I like the candy, I hate the wrapper: the (32)P radioactive stent

Oral Mycophenolate Mofetil Prevents In-Stent Intimal Hyperplasia Without Edge Effect

Neointimal hyperplasia is in the forefront in in-stent restenosis. Prevention of in-stent restenosis is possible by reducing and inhibiting the hyperplasia of smooth muscle cells. The authors planned this study to test the hypothesis that when administered orally, mycophenolate mofetil (MMF) could inhibit in-stent neointimal hyperplasia. The study included 14 New Zealand rabbits. The rabbits were allocated to 2 different groups: Group 1 included 7 rabbits that were given MMF, 40 mg/kg/day by oral route. Group 2 included 7 rabbits that were not given MMF after the stenting. Sampling materials were taken before and after stenting by incising the artery so as to cover a 5-mm area. The samples taken from the edge of the stent in Group 1 showed focal neointimal cell proliferation, but it was less than that from the control group. Neointimal thickness was 0.048 ±0.009 mm and neointimal area was 0.0925 ±0.019 mm2. Apparent neointimal cell proliferation and thickening of the intimal layer were observed in Group 2. Neointimal thickness at the stent edge was 0.147 ±0.051 mm and the neointimal area was 0.154 ±0.023 mm2. The differences between groups in terms of neointimal thickness and neointimal area were statistically significant (p=0.001 for thickness and p=0.001 for area). In-stent artery samples of Group 1 showed that some subjects had no neointimal cell proliferation, while others had very limited focal intimal thickening. Neointimal thickening was 0.071 ±0.003 mm and neointimal area was 0.073 ±0.003 mm2. In Group 2 apparent, and mostly focal, neointimal cell proliferation and formation of intimal layer were observed in the stent. Neointimal thickening was 0.154 ±0.069 mm and neointimal area was 0.279 ±0.059 mm2. The comparison between groups showed significant differences (p=0.011 for thickness and p=0.001 for area). It was established in the third month that endothelialization was completed in both groups. Oral MMF decreased in-stent intimal hyperplasia without edge effect. It was concluded that for the prevention of in-stent restenosis, studies should be conducted for using systemic immunosuppressive treatments in humans as well.

Biocompatibility and Biostability of Metallic Endovascular Implants: State of the Art and Perspectives

This work was partly supported by the Natural Science and Engineering Research Council (NSERC) of Canada.

More than a million metallic endovascular devices are implanted each year, but the quest for the perfect material continues. The importance of interfacial properties in the overall biocompatibility of metals and alloys has been recognized for a long time. In particular, these properties modulate the hemocompatibility of devices in contact with blood and, in turn, strongly influence implantation outcomes. In this article, the relative properties of metallic materials commonly used in endovascular applications are reviewed. Particular emphasis is given to the corrosion behavior of metallic endovascular materials and the specific surface treatments used in the production processes. Issues relative to corrosion assays will also be reviewed in terms of their relevance to in vivo applications. The potential adverse effects of degradation products with respect to endovascular applications will be described. Finally, this review addresses future perspectives of metallic devices in endovascular procedures in view of the recent promises of antiproliferative strategies that are likely to profoundly modify current procedures.

The edge vascular response following implantation of the Absorb everolimus-eluting bioresorbable vascular scaffold and the XIENCE V metallic everolimus-eluting stent. First serial follow-up assessment at six months and two years: insights from the first-in-man ABSORB Cohort B and SPIRIT II trials

AIMS

To assess serially the edge vascular response (EVR) of a bioresorbable vascular scaffold (BVS) compared to a metallic everolimus-eluting stent (EES).

METHODS AND RESULTS

Non-serial evaluations of the Absorb BVS at one year have previously demonstrated proximal edge constrictive remodelling and distal edge changes in plaque composition with increase of the percent fibro-fatty (FF) tissue component. The 5 mm proximal and distal segments adjacent to the implanted devices were investigated serially with intravascular ultrasound (IVUS), post procedure, at six months and at two years, from the ABSORB Cohort B1 (n=45) and the SPIRIT II (n=113) trials. Twenty-two proximal and twenty-four distal edge segments were available for analysis in the ABSORB Cohort B1 trial. In the SPIRIT II trial, thirty-three proximal and forty-six distal edge segments were analysed. At the 5-mm proximal edge, the vessels treated with an Absorb BVS from post procedure to two years demonstrated a lumen loss (LL) of 6.68% (-17.33; 2.08) (p=0.027) with a trend toward plaque area increase of 7.55% (-4.68; 27.11) (p=0.06). At the 5-mm distal edge no major changes were evident at either time point. At the 5-mm proximal edge the vessels treated with a XIENCE V EES from post procedure to two years did not show any signs of LL, only plaque area decrease of 6.90% (-17.86; 4.23) (p=0.035). At the distal edge no major changes were evident with regard to either lumen area or vessel remodelling at the same time point.

CONCLUSIONS

The IVUS-based serial evaluation of the EVR up to two years following implantation of a bioresorbable everolimus-eluting scaffold shows a statistically significant proximal edge LL; however, this finding did not seem to have any clinical implications in the serial assessment. The upcoming imaging follow-up of the Absorb BVS at three years is anticipated to provide further information regarding the vessel wall behaviour at the edges.

Edge Vascular Response After Resorption of the Everolimus-Eluting Bioresorbable Vascular Scaffold - A 5-Year Serial Optical Coherence Tomography Study

BACKGROUND

The edge vascular response (EVR) has been linked to important prognostic implications in patients treated with permanent metallic stents. We aimed to investigate the relationship of EVR with the geometric changes in the everolimus-eluting bioresorbable scaffold using serial optical coherence tomography (OCT) analysis.

METHODS AND RESULTS

In the first-in-man ABSORB trial, 28 patients (29 lesions) underwent serial OCT at 4 different time points (Cohort B1: post-procedure, 6, 24, and 60 months [n=13]; Cohort B2: post-procedure, 12, 36, and 60 months [n=15]) following implantation of the scaffold. In Cohort B1, there was no significant luminal change at the distal or proximal edge segment throughout the entire follow-up. In contrast, there was a significant reduction of the lumen flow area (LFA) of the scaffold between post-procedure and 6 months (-1.03±0.49 mm(2)[P<0.001]), whereas between 6 and 60 months the LFA remained stable (+0.31±1.00 mm(2)[P=0.293]). In Cohort B2, there was a significant luminal reduction of the proximal edge between post-procedure and 12 months (-0.57±0.74 mm(2)[P=0.017]), whereas the lumen area remained stable (-0.26±1.22 mm(2)[P=0.462]) between 12 and 60 months. The scaffold LFA showed a change similar to that observed in Cohort B1.

CONCLUSIONS

Our study demonstrated a reduction in the scaffold luminal area in the absence of major EVR, suggesting that the physiological continuity of the lumen contour is restored long term. (Circ J 2016; 80: 1131-1141).

Scaffold and edge vascular response following implantation of everolimus-eluting bioresorbable vascular scaffold: a 3-year serial optical coherence tomography study

OBJECTIVES

This study sought to investigate the in-scaffold vascular response (SVR) and edge vascular response (EVR) after implantation of an everolimus-eluting bioresorbable scaffold (BRS) using serial optical coherence tomography (OCT) imaging.

BACKGROUND

Although studies using intravascular ultrasound have evaluated the EVR in metal stents and BRSs, there is a lack of OCT-based SVR and EVR assessment after BRS implantation.

METHODS

In the ABSORB Cohort B (ABSORB Clinical Investigation, Cohort B) study, 23 patients (23 lesions) in Cohort B1 and 17 patients (18 lesions) in Cohort B2 underwent truly serial OCT examinations at 3 different time points (Cohort B1: post-procedure, 6 months, and 2 years; B2: post-procedure, 1 year, and 3 years) after implantation of an 18-mm scaffold. A frame-by-frame OCT analysis was performed at the 5-mm proximal, 5-mm distal edge, and 2-mm in-scaffold margins, whereas the middle 14-mm in-scaffold segment was analyzed at 1-mm intervals.

RESULTS

The in-scaffold mean luminal area significantly decreased from baseline to 6 months or 1 year (7.22 ± 1.24 mm(2) vs. 6.05 ± 1.38 mm(2) and 7.64 ± 1.19 mm(2) vs. 5.72 ± 0.89 mm(2), respectively; both p < 0.01), but remained unchanged from then onward. In Cohort B1, a significant increase in mean luminal area of the distal edge was observed (5.42 ± 1.81 mm(2) vs. 5.58 ± 1.53 mm(2); p < 0.01), whereas the mean luminal area of the proximal edge remained unchanged at 6 months. In Cohort B2, the mean luminal areas of the proximal and distal edges were significantly smaller than post-procedure measurements at 3 years. The mean luminal area loss at both edges was significantly less than the mean luminal area loss of the in-scaffold segment at both 6-month and 2-year follow-up in Cohort B1 or at 1 year and 3 years in Cohort B2.

CONCLUSIONS

This OCT-based serial EVR and SVR evaluation of the Absorb Bioresorbable Vascular Scaffold (Abbott Vascular, Santa Clara, California) showed less luminal loss at the edges than luminal loss within the scaffold. The luminal reduction of both edges is not a nosologic entity, but an EVR in continuity with the SVR, extending from the in-scaffold margin to both edges. (ABSORB Clinical Investigation, Cohort B [ABSORB B]; NCT00856856).

Eight-year clinical outcome after radioactive stent implantation: a treatment failure without irreversible long-term clinical sequelae

AIMS

To assess the long-term outcome of patients who underwent radioactive stent (RS) implantation.

METHODS AND RESULTS

The RS study population consisted of 133 consecutive patients who underwent RS implantation between November 1997 and July 2000. They were matched using the propensity score method with 266 patients who underwent bare metal stenting (BMS) in the same span. Long-term survival status and information on MACE (death, non-fatal myocardial infarction or any re-intervention) was retrospectively obtained. Eight-year cumulative survival (90.2% vs. 87.4%, p = 0.57) was similar between the RS and BMS group respectively, while 8-year cumulative MACE-free survival was significantly lower in RS patients (42.1% vs. 64.3%, p < 0.001) due to the difference in events (mainly target lesion revascularisations [TLRs]) during the first year of follow-up (cumulative 1-year MACE-free survival: 59.4% vs. 86.7%, p < 0.001); there was no difference in the MACE rate after the first year (p = 0.71). The TLR rate at six months in the RS group was 29.3%, mainly due to edge restenosis and at one year 36.2% (control group: 9.5%, p < 0.001).

CONCLUSIONS

A high incidence of MACE and re-intervention was observed during the first year following RS implantation, mainly related to TLR for edge restenosis. After the first year, the clinical outcome of RS patients was similar to the control group indicating that there are no late adverse effects related to low dose-rate intracoronary radiation therapy.

Preventing restenosis in early drug-eluting stent era: recent developments and future perspectives

Restenosis is the major limitation of the successful therapy of percutaneous coronary intervention (PCI) for patients with coronary artery disease. The problem was appreciated in the late 1970s to early 1980s. Only in recent years, anti-restenotic therapy has achieved a breakthrough with the development of drug-eluting stents. Here, we provide an overview about pathological mechanisms of restenosis after PCI. Present therapeutic approaches to overcome restenosis and recent clinical results are revisited, and some major concerns in the post-drug-eluting stent era are discussed.

Peripheral bolus-chase MR angiography: analysis of risk factors for nondiagnostic image quality of the calf vessels--a combined retrospective and prospective study

OBJECTIVE

The objective of our study was to evaluate the influence of endogenous and exogenous risk factors on the rate of nondiagnostic examinations of the calves in peripheral bolus-chase MR angiography (MRA).

SUBJECTS AND METHODS

Peripheral bolus-chase MRA runoff studies in 177 patients with peripheral arterial occlusive disease (PAOD) were retrospectively assessed with regard to the rate of nondiagnostic image quality due to substantial venous overlay in the calf arteries requiring repeated MRA examinations. Logistic regression was used to analyze the rate of nondiagnostic MRA examinations as a function of several endogenous and exogenous risk factors and of the stage of PAOD. To probe the retrospective data, 22 consecutive patients were prospectively included and underwent a standard peripheral MRA examination if the probability of a nondiagnostic examination was less than 50% based on the results of logistic regression; otherwise, a hybrid MRA examination was ordered.

RESULTS

Nondiagnostic image quality of the calf arteries was found in 53 patients (30%). The incidence increased with each stage of PAOD up to 39% for stage IV. For each increase in the stage of PAOD, the probability of nondiagnostic image quality increased by a factor of 1.5561 (p = 0.0024). With an increasing number of risk factors, a significantly (p = 0.0074) higher rate of nondiagnostic images was found.

CONCLUSION

Based on the retrospective statistical analysis of PAOD stages and risk factors, selected patients can be triaged to undergo a specific hybrid MRA technique and thus circumvent the occurrence of nondiagnostic images and the need for repeated MRA examinations.

Impact of stent deployment procedural factors on long-term effectiveness and safety of sirolimus-eluting stents (final results of the multicenter prospective STLLR trial)

Drug-eluting stent failures were associated with various clinical factors. However, the clinical impact of stent deployment technique was unknown. This study was designed to evaluate the frequency and impact of suboptimal percutaneous coronary intervention on long-term outcomes of 1,557 patients treated with sirolimus-eluting stents (SESs) in 41 US hospitals. All steps of the interventional procedure were scrutinized by an independent core laboratory to determine the occurrence of geographic miss (GM). GM included longitudinal (LGM; injured or diseased segment not covered by SES) or axial GM (balloon-artery size ratio <0.9 or >1.3) mismatches. Patients with and without GM were stratified (GM vs no-GM group). Patients, investigators, and the independent clinical event adjudication committee were blind to study group assignments. The primary end point was 1-year target-vessel revascularization (TVR) rate. Incidences and predictors of GM and safety outcomes were secondary end points. GM occurred in 943 patients (66.5%): 47.6% had LGM, 35.2% had axial GM, and 16.5% had both. One-year TVR rates were 5.1% in the GM group versus 2.5% in the no-GM group (p=0.025). TVR was 6.1% in the LGM versus 2.6% in the no-LGM subgroups (p=0.001). The association of GM with 1-year TVR was independent of clinical or anatomic factors (hazard ratio 2.0, 95% confidence interval 1.0 to 4.02, p=0.05). There was a 3-fold increase in myocardial infarction rates associated with GM (2.4% vs 0.8%; p=0.04). In conclusion, GM occurred frequently during SES implantation and was associated with increased risk of TVR and myocardial infarction at 1 year. These results emphasized the need for improvement in contemporary percutaneous coronary intervention practices and technologies.

Adenosine A1 receptors in neointimal hyperplasia and in-stent stenosis in Ossabaw miniature swine

BACKGROUND

Stent-induced neointimal hyperplasia is a major cause of morbidity following stent deployment in patients with coronary artery disease. Importantly, however, mechanisms underlying stent-induced neointimal hyperplasia are unclear. This pathological response to stent placement is more aggressive when stents are over-expanded, suggesting that vascular injury may play a role. In this study we tested the hypothesis that adenosine A1 receptor upregulation is associated with neointimal hyperplasia within coronary artery stents.

METHODS

Adult male Ossabaw swine were used as our experimental model. Neointima formation and gene expression were studied 4 weeks after coronary stents were placed at 1.0x or 1.3x luminal diameter.

RESULTS

Neointima formation was observed in 1.0x stents and more than doubled in 1.3x stents, thus verifying the response to overexpansion injury. A1 receptor mRNA was increased four-fold and seven-fold in stents at 1.0x and 1.3x luminal diameter, suggesting that increased A1 receptor activity might contribute to stent-induced neointimal hyperplasia. Coronary artery organ culture model of arterial injury demonstrated A1 receptor activation increased DNA synthesis three-fold, an effect abolished by A1 receptor antagonism.

CONCLUSION

Our data indicate that A1 receptor expression is increased within stents and that activation of A1 receptors increases smooth muscle cell proliferation. We suggest that inhibition of A1 receptor signaling may be a promising therapeutic target for management of in-stent stenosis.

Treatment of severe sepsis: where next? Current and future treatment approaches after the introduction of drotrecogin alfa

Severely septic patients continue to experience excessive morbidity and mortality despite recent advances in critical care. Although significant resources have been invested in new treatments, almost all have failed to improve outcomes. An improved understanding of sepsis pathophysiology, including the complex interactions between inflammatory, coagulation, and fibrinolytic systems, has accelerated the development of novel treatments. Recombinant human activated protein C (rhAPC), or drotrecogin alfa (activated) (DAA), is currently the only US Food and Drug Administration (FDA)-approved medicine for the treatment of severe sepsis, and only in patients with a high risk of death. This review will discuss the treatment of severe sepsis, focusing on recent discoveries and unresolved questions about DAA's optimal use. Increasing pharmacological experience has generated enthusiasm for investigating medicines already approved for other indications as treatments for severe sepsis. Replacement doses of hydrocortisone and vasopressin may reduce mortality and improve hypotension, respectively, in a subgroup of patients with catecholamine-refractory septic shock. In addition to discussing these new indications, this review will detail the provocative preliminary data from four promising treatments, including two novel modalities: antagonizing high mobility group box protein and inhibiting tissue factor (TF). Observational data from the uncontrolled administration of heparin or statins in septic patients will also be reviewed.

Low-energy gamma-emitting stents inhibit intimal hyperplasia with minimal "edge effects" in a pig coronary artery model

PURPOSE

The objective of this study was to determine the effects of different doses of gamma-emitting radioactive stents on intimal hyperplasia in a porcine coronary stent model at 28 days.

METHODS

Sixty-four bare stents and those coated with palladium-103 [activities of 0 (control), 0.5, 1.0, 2.0, and 4.0 mCi] were implanted in the coronary arteries of 32 pigs. Stented segments were evaluated by histomorphometry at 28 days.

RESULTS

There was significantly more intima in the 0.5- and 1-mCi stents than in controls (4.27+/-0.52 and 4.71+/-1.13 vs. 1.71+/-0.61 mm(2); P<.0001). Neointimal formation in 2-mCi stents was similar to that in controls, while that in 4-mCi stents was reduced compared to that in controls (2.34+/-1.61 and 0.82+/-0.25 vs. 1.71+/-0.61 mm(2); P=NS and P<.05, respectively). Stent margin neointimal response was representative of that within the stent body, with nonsignficant modest increases in intimal area at adjacent nonstented segments in radioactive stent groups. There was a dose-dependent increase in inflammation scores. Radioactive stents had lower intimal smooth muscle and higher fibrin scores. There was an increase in adventitial fibrosis in 1- and 2-mCi stents versus controls (1.26+/-0.99, and 2.25+/-1.27 vs. 0.21+/-0.31; P<.001).

CONCLUSION

Dose-response inhibition of in-stent hyperplasia with minimal "edge effects" occurs with low-energy gamma-emitting stents. An increased inflammatory response at higher doses in palladium-103 stents indicates that later follow-up studies are necessary.

Late vascular response at the edges of sirolimus analogous-eluting stents in diabetic patients: An intravascular ultrasound study

INTRODUCTION

Vascular response at edges of drug-eluting stents is still not well established, particularly in diabetic patients who are prone to aggressive atherosclerosis progression. Recently, Biolimus and Zotarolimus have demonstrated potent antiproliferative effects.

OBJECTIVE

To compare the vascular responses at edges of sirolimus analogous-eluting stents in patients with and without diabetes, using intravascular ultrasound (IVUS).

METHODS

306 edges were analyzed in 153 patients treated with drug-eluting stents and divided in: diabetics (122 edges) and nondiabetics (166 edges). IVUS was performed postintervention and at 6-month follow-up and included 5 mm distal and proximal to the stented segment. Vessel, lumen, and plaque volumes were calculated. Volume variation (follow-up minus basal) was also calculated. Edge restenosis was defined as obstruction >50%.

RESULTS

Baseline characteristics were similar between groups. In both groups the entire lesion length was covered (stent length/lesion length ratio was 1.5 for both groups). There were no differences in edge volumes and restenosis rate between the groups. Among diabetics, there was no significant volume variation. However, in nondiabetic patients there was significant increase in vessel volume in proximal (from 67.1 +/- 22 mm(3) to 72.2 +/- 25 mm(3): P = 0.02) and distal (from 54.4 +/- 22 mm(3) to 59.8 +/- 22 mm(3): P = 0.001) edges.

CONCLUSION

Nondiabetic patients showed a significant positive vascular remodeling in proximal and distal edges of sirolimus analogous-eluting stent. This vascular mechanism was not observed in diabetic patients. Although different vascular responses were observed, restenosis rates were equivalent between the 2 groups at 6-month follow-up.

Prevention of coronary restenosis with radiation therapy: a review

The problem of restenosis after percutaneous transluminal coronary angioplasty remains the major limiting factor of the procedure. Over the last 10 years, investigators have been studying the use of radiation therapy for preventing restenosis after angioplasty or stent placement. Since radiotherapy has been proven in other cases to be effective in disrupting the cell cycle regulatory proteins and thereby slowing or stopping growth, it was decided to apply the same principle to neointimal hyperplasia. To review the data that have emerged regarding vascular radiation with an emphasis on irradiated stents, 65 articles were reviewed and both preclinical and clinical experiments were included. Overall, studies with gamma and beta radiation show promising results. Endovascular gamma radiation has been shown effective in randomized trials, even at 3-year follow-up. Beta radiation is preferred because of greater safety and localization, and because it has also shown encouraging results in initial clinical trials, as well as in larger randomized studies. Consequently, the Federal Drug Administration has approved the use of both. In both types of endovascular brachytherapy, it seems the greater the dose, the better the initial response. Safety concerns include an increased incidence of late thrombosis and greater restenosis at margins. With irradiated stents, however, the situation is not as clear. At times, animal models have presented confusing results. These have ranged from significant suppression of hyperplasia to outright adverse effects of radiation on the vessel wall. While some clinical trials have been encouraging, others have not. Follow-up of up to 1 year has been disappointing so far. Many issues, such as the "candy wrapper" effect and rebound hyperplasia, must be dealt with before this becomes a viable form of therapy. It has become clear that radiation therapy in this setting, while having potentially great benefits, can cause deleterious effects as well. However, the mixed bag of positive and negative results seen so far, and the attractiveness of stents or percutaneous transluminal coronary angioplasty being "restenosis-proofed," eventually is cause for cautious optimism.

Drug-eluting stents for infrainguinal occlusive disease: progress and challenges

High restenosis rate is still the major limitation of peripheral arterial interventions. Within the last years, drug-eluting stents have gained wide acceptance in the coronary arteries, however, these devices are not currently available for arteries outside the coronary vasculature. This article summarizes the special role of the superficial femoral artery in restenosis, with efforts being made to reduce the restenosis rate in this artery, focusing on stents and drug-eluting stents.

Prediction of lifetime risk for cardiovascular disease by risk factor burden at 50 years of age

BACKGROUND

Lifetime risk for atherosclerotic cardiovascular disease (CVD) has not previously been estimated, and the effect of risk factor burden on lifetime risk is unknown.

METHODS AND RESULTS

We included all Framingham Heart Study participants who were free of CVD (myocardial infarction, coronary insufficiency, angina, stroke, claudication) at 50 years of age. Lifetime risks to 95 years of age were estimated for men and women, with death free of CVD as a competing event. We followed up 3564 men and 4362 women for 111,777 person-years; 1757 had CVD events and 1641 died free of CVD. At 50 years of age, lifetime risks were 51.7% (95% CI, 49.3 to 54.2) for men and 39.2% (95% CI, 37.0 to 41.4) for women, with median survivals of 30 and 36 years, respectively. With more adverse levels of single risk factors, lifetime risks increased and median survivals decreased. Compared with participants with > or =2 major risk factors, those with optimal levels had substantially lower lifetime risks (5.2% versus 68.9% in men, 8.2% versus 50.2% in women) and markedly longer median survivals (>39 versus 28 years in men, >39 versus 31 years in women).

CONCLUSIONS

The absence of established risk factors at 50 years of age is associated with very low lifetime risk for CVD and markedly longer survival. These results should promote efforts aimed at preventing development of risk factors in young individuals. Given the high lifetime risks and lower survival in those with intermediate or high risk factor burden at 50 years of age, these data may be useful in communicating risks and supporting intensive preventive therapy.

Gadolinium neutron capture brachytherapy (GdNCB), a new treatment method for intravascular brachytherapy

Restenosis is a major problem after balloon angioplasty and stent implantation. The aim of this study is to introduce gadolinium neutron capture brachytherapy (GdNCB) as a suitable modality for treatment of stenosis. The utility of GdNCB in intravascular brachytherapy (IVBT) of stent stenosis is investigated by using the GEANT4 and MCNP4B Monte Carlo radiation transport codes. To study capture rate, Kerma, absorbed dose and absorbed dose rate around a Gd-containing stent activated with neutrons, a 30 mm long, 5 mm diameter gadolinium foil is chosen. The input data is a neutron spectrum used for clinical neutron capture therapy in Studsvik, Sweden. Thermal neutron capture in gadolinium yields a spectrum of high-energy gamma photons, which due to the build-up effect gives an almost flat dose delivery pattern to the first 4 mm around the stent. The absorbed dose rate is 1.33 Gy/min, 0.25 mm from the stent surface while the dose to normal tissue is in order of 0.22 Gy/min, i.e., a factor of 6 lower. To spare normal tissue further fractionation of the dose is also possible. The capture rate is relatively high at both ends of the foil. The dose distribution from gamma and charge particle radiation at the edges and inside the stent contributes to a nonuniform dose distribution. This will lead to higher doses to the surrounding tissue and may prevent stent edge and in-stent restenosis. The position of the stent can be verified and corrected by the treatment plan prior to activation. Activation of the stent by an external neutron field can be performed days after catherization when the target cells start to proliferate and can be expected to be more radiation sensitive. Another advantage of the nonradioactive gadolinium stent is the possibility to avoid radiation hazard to personnel.

Pharmacological treatment for prevention of restenosis

Coronary artery disease (CAD) is the leading cause of mortality and morbidity among adults in the Western world. Coronary artery bypass grafting and percutaneous coronary interventions (PCI) have gained widespread acceptance for the treatment of symptomatic CAD. There has been an explosive growth worldwide in the utilisation of PCI, such as balloon angioplasty and stenting, which now accounts for over 50% of coronary revascularisation. Despite the popularity of PCI, the problem of recurrent narrowing of the dilated artery (restenosis) continues to vex investigators. In recent years, significant advances have occurred in the understanding of restenosis. Two processes seem to contribute to restenosis: remodelling (vessel size changes) and intimal hyperplasia (vascular smooth muscle cell [VSMC] proliferation and extracellular matrix [ECM] deposition). Despite considerable efforts, pharmacological approaches to decrease restenosis have been largely unsuccessful and the only currently applied modality to reduce the restenosis rate is stenting. However, stenting only prevents remodelling and does not inhibit intimal hyperplasia. Several potential targets for inhibiting restenosis are currently under investigation including platelet activation, the coagulation cascade, VSMC proliferation and migration, and ECM synthesis. In addition, new approaches for local drug therapy, such as drug eluting stents, are currently being evaluated in preclinical and clinical studies. In this article, we critically review the current status of drugs that are being evaluated for restenosis at various stages of development (in vitro, preclinical animal models and human trials).

Radionuclides-hyaluronan-conjugate thromboresistant coatings to prevent in-stent restenosis

Catheter-based brachytherapy is one of the most effective modalities to inhibit hyperplasia following revascularization procedures. Radioactive stents have failed, however, to prevent clinical hyperplasia due to excessive late lumen loss on the edge of the devices. Numerous strategies have been proposed to circumvent the drawbacks of irradiation therapies, such as the use of more appropriate radionuclides or the "hot-end" stents approach. This paper describes versatile radioactive devices obtained by coating plasma functionalized surfaces-stents or catheters-with a hyaluronan (HA)-diethylenetriamine pentaacetic acid (DTPA) conjugate (HA-DTPA) complexed with a gamma or beta radionuclide. Yttrium and indium were used as radionuclide models, due to their suitability for endovascular radiotherapy. X-ray photoelectron microscopy and time-of-flight secondary ions mass spectrometry analyses confirmed the successful immobilization of the HA-DTPA conjugate on both the metallic (NiTi) and polymeric (Teflon) plasma functionalized surfaces. HA-DTPA-coated surfaces were significantly more hydrophilic than bare surfaces (39.5 degrees vs. 67 degrees on NiTi substrate and 29 degrees vs. 128 degrees on Teflon substrate). Therapeutic doses of yttrium and indium were easily loaded onto the surfaces and remained stable over 2 weeks with a radionuclide loss of about 6%. The HA-DTPA-coated Teflon surfaces presented significantly less fibrinogen adsorption than uncoated materials in an in vitro flow model. This approach, which combines the hemocompatibility of HA-coated surfaces and the anti-proliferative effects of an appropriate radiotherapy, constitutes a promising methodology to alleviate the restenosis induced by existing devices.

Irradiation of mechanically-injured human arterial endothelial cells leads to increased gene expression and secretion of inflammatory and growth promoting cytokines

Radiation therapy is applied to inhibit neointima formation after percutaneous transluminal coronary angioplasty (PTCA). In this study, we evaluated the effect of irradiation on re-endothelialisation of circular denuded tracks made in post-confluent cultures of arterial endothelial cells (ECs) and on cellular factors involved in this process. Image analysis and time-lapse microcinematography revealed cell migration into denuded areas starting 4h after injury. Fifty percent coverage was achieved at 14.8 +/- 2.0 h. Using competitive PCR and flow cytometry techniques, no significant changes in mRNA expression of interleukin-1beta (IL-1beta), interleukin-8 (IL-8), basic fibroblast growth factor (bFGF or FGF-2), transforming growth factor-beta1 (TGF-beta1), platelet-derived growth factor A (PDGF-A), platelet-derived growth factor B (PDGF-B) and tissue factor (TF), and surface molecule expression of anti-intercellular adhesion molecule-1 (ICAM-1), anti-vascular cell adhesion molecule-1 (VCAM-1), anti-platelet/endothelial cell adhesion molecule-1 (PECAM-1), MHC-1, TF and Fas were observed. However, injury did significantly (P < 0.05) elevate the release of IL-8 and FGF-2 protein in the cell culture supernatant, as assessed by ELISA. Radiation (15Gy) given immediately after injury did not affect the kinetics of re-endothelialisation up to 48 h, in spite of the fact that no cell divisions were observed. Thereafter cell density decreased and cultures deteriorated. Compared to cultures exposed to injury alone, radiation induced significant (P < 0.05) increases in mRNA levels of IL-8 (1.35 +/- 0.10-fold increase at 4h), FGF-2 (1.62 +/- 0.10-fold at 4h; 1.76 +/- 0.33-fold at 24h) and IL-1beta (2.76 +/- 0.40-fold at 24h), whereas mRNA levels of TGF-beta1, PDGF-A and PDGF-B increased about 1.2-fold. IL-8 and FGF-2 protein concentrations in the media were higher than those observed in non-irradiated injured cell cultures; however, this difference was not significant. Radiation induced a 2.3 +/- 0.3-fold increase (P < 0.05) in Fas surface expression only. In conclusion, irradiation of mechanically-injured human EC leads to increased gene expression and protein secretion of inflammatory and growth promoting cytokines.

Reoxygenation of hypoxic coronary smooth muscle cells amplifies growth-retarding effects of ionizing irradiation

BACKGROUND

Hypoxic human coronary smooth muscle cells (HCSMCs) are possible targets for brachytherapy to prevent restenosis after percutaneous transluminal coronary angiography. It is unclear whether growth kinetics and gene expression of these cells undergoing gamma-irradiation are changed by reoxygenation.

METHODS AND RESULTS

Hypoxic (H) and hypoxia-reoxygenated (H-R) HCSMCs were irradiated with gamma-radiation at single doses of 4, 8, and 16 Gy using a 60Co-source. Vascular endothelial growth factor gene expression of HCSMCs was dramatically suppressed in H-R versus H cells independent of the radiation dose (15+/-7% versus 2183+/-2023%, P<0.01, H-R versus H cells). An oxygen enhancement ratio of 1.8 was calculated after irradiation from the retarded growth of H-R versus hypoxic HCSMCs. Production of reactive oxygen species by HCSMCs after irradiation increased by 15+/-2% in H-R cells versus 7+/-1% in H cells (P<0.05).

CONCLUSIONS

Reoxygenation of hypoxic HCSMCs markedly amplifies growth-retarding effects of ionizing irradiation. On the basis of these findings, oxygenating radiosensitizers should be analyzed with regard to suitability for coronary brachytherapy to prevent restenosis.

Intravascular ultrasound study of the effect of beta-emitting ((55)Co) stents on vascular remodeling and intimal proliferation

The aim of this study was to evaluate vessel remodeling after implantation of high-activity (mean, 41.1 +/- 1.2 microCi) beta-emitting ((55)Co) stents. Proton bombarding in cyclotron has brought the radioactivity. Intravascular ultrasound (IVUS) investigation has been completed in 10 patients. The angiographies performed at 6 months revealed restenosis > 50% in five cases (50%). IVUS analysis demonstrated an absence of remodeling behind the stent, with no changes in total vessel volume (TVV; 353.6 +/- 126.3 and 343.9 +/- 90.6 mm(3)) or plaque + media volume (PMV; 171.7 +/- 57.4 and 166.8 +/- 42.6 mm(3)). On the other hand, lumen volume (LV) within the stent decreased significantly from 181.9 +/- 80.2 to 154.6 +/- 45.2 mm(3) (P < 0.02). This was due to presence of neointimal hyperplasia (NIH) at both extremities of implanted stents. No chronic recoil of the implanted stents was found. The analysis of edges (5 mm distally and proximally to the last stent struts) showed no significant changes in TVV (187.3 +/- 62.60 and 176.9 +/- 53.5 mm(3)), but PMV increase significantly from 61.9 +/- 31.2 to 82.2 +/- 43.4 mm(3) (P < 0.04) and LV decreased from 125.2 +/- 40.7 to 94.7 +/- 22.0 mm(3) (P < 0.02). In conclusion, single (55)Co radioactive beta-emitting stents with high initial activity are effective in reducing neointimal hyperplasia only within the stent body, as measured by IVUS, and they do not solve the problem of restenosis at the stent extremities as well as at the stent edges. Edge restenosis in this high radioactive stents was mainly (from 66%) due to neointimal proliferation.

Intracoronary brachytherapy for the prevention of restenosis after percutaneous coronary revascularization

PURPOSE

The purpose of this article is to review the current literature pertaining to intracoronary brachytherapy for the prevention of restenosis after percutaneous coronary revascularization (PCR).

METHODS

English-language articles were identified through a MEDLINE search (January 1984 to January 2003) using the keywords brachytherapy, radioactive stents, and coronary arteries. In addition, pertinent reference citations from relevant articles were reviewed.

RESULTS

Restenosis after PCR is a complex process, thought to be due to a combination of vessel wall remodeling and neointimal proliferation. To date, catheter-based delivery of intracoronary brachytherapy has been found to prevent vessel wall remodeling and causes a reduction in the proliferation of the neointima. Neointimal proliferation, as measured by mean neointimal area, was reduced in all animal studies (range 26%-91%). In contrast, animal studies examining radioactive stents demonstrated an increase in neointimal proliferation, suggesting that they may not be helpful at preventing post-PCR restenosis. All human studies using catheter-based intracoronary brachytherapy for in-stent restenosis have employed either beta (beta) or gamma (gamma) radiation sources with variable doses of radiation (range 7-56 Grays [Gy]). Restenosis occurred in 12% to 40% of patients in nonrandomized studies, and clinical events occurred in 13% to 50% of patients. To date, there have been 7 published randomized trials in humans comparing catheter-based intracoronary brachytherapy to placebo, with a total of 1047 patients. The dose of radiation in the trials ranged from 14 Gy to 30 Gy. During follow-up, 8% to 33% of patients who received brachytherapy had restenosis versus 39% to 64% of patients receiving placebo. Clinical events occurred in 19% to 50% among patients who received brachytherapy versus 29% to 79% among patients receiving placebo. The majority of human studies examining radioactive stents do not demonstrate a reduction in restenosis in patients post-PCR. There are no randomized trials examining radioactive stents in humans.

CONCLUSION

Nonrandomized studies of radioactive stents suggest they are not effective at preventing in-stent restenosis. In contrast, data from animal and human studies suggest that catheter-based intracoronary brachytherapy can prevent in-stent restenosis and reduce clinical events post-PCR.

Vascular Responses at Proximal and Distal Edges of Paclitaxel-Eluting Stents

Background— On the basis of brachytherapy experience, edge stenosis has been raised as a potential limitation for drug-eluting stents. We used serial intravascular ultrasound (IVUS) to prospectively analyze vessel responses in adjacent reference segments after implantation of polymer-controlled paclitaxel-eluting stents.

Methods and Results— TAXUS II was a randomized, double-blind trial with 2 consecutive patient cohorts that compared slow-release (SR) and moderate-release (MR) paclitaxel-eluting stents with control bare metal stents (BMS). By protocol, all patients had postprocedure and 6-month follow-up IVUS. Quantitative IVUS analysis was performed by an independent core laboratory, blinded to treatment allocation, in 5-mm vessel segments immediately proximal and distal to the stent. Serial IVUS was available for 106 SR, 107 MR, and 214 BMS patients. For all 3 groups, a significant decrease in proximal-edge lumen area was observed at 6 months. The decrease was comparable (by ANOVA, P =0.194) for patients in the SR (−0.54±2.1 mm 2 ) and MR (−0.88±1.9 mm 2 ) groups compared with the BMS (−1.02±1.9 mm 2 ) group. For the distal edge, a significant decrease in lumen area was only observed with BMS (−0.91±2.0 mm 2 , P <0.0001); this decrease was significantly attenuated with SR (0.08±2.0 mm 2 ) and MR (−0.19±1.7 mm 2 ) stents ( P <0.0001 by ANOVA). Negative vessel remodeling was observed at the proximal (−0.48±2.2 mm 2 , P =0.011) but not the distal edges of BMS and at neither edge of SR or MR stents.

Conclusions— The marked reduction in in-stent restenosis with SR or MR stents is not associated with increased edge stenosis at 6-month follow-up IVUS. In fact, compared with BMS, there is instead a significant reduction in late lumen loss at the distal edge with TAXUS stents.

Inhibition of Neointimal Proliferation with188Re-labeled Self-Expanding Nitinol Stent in a Sheep Model

PURPOSE

To evaluate a self-expanding rhenium 188 (188Re) radiochemically labeled radioactive stent in sheep.

MATERIALS AND METHODS

A self-expanding nitinol stent (30 mm in length, 8 mm in diameter) coated with a functionalized polymer layer was radiolabeled with 188Re. Fifty prostheses, 25 of which were radioactive (mean radioactivity, 20 MBq +/- 3.8 [SD]) and 25 of which were nonradioactive, were implanted into the external iliac arteries of 25 sheep. Stent patency was assessed with angiography. Neointimal formation was assessed with intravascular ultrasonography and histologic examination 1 month (in all sheep) and 3 months (in 12 sheep) after implantation. The results were analyzed by using repeated-measures analysis of variance with two repeated factors and paired t tests for comparison at each measuring point.

RESULTS

All stents were placed successfully. Data in one animal had to be excluded from the study. After 3 months, a mean neointimal area reduction of 70 mm2 +/- 55 (SD) was observed inside the radioactive stents, and a mean lumen reduction of 126 mm2 +/- 39 was observed inside the nonradioactive control stents (P =.022). An edge effect was observed in the radioactive stents in that they showed an amount of neointimal formation at the edges that was similar to that seen in control stents. This neointimal formation accounted for the maximum lumen loss in the vascular segment with the stent.

CONCLUSION

As compared with a nonradioactive stent, a beta particle-emitting stent, through endovascular irradiation, significantly inhibits neointimal formation inside the stent but not at the stent edges.

Beta emitter systems and results from clinical trials

Vascular brachytherapy has been established as the standard of care for the treatment of in-stent restenosis (ISR). Both beta and gamma emitters are currently in use for the prevention of ISR recurrence. The use of beta sources for vascular application is attractive from both the radiation exposure and safety points of view, and a wide variety of beta sources are available for this application. This review is intended to summarize the clinical trials utilizing beta emitter systems for the treatment of ISR and de novo lesions and their subsequent results.

[Brachytherapy for coronary restenosis: state of art in 2003]

Based on therapeutic approach for benign diseases, vascular brachytherapy decreases smooth vascular muscle cells proliferation and multiplication which lead to the formation of the neo-intima. The radioactive positive action affects arterial recoil due to post angioplasty vessel injury. Randomised studies has shown good angiographic results up to 6 months of follow-up, with 50% in-stent restenosis rate decrease and on the analysed segment as well. Decrease on Mace and TLR show statistically significance. Results don't correlate with emitter and bêta emitters had been introduced in France recently. Vascular brachytherapy is actually indicated for in-stent restenosis, there is no evidence to perform this treatment for de novo lesion. Geographic miss, source centering, late thrombosis and pullback procedure may interfere with treatment quality. IVUS allows best target volume determination to a higher quality level. Internationals guidelines such as Eva-Gec-Estro recommendations could increase treatment safety and enable development of an optimal technique.

Pathophysiological effects of radiation on atherosclerosis development and progression, and the incidence of cardiovascular complications

Radiation therapy while important in the management of several diseases, is implicated in the causation of atherosclerosis and other cardiovascular complications. Cancer and atherosclerosis go through the same stages of initiation, promotion, and complication, beginning with a mutation in a single cell. Clinical observations before the 1960s lead to the belief that the heart is relatively resistant to the doses of radiation used in radiotherapy. Subsequently, it was discovered that the heart is sensitive to radiation and many cardiac structures may be damaged by radiation exposure. A significantly higher risk of death due to ischemic heart disease has been reported for patients treated with radiation for Hodgkin's disease and breast cancer. Certain cytokines and growth factors, such as TGF-beta1 and IL-1 beta, may stimulate radiation-induced endothelial proliferation, fibroblast proliferation, collagen deposition, and fibrosis leading to advanced lesions of atherosclerosis. The treatment for radiation-induced ischemic heart disease includes conventional pharmacological therapy, balloon angioplasty, and bypass surgery. Endovascular irradiation has been shown to be effective in reducing restenosis-like response to balloon-catheter injury in animal models. Caution must be exercised when radiation therapy is combined with doxorubicin because there appears to be a synergistic toxic effect on the myocardium. Damage to endothelial cells is a central event in the pathogenesis of damage to the coronary arteries. Certain growth factors that interfere with the apoptotic pathway may provide new therapeutic strategies for reducing the risk of radiation-induced damage to the heart. Exposure to low level occupational or environmental radiation appears to pose no undue risk of atherosclerosis development or cardiovascular mortality. But, other radiation-induced processes such as the bystander effects, abscopal effects, hormesis, and individual variations in radiosensitivity may be important in certain circumstances.

Late effects of low-energy gamma-emitting stents in a rabbit iliac artery model 1 1This study is dedicated to the memory of Robyn Strauss Albert

PURPOSE

To determine the long-term dose response of novel low-dose gamma-emitting stents in a rabbit iliac artery model.

METHODS AND MATERIALS

Control stents (n=24) and 103Pd stents 1.0 to 4.0 mCi (n=36) were implanted in the iliac arteries of 30 New Zealand rabbits. Stents were evaluated by intravascular ultrasound (immediately post procedure and before killing) and by histomorphometry.

RESULTS

At 26 weeks, 28 rabbits were killed, with no evidence of stent thrombosis. In the body of the stent there was a dose-response relationship with 50% inhibition of intimal hyperplasia at the highest activity compared to control stents (p=0.07) and a significant increase in intimal hyperplasia at the lowest activity (p < 0.01). At the stent edges, there was a significant reduction of lumen area at all activity levels compared to control stents, which was most prominent at the proximal stent edge. Higher-activity stents demonstrated incomplete endothelialization and immature neointimal formation.

CONCLUSIONS

Continuous low-dose-rate irradiation by gamma-emitting 103Pd stents is feasible with reduction of in-stent hyperplasia in a dose-related manner. However, significant narrowing at the stent edges, increased in-stent hyperplasia at lower activities, and incomplete vascular healing with persistence of immature neointima at higher activities are significant limitations.

Coronary artery brachytherapy

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

Monte Carlo dosimetry of a tandem positioned beta-emitting intravascular brachytherapy source train

Prevention of restenosis following interventional coronary procedures with catheter based beta-emitting sources is currently under clinical trial investigations. Systems utilizing fixed length source trains limit the clinician's ability to increase the radiation source length as required. A technique known as "pull back" is used when the segment of artery requiring radiation is longer than the available fixed length source train. In this instance, tandem positioning of the fixed length source is used to treat the longer length of artery. The aim of this study was to examine the dosimetry of the junction region associated with pull back treatments using a commercially available 90Sr/Y catheter based intravascular brachytherapy source train. Dose profiles were calculated, using the Monte Carlo code MCNP4B, at radial distances of 1.5, 2.0, and 2.5 mm for pull back techniques using 2.5 mm overlapping, abutting, and 2.5 mm spaced source trains. Results at the protocol prescription radius of 2 mm showed a junction dose elevated 61% above prescription for 2.5 mm overlapping source trains. For 2.5 mm spaced trains, this figure falls to 64% below prescription dose. In contrast, abutted source trains exhibited only a 1% depression below prescription dose in the junction region. The reference point dose rate per unit activity of this source was found to be consistent with previous studies.

Intravascular brachytherapy of the coronary arteries

This is a review of the relatively recently developed field of intravascular brachytherapy of coronary arteries. It presents a brief overview of the discipline of coronary angioplasty describing the problem of restenosis and discusses the potential for ionizing radiation to overcome this problem. It examines the various methods that have been used to irradiate the coronary arteries comparing their advantages and disadvantages. Special consideration is given to seeds and wires in the artery, radioactive liquids in the angioplasty balloon and radioactive stents. Passing reference is made to a number of other methods that have also been proposed, but which are not commonly used to irradiate the coronary arteries at present. The dosimetry of each of the major techniques is discussed and the data from different laboratories compared. Specific consideration is given to the need for centring of the radioactive source and the factors affecting the selection of a dose prescription. A brief review of recent clinical trials is followed by an examination of possible future directions in this field including the use of intravascular ultrasound to improve dosimetry, the use of gas-filled balloons to enhance the penetration of beta-emitting sources and the use of gamma-emitting stents to overcome the problems associated with edge restenosis.

New tools for coronary risk assessment: what are their advantages and limitations?

The concept of risk assessment and reduction, introduced initially by the Framingham Heart Study and refined in other models, forms the cornerstone of preventive cardiology. Risk factor assessment determines the therapeutic strategy, because the intensity of preventive intervention is tailored to the patient's risk of coronary heart disease. The conventional risk factors for coronary heart disease include elevated serum total cholesterol and LDL cholesterol, low HDL cholesterol, elevated blood pressure, cigarette smoking, diabetes, vascular disease, menopausal status (women only), and age. Aggressive risk factor reduction, formerly used exclusively in secondary prevention, may be pivotal to optimal patient management in high-risk primary prevention. A number of noninvasive imaging modalities have the potential to measure and to monitor atherosclerosis in asymptomatic individuals and include exercise ECG testing, electron beam computed tomography, magnetic resonance coronary angiography, positron emission tomography, ankle-brachial index, and B-mode ultrasound. Novel serum markers, including C-reactive protein and homocysteine, have the ability to gauge risk in the individual patient. Systemic therapy for risk reduction in primary prevention may be preferable to local therapy (eg, angioplasty and bypass) and may more effectively prevent acute coronary events than these more invasive approaches.

Impact of geographic miss on adjacent coronary artery segments in diffuse in-stent restenosis with beta-radiation therapy: angiographic and intravascular ultrasound analysis

BACKGROUND

The impacts of geographic miss on edge restenosis have not been sufficiently evaluated.

METHODS

Beta-radiation therapy with rhenium 188-filled balloon after rotational atherectomy for diffuse in-stent restenosis was performed in 50 patients. We evaluated the impacts of geographic miss on adjacent coronary artery segments beyond the stent by angiographic (QCA) and intravascular ultrasound (IVUS) analysis in 50 irradiated lesions and 100 edges. Serial IVUS and QCA comparisons between postradiation and 6 months' follow-up were available in 44 and 47 of 50 patients, respectively. QCA measurements of minimal lumen diameter (MLD) and IVUS analysis were performed in the reference and radiation segments. Edges that were touched by the angioplasty balloon but were not adequately covered by radiation constituted the geographic miss edges.

RESULTS

Geographic miss was observed in 55.6% and 52.6% in QCA and IVUS analysis, respectively. Edge restenosis after radiation therapy in 3 patients was associated with geographic miss. In contrast to uninjured edges (postradiation 2.9 +/- 0.6 mm to follow-up 2.8 +/- 0.6 mm, P =.292), MLD in the radiation segment by QCA analysis significantly decreased from 2.7 +/- 0.4 mm to 2.4 +/- 0.6 mm in geographic miss edges (P =.002). IVUS analysis showed that significant positive remodeling in the radiation segment occurred in uninjured edges (vessel area from 15.4 +/- 4.4 mm2 to 15.8 +/- 4.4 mm2, P =.001) but not in geographic miss edges (vessel area from 12.8 +/- 3.6 mm2 to 13.0 +/- 3.6 mm2, P =.119).

CONCLUSION

The geographic miss might be one of the predictors, which resulted in decreased MLD at follow-up in beta-radiation therapy. Sufficient lesion coverage with radiation might be associated with positive remodeling in the radiation segment.

Ubiquitin-proteasome pathway as a new target for the prevention of restenosis

BACKGROUND

The ubiquitin-proteasome system is the major intracellular protein degradation pathway in eucaryotic cells. It regulates central mediators of proliferation, inflammation, and apoptosis that are fundamental pathomechanisms in the development of vascular restenosis.

METHODS AND RESULTS

Effects of proteasome inhibition on neointima formation were studied in a balloon injury model in the rat carotid artery. Local application of the proteasome inhibitor MG132 (1 mmol/L) resulted in significant inhibition of intimal hyperplasia, that is, by 74% (P=0.008). This effect was accompanied by decreased proliferation, reduced infiltration of macrophages, and prolonged apoptosis, as determined by immunohistochemical and TUNEL analyses. Functional effects of proteasome inhibition on proliferation, activation of nuclear factor kappa B, and apoptosis were further characterized in rat primary vascular smooth muscle cells. MG132 dose-dependently inhibited vascular smooth muscle cell proliferation with 50% inhibition at 10 micromol/L. TNFalpha-induced degradation of IkappaBalpha and beta was blocked, and activation of nuclear factor kappa B was suppressed in a concentration-dependent manner in bandshift assays. Moreover, proteasome inhibition (1 to 50 micromol/L MG132) induced apoptotic cell death up to 80%, as confirmed by DNA/Histone-ELISA and TUNEL-FACS analysis. Specificity of proteasome inhibition was shown by accumulation of multiubiquitinylated proteins and accumulation of specific proteasomal substrates.

CONCLUSIONS

These proof-of-principle experiments demonstrate that inhibition of the ubiquitin-proteasome system effectively reduces neointima formation in vivo, which corresponds to strong antiproliferative, anti-inflammatory, and proapoptotic effects in vitro and in vivo. Our data suggest the ubiquitin-proteasome system as a new target in the prevention of vascular restenosis.

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.

Intracoronary beta radiation: state of the art

This state-of-the-art review is intended to explore the development of beta radiation including catheter delivered and permanent implants from its inception to current practice. Specific focus will be given to the isotopes currently available, radiation physics of beta emitters, preclinical studies, clinical trials, beta radiation delivery systems, and implications for future practice. The encouraging results from the clinical trials have established vascular brachytherapy as a standard of care for patients with in-stent restenosis. Vascular brachytherapy requires additional "fine-tuning" to achieve full optimization.

Failure of a novel balloon-expandable gamma-emitting ((103)Pd) stent to prevent edge effects

BACKGROUND

Balloon-expandable beta-particle-emitting ((32)P) stents inhibit within-stent neointimal hyperplasia but induce lumen narrowing beyond the stent margins, ie, the so-called "edge effects."

METHODS AND RESULTS

We prospectively investigated the performance of novel stents impregnated with the gamma-emitting isotope (103)Pd, designed to reduce edge effects, in 24 rabbits. The stents had a length of 18 mm and were mounted on 20-mm-long delivery balloons for deployment. Angiograms were obtained immediately and 1 month after direct implantation of control and 1-, 2-, and 4-mCi (103)Pd stents into the iliac arteries without predilatation or postdilatation. Late lumen loss was measured with quantitative angiography. Neointimal hyperplasia and vascular remodeling were evaluated by histomorphometry. Late lumen loss was inhibited within (103)Pd stents (control 0.18 mm, 1 mCi 0.08 mm, 2 mCi 0.05 mm, and 4 mCi -0.03 mm, P<0.05 all activities versus control). Conversely, late lumen loss occurred at the edges of (103)Pd stents, correlating with areas of high balloon/artery ratios and vessel overstretch injury. Edge effects were primarily due to neointimal hyperplasia but were also caused by negative vessel remodeling at high stent activities.

CONCLUSIONS

Edge effects after implantation of radioisotope stents can occur independently of the isotope chosen for stent impregnation.