling in porcine coronary arteries in vivo

OBJECTIVE

This study was designed to examine whether or not adenovirus-mediated gene transfer of C-type natriuretic peptide (CNP) can prevent coronary restenotic changes after balloon injury in pigs in vivo.

BACKGROUND

Gene therapy to prevent restenosis after percutaneous transluminal coronary angioplasty (PTCA) might be useful but requires a method applicable for in vivo gene delivery into the coronary artery as well as the efficient vector encoding a potent antiproliferative substance. We tested whether the adenovirus-mediated gene transfer of CNP by use of an infiltrator angioplasty balloon catheter (IABC) might prevent the coronary restenotic changes after balloon injury.

METHODS

Balloon angioplasty was performed in the left anterior descending and the left circumflex coronary artery in pigs. Immediately after the balloon injury, adenovirus solution encoding either CNP (AdCACNP) or beta-galactosidase (AdCALacZ) gene was injected with IABC into the balloon-injured coronary segments. Expression of CNP was assessed by immunohistochemical staining and cyclic guanosine 3',5'-monophosphate (cGMP) measurement. Coronary restenotic changes were evaluated by both angiographic and histological examinations.

RESULTS

CNP was highly expressed in the media and the adventitia of the coronary artery at the AdCACNP-transfected but not at the AdCALacZ-transfected segment. In the AdCALacZ-transfected segment, vascular cGMP levels tended to be reduced as compared with the untreated segment, whereas in the AdCACNP-transfected segment, vascular cGMP levels were restored. Angiographic coronary stenosis was significantly less at the AdCACNP-transfected than at the AdCALacZ-transfected segment. Histological examination revealed that this was achieved primarily by the marked inhibition of the geometric remodeling of the coronary artery by the CNP gene transfer.

CONCLUSIONS

Adenovirus-mediated CNP gene transfer with the IABC system may be a useful gene therapy to prevent restenosis after PTCA in vivo.

Stents covered by autologous venous grafts: feasibility and immediate and long-term results

BACKGROUND

Previous experimental studies with a new covered stent, the autologous venous graft-covered stent (AVGCS), have shown favorable results. The aim of this study was to evaluate the feasibility and safety of this new technique in human coronary arteries and to compare the long-term outcome with uncovered stents.

METHODS AND RESULTS

A venous graft was removed from an upper limb. A conventional stent then was covered by the venous graft. Fifty-eight AVGCS were implanted in 56 patients, including 16 patients with acute coronary syndromes (ACS). Additionally, in 114 patients, 138 uncovered stents were implanted, serving as a control group, including 38 patients with ACS. The procedure was successful in all patients. Stent thrombosis was observed in 3 patients in the control group and in 1 patient with an AVGCS. There was a trend for the minimal luminal diameter to be greater in the AVGCS group at follow-up (P =.07), and statistical significance was observed in patients with ACS (P <.01). The target vessel revascularization and the restenosis rates were similar between the 2 groups. In patients with ACS, the restenosis rate was less (P <.04) and there was a trend for target vessel revascularization to be less in covered stents (P =.09). The event-free survival rate at 4 years was 85% in the AVGCS group versus 81% in the control group (P = not significant); in ACS it was 94% versus 78%, respectively (P = not significant). Stents covered by thicker venous grafts were associated with improved clinical outcome.

CONCLUSIONS

Stents covered by autologous venous grafts may be safely prepared without complications. This technique may prove to be a useful means, especially in patients with ACS.

Acute and chronic tissue response to coronary stent implantation: pathologic findings in human specimen

OBJECTIVES

The aim of our study was to analyze the cellular components of neointimal tissue regeneration after coronary stenting.

BACKGROUND

High restenosis rates are a major limiting factor of coronary stenting. To reduce the occurrence of restenoses, more insights into the mechanisms leading to proliferation and expression of extracellular matrix are necessary.

METHODS

Twenty-one autopsy cases with coronary stents implanted 25 h to 340 days before death were studied. The stented vessel segments were analyzed postmortem by light microscopy and immunohistochemical staining.

RESULTS

In the initial phase stents are covered by a thin multilayered thrombus. Alpha-actin-positive smooth muscle cells (SMCs) are found as the main cellular component of the neointimal tissue. Later (>6 weeks) extracellular matrix increases and fewer SMCs can be found. In every phase the SMC layers are loosely infiltrated by inflammatory cells (T lymphocytes). In the early postinterventional phase all endothelial cells are destroyed. The borderline between the vessel lumen and the vascular wall is constituted by a thin, membranous thrombus. Six weeks after stenting, SMCs form the vessel surface. Complete reendothelialization is first found 12 weeks after stenting.

CONCLUSIONS

Stent integration is a multifactorally triggered process with proliferating SMCs generating regenerative tissue. In the early phase predominantly thrombotic material can be observed at the site of stenting, followed by the invasion of SMCs, T lymphocytes and macrophages. The incidence of delayed reendothelializations and the occurrence of deep dissections may be associated with excessive SMC hyperplasia.

Long-term outcome after coronary stenting

The present review assesses the data on long-term outcome after coronary stenting. Histological, angiographical and intravascular imaging data have shown that the insertion of stents constitutes only a transient stimulus to lumen renarrowing, that this process is almost complete at 6 months and that a certain degree of neointima regression is also possible after this time. Clinical data have confirmed the sustained benefit of stenting in the long term. Careful selection of optimal stent designs and application of the recent advances in adjunctive pharmacological therapy are currently effective strategies to improve both short-and long-term results with coronary stenting. However, further efforts are needed and are ongoing to combat restenosis, a process that counters the excellent short-term results of stenting in the long term.

Clinical applications of brachytherapy for the prevention of restenosis

Restenosis remains the bane of percutaneous coronary intervention. Local delivery of radiation, brachytherapy, is a promising therapy for the prevention of restenosis. Animal studies have suggested that brachytherapy may be an effective treatment for preventing restenosis. The type of radiation as well as the doses and delivery systems are currently under study; several clinical trials are underway. This paper reviews the biological basis, including animal studies, of intracoronary brachytherapy as well as the current data from clinical trials.

Intracoronary serotonin release after high-pressure coronary stenting

It is known that platelet-derived serotonin at the site of coronary angioplasty induces an increase in coronary tone and plays a role in vasoconstriction after balloon angioplasty. The goal of the present investigation was to compare local release of serotonin with changes in coronary tone after coronary stenting and coronary angioplasty. Twenty patients with significant stenosis (> or =50% diameter narrowing) of the left anterior descending coronary artery were referred to traditional coronary angioplasty (10 patients; group 1) or high-pressure coronary stenting (10 patients; group 2). An additional 16 patients with similar angiographic characteristics were referred to the coronary angioplasty group (8 patients; group 1a) or stenting group (8 patients; group 2a) after pretreatment with ketanserin. Serotonin plasma levels in coronary sinus and coronary cross-sectional area distal to the site of dilatation were measured before and after bath revascularization procedures. In groups 1 and 1a, plasma serotonin levels in coronary sinus increased from basal values of 3.2+/-0.8 and 3.2+/-0.5 ng/ml to 29.5+/-13 and 25.6+/-9 ng/ml after ballooning (p <0.001 vs baseline). In groups 2 and 2a, plasma serotonin levels in coronary sinus increased from basal values of 3.5+/-0.3 and 3.5+/-0.7 ng/ml to 114.6+/-34 and 113+/-29 ng/ml after stenting (p <0.001 vs baseline and vs postangioplasty values in groups 1 and 1a). Coronary cross-sectional area distal to the site of dilatation significantly decreased after angioplasty in group 1 (from 4.33+/-0.4 to 3.32+/-0.3 mm2; p <0.001), and after stenting in group 2 (from 4.27+/-0.3 to 2.86+/-0.2 mm2; p <0.001 vs baseline, and p <0.02 vs values after coronary angioplasty in group 1). Pretreatment with ketanserin significantly reduced distal coronary vasoconstriction after angioplasty and stenting. It is concluded that the higher local serotonin release after coronary stenting may explain the more marked coronary constriction observed after prosthesis deployment with respect to traditional coronary angioplasty. Ketanserin is able to significantly attenuate the increase in distal coronary tone induced by both revascularization procedures.