Intimal hyperplasia regression from 6 to 12 months after stenting

Tissue engineered vascular grafts transform into autologous neovessels capable of native function and growth

Background

Tissue-engineered vascular grafts (TEVGs) have the potential to advance the surgical management of infants and children requiring congenital heart surgery by creating functional vascular conduits with growth capacity.

Methods

Herein, we used an integrative computational-experimental approach to elucidate the natural history of neovessel formation in a large animal preclinical model; combining an in vitro accelerated degradation study with mechanical testing, large animal implantation studies with in vivo imaging and histology, and data-informed computational growth and remodeling models.

Results

Our findings demonstrate that the structural integrity of the polymeric scaffold is lost over the first 26 weeks in vivo, while polymeric fragments persist for up to 52 weeks. Our models predict that early neotissue accumulation is driven primarily by inflammatory processes in response to the implanted polymeric scaffold, but that turnover becomes progressively mechano-mediated as the scaffold degrades. Using a lamb model, we confirm that early neotissue formation results primarily from the foreign body reaction induced by the scaffold, resulting in an early period of dynamic remodeling characterized by transient TEVG narrowing. As the scaffold degrades, mechano-mediated neotissue remodeling becomes dominant around 26 weeks. After the scaffold degrades completely, the resulting neovessel undergoes growth and remodeling that mimicks native vessel behavior, including biological growth capacity, further supported by fluid-structure interaction simulations providing detailed hemodynamic and wall stress information.

Conclusions

These findings provide insights into TEVG remodeling, and have important implications for clinical use and future development of TEVGs for children with congenital heart disease.

Risk prediction of in-stent restenosis among patients with coronary drug-eluting stents: current clinical approaches and challenges

Introduction: In-stent restenosis (ISR) has been one of the biggest limitations to the success of percutaneous coronary intervention for the treatment of coronary artery disease (CAD). The introduction of drug-eluting stent (DES) was a revolution in the treatment of CAD because these devices drastically reduced ISR to very low levels (<5%). Subsequently, newer generation DES treatments have overcome the drawbacks of first-generation DES, i.e. delayed endothelialization, and late stent thrombosis. However, the issue of late ISR, including neoatherosclerosis after DES implantation especially in high-risk patients and complex lesions, still exists as a challenge to be overcome.Areas covered: We discuss the mechanisms of ISR development including neoatherosclerosis, past and current clinical status of ISR, and methods to predict and overcome this issue from pathological and clinical points of view.Expert opinion: The initial drawbacks of first-generation DES, such as delayed endothelial healing and subsequent risk of late stent thrombosis, have been improved upon by the current generation DES. To achieve better long-term clinical outcomes, further titration of drug-release and polymer degradation profile, strut thickness as well as material innovation are needed.

The Predictors of Target Lesion Revascularization and Rate of In-Stent Restenosis in the Second-Generation Drug-Eluting Stent Era

Objectives

The aim of our study was to investigate the predictors of target lesion revascularization (TLR) and to compare the in-stent restenosis (ISR) progression rates of different 2nd-generation drug-eluting stents (DES).

Background

The predictors of early and late TLR after 2nd-generation DES implantation have not been fully evaluated.

Methods

We analyzed 944 stented lesions from 394 patients who had at least two serial follow-up angiograms, using quantitative coronary angiography (QCA) analysis. The study endpoints were TLR and the velocity of diameter stenosis (DS) progression.

Results

TLR occurred in 58 lesions (6.1%) during the first angiographic follow-up period and 23 de novo lesions (2.4%) during the following second interval. Independent predictors for early TLR were diabetes mellitus (DM) (HR 2.58, 95% CI 1.29–5.15, p=0.007), previous percutaneous coronary intervention (PCI) (HR 2.41, 95% CI 1.03–5.65, p=0.043), and postprocedure DS% (HR 1.08, 95% CI 1.05–1.11, p<0.001, per 1%), while predictors of late TLR were previous PCI (HR 9.43, 95% CI 2.58-34.52, p=0.001) and serum C-reactive protein (CRP) (HR 1.60, 95% CI 1.28-2.00, p<0.001). The ISR progression velocity (by DS%) was 12.1 ±21.0%/year and 3.7 ±10.1%/year during the first and second follow-up periods, respectively, which had no significant difference (p>0.05) between the four types of DESs.

Conclusions

Our data showed that predictors for TLR may be different at different time intervals. DM, pervious PCI, and postprocedure DS could predict early TLR, while previous PCI and CRP level could predict late TLR. Contemporary DESs had similar rates of ISR progression rates.

Trial Registration

This study was retrospectively registered and approved by the institutional review board of Seoul National University Hospital (no. 1801–138-918).

Pathology of Endovascular Stents

Contemporary endovascular stents are the product of an iterative design and development process that leverages evolving concepts in vascular biology and engineering. This article reviews how insights into vascular pathophysiology, materials science, and design mechanics drive stent design and explain modes of stent failure. Current knowledge of pathologic processes is providing a more complete picture of the factors mediating stent failure. Further evolution of endovascular stents includes bioresorbable platforms tailored to treat plaques acutely and to then disappear after lesion pacification. Ongoing refinement of stent technology will continue to require insights from pathology to understand adverse events, refine clinical protocols, and drive innovation.

Serial changes of neointimal tissue after everolimus-eluting stent implantation in porcine coronary artery: an optical coherence tomography analysis

Purposes. The serial changes in neointimal tissues were compared between everolimus-eluting stent (EES) and bare-metal stent (BMS) in the porcine coronary artery using optical coherence tomography (OCT). Methods. Serial (1, 3, and 6 month follow-up after stent implantation) OCT examinations were performed in 15 swine with 15 BMS- and 15 EES-treated lesions in porcine coronary arteries. Results. In BMS-implanted lesions, neointimal volume decreased from 7.3 mm³ to 6.9 mm³ and 6.4 mm³ at 1, 3, and 6 months follow-up without statistical significance (P = 0.369). At the time points of 1, 3, and 6 months, neointimal tissue appearance was mainly a homogeneous pattern (80.0%, 93.3%, and 100%, resp.), while the other pattern was layered. In contrast, in EES-implanted lesions, neointimal volume significantly increased from 4.8 mm³ to 9.8 mm³ between 1 and 3 months but significantly decreased to 8.6 mm³ between 3 and 6 months (P < 0.001). Between 1 and 3 months, the layered pattern of neointimal tissue increased from 26.7% to 66.7% but decreased to 20.0% between 3 and 6 months. Conclusions. EES had a biphasic pattern of neointimal amounts that correlated with changes in neointimal morphology.

A link between smooth muscle cell death and extracellular matrix degradation during vascular atrophy

OBJECTIVE

High blood flow induces neointimal atrophy in polytetrafluoroethylene (PTFE) aortoiliac grafts and a tight external PTFE wrap of the iliac artery induces medial atrophy. In both nonhuman primate models, atrophy with loss of smooth muscle cells and extracellular matrix (ECM) begins at ≤4 days. We hypothesized that matrix loss would be linked to cell death, but the factors and mechanisms involved are not known. The purpose of this study was to determine commonly regulated genes in these two models, which we hypothesized would be a small set of genes that might be key regulators of vascular atrophy.

METHODS

DNA microarray analysis (Sentrix Human Ref 8; Illumina, San Diego, Calif; ∼23,000 genes) was performed on arterial tissue from the wrap model (n = 9) and graft neointima from the graft model (n = 5) 1 day after wrapping or the switch to high flow, respectively. Quantitative reverse-transcription polymerase chain reaction (qRT-PCR) was also performed. Expression of this vascular atrophy gene set was also studied after Fas ligand-induced cell death in cultured smooth muscle cells and organ cultured arteries.

RESULTS

Microarray analysis showed 15 genes were regulated in the same direction in both atrophy models: 9 upregulated and 6 downregulated. Seven of nine upregulated genes were confirmed by qRT-PCR in both models. Upregulated genes included the ECM-degrading enzymes ADAMTS4, tissue plasminogen activator (PLAT), and hyaluronidase 2; possible growth regulatory factors, including chromosome 8 open reading frame 4 and leucine-rich repeat family containing 8; a differentiation regulatory factor (musculoskeletal embryonic nuclear protein 1); a dead cell removal factor (ficolin 3); and a prostaglandin transporter (solute carrier organic anion transporter family member 2A1). Five downregulated genes were confirmed but only in one or the other model. Of the seven upregulated genes, ADAMTS4, PLAT, hyaluronidase 2, solute carrier organic anion transporter family member 2A1, leucine-rich repeat family containing 8, and chromosome 8 open reading frame 4 were also upregulated in vitro in cultured smooth muscle cells or cultured iliac artery by treatment with FasL, which causes cell death. However, blockade of caspase activity with Z-VAD inhibited FasL-mediated cell death, but not gene induction.

CONCLUSION

Seven gene products were upregulated in two distinctly different in vivo nonhuman primate vascular atrophy models. Induction of cell death by FasL in vitro induced six of these genes, including the ECM-degrading factors ADAMTS4, hyaluronidase 2, and PLAT, suggesting a mechanism by which the program of tissue atrophy coordinately removes extracellular matrix as cells die. These genes may be key regulators of vascular atrophy.

Late restenosis following sirolimus-eluting stent implantation

OBJECTIVES

This serial angiographic study evaluated the incidence and predictors of late restenosis after sirolimus-eluting stent (SES) implantation.

BACKGROUND

Previous studies showed late restenosis (i.e., late catch-up phenomenon) after implantation of 7-hexanoyltaxol-eluting stents and nonpolymeric, paclitaxel-eluting stents.

METHODS

Between August 2004 and December 2006, SES implantation was performed in 1,393 patients with 2,008 lesions, in whom 8-month and 2-year follow-up coronary angiography were planned.

RESULTS

Of 2,008 lesions, 1,659 (83%) underwent 8-month follow-up angiography (8.3 ± 2.2 months). Restenosis was observed in 122 lesions (7.4%). Coronary angiography 2 years (1.9 ± 0.4 years) after SES deployment was performed in 1,168 lesions (74% of lesions without restenosis at 8-month follow-up angiography). Late restenosis was observed in 83 lesions (7.1%). There was significant decrease in minimum luminal diameter (MLD) between 8-month and 2-year follow-up (2.56 ± 0.56 mm vs. 2.35 ± 0.71 mm, p < 0.001). Multivariate analysis showed in-stent restenosis before SES implantation and MLD at 8-month follow-up as independent predictors of late restenosis.

CONCLUSIONS

Between 8-month and 2-year follow-up after SES implantation, MLD decreases, which results in late restenosis in some lesions. In-stent restenosis before SES implantation and MLD at 8-month follow-up are independent predictors of late restenosis.

Serial angiographic findings and prognosis of stent fracture site without early restenosis after sirolimus-eluting stent implantation

BACKGROUND

Stent fracture is one of the possible causes of in-stent restenosis after sirolimus-eluting stent (SES) implantation. However, long-term prognosis including late restenosis in stent fracture site without early restenosis remains unknown. The aim of this study is to investigate the risk of late restenosis at the stent fracture site without early restenosis after SES implantation.

METHODS

We divided 366 patients with 490 lesions into 2 groups with or without stent fracture based on the first scheduled follow-up coronary angiography (fracture group, 21 lesions; nonfracture group, 469 lesions). The second scheduled follow-up coronary angiography (>15 months after SES implantation) was performed in 83 patients with 124 lesions.

RESULTS

Target lesion revascularization due to late restenosis at the stent fracture site did not occur in the fracture group, but occurred in 5 lesions in the nonfracture group. At the first follow-up, minimal luminal diameter was significantly smaller and percentage diameter stenosis was significantly larger in the fracture group (1.98 ± 0.41 vs 2.52 ± 0.49 mm, P = .001 and 30.5% ± 13.1% vs 13.0% ± 8.8%, P < .0001, respectively). These differences were also present at the second follow-up (P = .01 and P = .007, respectively). In each group, there were no significant changes in minimal luminal diameter, percentage diameter stenosis, and late lumen loss between the first and second follow-up.

CONCLUSIONS

Late restenosis was not observed in stent fracture sites without early restenosis during the midterm follow-up after SES implantation.

Bare metal stent restenosis is benign clinical entity in Japanese patients

Recently, several studies have showed that bare metal stent (BMS) restenosis is not a benign clinical entity. However, clinical presentation of BMS restenosis in Japanese patients has not been fully evaluated. Follow-up coronary angiography after BMS implantation was performed in 473 patients with 523 lesions. Of these, BMS restenosis was observed in 167 lesions (31.9%). Clinical presentation of BMS restenosis was classified into 4 categories: 1) acute myocardial in-farction, 2) unstable angina, 3) stable angina, and 4) no symptom. Acute myocardial infarction (0%) and unstable angina (3.8%) were infrequent clinical presentations in patients with BMS restenosis compared to stable angina (26.9%) and no symptom (69.2%). BMS restenosis may be a benign clinical entity in Japanese patients.

Coronary microvascular endothelial function deteriorates late (12 months) after sirolimus-eluting stent implantation

BACKGROUND

Coronary flow velocity reserve (CFVR) may reflect coronary microvascular endothelial function in the absence of significant epicardial coronary artery stenosis. The purpose of this study was to evaluate coronary microvascular endothelial function late (6 and 12 months) after sirolimus-eluting stent (SES) implantation using transthoracic Doppler echocardiography.

METHODS AND RESULTS

A total of 21 lesions from 21 patients with significant left anterior descending artery stenosis who underwent percutaneous coronary intervention (PCI) with SES were enrolled and studied. As a control group, 10 patients who were treated with bare metal stent (BMS) were also studied. CFVR was measured at 6 and 12 months after PCI. Coronary angiography was also performed at 6 and 12 months (SES only) after stenting. Between 6 and 12 months after SES implantation, there was no significant difference in angiographical diameter stenosis. On the other hand, CFVR significantly decreased between 6 and 12 months in the SES group (2.5±0.5 vs. 2.2±0.5, p<0.01), but not in the BMS group (2.3±0.4 vs. 2.5±0.3, p=0.1).

CONCLUSIONS

Coronary microvascular endothelial function may deteriorate between 6 and 12 months after SES implantation.

Preclinical Models of Restenosis and Their Application in the Evaluation of Drug-Eluting Stent Systems

Coronary arterial disease (CAD) is the leading cause of death in the United States, the European Union, and Canada. Percutaneous coronary intervention (PCI) has revolutionized the treatment of CAD, and it is the advent of drug-eluting stent (DES) systems that has effectively allayed much of the challenge of restenosis that has plagued the success of PCI through its 30-year history. However, DES systems have not been a panacea: There yet remain the challenges associated with interventions involving bare metallic stents as well as newly arisen concerns related to the application of DES systems. To effectively address these novel and ongoing issues, animal models are relied on both to project the safety and efficacy of endovascular devices and to provide insight into the pathophysiology underlying the vascular response to injury and mechanisms of restenosis. In this review, preclinical models of restenosis are presented, and their application and limitation in the evaluation of device-based interventional technologies for the treatment of CAD are discussed.

Impact of In-Stent Minimal Lumen Area at 9 Months Poststent Implantation on 3-Year Target Lesion Revascularization–Free Survival

Background— Intravascular ultrasound (IVUS) is used to assess intermediate lesions in native coronary arteries; minimum lumen area (MLA) <4.0 mm 2 is accepted as a cutoff for a significant stenosis. We evaluated the IVUS in-stent MLA at 9-month follow-up that best predicted subsequent target lesion revascularization (TLR)–free survival in patients from the TAXUS IV, V, and VI studies.

Methods and Results— In the combined TAXUS IV, V, and VI randomized trials, 9-month IVUS was available in 635 patients (331 treated with paclitaxel-eluting stents [PES] and 304 treated with bare-metal stents [BMS]) who did not require TLR in the first 9 months postintervention and who were followed for 3 years. The in-stent MLA that best predicted 3-year TLR-free survival was determined. At 9-months follow-up, IVUS-measured in-stent MLA was 5.7�2.3 mm 2 in the PES group and 4.8�2.3 mm 2 in the BMS group. Between 9 months and 3 years, TLR was required in 4.9% of patients who were treated with PES and 6.7% of patients who were treated with BMS. Multivariate analysis identified MLA at 9 months as a significant predictor of late TLR (hazard ratio, 0.63 [0.43–0.93]; P =0.02). The ability of MLA to predict late TLR was further assessed using receiver operating characteristic analysis. MLA was found to be an acceptable discriminator for both PES (c=0.7448) and BMS (c=0.7329). Finally, the optimal thresholds of MLA that best predicted subsequent TLR-free survival were determined to be 4.2 mm 2 for PES and 4.0 mm 2 for BMS.

Conclusion— In the combined IVUS analysis of TAXUS IV, V, and VI, patients who did not require TLR within the first 9 months had a high subsequent TLR-free survival rate whether treated with PES or BMS. MLA measured by IVUS at 9 months predicted subsequent TLR with a cutoff similar to intermediate, de novo lesions in native coronary arteries.

Effects of external wrapping and increased blood flow on atrophy of the baboon iliac artery

OBJECTIVE

Increased blood flow causes neointimal atrophy, whereas relief of wall tension with an external wrap causes arterial medial atrophy. To study the effects of blood flow and wall tension separately and together, we applied tight or loose wraps on high-flow or normal-flow iliac arteries in baboons.

METHOD

Baboon external iliac arteries were wrapped with loose-fitting and tight-fitting expanded polytetrafluoroethylene (ePTFE), leaving part unwrapped. A downstream arteriovenous fistula was constructed on one side to increase blood flow approximately twofold. The arteries were perfusion-fixed with 10% formalin after 4 (n = 5) and 28 days (n = 5).

RESULTS

At 4 days, compared with the unwrapped artery, the loosely and tightly wrapped normal-flow artery showed significant medial atrophy (23% and 30%, respectively; P < .05). The tightly wrapped artery showed a loss of cells (27%; P = .02) but no change in cell density. At 28 days, the medial cross-sectional area was decreased by the tight wrap and loose wrap under normal (45% and 28%, respectively; P < .05) and high (43% and 29%, respectively; P < .05) flow. High flow did not alter the effect of wrapping nor did it affect the unwrapped medial area. At 28 days, the normal and high flow tightly wrapped media showed an insignificant loss of cells but had increased cell density (47% and 30%, respectively; P < .05), suggesting preferential loss of extracellular matrix. Decorin was expressed at the late time only in the tightly wrapped normal and high-flow media and was associated with tight packing of the collagen, as detected by picrosirius red staining.

CONCLUSION

Loose-fitting and tight-fitting ePTFE wraps induced an inflammatory foreign body response that caused medial atrophy with loss of cells and extracellular matrix; the tight wrap was more effective. High blood flow did not prevent or augment medial atrophy.

CLINICAL RELEVANCE

Research in arterial restenosis has focused on the biologic mechanisms and pharmacologic approaches to the prevention of intimal hyperplasia. An alternative therapeutic approach might be to induce atrophy of established intimal hyperplasia. We have previously reported that high blood flow induces neointimal regression in expanded polytetrafluoroethylene grafts in baboons. Here we provide another model of vascular atrophy induced by external wrapping. The similarity between baboons and humans in their vascular systems and individual genetic heterogeneity makes these experiments of great relevance. Up- or down-regulated genes common to both models might be key regulators of vascular atrophy and therefore suitable therapeutic targets for pharmacologic treatment of established lesions.

Induction of vascular atrophy as a novel approach to treating restenosis. A review

Regardless of the type of arterial reconstruction, luminal narrowing (stenosis or restenosis) develops in approximately one third of the vessels. In the past, the focus of research has been on the mechanisms of stenosis (intimal hyperplasia, pathologic remodeling) and pharmacologic approaches to prevention. An alternative approach is to induce intimal atrophy after luminal narrowing has developed, thus limiting treatment to only those patients that develop a problem. This approach to treat established disease by reducing wall mass through induction of cell death and extracellular matrix removal would be particularly useful for treating stenosis in synthetic bypass grafts or stented vessels, in which intimal hyperplasia is the primary mechanism of stenosis. This approach may be applicable as well to other vascular proliferative disorders, such as pulmonary hypertension and chronic transplant arteriopathy. Proof of principle has been shown in experiments with antibodies to platelet-derived growth factor (PDGF) receptors that cause neointimal regression in baboon polytetrafluoroethylene (PTFE) grafts and with angiotensin-converting enzyme inhibitors that induce medial atrophy in hypertensive arteries. Possible molecular targets could include PDGF receptors, A20, and BMP4. Further studies are needed to determine the utility of such a therapeutic approach to vascular disease.

Serial Angioscopic Evidence of Incomplete Neointimal Coverage After Sirolimus-Eluting Stent Implantation

Background— The time course of neointimal formation after stent implantation has not been studied extensively by angioscopy in the drug-eluting stent era.

Methods and Results— Serial angioscopic findings at first follow-up (3.6±1.1 months), second follow-up (10.5±1.6 months), and third follow-up (21.2±2.2 months) after stent implantation were compared between sirolimus-eluting stents (SES, n=17) and bare-metal stents (BMS, n=11). Neointimal coverage, thrombus, and presence of yellow plaques underneath the stents were assessed. Neointimal coverage was graded as follows: grade 0, stent struts were fully visible; grade 1, struts bulged into the lumen, although they were covered; grade 2, struts were embedded by the neointima but were seen translucently; or grade 3, struts were fully embedded and invisible. Neointimal coverage was remarkably different between SES and BMS at each follow-up point. Neointimal coverage grade was 1.1±0.5 in SES versus 2.9±0.3 in BMS at the first follow-up ( P <0.0001), 1.1±0.5 in SES versus 3.0±0.0 in BMS ( P <0.0001) at the second follow-up, and 1.3±0.5 in SES versus 3.0±0.0 in BMS at the third follow-up ( P =0.0009). No significant serial changes in coverage grade were noted in the BMS group, whereas coverage grade slightly but significantly increased at the third follow-up in the SES group ( P <0.05). Thrombi were detected in 4 SES: a red thrombus was seen from the first to the third follow-up in 2; another was detected only at the third follow-up; and the fourth was seen at the first follow-up but disappeared at the second follow-up, associated with a new white thrombus despite dual antiplatelet therapy. Yellow plaques had disappeared by the time of the second follow-up in BMS. In contrast, yellow plaques were exposed in 71% of SES at the first follow-up and remained exposed until the third follow-up. Neointimal coverage grades correlated with thrombi ( P =0.002) and with yellow plaques ( P <0.0001).

Conclusions— Serial angioscopic findings up to 2 years after SES implantation were markedly different from those after BMS. Neointimal coverage was completed by 3 to 6 months in BMS. In contrast, SES demonstrated the presence of thrombi and yellow plaques even as much as 2 years after implantation.

Clinical in-stent restenosis with bare metal stents: is it truly a benign phenomenon?

OBJECTIVE

In-stent restenosis (ISR) remains an important problem following percutaneous coronary intervention (PCI). Although it is generally believed that patients with ISR present with stable angina, this has not been well characterized. The aim of this study was to define the incidence, predictors, timing and clinical presentation of patients with ISR requiring repeat catheterization.

DESIGN

Using a multiregion prospective database which captures all patients undergoing cardiac catheterization and revascularization in the Province of Alberta, Canada, consecutive bare metal stent (BMS) implantations from January 1, 1998 to December 31, 2002 were analyzed. All patients with a repeat angiogram within one year of the index PCI were reviewed for evidence of clinical-ISR (CISR), defined as ISR as the cause for clinical presentation at angiography.

RESULTS

Of the 12,492 consecutive PCI patients reviewed, 2521 had repeat angiography and 744 patients (6.0%) had CISR by study definition. The mean time to repeat angiography in CISR patients was 5.4+/-2.7 months and multivariate analysis identified female gender, diabetes mellitus, and prior PCI as predictors. The majority of patients presented with an acute coronary syndrome: 52.2% unstable angina/non-ST elevation myocardial infarction and 18.5% ST elevation myocardial infarction. Only 25.3% presented with stable exertional angina.

CONCLUSION

Although the incidence of CISR within one year after BMS was relatively low, the recurrent clinical event in the majority of cases was a high-risk coronary syndrome. Thus, careful consideration of the risks of ISR to a specific patient against the cost implications of novel and expensive means to decrease its occurrence is required.

Neointimal progression and luminal narrowing in sirolimus-eluting stent treatment for bare metal in-stent restenosis: a quantitative intravascular ultrasound analysis

BACKGROUND

Recurrent restenosis may occur after drug-eluting stent implantation for in-stent restenosis (ISR) of bare metal stents (BMSs), especially in areas involving drug-eluting stent gaps.

METHODS

To investigate the details of neointimal progression and luminal narrowing after the treatment of ISR using sirolimus-eluting stents (SESs), serial intravascular ultrasound analysis was performed in 65 patients with ISR at postintervention and at 6-month follow-up. The total stented segment was categorized into 3 compartments: new SES (N), new SES and old BMS overlap (N/O), and old BMS (O). In each of the 190 compartments, serial intravascular ultrasound parameters were analyzed at the cross section of the maximum change in neointimal area (delta neointimal area) from postintervention to follow-up or the minimum lumen area at follow-up if delta neointimal area was 0. Minimum lumen area in each compartment was also investigated serially.

RESULTS

At postintervention, lumen area was the smallest in compartment N/O (N 5.8 +/- 1.5, N/O 5.1 +/- 1.3, O 6.0 +/- 1.4 mm2, P = .005). Not only the average of maximum delta neointimal area (N 0.2 +/- 0.4, N/O 0.2 +/- 0.4, O 0.8 +/- 1.0 mm2, P < .0001) but also the frequency of minimum lumen area decreasing from > or = 4.0 mm2 at postintervention to < 4.0 mm2 at follow-up (N 4.0%, N/O 5.1%, O 23.5%, P = .012) was the largest in compartment O.

CONCLUSIONS

Neointimal progression and consequent luminal narrowing tend to occur where BMS is uncovered with SES in treatment of ISR, even in the absence of an obvious stenosis at postintervention.

Efficacy of reduced-dose sirolimus-eluting stents in the human coronary artery: Serial IVUS analysis of neointimal hyperplasia and luminal dimension

STUDY OBJECTIVE

Using serial intravascular ultrasound (IVUS), the efficacy of reduced-dose sirolimus-eluting stents (SESs) in the prevention of neointimal hyperplasia (NH) and maintenance of luminal patency in human coronary arteries was evaluated.

BACKGROUND

In the animal model, a broad therapeutic window regarding sirolimus doses in suppressing NH has been reported.

METHODS

Serial cross-sectional and volumetric IVUS analyses were performed in 44 patients treated with SES that contained lower sirolimus doses (either 45% or 70%) than standard SES. For cross-sectional analysis, minimum lumen area (MLA) was measured. Percent (%) NH volumetric obstruction was calculated as 100 x NH volume/stent volume.

RESULTS

IVUS measurements were similar between the two drug-dose groups. At 12 months follow-up, only one case developed late incomplete stent apposition. Between 4 and 12 months, a slight increase of in-stent % area loss and % NH obstruction was noted (3.5% +/- 10.4% to 6.7% +/- 10.7% and 1.9% +/- 5.0% to 4.4% +/- 8.0%, respectively). The majority of studied cases, however, sustained less than a 10% volumetric (93% of studied cases) and area loss (75% of studied cases) in the stented segment up to 12 months. At 12 months, % area loss within the stented segments and 5-mm reference segments were comparable (7.0% +/- 19.6% versus 6.7% +/- 10.7%).

CONCLUSIONS

Although slight increases of NH were noted, SESs, delivering two reduced drug doses, appeared to be effective for maintaining luminal patency during 12 months follow-up.

Bone morphogenetic protein 4: potential regulator of shear stress-induced graft neointimal atrophy

OBJECTIVE

Placement in baboons of a distal femoral arteriovenous fistula increases shear stress through aortoiliac polytetrafluoroethylene (PTFE) grafts and induces regression of a preformed neointima. Atrophy of the neointima might be controlled by shear stress-induced genes, including the bone morphogenetic proteins (BMPs). We have investigated the expression and function of BMPs 2, 4, and 5 in the graft neointima and in cultured baboon smooth muscle cells (SMCs).

METHODS

Baboons received bilateral aortoiliac PTFE grafts and 8 weeks later, a unilateral femoral arteriovenous fistula.

RESULTS

Quantitative polymerase chain reaction showed that high shear stress increased BMP2, 4, and 5 messenger RNA (mRNA) in graft intima between 1 and 7 days, while noggin (a BMP inhibitor) mRNA was decreased. BMP4 most potently (60% inhibition) inhibited platelet-derived growth factor-stimulated SMC proliferation compared with BMP2 and BMP5 (31% and 26%, respectively). BMP4 also increased SMC death by 190% +/- 10%. Noggin reversed the antiproliferative and proapoptotic effects of BMP4. Finally, Western blotting confirmed BMP4 protein upregulation by high shear stress at 4 days. BMP4 expression demonstrated by in situ hybridization was confined to endothelial cells.

CONCLUSIONS

Increased BMPs (particularly BMP4) coupled with decreased noggin may promote high shear stress-mediated graft neointimal atrophy by inhibiting SMC proliferation and increasing SMC death.

Two-year follow-up intravascular ultrasound analysis after bare metal stent implantation in 120 lesions

The objective of this study was to examine long-term changes after bare metal stent implantation in a relatively large number of patients. There are few reports of intravascular ultrasound (IVUS) studies performed on stented and nonstented (reference) segments beyond 6 months after bare metal stenting. Using IVUS, we evaluated serial changes in stented and reference segments between 6 and 24 months after stent implantation in 110 patients with 120 lesions. Serial IVUS images were acquired at five equidistant intrastent sites and at two different reference segment sites. Measurements were made of the external elastic membrane (EEM), stent, lumen, and intimal hyperplasia (IH = stent - lumen) area. For the whole patient group, between 6 and 24 months, the mean IH area in stented segments decreased from 2.6 +/- 1.0 to 2.3 36+/- 0.9 mm2 (P < 0.001), and the mean lumen area increased from 6.2 +/- 2.0 to 6.5 +/- 1.9 mm2 (P < 0.001). The mean IH area decreased in 91 lesions (76%) and increased in 29 lesions (24%) between 6 and 24 months. There were no significant changes in EEM or lumen area in the reference segments. Late angiographic restenosis (diameter stenosis > or = 50%) occurred in three lesions between 6 and 24 months. A late target lesion revascularization was performed for one lesion. In the period of time between 6 and 24 months after stenting, IH regression occurred in most (76%) stent lesions, resulting in late lumen increase. However, IH progression was observed in 24% of in-stent lesions. No significant changes of EEM or lumen area occurred in the reference segments.

Drug-eluting stents: results, promises and problems

In-stent restenosis is the major drawback of percutaneous coronary interventions, occurring in 10-40% of the patients. Recently, new stents have emerged which are loaded with anti-inflammatory, anti-migratory, anti-proliferative or pro-healing drugs. These drugs are supposed to inhibit inflammation and neointimal growth and subsequently in-stent restenosis. In this review article the results of human clinical studies investigating drug-eluting stents are discussed from a clinical point of view, focussing on the efficacy in the prevention of restenosis and their potential side effects. Both success and failure in the field of drug-eluting stents have been described. Successful devices are the sirolimus-eluting and the polymer-based paclitaxel-eluting stents. Potentially dangerous side effects of drug-eluting stents are adverse drug interactions, incomplete stent apposition and increased in-stent thrombosis rates. Demonstration of long-term efficacy is mandatory since in some animal studies a delayed healing has been observed. Currently, the successful drug-eluting stents are under investigation in all types of lesions. We conclude that the results with some drug-eluting stents are promising, but further evidence on long-term efficacy and safety, also in high-risk subgroups, is needed.

Accumulation and loss of extracellular matrix during shear stress-mediated intimal growth and regression in baboon vascular grafts

The composition of extracellular matrix during growth and regression of the neointima was analyzed during healing in a baboon aorto-iliac polytetrafluoroethylene graft. Graft neointimal thickening can be modulated by altering blood flow by construction of downstream arteriovenous fistulas. Normal flow with normal shear stress induces neointimal thickening, whereas high flow with high shear stress upstream of a fistula induces regression of established neointima. The neointima formed under normal shear stress is enriched in hyaluronan and proteoglycans, particularly versican. On the other hand, the neointima near the graft material is enriched in collagen and biglycan. Neointimal regression in response to high shear stress is associated with a loss of proteoglycans as detected by histochemical staining. Immunostaining with an antibody against an ADAMTS cleavage neoepitope of versican increases after switching to high flow, although immunostaining for versican core protein is not appreciably changed by high flow. The present data demonstrate that the graft neointima is enriched with proteoglycans, particularly versican and hyaluronan, as well as collagen, and there is a differential distribution of each. Neointimal atrophy occurs with an apparent loss of proteoglycans and evidence of versican degradation.

Accumulation and loss of extracellular matrix during shear stress-mediated intimal growth and regression in baboon vascular grafts

The composition of extracellular matrix during growth and regression of the neointima was analyzed during healing in a baboon aorto-iliac polytetrafluoroethylene graft. Graft neointimal thickening can be modulated by altering blood flow by construction of downstream arteriovenous fistulas. Normal flow with normal shear stress induces neointimal thickening, whereas high flow with high shear stress upstream of a fistula induces regression of established neointima. The neointima formed under normal shear stress is enriched in hyaluronan and proteoglycans, particularly versican. On the other hand, the neointima near the graft material is enriched in collagen and biglycan. Neointimal regression in response to high shear stress is associated with a loss of proteoglycans as detected by histochemical staining. Immunostaining with an antibody against an ADAMTS cleavage neoepitope of versican increases after switching to high flow, although immunostaining for versican core protein is not appreciably changed by high flow. The present data demonstrate that the graft neointima is enriched with proteoglycans, particularly versican and hyaluronan, as well as collagen, and there is a differential distribution of each. Neointimal atrophy occurs with an apparent loss of proteoglycans and evidence of versican degradation.

Clinical and angiographic predictors of luminal changes beyond 6 months after implantation of thicker strut coronary stents

BACKGROUND

Late luminal changes beyond 6 months after thicker strut stent implantation have not been fully elucidated. The purpose of this study was to clarify the clinical and angiographic predictors of late changes in minimal lumen diameter (MLD) after 6-month follow-up of stenting.

METHODS AND RESULTS

Fifty-one lesions from 44 patients who underwent successfully S670/660 stent (Medtronic Vascular, Santa Rosa, CA, USA) implantations without target lesion revascularization were studied at 6-month follow-up and coronary angiography was repeated after the follow-up. Late luminal loss beyond 6 months after stenting significantly correlated with late loss (r=-0.42, p=0.0025) and MLD (r=0.28, p=0.047) at 6-month follow-up. On multivariate analysis, age (p=0.005), diabetes mellitus (p=0.002), hyperlipidemia (p=0.023), smoking (p=0.015), bifurcation lesion (p=0.018), small stent diameter (p=0.001) and MLD at 6-month follow-up (p<0.001) were identified as independent predictors of late luminal loss.

CONCLUSIONS

This study demonstrated that older age, diabetes mellitus, hyperlipidemia, smoking and small stent diameter (<3.0 mm) were associated with late luminal loss beyond 6 months after stenting, and that a bifurcation lesion and small lumen diameter at 6 months were associated with late luminal recovery.

Extracellular Matrix Changes in Stented Human Coronary Arteries

Background— Restenosis after stenting occurs secondary to the accumulation of smooth muscle cells (SMCs) and extracellular matrix (ECM), with the ECM accounting for >50% of the neointimal volume. The composition of the in-stent ECM has not been well characterized in humans.

Methods and Results— Postmortem human coronary arteries (n=45) containing stents underwent histological assessment of neointimal proteoglycans, hyaluronan, collagen (types I and III), SMCs, and CD44 (a cell surface receptor for hyaluronan). The mean duration of stent implantation was 18.7 months; stents in place ≥3 to <9 months (n=17) were assigned to group 1, stents ≥9 to <18 months old (n=19) to group 2, and stents ≥18 months old (n=9) to group 3. In groups 1 and 2, neointimal versican and hyaluronan staining was strongly positive, colocalized with α-actin-positive SMCs, and was greater in intensity compared with group 3. Conversely, decorin staining was greatest in group 3. The neointima of both group 1 and 2 stents was rich in type III collagen, with reduced staining in group 3. Type I collagen staining was weakest in group 1 stents, with progressively stronger staining in groups 2 and 3. SMC density and stent stenosis were significantly reduced in group 3 stents compared with groups 1 and 2. CD44 staining colocalized with macrophages and was associated with increased neointimal thickness.

Conclusions— The ECM within human coronary stents resembles a wound that is not fully healed until 18 months after deployment, followed by neointimal retraction. ECM contraction may be a target for therapies aimed at stent restenosis prevention.

Luminal recovery from six to twelve months after implantation of "thicker strut" coronary stents

A group of 50 patients with 51 de novo lesions treated with thicker strut stents (strut thickness >100 microm) was angiographically evaluated at baseline, after stenting, and at 6 and 12 months. Minimal luminal diameter (MLD) significantly increased from 6 to 12 months (6 months: 1.72 +/- 0.50 mm vs 12 months: 1.81 +/- 0.47 mm; p <0.01). The binary restenosis (diameter stenosis >50%) rate was 17% at 6 months and 11% at 12 months (p = NS). At multivariate analysis, lumen loss at 6 months (p = 0.018) and deployment pressure (p = 0.041) independently predicted the changes in MLD between 6 and 12 months.