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

Late stent thrombosis, endothelialisation and drug-eluting stents

Drug-eluting stents (DES) significantly reduce the risk of restenosis after percutaneous coronary revascularisation, but an increased risk of late stent thrombosis (LST) has been put forward as a major safety concern. Meta-analysis of clinical trials, however, does not support this caveat. Even so, many interventional cardiologists think that LST is associated with DES and related to delayed endothelialisation. This hypothesis is based on autopsy studies and clinical intracoronary angioscopy. In autopsy studies, differences between endothelialisation of DES and baremetal stents (BMS) have been reported. Most preclinical studies, however, have failed to show any significant differences in endothelialisation between DES and BMS. Our own studies, using the porcine coronary artery model, also suggest that DES show no differences in re-endothelialisation. However, DES do delay vascular healing and induce endothelial dysfunction. This paper will review clinical and animal studies which consider re-endothelialisation and LST. (Neth Heart J 2009;17:177-81.).

Early Stent Thrombosis in Patients With Acute Coronary Syndromes Treated With Drug-Eluting and Bare Metal Stents

Background— The clinical and angiographic predictors of early (<30 days) stent thrombosis (ST) have not been reported in high-risk patients with acute coronary syndromes.

Methods and Results— Qualitative and quantitative coronary angiographic analyses were performed in 3405 patients with moderate- and high-risk acute coronary syndromes in whom stents were implanted in the prospective randomized Acute Catheterization and Urgent Intervention Triage Strategy (ACUITY) trial, including 3043 patients (89.4%) in whom drug-eluting stents were implanted. Within 30 days, definite or probable ST occurred in 48 patients (1.4%). ST rates were not significantly different in patients treated with bare metal stents compared with drug-eluting stents (1.4% versus 1.4%; P =1.00) or with heparin plus glycoprotein IIb/IIIa inhibitors (1.1%) compared with bivalirudin with or without IIb/IIIa inhibitors (1.6% and 1.5%, respectively; P =0.26 and P =0.37, respectively). Compared with patients without ST, patients with ST more frequently had insulin-requiring diabetes mellitus and baseline renal insufficiency, a greater overall burden of coronary atherosclerosis, and suboptimal final angiographic results. ST also was more common in patients without preprocedural thienopyridine administration and with inconsistent antiplatelet drug use within 30 days. By multivariable analysis, the strongest independent predictors of definite ST were a smaller final stent minimal lumen diameter, a lack of preprocedural thienopyridine administration, the extent of coronary artery disease, and higher baseline hemoglobin level.

Conclusions— Occurring in nearly 1 in 70 patients, early ST is relatively common in acute coronary syndromes, occurs with similar frequency after anticoagulation with either heparin plus glycoprotein IIb/IIIa inhibitors or bivalirudin with or without IIb/IIIa inhibitors, and is predicted by diffuse atherosclerosis, suboptimal angiographic results, and inadequate pharmacotherapy.

Coronary ischemia and percutaneous intervention

The interventional treatment of ischemia is a complex issue grounded on an understanding of basic pathophysiology, but translated and implemented in practice by extensive clinical trial data representing patients with a spectrum of ischemia-causing clinical syndromes and anatomical variations of coronary artery disease (CAD). Percutaneous coronary intervention (PCI) has evolved to treat ischemia within this matrix of clinical and anatomical subsets using a wide array of techniques. Initial techniques using balloon angioplasty were promising, but demonstrated significant rates of restenosis due to negative arterial remodeling. The advent of stent technology prevented arterial recoil and provided a viable treatment for flow-limiting coronary dissections, thereby facilitating improved long-term patency of coronary vessels without the need for repeat revascularization. In-stent restenosis has been successfully addressed with drug elution, but late stent thrombosis has emerged as a complex issue involving dual antiplatelet therapy, patient compliance, and reexamination of the delicate balance between reducing restenosis and promoting endothelial proliferation. Finally, complex coronary lesions associated with heavy calcification or extensive plaque/thrombus burden that introduce unique challenges in obtaining ideal angiographic results have led to the development of new debulking devices aimed at optimizing procedural outcomes. This review will describe a variety of percutaneous coronary interventional techniques and technologies that are employed in the invasive treatment of ischemia under the guidance of clinical guidelines and evidence-based medicine.

Contribution of circulating vascular progenitors in lesion formation and vascular healing: lessons from animal models

PURPOSE OF REVIEW

It is a widely accepted view that vascular repair results from migration and proliferation of adjacent cells in animal models. On the contrary, accumulating evidence suggests that bone marrow can give rise to endothelial-like cells and smooth muscle like cells that potentially contribute to vascular healing, remodeling, and lesion formation under physiological and pathological conditions. The aim of this article is to review recent findings obtained from animal models of vascular diseases regarding bone marrow derived progenitor cells.

RECENT FINDINGS

Studies using chimeric animals revealed that bone marrow derived cells exist at the sites of vascular healing and lesion formation after injury. High-resolution histological analyses revealed that those bone marrow derived cells do express some markers for endothelial cells or smooth muscle cells. Peripheral mononuclear cells could differentiate into endothelial-like cells or smooth muscle like cells in vitro according to the culture conditions.

SUMMARY

Circulating progenitors significantly contribute to vascular repair and lesion formation. These findings provide the basis for the development of new therapeutic strategies that involve targeting the mobilization, homing, differentiation, and proliferation of bone marrow- derived vascular progenitor cells.

Platelet function in intravascular device implant-induced intimal injury

Platelets are involved in the rapid response to intimal injury in which the underlying thrombogenic subendothelial matrix is exposed, leading to platelet adhesion, secretion, aggregation, and initiation of arterial thrombus formation. The platelet activation pathway involves a multistep process of distinct receptors, adhesive ligands, release of mediators, receptor-ligand interactions, and recruitment of more platelets to the site of injury. The balance between blood fluidity and intimal injury-induced arterial thrombosis is maintained by an intact endothelium that controls vessel tone, synthesizes inhibitors and activators of platelet function, and thereby allows the free flow of blood cell elements. An intravascular device implant causes intimal injury, which is accompanied by decreased antithrombotic potential of the endothelial cells and increased release of prothrombotic substances. A trigger for the formation of intimal injury-induced thrombus formation may be due to endothelial dysfunction and/or the loss of endothelial cell barrier between the subendothelial matrix and flowing blood, which allows initiation of platelet activation. A thorough understanding of the platelet regulatory mechanisms is necessary to develop effective antiplatelet therapy to prevent the complications of thrombosis following revascularization procedures using percutaneous coronary intervention. This review summarizes the temporal events following intravascular device implants, including endothelial cell injury, platelet activation, receptor-mediated signaling events, platelet-rich thrombus formation, and the redundant platelet pathways, all of which may be potential therapeutic targets.

Catheter-Based Treatment of Coronary Artery Disease

September 2007 marked the 30-year anniversary of the first human percutaneous coronary intervention, an index event that changed the course of modern-day cardiovascular care. Before that first procedure, adult invasive cardiology focused on diagnostic angiography as well as hemodynamic assessment of structural heart disease. Since that initial procedure, percutaneous coronary intervention has become the most frequently performed coronary revascularization procedure worldwide. Several factors have been responsible for this dramatic paradigm shift, the most prominent being identification of opportunities for technical improvement and the application of innovation and investigation in concert with colleagues, professional societies, and industry. These approaches will continue to be of paramount importance as new technologies are brought to bear on an increasingly broader group of patients with cardiovascular disease.

Intensive oral antiplatelet therapy for reduction of ischaemic events including stent thrombosis in patients with acute coronary syndromes treated with percutaneous coronary intervention and stenting in the TRITON-TIMI 38 trial: a subanalysis of a randomised trial

BACKGROUND

Intracoronary stenting can improve procedural success and reduce restenosis compared with balloon angioplasty in patients with acute coronary syndromes, but can also increase the rate of thrombotic complications including stent thrombosis. The TRITON-TIMI 38 trial has shown that prasugrel-a novel, potent thienopyridine-can reduce ischaemic events compared with standard clopidogrel therapy. We assessed the rate, outcomes, and prevention of ischaemic events in patients treated with prasugrel or clopidogrel with stents in the TRITON-TIMI 38 study.

METHODS

Patients with moderate-risk to high-risk acute coronary syndromes were included in our analysis if they had received at least one coronary stent at the time of the index procedure following randomisation in TRITON-TIMI 38, and were further subdivided by type of stent received. Patients were randomly assigned in a 1 to 1 fashion to receive a loading dose of study drug (prasugrel 60 mg or clopidogrel 300 mg) as soon as possible after randomisation, followed by daily maintenance therapy (prasugrel 10 mg or clopidogrel 75 mg). All patients were to receive aspirin therapy. Treatment was to be continued for a minimum of 6 months and a maximum of 15 months. Randomisation was not stratified by stents used or stent type. The primary endpoint was the composite of cardiovascular death, non-fatal myocardial infarction, or non-fatal stroke. Stent thrombosis was assessed using Academic Research Consortium definitions, and analysis was by intention to treat. TRITON-TIMI 38 is registered with ClinicalTrials.gov, number NCT00097591.

FINDINGS

12,844 patients received at least one coronary stent; 5743 received only drug-eluting stents, and 6461 received only bare-metal stents. Prasugrel compared with clopidogrel reduced the primary endpoint (9.7 vs 11.9%, HR 0.81, p=0.0001) in the stented cohort, in patients with only drug-eluting stents (9.0 vs 11.1%, HR 0.82, p=0.019), and in patients with only bare-metal stents (10.0 vs 12.2%, HR 0.80, p=0.003). Stent thrombosis was associated with death or myocardial infarction in 89% (186/210) of patients. Stent thrombosis was reduced with prasugrel overall (1.13 vs 2.35%, HR 0.48, p<0.0001), in patients with drug-eluting stents only (0.84 vs 2.31%, HR 0.36, p<0.0001), and in those with bare-metal stents only (1.27 vs 2.41%, HR 0.52, p=0.0009).

INTERPRETATION

Intensive antiplatelet therapy with prasugrel resulted in fewer ischaemic outcomes including stent thrombosis than with standard clopidogrel. These findings were statistically robust irrespective of stent type, and the data affirm the importance of intensive platelet inhibition in patients with intracoronary stents.

Local delivery of gene vectors from bare-metal stents by use of a biodegradable synthetic complex inhibits in-stent restenosis in rat carotid arteries

BACKGROUND

Local drug delivery from polymer-coated stents has demonstrated efficacy for preventing in-stent restenosis; however, both the inflammatory effects of polymer coatings and concerns about late outcomes of drug-eluting stent use indicate the need to investigate innovative approaches, such as combining localized gene therapy with stent angioplasty. Thus, we investigated the hypothesis that adenoviral vectors (Ad) could be delivered from the bare-metal surfaces of stents with a synthetic complex for reversible vector binding.

METHODS AND RESULTS

We synthesized the 3 components of a gene vector binding complex: (1) A polyallylamine bisphosphonate with latent thiol groups (PABT), (2) a polyethyleneimine (PEI) with pyridyldithio groups for amplification of attachment sites [PEI(PDT)], and (3) a bifunctional (amine- and thiol-reactive) cross-linker with a labile ester bond (HL). HL-modified Ad attached to PABT/PEI(PDT)-treated steel surfaces demonstrated both sustained release in vitro over 30 days and localized green fluorescent protein expression in rat arterial smooth muscle cell cultures, which were not sensitive to either inhibition by neutralizing anti-Ad antibodies or inactivation after storage at 37 degrees C. In rat carotid studies, deployment of steel stents configured with PABT/PEI(PDT)/HL-tethered adenoviral vectors demonstrated both site-specific arterial Ad(GFP) expression and adenovirus-luciferase transgene activity per optical imaging. Rat carotid stent delivery of adenovirus encoding inducible nitric oxide synthase resulted in significant inhibition of restenosis.

CONCLUSIONS

Reversible immobilization of adenovirus vectors on the bare-metal surfaces of endovascular stents via a synthetic complex represents an efficient, tunable method for sustained release of gene vectors to the vasculature.

Late stent thrombosis in patients receiving ticlopidine and aspirin after sirolimus-eluting stent implantation

BACKGROUND

There is little information about the efficacy of ticlopidine plus aspirin after sirolimus-eluting stent (SES) implantation.

METHODS AND RESULTS

The incidence of stent thrombosis was evaluated in 1,029 patients receiving ticlopidine and aspirin after SES deployment. Clinical follow-up was obtained in 98.9% (mean follow-up 17.0+/-7.9 months). Early stent thrombosis was observed in 5 patients (0.49%). There was 1 case each of late (0.1%) and very late stent thrombosis (0.1%).

CONCLUSION

Late and very late stent thrombosis in Japanese patients receiving ticlopidine and aspirin after SES deployment occurs infrequently.

The future of drug-eluting stents

This review aims to provide a glimpse into the future of drug-eluting stents (DES). Since their arrival in 2002, DES have transformed the practice of interventional cardiology by drastically reducing restenosis and the need for repeat revascularization. However, data about the potentially fatal long-term risk of stent thrombosis have spurred on research and development to improve upon the first generation of devices. The initial commercially available DES used a stainless steel platform coated with a permanent polymer to provide controlled release of the anti-restenotic drug. The platform, polymer and drug are all targets for improvement. More advanced metallic and fully biodegradable stent platforms are currently under investigation. The permanent polymer coating, a likely contributor adverse events, is being superseded by biocompatible and bioabsorbable alternatives. New drugs and drug combinations are also a research goal, as interventional cardiologists and the industry strive towards safer anti-restenotic DES.