Adjuvant therapy for intracoronary stents. Investigations in atherosclerotic swine

Cardiovascular Tissue Engineering Models for Atherosclerosis Treatment Development

In the early years of tissue engineering, scientists focused on the generation of healthy-like tissues and organs to replace diseased tissue areas with the aim of filling the gap between organ demands and actual organ donations. Over time, the realization has set in that there is an additional large unmet need for suitable disease models to study their progression and to test and refine different treatment approaches. Increasingly, researchers have turned to tissue engineering to address this need for controllable translational disease models. We review existing and potential uses of tissue-engineered disease models in cardiovascular research and suggest guidelines for generating adequate disease models, aimed both at studying disease progression mechanisms and supporting the development of dedicated drug-delivery therapies. This involves the discussion of different requirements for disease models to test drugs, nanoparticles, and drug-eluting devices. In addition to realistic cellular composition, the different mechanical and structural properties that are needed to simulate pathological reality are addressed.

Direct percutaneous carotid artery stenting with distal protection: technical case report

We describe the technique of percutaneous carotid artery stent placement with distal protection in a patient in whom marked innominate artery ectasia prevented transfemoral access to the right common carotid artery. After induction of general anesthesia, ultrasound was used to guide direct puncture of the common carotid artery followed by the introduction of a 5 French sheath. A GuardWire distal protection balloon (Medtronic, Santa Rosa, CA) was placed distal to the lesion and deployed at nominal diameter. A balloon-expandable stent was deployed without difficulty. Following stent placement, angiography demonstrated improved flow in the entire right carotid artery territory. There were no complications related to cervical soft tissue damage or clinical embolism. The patient tolerated the procedure well and was discharged in 24 hours. Direct carotid access is acceptable in select patients in whom a transfemoral, brachial, or transradial approach is technically difficult. The use of distal cerebral protection devices may reduce cerebral embolism associated with these procedures.

A novel model of accelerated intimal hyperplasia in the pig iliac artery

There is no good animal model of large artery injury-induced intimal hyperplasia (IH). Those available are reproducible, providing only a few layers of proliferating cells or have the disadvantage of the presence of a metallic stent that complicates histology evaluation. This study was designed to develop a new, simple model of accelerated IH based on balloon injury in conjunction with disruption of the Internal Elastic Lamina (IEL) in pig external iliac arteries. Iliac artery injury (n = 24) was performed in 12 Yorkshire pigs divided in two groups: Group I (n = 10), overdistention injury induced by an oversized non-compliant balloon; Group II (n = 14), arterial wall disruption by pulling back an isometric cutting balloon (CB) followed by stretching with a compliant Fogarty Balloon (FB). At two weeks, arteries were processed for morphometric analysis and immunohistochemistry (IHC) for smooth muscle cells (SMC) and proliferating cell nuclear antigen (PCNA). When comparing the two groups, at 2 weeks, arteries of group II had a higher incidence of IH (100%vs. 50%, P = 0.0059), increased intimal areas (2.54 ± 0.33 mm(2) vs. 0.93 ± 0.36 mm(2) , P = 0.004), increased intimal area/Media area ratios (0.95 ± 0.1 vs. 0.28 ± 0.05; P < 0.0001) and decreased lumen areas (6.24 ± 0.44 vs. 9.48 ± 1.56, P = 0.026). No thrombosis was noticed in Group II. Neointima was composed by proliferating SMC located with the highest concentration in the area of IEL disruption (IHC). Arterial injury by pulling back CB and FB induces significant IH in pig iliac arteries by two weeks without thrombosis. This model is superior to the classical overdistention non-compliant model and should be useful and cost-effective for preclinical testing of procedures designed to inhibit IH in large peripheral arteries.

Atherosclerosis and thrombosis: insights from large animal models

Atherosclerosis and its thrombotic complications are responsible for remarkably high numbers of deaths. The combination of in vitro, ex vivo, and in vivo experimental approaches has largely contributed to a better understanding of the mechanisms underlying the atherothrombotic process. Indeed, different animal models have been implemented in atherosclerosis and thrombosis research in order to provide new insights into the mechanisms that have already been outlined in isolated cells and protein studies. Yet, although no model completely mimics the human pathology, large animal models have demonstrated better suitability for translation to humans. Indeed, direct translation from mice to humans should be taken with caution because of the well-reported species-related differences. This paper provides an overview of the available atherothrombotic-like animal models, with a particular focus on large animal models of thrombosis and atherosclerosis, and examines their applicability for translational research purposes as well as highlights species-related differences with humans.

Preclinical restenosis models and drug-eluting stents: still important, still much to learn

Percutaneous coronary intervention continues to revolutionize the treatment of coronary atherosclerosis. Restenosis remains a significant problem but may at last be yielding to technologic advances. The examination of neointimal hyperplasia in injured animal artery models has helped in our understanding of angioplasty and stenting mechanisms, and as drug-eluting stent (DES) technologies have arrived, they too have been advanced through the study of animal models. These models are useful for predicting adverse clinical outcomes in patients with DESs because suboptimal animal model studies typically lead to problematic human trials. Similarly, stent thrombosis in animal models suggests stent thrombogenicity in human patients. Equivocal animal model results at six or nine months occasionally have been mirrored by excellent clinical outcomes in patients. The causes of such disparities are unclear but may result from differing methods, including less injury severity than originally described in the models. Ongoing research into animal models will reconcile apparent differences with clinical trials and advance our understanding of how to apply animal models to clinical stenting in the era of DESs.

Coronary in-stent restenosis: current status and future strategies

In-stent restenosis (ISR) is a novel pathobiologic process, histologically distinct from restenosis after balloon angioplasty and comprised largely of neointima formation. As percutaneous coronary intervention increasingly involves the use of stents, ISR is also becoming correspondingly more frequent. In this review, we examine the available studies of the histology and pathogenesis of ISR, with particular reference to porcine and other animal models. An overview of mechanical treatments is then provided, which includes PTCA, directional coronary atherectomy and high speed rotational atherectomy. Radiation-based therapies are discussed, including a summary of current problems associated with this modality of treatment. Finally, novel strategies for the prevention of ISR are addressed, including novel developments in stents and stent coatings, conventional drugs, nucleic acid-based drugs and gene transfer. Until recently, limited pharmacologic and mechanical treatment options have been available for both treatment and prevention of ISR. However, recent advances in gene modification and gene transfer therapies and, more particularly, in local stent-based drug delivery systems make it conceivable that the incidence of ISR will now be seriously challenged.

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.

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.

Morphological effects on in-stent restenosis assessed by intravascular ultrasound imaging

The purpose of this study was to evaluate the rupture and dissection of the vessel wall immediately after balloon dilatation by intravascular ultrasound (IVUS) imaging and to predict restenosis in patients who underwent subsequent coronary stent implantation. Stent implantation improves the long-term results of coronary angioplasty by reducing lesion elastic recoil and arterial remodeling. However, several studies have suggested that neointimal hyperplasia is the cause of instant restenosis. We recruited 60 patients in whom IVUS studies were performed immediately after successful balloon dilatation and just before stent implantation. We compared IVUS parameters with 6-month follow-up quantitative coronary angiography. This was performed in 51 lesions of 51 patients (85%). Qualitative analysis included assessment of plaque composition, plaque eccentricity, plaque fracture and the presence of dissection. In addition, minimal luminal diameter, percent diameter stenosis, percent area stenosis and plaque burden were quantitatively analyzed. Two morphological patterns after balloon dilatation were classified by IVUS. Type I was defined as absence or partial tear of the plaque without disclosure of the media to lumen (22 lesions). Type II was defined as a split in the plaque or dissection of the vessel wall with disclosure of the media to the lumen (29 lesions). At 6 months follow-up, angiographic restenosis occurred in 17 of the 51 lesions (33%). Restenosis was significantly (p < 0.05) more likely to occur in type II (13/29: 45% incidence) than in type I (4/22: 18% incidence). The assessment of plaque morphology immediately after balloon dilatation and before stent implantation provides important therapeutic and prognostic implications.

Biocompatibility of polyurethane-coated stents: tissue and vascular aspects

To assess the arterial injury triggered by polyurethane-coated vs. uncoated stents, six polyurethane-coated and six bare nitinol stents were implanted in rabbit carotid arteries. All animals were sacrificed 4 wk after stent placement. Sections were evaluated by histology and morphometric analysis. At 4 wk, both the coated and uncoated stent struts were entirely endothelialized. The spaces between the struts showed a relatively mild proliferative response, with a few sections demonstrating neovascularization around the struts. Polyurethane coating was associated with an inflammatory tissue response consisting of lymphocytic infiltration and foreign-body reaction, with the appearance of multinucleated giant cells. Lumen, intimal, and medial cross-sectional areas varied little between coated and uncoated stented vessels (2.45+/-0.19 vs. 2.47+/-0.47 mm2, 1.17+/-0.52 vs. 0.78+/-0.30 mm2, and 0.66+/-0.18 vs. 0.58+/-0.27 mm2, respectively). In the rabbit carotid artery model, polyurethane coating does not affect the degree of neointimal proliferation after endovascular stenting compared with the conventional stenting approach. However, the inflammatory tissue response may indicate a low intrinsic biocompatibility of this stable polymer, so that it may not be an ideal material for coating intravascular devices.

Temporary arterial stenting: comparison to permanent stenting and conventional balloon injury in a rabbit carotid artery model

The objective was to assess the arterial wall response to temporary stenting with a removable nitinol stent in comparison with permanent stenting and balloon injury at 28 days in the rabbit carotid artery. Restenosis remains an important limiting factor after the implantation of permanent metallic stents and balloon angioplasty. We have developed a temporary nitinol stent that uses a bolus injection of warmed saline to collapse the stent for percutaneous removal. Vascular changes related to the thermal saline bolus injection required to remove a nitinol implanted stent were assessed in 12 rabbit carotid arteries at 7 and 28 days postinjection. Nitinol stents, inflated to 3.0 mm diameter, were implanted for 3 days (n = 6) and histology and quantitative histomorphometry examined at 28 days. Results were compared with permanently implanted stents (n = 5) and balloon injury (n = 9). Dual bolus injection of 10 ml at 70 degrees C created an acute necrotizing injury and chronic neointimal proliferation, whereas injections of 5 ml at 63 degrees C were minimally injurious. Temporary stenting resulted in the least neointimal proliferation measured by the intima to media ratio (0.22 +/- 0.10 vs. 1.59 +/- 0.31 for permanent stenting and; 0.49 +/- 0.14 for balloon injury; P < 0.001). Temporary stenting maintained a significantly larger lumen than balloon (1.53 +/- 0.72 mm2 vs. 0.64 +/- 0.14 mm2; P < 0.001), which could not be explained by absolute changes in intimal cross sectional area (0.14 +/- 0.07 mm2 vs. 0.21 +/- 0.06 mm2 respectively; P = 0.33). Temporary stenting resulted in a relatively larger vessel area within the external elastic lamina than with balloon (2.28 +/- 1.06 mm2 vs. 1.30 +/- 0.18 mm2; P = 0.007). The thermal stent recovery process can create necrotizing vascular injury and neointimal proliferation at higher temperatures and injectate volumes. Stent removal after 3 days using 63 degrees C saline bolus injection results in less neointimal proliferation than with permanent stents or balloon injury. In comparison to balloon injury, temporary stenting also may have a long-lasting beneficial effect on vessel recoil and remodeling, resulting in larger lumen size after stent removal.

Relationship of vascular thrombosis and inflammatory leukocyte infiltration to neointimal growth following porcine coronary artery stent placement

BACKGROUND

Superficial and intramural thrombosis are reproducible histopathological features of the porcine coronary oversized stent injury model. Fibrin and its degradation products are chemotactic for mononuclear leukocytes, and promote the proliferation and migration of vascular smooth muscle cells (VSMC) in vitro. The goal of this study was to quantitate the serial histomorphologic evolution of thrombosis, leukocyte infiltration, VSMC proliferation and collagen accumulation following porcine coronary artery stent placement in a porcine model.

METHODS

Twenty-four normocholesterolemic swine underwent oversized balloon (3.5-4.0 mm) coronary angioplasty and tantalum metal stent placement. Twenty-six different arterial sites were injured, followed by serial sacrifice at day 4 (n = 6), 8 (n = 6), 14 (n = 6), and 28 (n = 6). Quantitative analysis of the neointima was performed using a high resolution video-microscopy interface and a validated histomorphometric software program. Alpha actin-positive VSMC density (per 10(4) micro(2) neointimal area) and collagen-specific picro-sirius red fluorescence (percent of neointima) were quantitated at sites adjacent to and distant from coronary artery stent placement.

RESULTS

The percent of total neointimal area occupied by resolving thrombus material was greater at days 4-8 compared to 14-28 days (59-63% vs. 1-2%; P = 0.001). Mononuclear leukocytes were also significantly increased at days 4 and 8 (92 +/- 1 and 70 +/- 8%) compared to days 14-28 (both 3 +/- 3%; P = 0.001), as a percentage of the total neointimal cellularity. Total neointimal cell density did not change (20 +/- 10, 12 +/- 6, 23 +/- 7 and 20 +/- 3 cells/10(4) micro(2); P-value, NS), despite progressive cross-sectional vascular area stenosis reduction from 7 +/- 3% at day 4 to 72 +/- 14% at day 28 (P = 0.001). Percent neointimal fibrinoid thrombus content and mononuclear leukocyte cellularity were correlated in this model (R = 0.81; P < 0.001). Peri-stent neointimal collagen staining exceeded that at vascular sites distant from porcine coronary stent placement by 14 days (29 +/- 6 vs. 15 +/- 3%), and remained greater at 28 days (35 +/- 11 vs. 16 +/- 12%) (both P < 0.05).

CONCLUSIONS

Quantitative serial histomorphometry of porcine coronary vascular stent delivery sites demonstrates early (4-8 day) neointimal mononuclear leukocyte infiltration which is histomorphologically and temporally related to intramural fibrinoid thrombosis. Significant vascular stenosis and collagen deposition occurs by 14-28 days at these vascular injury sites. These data suggest a local interaction between thrombotic and inflammatory elements in porcine coronary neointima following oversized stent injury.

Therapeutic effects of nitric oxide-donor isosorbide dinitrate on atherosclerosis-induced alterations in hemodynamics and arterial viscoelasticity are independent of the wall elastic component

Whether the arterial elastic structures are involved in the beneficial effects of long-term treatment with organic nitrates on atherosclerosis-induced changes in hemodynamics and arterial wall viscoelastic properties, are case for angiotensin-converting enzyme (ACE) inhibitors, is not known. In the present study, atherogenic (A) diet, and isosorbide dinitrate (ISDN) (I) (60 mg Risordan LP, daily dose) were given concomitantly for 4 months to adult Pitman-Moore minipigs (A + I animals, n = 8), which were compared with A (n = 8) or control (C, n = 8) animals. Blood flow was investigated by hemodynamics in the hindlimb arterial bed; and wall rheology, histomorphometry and elastin; and desmosine (DES) and isodesmosine (IDE) contents in the abdominal aorta. Atherosclerosis prominently impaired the function of capacitance and resistance arteries, altered blood pressure contours, increased aortic stiffness and wall tension, and reduced parietal viscoelasticity through viscous component blunting. The treatment with ISDN significantly improved aortic pulsatility, arteriolar opposition to blood flow, and blood pressure (BP) contours by restoring, at least in part, the wall viscoelastic properties. However, there was no significant change in the area of the pressure-diameter curve hysteresis between the three animal groups. In contrast, ISDN reduced neither the cross-sectional area of lesions nor the losses in wall elastin content and had no influence on lipid accumulations in vessels and in the blood. The present results demonstrate that the beneficial hemodynamic and wall viscoelastic effects elicited by ISDN in atherosclerotic minipigs are not accounted for by therapeutic properties of the nitric oxide (NO) donor against alterations of elastic structures, but by the viscoelastic properties in the arterial wall.

Long-term intracoronary stent placement: arteriographic and histologic results after 7 years in a dog model

Prosthetic intracoronary stenting has become an important adjunct to balloon angioplasty in the percutaneous treatment of coronary artery disease. However, there are few reports of the long-term histologic consequences of stenting in the world literature. We report the arteriographic, histologic, and ultrastructural examination of a flexible tantalum wire coil stent implanted in the coronary artery of a dog for 7 years. The vessel was arteriographically patent without evidence of either stenosis or ectasia. The stent had been incorporated into the arterial wall, and was covered with a neointima of approximately 100 microns maximum thickness. There was necrosis of the tunica media adjacent to the stent but the inflammatory response was restricted to occasional macrophages in the neointima of the immediate vicinity of the stent wire. The endothelial cell layer was normal in its morphologic appearance. In summary, the flexible tantalum wire coil stent was well tolerated by the host blood vessel and demonstrated acceptable biocompatibility for the 7-year duration of its implantation in the normal dog coronary artery.

Coronary stenting with a novel stainless steel balloon-expandable stent: determinants of neointimal formation and changes in arterial geometry after placement in an atherosclerotic model

OBJECTIVES

This study evaluated the delivery characteristics and vascular response to placement of a novel balloon-expandable stent in swine with experimentally induced atherosclerosis.

BACKGROUND

The Multi-Link stent is a balloon-expandable stainless steel stent with an interconnected ring structure designed to provide a high degree of compressive resistance while preserving longitudinal flexibility. The placement characteristics and vascular response to this stent in atherosclerotic coronary arteries have not been characterized.

METHODS

We tested the delivery characteristics and vascular response to the Multi-Link stent in 19 miniature swine with experimentally induced coronary atherosclerosis created in 37 coronary artery segments by overstretch balloon injury and high cholesterol diet. Quantitative coronary angiography was used to define stent performance characteristics, such as lesion dilation and compressive resistance. Pathologic assessment of the stented arteries was used to evaluate the immediate and long-term vascular response to stent placement.

RESULTS

Nineteen (95%) of 20 stents were successfully implanted in the left anterior descending (n = 11), left circumflex (n = 7) or right (n = 1) coronary artery. The baseline angiographic minimal lumen diameter of the stented coronary segment was 2.48 +/- 0.09 mm (reference diameter 2.87 +/- 0.06 mm, mean +/- SE) and increased to 2.82 +/- 0.05 mm (p < 0.001) after stent placement. The balloon-inflated stent diameter was 2.98 +/- 0.06 mm with minimal recoil to a final minimal lumen diameter of 2.82 +/- 0.06 mm at 15 min after implantation (p = 0.001). Angiographic and histologic follow-up at 72 h (n = 7), 14 days (n = 4) and 56 days (n = 8) demonstrated that all stents were patent, without evidence of migration, intraluminal filling defects or side branch occlusion. At 56 days, mean neointimal thickness was significantly greater at the stent wire sites in the region of the plaque where the media was absent than the stent wire sites, where the internal elastic lamina was intact with underlying normal media (0.48 +/- 0.01 vs. 0.27 +/- 0.02 mm, p < 0.0001). Compared with the nonstented atherosclerotic lesions, after 56 days the stented vessels had a mildly reduced lumen area when normalized to the proximal reference vessel (2.81 +/- 0.27 vs. 2.68 +/- 0.30 mm2, p = 0.07). The mean change in the area within the external elastic lamina relative to a normal proximal reference segment was significantly greater in stented vessels (1.45 +/- 0.34 mm2) than nonstented atherosclerotic vessels (0.44 +/- 0.28 mm2, p = 0.033).

CONCLUSIONS

Morphologic data confirm that the principal beneficial effect of stent placement is vessel expansion and attenuation of constrictive remodeling. In vessels with eccentric atherosclerotic fibrocellular plaques, the presence of normal media underlying the stent determines the degree of neointimal formation. These data may be useful in understanding the mechanism of stent restenosis in patients with prior percutaneous transluminal coronary angioplasty.

Kinetics of smooth muscle cell proliferation and intimal thickening in a pig carotid model of balloon injury

Restenosis as a result of neointimal smooth muscle cell accumulation is an important limitation to the effectiveness of balloon angioplasty as a treatment for end-stage atherosclerosis. Quantitative animal models allow the definition of pathophysiological mechanisms and the evaluation of new therapeutic strategies. In this study we quantified the time course of neointima formation by morphometry, and smooth muscle cell (SMC) proliferation by immunocytochemistry for proliferating cell nuclear antigen (PCNA), in the pig carotid artery 0-28 days following balloon injury. This led to two distinct kinds of injury observed also in clinical studies, namely medial dilatation or deep medial tearing with rupture of the internal elastic lamina. Dilatation injury alone led to medial enlargement and neointima formation by 7 days, which did not increase further up to 28 days. Medial enlargement was similar following rupture of the internal elastic lamina; however the sum of neointima formation plus the area of medial repair ('neomedia') increased progressively up to 21 days after balloon injury. Balloon injury increased the PCNA index of smooth muscle cells in the media underlying an intact internal elastic lamina maximally after 3 days. The PCNA index in the neointima and especially in the neomedia was greater and maximal after 7 days. Endothelial regrowth occurred by 21 days in the presence or absence of medial tears. Our results establish a quantitative pig model of balloon injury which will allow the assessment of new therapeutic strategies directed at two clinically relevant types of injury. Medial tearing is associated with an enhanced and localized proliferative response and may therefore be especially important in human restenosis.

Emergency coronary stenting for dissection during percutaneous transluminal coronary angioplasty: angiographic follow-up after stenting and after repeat angioplasty of the stented segment

OBJECTIVES

The purpose of this study was to assess the angiographic results after emergency coronary stenting and after repeat angioplasty for restenosis within the stent.

BACKGROUND

There is still little angiographic information about lumen renarrowing and its correlates after emergency stenting, and data with regard to the angiographic outcome of repeat angioplasty within the stent are almost nonexistent.

METHODS

This study was based on the quantitative evaluation of angiograms performed before and immediately after intervention and at 6-month follow-up. The study included 164 of the 183 eligible patients with emergency Palmaz-Schatz stent implantation and 31 of those with restenosis within the stent who had repeat angioplasty.

RESULTS

Stenting produced an improvement in minimal lumen diameter from 0.82 +/- 0.41 to 2.76 +/- 0.47 mm (mean +/- SD) and in diameter stenosis from 74.9 +/- 11.5% to 18.3 +/- 8.1%. Elastic recoil was 0.51 +/- 0.34 mm, or 16%. At 6-month follow-up, 32.3% of the patients had restenosis (> or = 50% stenosis). Minimal lumen diameter decreased to 1.84 +/- 0.78 mm, and diameter stenosis increased to 41.7 +/- 21.0%. The degree of lumen loss correlated significantly with the length of the original stenosis and the initial lumen gain achieved by stenting. Thirty-one patients with in-stent restenosis underwent repeat angioplasty. The primary success rate was 100%, and no abrupt vessel closure was verified. Minimal lumen diameter increased from 0.85 +/- 0.35 to 2.18 +/- 0.39 mm, and diameter stenosis decreased from 69.7 +/- 12.9% to 28.6 +/- 9.4%. Elastic recoil was 0.82 +/- 0.38 mm, or 27%. At follow-up, 38.5% of the patients had restenosis. Minimal lumen diameter was reduced to 1.72 +/- 0.67 mm, and diameter stenosis increased to 42.4 +/- 18.1%.

CONCLUSIONS

Angiographic results of emergency coronary stenting compare favorably with those of conventional angioplasty. In-stent balloon redilation in patients with restenosis is associated with excellent short-term results and a restenosis rate not different from that reported for nonstented vessels.

Multicenter investigation of coronary stenting to treat acute or threatened closure after percutaneous transluminal coronary angioplasty: clinical and angiographic outcomes

OBJECTIVES

This study reports on the initial experience with the Gianturco-Roubin flexible coronary stent. The immediate and 6-month efficacy of the device and the incidence of the complications of death, myocardial infarction, emergency coronary artery bypass surgery and recurrent ischemic events are presented.

BACKGROUND

Abrupt or threatened vessel closure after coronary angioplasty is associated with increased risk of myocardial infarction, emergency coronary artery bypass graft surgery and in-hospital death. When dissection or prolapse of dilated plaque into the lumen is unresponsive to additional or prolonged balloon catheter inflation, coronary stenting offers a nonsurgical mechanical means to rapidly restore stable vessel geometry and adequate coronary blood flow.

METHODS

From September 1988 through June 1991, 518 patients underwent attempted coronary stenting with the 20-mm long Gianturco-Roubin coronary stent for acute or threatened vessel closure after angioplasty. In 494 patients, one or more stents were deployed. Thirty-two percent of patients received stents for acute closure and 69% for threatened closure.

RESULTS

Successful deployment was achieved in 95.4% of patients. Overall, stenting resulted in an immediate angiographic improvement in the diameter stenosis from 63 +/- 25% before stenting to 15 +/- 14% after stenting. Emergency coronary artery bypass graft surgery was required in 4.3% (21 of 493 patients). The incidence of in-hospital myocardial infarction (Q wave and non-Q wave) was 5.5% (27 of 493 patients). At 6 months, myocardial infarction was infrequent, occurring in 1.6% (8 of 493 patients). The incidence of in-hospital death was 2.2% (11 of 493 patients). Late death occurred in 7 patients (1.4%) and 34 patients (6.9%) required later bypass graft surgery. Complications included blood loss, primarily from the arterial access site, and subacute thrombosis of the stented vessel in 43 patients (8.7%).

CONCLUSIONS

The early multicenter experience suggests that this stent is a useful adjunct to coronary angioplasty to prevent or minimize complications associated with flow-limiting coronary artery dissections previously correctable only by surgery. Although this study was not randomized, it demonstrated a high technical success rate and encouraging results with respect to the low incidence of emergency coronary artery bypass graft surgery and myocardial infarction.

Mechanisms of restenosis and redilation within coronary stents--quantitative angiographic assessment

OBJECTIVES

This study was designed to assess the relative contributions of intimal hyperplasia and stent compression to the lumen narrowing seen after intracoronary stenting and to determine whether the lumen enlargement produced by angioplasty of in-stent restenosis results primarily from compression or extrusion of intimal hyperplasia through the stent or from additional stent expansion.

BACKGROUND

Palmaz-Schatz stent placement outwardly displaces plaque and eliminates elastic vessel recoil to provide a large and smooth lumen. Some degree of late lumen narrowing occurs within each stent and causes significant restenosis (> or = 50% stenosis) in 25% to 30% of treated lesions. It has not been clear, however, whether this narrowing results from stent compression (crush) or from in-stent intimal hyperplasia. Because the Palmaz-Schatz stent has a distinct radiographic shadow, it is possible to determine the late diameter of both the stent and the enclosed vessel lumen to assess the relative contributions of these two processes.

METHODS

From cineangiograms, initial (after stenting) and late (follow-up) lumen and stent diameters were examined in 55 patients (59 stents, group I) who had both immediate and 6-month (192 +/- 117 days) angiography. Lumen and stent diameter were also examined before and after dilation in 30 patients (30 stents, group II) who underwent angioplasty of severe in-stent restenosis.

RESULTS

Late loss in minimal lumen diameter was 0.99 +/- 0.87 mm for group I despite only a slight (0.03 +/- 0.23-mm) reduction in the corresponding stent diameter. After redilation for in-stent restenosis, the acute gain in minimal lumen diameter was 1.51 +/- 0.82 mm for group II, again without appreciable increase (0.06 +/- 0.20 mm) in stent diameter.

CONCLUSIONS

Restenosis after intracoronary Palmaz-Schatz stenting appears to be due predominantly to lumen encroachment by intimal hyperplasia within the stent, with minimal contribution of stent compression. Lumen enlargement after coronary angioplasty of in-stent restenosis appears to be due primarily to compression or extrusion of intimal hyperplasia through the stent, or both, rather than to further stent expansion.

Platelet and fibrin deposition on coronary stents in minipigs: effect of hirudin versus heparin

OBJECTIVES

The present study was designed to test the hypothesis that the direct thrombin hirudin is more efficient than heparin in reducing thrombus formation after coronary stenting.

BACKGROUND

Despite aggressive anticoagulation, subacute thrombosis of coronary stents is a major complication associated with these new devices.

METHODS

In 19 minipigs indium-111-labeled thrombocytes and iodine-125-labeled fibrinogen were injected 14 to 19 h before coronary implantation of tantalum balloon-expandable stents. In group 1 (n = 6, seven stents), a bolus of heparin (100 U/kg body weight) was given before stenting. Group 2 (n = 6, 11 stents) received both dextran (500 ml) and heparin (a 100-U/kg bolus followed by a continuous infusion of 50 U/kg per h). In group 3 (n = 7, 13 stents), hirudin (recombinant desulphatohirudin HV 1 [CGP 39393] [1 mg/kg]) was given before stent implantation, followed by an infusion of 1 mg/kg per h. All animals were pretreated with aspirin (250 mg intravenously).

RESULTS

Activated partial thromboplastin time was prolonged to > 1.8 times control values in groups 2 and 3. Histologic examination after perfusion fixation 12 h after stenting showed a variable extent of thrombus on all stents. Medial tear was observed in three stents in group 1, six stents in group 2 and six stents in group 3. The number of platelets on all stents averaged 116.2 (range 22 to 522) x 10(6) in group 1, 64.3 (range 11 to 169) x 10(6) in group 2 and 19.7 (range 9 to 38) x 10(6) in group 3 (p < 0.05 vs. group 1 and vs. group 2). The increase in platelet deposition, associated with medial tear in all groups, was lowest in the hirudin group. Similarly, fibrin deposition was lowest on stents in hirudin-treated animals.

CONCLUSIONS

Recombinant hirudin significantly reduces platelet and fibrin deposition on coronary stents compared with the reduction achieved with combined heparin, dextran and aspirin.

Restenosis and the proportional neointimal response to coronary artery injury: results in a porcine model

Restenosis is a reparative response to arterial injury occurring with percutaneous coronary revascularization. However, the quantitative characteristics of the relation between vessel injury and the magnitude of restenotic response remain unknown. This study was thus performed to determine the relation between severity of vessel wall injury and the thickness of resulting neointimal proliferation in a porcine model of coronary restenosis. Twenty-six porcine coronary artery segments in 24 pigs were subjected to deep arterial injury with use of overexpanded, percutaneously delivered tantalum wire coils. The vessels were studied microscopically 4 weeks after coil implantation to measure the relation between the extent of injury and the resulting neointimal thickness. For each wire site, a histopathologic score proportional to injury depth and the neointimal thicknesses at that site were determined. Mean injury scores were compared with both mean neointimal thickness and planimetry-derived area percent lumen stenosis. The severity of vessel injury strongly correlated with neointimal thickness and percent diameter stenosis (p less than 0.001). Neointimal proliferation resulting from a given wire was related to injury severity in adjacent wires, suggesting an interaction among effects at injured sites. If the results in this model apply to human coronary arteries, restenosis may depend on the degree of vessel injury sustained during angioplasty.

Vascular pathology of balloon-expandable flexible coil stents in humans

The morphologic changes in atherosclerotic coronary arteries and saphenous vein bypass grafts after placement of a balloon-expandable flexible coil stent (Cook) are described. In each case, the vessels were patent despite morphologic evidence of injury and dissection in the vessel wall. The stented region was reendothelialized and the tissue overlying the stent wires consisted primarily of smooth muscle cells. There was minimal inflammatory reaction to the stent wires. These findings suggest that the balloon-expandable flexible coil stent can effectively maintain vessel patency even in the setting of postangioplasty lumen disruption. In addition, the vessels tolerate the metal prosthesis with little evidence of tissue inflammatory reaction.

Experimental models of coronary artery restenosis

The study of potentially effective drug therapies and mechanical devices for the prevention of restenosis after percutaneous coronary revascularization has relied heavily on the use of experimental animal models. To date, greater than 50 experimental studies have been reported and have suggested that at least nine different classes of pharmacologic agents inhibit the intimal proliferative response to arterial injury. However, no pharmacologic intervention has yet been shown to reproducibly reduce the incidence of restenosis after coronary balloon angioplasty in humans. To identify the reasons for the apparent nonspecificity of the animal models and to determine which model should most reliably predict the efficacy of individual therapies in humans, the distinguishing characteristics of the experimental models were compared. Particular attention was paid to the size and morphologic structure of the treated artery, the susceptibility of the species to spontaneous and diet-induced arterial disease, the nature of the stimulus to intimal proliferation and several practical and logistic considerations. Finally, the reported efficacies of specific drug therapies in the respective animal models and in humans were compared. This review suggests that significant interspecies and occasionally intraspecies differences do exist among the respective animal models, particularly in the extent and composition of the neointimal thickening.(ABSTRACT TRUNCATED AT 250 WORDS)