Effect of intravascular irradiation on cell proliferation, apoptosis, and vascular remodeling after balloon overstretch injury of porcine coronary arteries

Recurrent drug eluting stent, in-stent restenosis (DES-ISR): Epidemiology, pathophysiology & treatment

Coronary artery in-stent restenosis (ISR) is driven by neointimal hyperplasia and neo-atherosclerosis in previously placed stents. Drug eluting stents (DES) have been adopted as first line therapy for the initial episode of ISR. However, recurrent ISR has limited durable salvage options. In this article we review the pathophysiology, incidence, and management options of recurrent DES- ISR.

Complications of intravascular brachytherapy

INTRODUCTION

There is some evidence of a dose-response relationship for intravascular brachytherapy (IVBT) of native vessel or first-time in-stent restenosis (ISR). It has also been shown that in-field failure predominates following intravascular brachytherapy-treated lesions. Accordingly, it may be advantageous to increase the radiation dose(s) currently used. Given the rationale for escalation from currently doses, a scrutiny of the potential complications that have been reported seems timely.

METHODS

PubMed was searched from 1966 through November 21st, 2023, using the terms coronary and brachytherapy, yielding 1287 references. A 10/16/24 follow-up search of Embase, using the terms "coronary and brachytherapy and complications", yielding 511 articles. In total, 68 articles were identified as adverse event reports based on their title, or by scrutinizing articles that did not mention adverse events in their titles.

RESULTS

The best documented adverse IVBT-related event is the occurrence of late (> 1 month) thrombosis. Following identification of the risk, longer DAPT regimens were adopted, bringing the incidence to non-IVBT levels. A variety of other adverse events have been reported, including aneurysms, dissections, arterial spasm, "black holes" and vasomotor response inhibition. However, none of which were associated with adverse clinical outcomes.

CONCLUSIONS

Nearly all reports regarding IVBT-related complications are retrospective analyses of a limited number of events, subject to reporting bias. Clinically important IVBT-related complications, at current doses, appear highly unlikely.

The contemporary use of intracoronary brachytherapy for instent restenosis: A review

In-stent restenosis (ISR) has been a major limitation in interventional cardiology and constitutes nearly 10 % of all percutaneous coronary interventions in the United States. Drug-eluting stent (DES) restenosis proves particularly difficult to manage and poses a high risk of recurrence and repeat intervention. Intra-coronary brachytherapy (IBT) has been traditionally viewed as a potential treatment modality for ISR. However, its use was hindered by procedural complexity, cost, and the advent of newer-generation DES. Recent data suggests promising results regarding IBT for the treatment of resistant DES-ISR. This review addresses the mechanism of action of IBT, procedural details, and associated risks and complications of its use. It will also highlight the available clinical evidence supporting the use of IBT and the future directions of its utilization in the treatment of ISR.

Intracoronary Brachytherapy for Drug-Eluting Stent Restenosis: Outcomes and Clinical Correlates

Background

This study aimed to report outcomes of intracoronary brachytherapy (ICBT) in treating drug-eluting stent (DES) in-stent restenosis (ISR) and identify correlated factors.

Methods

Patients who underwent ICBT for DES ISR from 2010 to 2021 were included in this single-institution retrospective PCI registry. Patients were treated with balloon angioplasty, laser atherectomy, and/or rotational atherectomy, followed by ICBT at a dose of 18.4-25 Gy delivered at the site of ISR with dose determined by the reference vessel size. The primary outcome was 3-year target lesion failure rate (TLF). Secondary end points were 1-year TLF, target lesion revascularization (TLR), all-cause mortality, and cardiac mortality.

Results

In total, 330 consecutive patients presented with 345 treated lesions; 70% were male, age was 66 ± 11 years, 55% were diabetic patients, 62% underwent previous bypass surgery, and 89% were placed with at least 2 stent layers at the treated site. The rate of TLF was 18% at 1 year and 46% at 3 years. All-cause mortality and cardiac mortality rates were 19.8% and 12.3% at 3 years. The number of stent layers was associated with 3-year TLF (1 layer, 33.3%; 2 layers, 47.0%, >3 layers, 60.2%; P = .045). Diabetes, repeat ICBT, final percent stenosis, lesion length, and intravascular imaging use were not correlated with the primary outcome. Lower ICBT dose (P = .035) and restenosis <1 year from previous percutaneous coronary intervention (P = .044) were correlated with early (1-year) TLF.

Conclusion

ICBT for recurrent DES ISR provided low recurrence rates at 1 year, which increased substantially by 3 years. Outcomes were most closely correlated with the number of stent layers, but early restenosis and lower ICBT dose adversely affected early TLF.

Coronary intravascular brachytherapy for in-stent restenosis: A review of the contemporary literature

Intracoronary stent restenosis (ISR) is a clinically relevant challenge in the modern era. Heterogeneity in patient- and lesion-specific factors can further compound this clinical challenge. Coronary intravascular brachytherapy (IVBT) was the standard therapeutic approach for ISR prior to the advent of drug-eluting stents (DES). Despite prospective data describing the superiority of DES over IVBT for treating de novo ISR, IVBT remains a treatment option for patients with complex disease. The purpose of this review is to evaluate the historical and contemporary literature surrounding IVBT in order to elucidate its role in modern cardiac care and to describe opportunities for future investigations to improve patient selection. Herein, we provide a review of the contemporary literature describing IVBT as a safe and effective treatment option for patients with recurrent, refractory ISR after multilayer DES and no good surgical or mechanical option. Combination therapy with emerging technologies such as DCBs may further increase efficacy.

Is Coronary Brachytherapy Staging a Comeback for the Treatment of In-Stent Restenosis?

PURPOSE OF REVIEW

The catheter-based coronary intervention has become a well-established therapeutic modality for obstructive coronary artery disease. However, in-stent restenosis remains a significant limitation of coronary intervention despite the use of newer devices. Intravascular brachytherapy was introduced to treat recurrent in-stent restenosis but only modestly adopted. This review will discuss the mechanism of intracoronary brachytherapy, available clinical evidence of brachytherapy in recurrent in-stent restenosis treatment, and the future of coronary brachytherapy in coronary intervention.

RECENT FINDINGS

Drug-eluting stents have an inherent limitation as they leave a permanent metal layer inside an artery when deployed. Recently, drug-coated balloon technology has emerged to treat coronary artery disease as a combination of balloon angioplasty and local drug delivery without leaving a metal layer behind. Recent European guidelines recommended using drug-coated balloons when treating in-stent restenosis treatment, while the US guidelines have not yet addressed the use of drug-coated balloons in such cases. Coronary brachytherapy is a valuable addition to treat these challenging diseases despite several logistic issues. If there are newer technologies with easier setup, such as drug-coated balloons, coronary brachytherapy resurgence is improbable in the contemporary era, although it may not become obsolete.

Coronary Intravascular Brachytherapy for Recurrent Coronary Drug-Eluting Stent In-Stent Restenosis: A Systematic Review and Meta-Analysis

OBJECTIVE

To examine the outcomes with intravascular brachytherapy (IVBT) in recurrent in-stent restenosis (ISR).

BACKGROUND

Recurrent ISR can be challenging to treat and IVBT can be used for recurrent ISR but has received limited study.

METHODS

We performed a systematic review and meta-analysis of five observational studies, including 917 patients (1014 lesions) with recurrent ISR, defined as having at least two prior ISR episodes with previous treatment with a stent, who underwent treatment with IVBT. Outcomes of interest included target vessel revascularization (TVR), myocardial infarction (MI), and all-cause mortality.

RESULTS

During a mean follow-up of 24 ± 7 months, the incidence of TVR was 29.2% (95% CI 18.0-40.4%). The incidence of MI and all-cause mortality were 4.3% (95% CI 1.7%-6.9%) and 7.3% (95% CI 3.2-11.5%), respectively. At one- and two-years after PCI the incidence of TVR was 17.5% (95% CI 13.6%-21.4%) and 26.7% (95% CI 16.6%-36.9%), respectively and the incidence of MI was 3.1% (95% CI 2-4.2%) and 3.9% (95% CI 1-6.8%), respectively.

CONCLUSION

Intravascular brachytherapy can be used to treat recurrent ISR, although TVR is needed in approximately one of four patients at two years.

Outcomes of intravascular brachytherapy for recurrent drug-eluting in-stent restenosis

OBJECTIVES

To examine the outcomes of vascular brachytherapy (VBT) for recurrent drug-eluting stents (DES) in-stent restenosis (ISR).

BACKGROUND

Recurrent DES-ISR can be challenging to treat. VBT has been used with encouraging results.

METHODS

We report the long-term outcomes of patients with recurrent DES-ISR treated with VBT between January 2014 and September 2018 at a tertiary care institution. The main outcome was target lesion failure (TLF), defined as the composite of clinically driven target lesion revascularization (TLR), target lesion myocardial infarction (MI), and target lesion-related cardiac death. Cox proportional hazards analysis was performed to identify variables associated with recurrent TLF.

RESULTS

During the study period, 116 patients (143 lesions) underwent VBT. Median follow-up was 24.7 (14.5-35.4) months. The incidence of TLR, target-lesion MI, and TLF was 18.9%, 5.6%,and 20.1% at 1 year, and 29.4%, 10.5%, and 32.9% at 2 years.Initial presentation with acute coronary syndrome (ACS) was independently associated with TLF (hazard ratio = 1.975, 95% CI [1.120, 3.485], p = .019). Lesions treated with intravascular ultrasound (IVUS) guidance had a lower incidence of TLR (14.3% vs. 39.6%, log-rank p = .038), and a trend toward lower incidence of TLF (19% vs. 42.6%, log-rank p = .086).

CONCLUSIONS

VBT can improve the treatment of recurrent DES-ISR, but TLF occurs in approximately one in three patients at 2 years. Initial presentation with ACS was associated with higher TLF and the use of IVUS with a trend for lower incidence of TLF.

Northwell intracoronary brachytherapy for the treatment of recurrent drug eluting stent in-stent restenosis (NITDI study group)

OBJECTIVE

The purpose of this study is to report on safety, short-term and long-term clinical efficacy following intracoronary brachytherapy (ICBT) for restenosis (ISR) in patients with drug eluting stents (DES).

BACKGROUND

ICBT is an effective treatment for ISR of bare metal stents (BMS) but its utilization has waned due to the advent of DES. ISR following DES occurs at a frequency of 8% or greater.

METHOD

A retrospective analysis was performed on patients treated on an institutional review board (IRB) approved protocol using ICBT for DES ISR between January 2011 and October 2016. All patients were followed for 24 months for procedural complications, mortality, clinical ISR/target lesion revascularization (TLR) and stroke.

RESULTS

A total of 290 patients were identified with a mean age of 66.6 years. All of them had high rates of typical coronary artery disease risk factors. Our primary outcome, composite of in-hospital mortality, myocardial infarction (MI), safety outcomes and procedural failure was noted in 1(0.3%) patient who had a MI. No other secondary outcome was noted in-hospital. At 1-year follow up, 12.4% patients had ISR, 1.7% patients died, and 1 (0.3%) had ischemic stroke. At 2-year, 14.7% had ISR, and total 6 (2.1%) patients had MI.

CONCLUSION

ICBT demonstrates excellent technical success rates for treatment, safety, and reasonable efficacy over 2-years to be free from recurrent clinical ISR. This study represents the largest ICBT data for DES ISR to date among very complex lesion subsets, however, more prospective data will be needed to determine the optimal patient for treatment.

Fractionated head and neck irradiation impacts taste progenitors, differentiated taste cells, and Wnt/β-catenin signaling in adult mice

Head and neck cancer patients receiving conventional repeated, low dose radiotherapy (fractionated IR) suffer from taste dysfunction that can persist for months and often years after treatment. To understand the mechanisms underlying functional taste loss, we established a fractionated IR mouse model to characterize how taste buds are affected. Following fractionated IR, we found as in our previous study using single dose IR, taste progenitor proliferation was reduced and progenitor cell number declined, leading to interruption in the supply of new taste receptor cells to taste buds. However, in contrast to a single dose of IR, we did not encounter increased progenitor cell death in response to fractionated IR. Instead, fractionated IR induced death of cells within taste buds. Overall, taste buds were smaller and fewer following fractionated IR, and contained fewer differentiated cells. In response to fractionated IR, expression of Wnt pathway genes, Ctnnb1, Tcf7, Lef1 and Lgr5 were reduced concomitantly with reduced progenitor proliferation. However, recovery of Wnt signaling post-IR lagged behind proliferative recovery. Overall, our data suggest carefully timed, local activation of Wnt/β-catenin signaling may mitigate radiation injury and/or speed recovery of taste cell renewal following fractionated IR.

Intravascular Brachytherapy for the Management of Repeated Multimetal-Layered Drug-Eluting Coronary Stent Restenosis

BACKGROUND

Because of the widespread acceptance of percutaneous coronary intervention with drug-eluting stents as an effective treatment strategy for in-stent restenosis, it is common to encounter multimetal layer stent restenosis in the recent years. This study aimed to evaluate the clinical outcomes of such patients treated with intravascular brachytherapy (IVBT) in comparison with other percutaneous options.

METHODS AND RESULTS

We enrolled patients who underwent percutaneous coronary intervention during the period between 2011 and 2015 for recurrent drug-eluting stents in-stent restenosis with at least 2 layers of stents at the lesion site. This analysis compared patients who underwent treatment with IVBT and those who did not (non-IVBT group). The primary end point measured was major adverse cardiac events defined as a composite of target lesion revascularization, myocardial infarction, and all-cause mortality at 12 months. Adjusted associations were measured using propensity score matching. A total of 328 percutaneous coronary intervention patients met the eligibility criteria, of which 197 patients received IVBT, and 131 patients underwent routine percutaneous intervention. The primary end point was significantly lower in patients undergoing IVBT (13.2% and 28.2%; P=0.01). A propensity score matching for risk factors of in-stent restenosis identified 182 patients. The advantages of IVBT with regard to 1-year major adverse cardiac events were confirmed in this matched cohort (13.2% and 30.8%; adjusted hazard ratio [95% CI]: 0.37 [0.18-0.73]; P<0.01).

CONCLUSIONS

In this analysis, IVBT led to significantly lower major adverse cardiac events in patients with multilayered drug-eluting stents restenosis when compared with other percutaneous options at 1-year follow-up.

Preclinical Restenosis Models: Challenges and Successes

Coronary artery disease remains a major problem for Western societies. The advent of percutaneous interventions, including stents has brought clinical care to a new level of efficacy, yet problems remain. Restenosis following stenting in human coronary arteries appears at last to be yielding to therapeutic strategies, especially drug eluting stents. Because therapeutic percutaneous coronary intervention is widely dominated by the intracoronary stent, restenosis therapies must include the stented coronary artery. Animal models and in particular the porcine coronary model seem to represent the human coronary artery reaction to stenting. It mimics several clinical conditions including thrombosis and neointimal formation. A key question in the era of intravascular technologies is how well this and other models can predict clinical events. This paper discusses the models and their application.

Intracoronary Brachytherapy for Recurrent Drug-Eluting Stent Failure

OBJECTIVES

The study sought to report safety and long-term clinical efficacy of intravascular brachytherapy (VBT) for recurrent drug-eluting stent in-stent restenosis (DES-ISR).

BACKGROUND

Recurrent DES-ISR remains a therapeutic challenge, and VBT has been used selectively in recurrent DES failure.

METHODS

Patients undergoing VBT for recurrent DES-ISR were enrolled from a percutaneous coronary intervention registry. Clinical, procedural, VBT, and outcome data were collected for DES-ISR treated with radiation. Follow-up was obtained by phone call and clinic visits.

RESULTS

A total of 186 patients (283 lesions) were included. Mean age was 65 ± 11 years, and 115 (61.8%) were men. Mean time to failure from last failed DES implantation was 450.65 ± 50 days. Majority (95%) had >2 episodes of target lesion revascularization (TLR). Commonest presentation of DES-ISR was unstable angina (68, 30%). All lesions were treated with balloon angioplasty followed by VBT using Beta-Cath system (Best Vascular Inc., Springfield, Virginia) with a dose of 23 to 25 Gy at 2 mm from source center. Radiation was delivered to site of ISR, without procedural adverse events, in 99% cases. Incidence of TLR was 3.3% at 6 months, 12.1% at 1 year, 19.1% at 2 years, and 20.7% at 3 years. No subacute thrombosis event was noted. One patient had late thrombosis during a 3-year follow-up.

CONCLUSIONS

VBT for recurrent DES-ISR is safe, with low recurrence rates at 12 months post-procedure, and can be safely used as an effective short-term strategy. Overtime, there is a gradual attrition in patency requiring repeat intervention.

Intracoronary brachytherapy for in-stent restenosis of drug-eluting stents

PURPOSE

Given the limited salvage options for in-stent restenosis (ISR) of drug-eluting stents (DES), our high-volume cardiac catheterization laboratory has been performing intracoronary brachytherapy (ICBT) in patients with recurrent ISR of DES. This study analyzes their baseline characteristics and assesses the safety/toxicity of ICBT in this high-risk population.

METHODS AND MATERIALS

A retrospective analysis of patients treated with ICBT between September 2012 and December 2014 was performed. Patients with ISR twice in a single location were eligible. Procedural complications included vessel dissection, perforation, tamponade, slow/absent blood flow, and vessel closure. Postprocedural events included myocardial infarction, coronary artery bypass graft, congestive heart failure, stroke, bleeding, thrombosis, embolism, dissection, dialysis, or death occurring within 72 hours. A control group of patients with 2 episodes of ISR at 1 location who underwent percutaneous coronary intervention without ICBT was identified. Unpaired t tests and χ2 tests were used to compare the groups.

RESULTS

There were 134 (78%) patients in the ICBT group with 141 treated lesions and 37 (22%) patients in the control group. There was a high prevalence of hyperlipidemia (>95%), hypertension (>95%), and diabetes (>50%) in both groups. The groups were well-balanced with respect to age, sex, and pre-existing medical conditions, with the exception of previous coronary artery bypass graft being more common the ICBT group. Procedural complication rates were low in the control and ICBT groups (0% vs 4.5%, P = .190). Postprocedural event rates were low (<5%) in both groups. Readmission rate at 30 days was 3.7% in the ICBT group and 5.4% in the control group (P = .649).

CONCLUSIONS

This is the largest recent known series looking at ICBT for recurrent ISR of DES. ICBT is a safe treatment option with similarly low rates (<5%) of procedural and postprocedural complications compared with percutaneous coronary intervention alone. This study establishes the safety of ICBT in a high-risk patient cohort.

Long term follow-up after endovascular brachytherapy of femoro-popliteal arteries

To perform a long term follow-up after endovascular brachytherapy (EVBT) and balloon angioplasty (PTA) regarding vessel patency and diameter. EVBT had been successfully used to decrease restenosis in short term, but long term data are lacking. Participants of a randomized study comparing EVBT and balloon angioplasty alone were invited for follow-up examination ten years after intervention. Using a standardized protocol measurement of the patency and vessel diameter was performed of femoral and popliteal arteries. 44 patients were included, 21 had been treated with EVBT and 23 had received PTA alone. Target lesion patency was similar between the two groups (90.5% vs. 87.0%). Vessel diameter of the target lesion was significantly greater in the EVBT group (6.4 mm, range 3.9-9.9) compared to the controls (5.0 mm, range 3.1-7.4; p = 0.002). Ten years after EVBT of femoro-popliteal arteries vessel diameter is significantly increased whereas patency rate is not different compared to angioplasty alone.

Impact of the distance from the stent edge to the residual plaque on edge restenosis following everolimus-eluting stent implantation

Objectives

This study aimed to assess the relation between stent edge restenosis (SER) and the distance from the stent edge to the residual plaque using quantitative intravascular ultrasound.

Background

Although percutaneous coronary intervention with drug-eluting stents has improved SER rates, determining an appropriate stent edge landing zone can be challenging in cases of diffuse plaque lesions. It is known that edge vascular response can occur within 2 mm from the edge of a bare metal stent, but the distance to the adjacent plaque has not been evaluated for drug-eluting stents.

Methods

A total of 97 proximal residual plaque lesions (plaque burden [PB] >40%) treated with everolimus-eluting stents were retrospectively evaluated to determine the distance from the stent edge to the residual plaque.

Results

The SER group had significantly higher PB (59.1 ± 6.1% vs. 51.9 ± 9.1% for non-SER; P = 0.04). Higher PB was associated with SER, with the cutoff value of 54.74% determined using receiver operating characteristic (ROC) curve analysis. At this cutoff value of PB, the distance from the stent edge to the lesion was significantly associated with SER (odds ratio = 2.05, P = 0.035). The corresponding area under the ROC curve was 0.725, and the cutoff distance value for predicting SER was 1.0 mm.

Conclusion

An interval less than 1 mm from the proximal stent edge to the nearest point with the determined PB cutoff value of 54.74% was significantly associated with SER in patients with residual plaque lesions.

Outcomes after percutaneous coronary intervention with stents in patients treated with thoracic external beam radiation for cancer

OBJECTIVES

The aim of this study was to assess outcomes after percutaneous coronary intervention (PCI) with stents in patients treated with thoracic external beam radiation therapy (EBRT).

BACKGROUND

Thoracic EBRT for cancer is associated with long-term cardiotoxic sequelae. The impact of EBRT on patients requiring coronary stents is unclear.

METHODS

We analyzed outcomes after PCI in cancer survivors treated with curative thoracic EBRT before and after stenting between 1998 and 2012. Reference groups were propensity-matched cohorts with stenting but no EBRT. Primary endpoint was target lesion revascularization (TLR), a clinical surrogate for restenosis. Secondary endpoints included myocardial infarction (MI) and cardiac and overall mortality.

RESULTS

We identified 115 patients treated with EBRT a median 3.6 years after stenting (group A) and 45 patients treated with EBRT a median 2.2 years before stenting (group B). Long-term mean TLR rates in group A (3.2 vs. 6.6%; hazard ratio: 0.6; 95% confidence interval: 0.2 to 1.6; p = 0.31) and group B (9.2 vs. 9.7%; hazard ratio: 1.2; 95% confidence interval: 0.4 to 3.4; p = 0.79) were similar to rates in corresponding control patients (group A: 1,390 control patients; group B: 439 control patients). Three years post-PCI, group A had higher overall mortality (48.6% vs. 13.9%; p < 0.001) but not MI (4.8% vs. 4.3%; p = 0.93) or cardiac mortality (2.3% vs. 3.6%; p = 0.66) rates versus control patients. There were no significant differences in MI, cardiac, or overall mortality rates in group B.

CONCLUSIONS

Thoracic EBRT is not associated with increased stent failure rates when used before or after PCI. A history of PCI should not preclude the use of curative thoracic EBRT in cancer patients or vice versa. Optimal treatment of cancer should be the goal.

Intravascular brachytherapy for peripheral vascular disease

BACKGROUND

Interventional treatment of arteries that are narrowed and obstructed by atherosclerosis involves either bypassing the blockage using a graft; widening the artery from the inside with a balloon, a procedure known as percutaneous transluminal angioplasty (PTA); or providing a strut to hold the vessel open, known as a stent. All of these treatments are, however, limited by the high numbers that fail within a year. Intravascular brachytherapy is the application of radiation directly to the site of vessel narrowing. It is known to inhibit the processes that lead to restenosis (narrowing) of vessels and grafts after treatment. This is an update of a review first published in 2002.

OBJECTIVES

To assess the efficacy of, and complications associated with, intravascular brachytherapy (IVBT) for maintaining patency after angioplasty or stent insertion in native vessels or bypass grafts of the iliac or infrainguinal arteries.

SEARCH METHODS

For this update the Cochrane Peripheral Vascular Diseases Group Trials Search Co-ordinator searched their Specialised Register (last searched August 2013) and CENTRAL (2013, Issue 7).

SELECTION CRITERIA

Randomised controlled trials of the use of brachytherapy as an adjunct to the endovascular treatment of people with peripheral arterial disease (PAD) or stenosed bypass grafts of the iliac or infrainguinal arteries versus the procedure without brachytherapy.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and two other review authors independently extracted the data. Adverse event information was collected from the trials.

MAIN RESULTS

Eight trials with a combined total of 1090 participants were included in this review. All included studies used the femoropopliteal artery. We did not identify any studies that used the iliac arteries. All studies compared PTA with or without stenting plus IVBT versus PTA with or without stenting alone. No trials were found comparing IVBT to technologies such as drug eluting stents or balloons, or cryoplasty. Follow-up ranged from six months to five years. The quality of the included trials was moderate with our concerns relating to the difficulty of blinding due to the nature of the procedures and the small sample sizes for some studies. Primary outcomes (patency or restenosis and need for re-intervention) were reported in the majority of the trials, but reporting at various time points and the use of multiple definitions of the outcomes by the included studies meant that not all data were available for pooling. The secondary outcomes were not reported in many of the included studies.For brachytherapy, cumulative patency was higher at 24 months (odds ratio (OR) 2.36, 95% confidence interval (CI) 1.36 to 4.10, n = 222, P = 0.002). A statistically significant difference was found for restenosis at six months (OR 0.27, 95% CI 0.11 to 0.66, n = 562, P = 0.004), 12 months (OR 0.44, 95% CI 0.28 to 0.68, n = 375, P = 0.0002) and 24 months (OR 0.41, 95% CI 0.21 to 0.78, n = 164, P = 0.007) in favour of IVBT. No difference was found after five years as measured in one study. The need for re-interventions was reported in six studies. Target lesion revascularisation was significantly reduced in trial participants treated with IVBT compared with angioplasty alone (OR 0.51, 95% CI 0.27 to 0.97, P = 0.04) at six months after the interventions. No statistically significant difference was found between the procedures on the need for re-intervention at 12 and 24 months after the procedures.A statistically significant lower number of occlusions was found in the control group at more than three months (OR 11.46, 95% CI 1.44 to 90.96, n = 363, P = 0.02) but no differences were found at less than one month nor at 12 months after the procedures making the clinical significance uncertain. Ankle brachial index was statistically significantly better for IVBT at the 12 month follow-up (mean difference 0.08, 95% CI 0.02 to 0.14, n = 100, P = 0.02) but no statistically significant differences were found at 24 hours and at six months.Quality of life, complications, limb loss, cardiovascular deaths, death from all causes, pain free walking distance and maximum walking distance on a treadmill were similar for the two arms of the trials with no statistically significant difference found between the treatment groups.

AUTHORS' CONCLUSIONS

The evidence for using peripheral artery brachytherapy as an adjunct to percutaneous transluminal angioplasty to maintain patency and for the prevention of restenosis in people with peripheral vascular disease is limited, mainly due to the inconsistency of assessment and reporting of clinically relevant outcomes. More data are needed on clinically relevant outcomes such as health related quality of life (HRQOL) or limb salvage and longer-term outcomes, together with comparisons with other techniques such as drug eluting balloons and stents. Adequately powered randomised controlled trials, health economics and cost-effectiveness data are required before the procedure could be recommended for widespread use.

Radiation therapy for dialysis access stenosis: unfulfilled promise or false expectations

Hemodialysis vascular access dysfunction is a major cause of morbidity and hospitalization in the hemodialysis population at a cost of well over $1 billion per annum. Venous stenosis (due to venous neointimal hyperplasia [VNH]) is the most common cause of polytetrafluroethylene PTFE) dialysis access graft and arteriovenous fistula (AVF) failure. Despite the magnitude of the clinical problem, however, there are currently no effective therapies for this condition. We and others have previously demonstrated that VNH in PTFE dialysis grafts and AVF is composed of smooth muscle cells/myofibroblasts, endothelial cells within neointimal microvessels, and peri-graft macrophages. Radiation therapy blocks the proliferation and activation of all these cell types. The current review will dissect out the available in vitro, experimental, and clinical data on the use of radiation therapy for vascular stenosis in general, and for dialysis access dysfunction in particular. It is important to try and identify whether there is still a role for radiation therapy in this specific clinical setting. We believe that this is a critically important question to answer in view of the huge unmet clinical need that is currently associated with hemodialysis vascular access dysfunction.

Role of myofibroblasts in vascular remodelling: focus on restenosis and aneurysm

Myofibroblasts (MFs) are contractile cells deriving from a multiplicity of resident cells and/or circulating progenitors that are known to play a key role in wound healing. They were first discovered and analysed in the early 1970s in granulation tissue. Since their first identification, the role of MF and their mechanisms of differentiation have been highlighted in a number of diseases, including organ fibrosis and tumours, with particular attention devoted to the liver, kidney, and pulmonary fibrosis. The aim of this review is to summarize the current evidence for the role played by MFs in two frequent vascular diseases related to the remodelling of the vascular wall: the different forms of arterial restenosis and the most common forms of thoracic aortic aneurysm. The in-depth knowledge of the molecular pathways involved in MF differentiation, contraction, and survival/apoptosis could contribute to the identification of novel therapeutic strategies for anti-fibrotic and anti-remodelling therapy of vascular diseases in which these cells are involved.

BRAVO I: A pilot study of vascular brachytherapy in polytetrafluoroethylene dialysis access grafts

Hemodialysis vascular access dysfunction owing to stenosis and thrombosis in polytetrafluoroethylene dialysis access grafts is a huge clinical problem for which there are currently no long lasting durable therapies. Vascular brachytherapy has been used successfully for the prevention of coronary restenosis following angioplasty and stent placement. The Beta Radiation for Treatment of Arterial-Venous Graft Outflow I study was a pilot study of vascular brachytherapy in hemodialysis patients with patent but dysfunctional grafts. Twenty-five patients were randomized to receive either radiation therapy (a single dose of 18.4 Gy) or sham radiation, following angioplasty. The primary efficacy end point of the study was target lesion primary patency at 6 months. The primary safety end point was a composite of death, emergency surgery on the graft, venous rupture, or aneurysm formation. Forty-two percent of the radiated grafts achieved the target lesion primary patency end point at 6 months as compared to 0% of the control group (P = 0.015), but this did not translate into an improvement in secondary patency at either 6 or 12 months. Radiation therapy was found to be safe in the setting of hemodialysis vascular access dysfunction. Our results suggest that vascular brachytherapy is an intervention that is worthy of further examination in the setting of non-thrombosed dialysis access grafts.

IVUS-based dosimetry on patients with repeat-radiated coronary arteries to the same site

BACKGROUND AND PURPOSE

Intracoronary radiation reduces recurrent in-stent restenosis (ISR). Repeat radiation may become necessary due to recurrent ISR. This study reports outcome-related dose calculations for twice-radiated coronary artery segments.

MATERIALS AND METHODS

A total of 22 patients with angiographic evidence of ISR in a previously treated native coronary artery were assigned for repeat percutaneous coronary intervention and intravascular brachytherapy (IVBT). Intravascular brachytherapy was performed either with a 192Ir- or a 90Sr/Y-source (prescription dose: 14-18 and 23 Gy each at 2 mm from the center of the source), or a 32P-source (20 Gy 1-mm deep to the vessel wall). The mean time interval between the two IVBT treatments was 394+/-306 days. For each patient, angiograms and intravascular ultrasound cross sections were reviewed, on the basis of anatomical landmarks, matched, and the twice-radiated vessel segment identified.

RESULTS

Clinical follow-up at 379+/-146 days revealed a target vessel revascularization rate of 18.2% and a target lesion revascularization rate of 13.6%. One death was reported. Maximal dose and average dose at the endothelium were 261 and 124+/-72.3 Gy, and maximal dose and average dose at the adventitia-media border were 159 and 50.3+/-29.3 Gy. Fourteen patients had 1.71 times longer recurrence-free interval compared to the interval between both IVBT treatments.

CONCLUSIONS

Repeat IVBT to the same ISR site is safe without any adverse clinical events at an average 12 months' follow-up. A second IVBT treatment led to a prolonged ISR-free survival for the majority of patients. The choice of isotope did not influence outcome.

Ionizing radiation to prevent arterial intimal hyperplasia at the edges of the stent: induces necrosis and fibrosis

BACKGROUND

Although ionizing radiation has been proposed for the prevention of intimal hyperplasia in coronary and peripheral arteries in multicenter clinical trials, information is lacking on how irradiation affects arterial histology after stenting and especially how it affects the edges of the stent. We investigated intimal hyperplasia recasting with histological changes in arterial wall at the edges of the stent after arterial stenting followed by adequate external radiation for the prevention of intimal hyperplasia in pigs.

MATERIALS AND METHODS

The aorta was experimentally stented in 30 pigs who were then assigned to two groups: irradiation with 20 Gy and a control group with no irradiation. The aorta was resected for morphometric and histological studies 6 weeks after procedure.

RESULTS

Intimal thickness was reduced and the intima/media ratio was significantly lower in irradiated groups than in control pigs. In the irradiated group histological examination at the edges of the stent showed thin neointimal proliferation with an intact endothelium. In all sections analyzed in the 20-Gy irradiated group the vascular media at 45 days contained necrotic areas and fibrosis with calcifications.

CONCLUSIONS

After arterial injury, adequate ionizing radiation effectively reduces neointimal thickening. Irradiation-induced histological changes include previously undetected recasting with necrosis and fibrosis at the arterial edges of the stent. The parietal recasting we observed in animal arteries irradiated at high doses is unclear and a cause of concern especially after clinical spontaneous dissection was recently reported. The use of ionizing radiation for the prevention of arterial restenosis awaits confirmation with a long-term follow-up including specific experimental histological analyses.

Three-year follow-up after intracoronary beta-radiation therapy for in-stent restenosis

BACKGROUND

Most studies that proved intracoronary radiation therapy (IRT) to be highly effective to reduce recurrent restenosis after treatment of in-stent restenosis (ISR) have looked at time periods up to 12 months. Whether the beneficial effect from radiation is sustained during long-term follow-up remains a concern. This study sought to evaluate the effectiveness of IRT using a beta-emitter during a 3-year follow-up period.

METHODS

One hundred twenty-eight consecutive symptomatic patients (mean age, 63 +/- 11 years) with 134 in-stent restenotic lesions were treated for ISR with IRT (noncentred beta-emitter, Novoste; radiation dosis 21.1 +/- 3.1 Gy). Six-month angiographic follow-up was obtained in 104 patients (81%) with 105 lesions (78%). All patients underwent 36-month clinical follow-up.

RESULTS

Six-month angiographic restenosis rate was 22% in stent (29% in lesion) with an in-stent late loss of 0.49 +/- 0.62 mm. Target lesion resvascularization (TLR) at 6-month follow-up was performed in 23 cases (18%). MACE (death, myocardial infarction, and target vessel revascularisation) was observed in 24 patients (19%). At 36-month follow-up, TLR increased to 36 cases (28%) and MACE was observed in 47 patients (37%). In a multivariate analysis, minimal lumen diameter before treatment of ISR using IRT was the only predictor of recurrent TLR at 36 months (OR = 0.131; 95% CI, 0.068-0.254; p = 0.002). In a subgroup of patients (N = 15) without restenosis at 6-month angiography but with clinically driven recurrent late angiography (mean, 18 +/- 7 months); in-lesion late loss increased from 0.47 +/- 0.54 mm at 6 months to 1.27 +/- 0.76 mm at repeated angiography (p = 0.005).

CONCLUSION

There is a considerable number of delayed recurrent restenosis post IRT for ISR. This is due to ongoing late loss more than 6-month post IRT. The minimal lumen diameter before IRT predicts the need for recurrent TLR at 36 months.

Beta radiation in the treatment of in-stent restenosis of an in situ saphenous vein bypass graft A case report

We describe a case of instent restenosis in a femoral-distal saphenous vein bypass graft successfully treated with brachytherapy. A 45-year-old insulin-requiring diabetic woman underwent an in-situ femoral-anterior tibial bypass graft for a non-healing ischemic ulcer. Despite a technically successful percutaneous transluminal angioplasty and endovascular stenting of a retained valve within the threatened graft, the wound failed to heal. At the 1-month follow-up, instent restenosis was documented and successful cutting balloon angioplasty, complemented by adjunctive beta-irradiation was successfully performed. Clinical and hemodynamic success was achieved, with prompt ulcer healing and intermediate-term graft patency maintained on surveillance duplex ultrasound follow-up. We review the literature on radiation therapy in the management of peripheral arterial disease and discuss therapeutic options in the management of restenosis.

Dose mapping of porcine coronary arteries using an optical fiber dosimeter

BACKGROUND

This study is about the measurement of radiation dose contribution to the coronary arteries during intravascular brachytherapy with beta and gamma emitters utilizing in vivo optical fiber dosimeters.

METHODS AND MATERIALS

Domestic pigs were used. With each measurement, catheters were introduced into two different coronary arteries, including the left circumflex (LCX), the left anterior descending (LAD), the first diagonal, and/or the right coronary artery (RCA). A radioactive source (192Ir, 90Sr/Y, or 32P) and the dosimeter were loaded in each of these catheters. Data were collected as the dosimeter was being retracted at a constant rate via computer control.

RESULTS

The radiation dose was normalized to 100% at a 2-mm radial distance from the source. When radiating a branching artery, the dose to the bifurcation at 5 mm from the source was 35%, 10%, and 3% for the 192Ir (10 seeds), 90Sr/Y (40 mm), and 32P sources, respectively. When utilizing a 23-seed 192Ir source, the dose is 40% at a 5-mm distance. However, radiation of the RCA did not result in dosing to the LAD or LCX using any source.

CONCLUSIONS

The dose to adjacent artery segments is less with beta than with gamma emitters. Significant dose exposition is noted when using gamma emitters at a distance of 5 mm. The results can serve as a guideline for establishing prescription doses and safety margins for the treatment of bifurcation lesions and retreatment of the arteries.

A novel method of brachytherapy using local delivery of 99mTc-HMPAO for coronary stent restenosis

BACKGROUND

Restenosis after percutaneous coronary intervention (PCI) is a matter that still remains to be resolved. Herein, the inhibitory effect of locally delivered 99mTc-HMPAO (hexamethyl propylene amine oxime) on neointimal hyperplasia after coronary stenting was examined in a pocine model, and its safety and efficacy observed in patients with coronary stent restenosis.

METHODS

After a stent overdilation injury, local radioisotope delivery using 99mTc-HMPAO was applied to one coronary artery (Group I) and control therapy to another (Group II) in each of 10 pigs. Follow-up coronary angiogram (CAG) and histopathologic assessment were performed 4 weeks after stenting. Eleven patients (10 males and one female, 62.4 +/- 5.7 years of age) underwent local administration of 30 mCi/ 2 mL 99mTc-HMPAO shortly after PCI, via a Dispatch Catheter, followed by a whole body scan to evaluate the distribution of the 99mTc-HMPAO, as well as a thallium-201 (TI-201) myocardial scan to evaluate myocardial perfusion. The major adverse cardiac events (MACE) were assessed during a one-year clinical follow-up.

RESULTS

On histopathological analysis, the neointimal areas were 1.2 +/- 0.6 and 2.7 +/- 0.4 mm2 (p=0.002), and the histopathological areas of stenosis were 27.16.3 and 53.4 +/- 5.2% in Groups I and II (p=0.001), respectively. In the clinical study, there was no in-hospital MACE. On a quantitative coronary angiographic analysis, the minimal luminal diameter was increased from 0.4 +/- 0.3 to 2.9 +/- 0.2 mm, and diameter stenosis decreased from 84.2 +/- 9.5 to 16.3 +/- 11.0% following PCI. Follow-up CAG was performed in 9 cases (81.8%) and restenosis occurred in 2 (22.2%). On a follow-up CAG, the minimal luminal diameter, diameter stenosis rate, lumen loss and loss index were 2.0 +/- 0.8 mm, 27.7 +/- 2.9%, 0.7 +/- 0.7 mm and 0.2 +/- 0.3, respectively. During the one-year clinical follow-up there were no cases of death or acute MI, but two cases of target vessel revascularization (18.2%).

CONCLUSION

Local delivery of 99mTc-HMPAO, a novel radiotherapy, can be used safely and effectively for coronary stent restenosis.

The natural history of collagen and α-actin expression after coronary angioplasty

BACKGROUND

Restenosis after percutaneous transluminal coronary angioplasty (PTCA) is a result of remodeling and deposition of new mass. The new mass is formed by invading and replicating cells and by extracellular matrix (ECM), of which collagens constitute the dominating component. Smooth muscle actin is an important element in cell contraction. We tested the hypothesis that the accumulation of collagen and actin correlates with the development of postinjury luminal narrowing.

METHODS AND RESULTS

Thirty-five pigs underwent balloon angioplasty and were killed 0, 1, 4, 7, 14, 28, and 56 days later. Tissue samples from the left circumflex artery were in paraffin, sectioned, and immunostained for Collagen Types I and III and alpha1-smooth muscle actin. Collagen accumulation was measured separately in intima, media, and adventitia using computerized semiautomatic planimetry. The injury produced a strong healing response, with a marked accumulation of collagen in all three vessel wall layers. However, the accumulation in adventitia began surprisingly early (1 to 4 days after PTCA) and stopped at Day 7, i.e., before luminal narrowing occurred (14 to 28 days after PTCA in our model). Furthermore, a conspicuous accretion of collagen occurred in the injured area of the medial layer. This response attenuated 14 days after PTCA. Neointimal collagen accumulation took place parallel to neointima formation 2 to 4 weeks after injury. Extramedial smooth muscle actin occurred predominantly from Days 4 to 14 in neointima. Only small quantities of actin were observed in the (neo-)adventitia. Furthermore, adventitial actin was a temporary phenomenon that disappeared between Days 14 and 28.

CONCLUSION

Adventitial and medial collagen deposition apparently occurs before luminal narrowing, indicating that the bulk of new mass in adventitia and media is not the cause of vessel remodeling, but possibly stabilizes the vessel wall and impairs compensatory outward remodeling. The accumulation of actin-positive cells and collagen takes place in neointima parallel to luminal narrowing, which suggests that a contraction within the neointimal mass may contribute to the remodeling process.

The role of brachytherapy and Cutting BalloonTM angioplasty in the current treatment of stent restenosis

The Gamma I, START and INHIBIT trials conclusively demonstrate the feasibility, safety and efficacy of intracoronary radiation as the treatment of choice for stent restenosis. Further reports confirm this finding and extend the indications. Vascular brachytherapy should be made available for all patients with diffuse stent restenosis. Specific devices such as cutting balloons may improve the procedure but does not seem to have an impact alone on the evolution.

Gamma-irradiation modulates vascular smooth muscle cell and extracellular matrix function: Implications for neointimal development

OBJECTIVE

Migration of vascular smooth muscle cells (SMCs) into the subintimal space, and their proliferation and resultant deposition of extracellular matrix are key processes in the development of intimal hyperplasia, leading to vascular recurrent stenosis. The purpose of this study was to investigate the effects of clinically administered doses of gamma-radiation on SMCs and extracellular matrix proteins in vitro, to better understand how it impinges on cellular and extracellular components of recurrent stenosis.

METHODS

The effects of gamma-irradiation (10, 20 Gy) on SMC migration into three-dimensional collagen matrix gels was quantitated by calibrated light microscopy, and the release of metalloproteinases into conditioned media was investigated with an enzyme-linked immunosorbent assay and zymography. Collagen production was assayed with [(3)H]-proline incorporation, and SMC phenotype changes with confocal microscopy with a fluorescent alpha-actin antibody. The effect of gamma-irradiation on extracellular matrix was investigated by quantitating untreated SMC proliferation ((3)H-thymidine incorporation) on irradiated endothelial cell-derived matrix and by assessing structural collagen matrix changes with sodium dodecylsulfate polyacrylamide gel electrophoresis. All groups were compared with nonirradiated control groups.

RESULTS

SMC vertical migration was significantly decreased by gamma-irradiation (48% and 55%, respectively; P <.0001). Irradiation did not generate measurable matrix protein crosslinks, nor did it alter the production of metalloproteinases or collagen synthesis. However, gamma-irradiation decreased the ability of extracellular matrix to induce nonirradiated SMC proliferation (15% reduction; P =.0028). Moreover, gamma-irradiation reversed the secretory phenotype of cultured SMCs to a contractile type.

CONCLUSIONS

The gamma-irradiation-induced reduction of cellular migration, changes in SMC phenotype, and functional activity of matrix-bound factors, and no measurable effects on the production of extracellular matrix proteins, may in part explain the diverse effects of gamma-irradiation on the restenotic response.

Morphometric and histological changes in the vascular wall after external radiation for the prevention of intimal hyperplasia

BACKGROUND

Recent reports describe spontaneous dissections and aneurysms after coronary and peripheral artery irradiation for the prevention of intimal hyperplasia. We investigated histological changes and the vasomotor reaction in the vascular wall after external radiation for the prevention of intimal hyperplasia in rabbits.

MATERIALS AND METHODS

The aorta was experimentally injured in 34 rabbits who were then assigned to one of three groups: irradiation with 20 Gy; with 25 Gy; and a control group with no irradiation. Before the arterial injury and 45 days later, vasomotor function was assessed with an intravascular ultrasound catheter. The aorta was resected for morphometric and histological studies.

RESULTS

After injury and irradiation, vasomotor responses were significantly lower in the two irradiated groups (P < 0.05). Intimal thickness and the intima/media ratio were significantly lower in irradiated groups. In the irradiated group histological examination showed reduced intimal proliferation with an intact endothelium. In the 20-Gy irradiated group the vascular media contained necrotic areas, and in the 25-Gy irradiated group, severe fibrosis.

CONCLUSION

After arterial injury, external irradiation at 20 and 25 Gy effectively reduces aortic intimal and medial thickening. Histological changes include recasting with necrosis and fibrosis causing a decreased vasomotor response. Further investigations are needed to confirm medial necrosis and replacement with fibrosis. Because the irradiation doses in this study match those currently used and also recommended for experimental and clinical use, if confirmed in humans parietal recasting might possibly explain the reported spontaneous dissections and aneurysm formation after irradiation.

Adventitial response to intravascular brachytherapy in a rabbit model of restenosis

BACKGROUND

The incidence of late major adverse cardiac events (MACE) after coronary brachytherapy is higher than in controls. Because expansive remodeling has been shown to correlate with poor clinical outcome after vascular interventions, we studied adventitial changes after intravascular irradiation in a rabbit model.

METHODS

Twenty normolipidemic rabbits underwent balloon injury in both external iliac arteries. One artery was assigned for subsequent irradiation with a 90Y source (15 Gy or 30 Gy at 0.5 mm in the vessel wall). After four weeks morphometric measurements were made and cell density and collagen amount determined. Staining for Ki67 identified proliferating cells; apoptotic cells were identified by TUNEL staining. Proliferative and apoptotic indices were calculated as the number of respective positive cells/total cell count x100.

RESULTS

The neointimal area decreased to 0.27 +/- 0.3 mm2 after irradiation compared with 0.55 +/- 0.2 mm2 in controls (p=0.007), whereas adventitial area increased from 0.62 +/- 0.3 mm2 to 0.87 +/- 0.3 mm2 (p=0.02). Irradiation reduced both the proliferative (0.95 +/- 2.6 vs. 3.73 +/- 4.7, p=0.026) and apoptotic (0.006 +/- 0.02 vs. 0.107 +/- 0.2, p=0.03) indices in the neointima, but not in the other arterial-wall layers. Collagen amount and arterial remodeling did not differ between the groups. There was no difference between 15 and 30 Gy in any of the parameters, although adventitial thickening was more pronounced in the high-dose group.

CONCLUSIONS

In normolipidemic rabbits, intravascular beta-irradiation after balloon angioplasty is associated with an increase in neoadventitia and a reduction of neointima. It is conceivable that this phenomenon may contribute to the increased incidence of late MACE after vascular brachytherapy.

Late neointimal tissue growth behind the stent after intravascular γ-radiation

PURPOSE

To determine the nature of the changes of the vascular wall after intravascular brachytherapy in stented arteries leading to incomplete stent apposition.

METHODS AND MATERIALS

Stents were implanted in the infrarenal aortas of rabbits, and gamma-intravascular brachytherapy (18 Gy) or a sham radiation procedure was immediately implemented. The arteries were harvested at 6 months for histologic analyses.

RESULTS

The external elastic lamina area, as well as the vascular wall area behind the stent, were significantly greater in irradiated vs. control arteries (8.94 +/- 0.68 mm2 vs. 6.87 +/- 0.40 mm2 [p <0.001] and 1.56 +/- 0.13 mm2 vs. 0.72 +/- 0.07 mm2 [p <0.001], respectively). The ratio of the intimal area behind the stent related to the total intimal area was greater in the irradiated segments (control vs. irradiated: 9.0% +/- 5.9% vs. 55.3% +/- 15.5%, p <0.05). Neointimal growth of the irradiated vessels outside the stent was characterized by marked fibrin depositions and an inflammatory response around the stent struts.

CONCLUSION

Our study revealed the presence of a neointimal layer specifically located behind the stent, which represented the result of an unhealed fibrin-rich tissue growth process 6 months after intravascular brachytherapy.

Incidence and mechanism of late stent malapposition after phosphorus-32 radioactive stent implantation

Late stent malapposition is a potential complication of intracoronary brachytherapy. The aim of our study was to determine the incidence and mechanism of late stent malapposition after implantation of phosphorus-32 radioactive stents. We analyzed 159 patients for de novo lesions after the implantation of phosphorus-32 radioactive stents. There were 15 late stent malappositions. The incidence of malapposition was higher in patients who received Hot-Ends Isostents. External elastic membrane expansion greater than plaque increase in malapposed segments was observed. Late stent malapposition is caused by a localized increase in external elastic membrane that is greater than the increase in plaque area; this is believed to be a dose-dependent phenomenon because it was more common with Hot-Ends Isostents.

Deposition of (90)YPO(4) and (144)CePO(4) radioisotopes on polymer surfaces for radiation delivery devices

Intravascular irradiation with beta emitters inhibits restenosis in arteries after balloon angioplasty or stent implantation. Yttrium-90 ((90)Y, T(1/2)=64 h) and cerium-144 ((144)Ce, T(1/2)=286 d) emit beta particles (E(max)=2.28--3.50 MeV) having an ideal energy range for brachytherapy delivery system. In this article, a previously reported method for depositing (32)P on poly(ethylene terephtalate) (PET) surfaces is generalized and modifications that allow deposition of other beta-emitting radioisotopes, such as (90)Y and (144)Ce, are demonstrated. PET films were first coated with chitosan hydrogel and then adsorbed different amounts of phosphoric acid (PA) in aqueous solutions. Yttrium was deposited onto the surface as YPO(4) after the films were immersed in YCl(3) solutions. 1 muCi (90)YCl(3) (2 x 10(-9) g) was used in each sample as a tracer for measuring the deposition efficiency, which is defined as the percentage of YCl(3) deposited on the surface compared to the amount of YCl(3) in solutions before the deposition. In order to improve the safety of brachytherapy treatments, polyurethanes were used to seal the deposited radioisotopes on the surface to minimize the leakage of the isotopes into the patients. The generality of this method presented here for a wide variety of particular radioisotopic components allows design of a broad range of versatile radioisotope sources.

Intravascular ultrasound based dose assessment in endovascular brachytherapy

BACKGROUND

the role of endovascular brachytherapy in restenosis prevention is well documented. Dose is usually prescribed at a fixed distance from the source axis by angiographic quantification of vessel diameter. Recently, intravascular ultrasound (IVUS) was introduced in dose prescription, allowing a better evaluation of the vessel anatomy. This study retrospectively explores the difference between prescription following angiographic vessel sizing and delivered dose calculated with IVUS.

METHODS AND RESULTS

Seventeen lesions were studied with IVUS, identifying on irradiated segment, three sections on which measuring minimal and maximal distance from the centre of IVUS catheter to the adventitia; using dedicated software, corresponding doses were calculated. The dose ranged widely, with maximal and minimal values of 71.6 and 4.9 Gy; furthermore, heterogeneity in dose among different sections was observed. In the central section, the maximal dose was 206% of the one prescribed with the QCA model at 2 mm from the source axis, while the minimal dose was 96%. In proximal and distal sections, respective values were 182, 45, 243, and 122%.

CONCLUSIONS

Our analysis confirmed the dose inhomogeneity delivered with an angiographic fixed-dose prescription strategy. A dose variation was found along the irradiated segment due to the differences in vessel thickness. IVUS emerged as an important tool in endovascular brachytherapy, especially for irregular-shaped vessels.

Effects of beta-radiation using a holmium-166 coated balloon on neointimal hyperplasia in a porcine coronary stent restenosis model

Brachytherapy is a promising method of preventing and treating coronary stent restenosis. The present study was designed to observe the therapeutic effects of a radioactive balloon loaded with Holmium-166 ((166)Ho) in a porcine coronary stent restenosis model. A radioisotope of (166)Ho was coated onto the balloon surface using polyurethane (20 Gy at 0.5 mm depth). Stent overdilation injuries were induced in 2 coronary arteries in each pig (n=8). Four weeks after the injury, control balloon dilation was performed in one coronary artery (Group I) and radiation therapy using the (166)Ho coated balloon in the other coronary artery (Group II) in each pig. Follow-up coronary angiography and histopathologic assessment were performed at 4 weeks after the radiation therapy or the control balloon dilations. With regard to complete blood cell counts, liver function tests, lipid profiles and coagulation tests, there were no differences between the baseline and after radiation. On quantitative coronary angiographic analysis, reference and target artery diameter showed no differences between the 2 groups before, or 4 and 8 weeks after stenting. On histopathologic analysis of groups I and II, the injury score was 1.34+/-0.09 and 1.32+/-0.10, the area of internal elastic lamina was 4.99+/-0.17 mm(2) and 4.82+/-0.20 mm(2), and the luminal area was 3.20+/-0.10 mm(2) and 3.45+/-0.14 mm(2), respectively (p=NS). The neointimal area was 1.78+/-0.11 mm(2) in group I and 1.36+/-0.12 mm(2) in group II (p=0.017), and the histopathologic area of stenosis was 35.1+/-1.6% in group I and 27.6+/-1.9% in group II (p=0.005). In conclusion, beta-radiation of the stented porcine coronary artery using a radioactive (166)Ho coated balloon inhibited stent restenosis without any side effects.

Aggressive venous neointimal hyperplasia in a pig model of arteriovenous graft stenosis

BACKGROUND

Vascular access dysfunction is the most important cause of morbidity and hospitalization in the hemodialysis population in the United States at a cost of well over one billion dollars per annum. Venous neointimal hyperplasia characterized by stenosis and subsequent thrombosis, is the major cause of polytetrafluoroethylene (PTFE) dialysis graft failure. Despite the magnitude of the problem, there are currently no effective therapies for the prevention or treatment of venous neointimal hyperplasia in PTFE dialysis grafts. We believe that this is partly due to the lack of a validated large animal model of arteriovenous stenosis that could be used to test out novel interventions.

METHODS

Seven-centimeter PTFE loop grafts were placed between the femoral artery and vein of domestic pigs. The grafts were removed at 2, 4, 7, 14 and 28 days after surgery and subjected to a detailed histological and immunohistochemical examination.

RESULTS

Significant neointimal hyperplasia and venous stenosis developed by 28 days at the graft-vein anastomosis. There was minimal neointimal hyperplasia at the graft-artery anastomosis. Venous neointimal hyperplasia (VNH) was characterized by (a) the presence of smooth muscle cells/myofibroblasts; (b) angiogenesis within both the neointima and adventitia; and (c) the presence of an active macrophage cell layer lining the PTFE graft material. These results are very similar to the human lesion previously described by us in dialysis patients.

CONCLUSIONS

We have developed and validated a pig model of venous neointimal hyperplasia that is very similar to the human lesion. We believe that this is an ideal model in which to test out novel interventions for the prevention and treatment of clinical hemodialysis vascular access dysfunction.

Initial experience with paclitaxel-coated stents

Local delivery of immunosuppressive or antiproliferative agents using a drug-eluting stent is a new technology that is supposed to inhibit in-stent restenosis, thus providing a biological and mechanical solution. This technique is a very promising. To date, several agents have been used, including paclitaxel, QP-2, rapamycin, actinomycin D, dexamethason, tacrolimus, and everolimus. Several studies, published recently or still ongoing, have evaluated these drugs as to their release kinetics, effective dosage, safety in clinical practice, and benefit. These studies include: SCORE (paclitaxel derivative), TAXUS I-VI, ELUTES, ASPECT, DELIVER (paclitaxel), RAVEL, SIRIUS (sirolimus), ACTION (actinomycin), EVIDENT, PRESENT (tacrolimus), EMPEROR (dexamethason), and FUTURE (everolimus). Paclitaxel was one of the first stent-based antiproliferative agents under clinical investigation that provided profound inhibition of neointimal thickening depending on delivery duration and drug dosage. The randomized, multicenter SCORE trail (Quanam stent, paclitaxel-coated) enrolled 266 patients at 17 sites. At 6-month's follow-up, a drop of 83% in stent restenosis using the drug-eluting stent could be achieved (6.4% drug-eluting stent vs 36.9% control group), which was attributable to a remarkable decrease in intimal proliferation. Unfortunately, due to frequent stent thrombosis and side-branch occlusions, the reported 30-day MACE rate was 10.2%. The randomized TAXUS-I safety trial (BSC, NIRx, paclitaxel-coated) also demonstrated beneficial reduction of restenotic lesions at 6-month's follow-up (0% vs 10%) but was associated with the absence of thrombotic events presumably due to less drug dosage. The ongoing TAXUS II-VI trials are addressing additional insight regarding the efficacy of the TAXUS paclitaxel-eluting stent. ASPECT and ELUTES evaluated paclitaxel-coated stents (i.e., Cook and Supra G), including subgroups with different drug dosages. With respect to stent restenosis and neointimal proliferation, both studies demonstrated a clear dose response. The RAVEL and the SIRIUS trials evaluated sirolimus-coated stents (i.e., Cordis, Johnson & Johnson, and Bx VELOCITY stents). Results confirmed the beneficial findings regarding reduction of renarrowing using a drug-eluting stent without any major adverse effects. Although parameters such as drug toxicity, optimal drug dosage, or delayed endothelial healing still need to be evaluated, today's clinical experience indicates that drug-coated stents are extremely beneficial in the interventional treatment of coronary lesions.

Balloon-based radiation therapy for treatment of in-stent restenosis in human coronary arteries: results from the BRITE I study

Catheter-based intracoronary radiation therapy demonstrated reduction of the recurrence rate of in-stent restenosis by 35%-50% when compared to conventional therapy. The objectives of this study were to determine the safety and feasibility of a new balloon-shaped source design and a higher applied dose to reduce the restenosis rates. Thirty-two patients with in-stent restenosis who met study eligibility criteria were successfully treated with standard PCI techniques. Following a successful intervention, a P-32 beta-balloon source was positioned to cover the angioplasty site and a dose of a 20 Gy at 1 mm from the surface of the source was administered. The primary endpoint was a composite of major adverse cardiac events (any death, MI, emergent CABG, or repeat target vessel revascularization) during 6 months of follow-up. At 6 months, only one patient underwent repeat PTCA to the target vessel (3%). There were no instances of death, emergency surgery, late thrombosis, total occlusions, or MI. Binary restenosis measured by QCA at the stented segment was 0% and for the whole analysis vessel was 7.5%. Beta-radiation delivered with a balloon P-32 source design for patients with in-stent restenosis results in lower than expected rate of angiographic and clinical restenosis and the absence of late complications.

[Coronary angioplasty in diabetic patients. Current and future perspectives]

It has been estimated that 15-25% of patients who undergo percutaneous or surgical coronary angioplasty are diabetics. The indications for coronary revascularization and initial results of the procedure do not differ substantially between patients with diabetes mellitus and non-diabetics. However, the long-term results of both percutaneous and surgical coronary angioplasty are less favorable in diabetics in terms of mortality and the need for new revascularization procedures. The development and widespread use of stents and glycoprotein IIb/IIIa receptor inhibiting drugs have improved the clinical evolution of diabetics treated with angioplasty. Currently available data show that the administration of glycoprotein IIb/IIIa inhibitors to patients undergoing coronary angioplasty is especially useful in diabetics and improves short-term and long-term results, decreasing one-year mortality by 45%. There seem to be indications for the routine use of glycoprotein IIb/IIIa inhibitors in diabetics treated with angioplasty. While the use of stents has improved long-term and short-term results in diabetics, the success rates of angioplasty in diabetics are still lower than in non-diabetics. Diabetes is still an independent predictor of restenosis and long-term events after stenting interventions. Analysis of the studies comparing percutaneous and surgical revascularization in diabetic patients with multivessel disease shows that surgery is superior in terms of long-term mortality and need for new revascularization procedures. Stenting has improved, but not substantially, the results of multivessel angioplasty in diabetics. Therefore, the indications for angioplasty in multivessel diabetics should be evaluated individually. Factors that contribute to the less favorable post-angioplasty evolution of diabetic patients are more rapid progression of atherosclerosis and, especially, a higher rate of restenosis. New angioplasty techniques, such as brachytherapy and drug-eluting stents, are likely to significantly improve the results of percutaneous interventions in diabetics, thus allowing the indications for angioplasty in diabetics to be extended even further in the near future.

Combined cutting balloon angioplasty and intracoronary beta radiation for treatment of in-stent restenosis: clinical outcomes and effect of pullback radiation for long lesions

Intracoronary beta (beta) radiation decreases the incidence of target lesion revascularization after percutaneous intervention (PCI) for in-stent restenosis (ISR). Cutting balloon (CB) angioplasty may also be superior to other percutaneous techniques for the treatment of ISR. We sought to study the outcomes of patients with ISR who underwent both CB angioplasty and intracoronay beta radiation and compare them to patients with ISR who underwent other PCI techniques without concomitant radiation. We also sought to evaluate the safety and efficacy of pullback intracoronary beta radiation for the treatment of long ISR lesions. Between January 2001 and November 2001, 102 patients (mean age = 55 +/- 13 years) with ISR underwent both CB angioplasty and intracoronay beta radiation. beta radiation was delivered using the Beta Cath (Novoste) 30 mm system, and pullback radiation was performed in 41 patients. A comparison group included a total of 393 patients with ISR who underwent other PCI techniques without concomitant intracoronary radiation therapy. Follow-up was obtained in 99 patients (97%) in the CB angioplasty with intracoronary radiation group and 377 patients (96%) in the comparison group. At follow-up, both target vessel revascularization (TVR) and major adverse cardiovascular events (MACE) occurred significantly less in the CB angioplasty with intracoronary radiation group than in the comparison group (7% vs. 18% for TVR, and 14% vs. 24% for MACE; P < 0.05 for both). In the pullback radiation group, TVR was performed in five patients (12%), and MACE occurred in eight patients (20%). A combination of CB angioplasty and intracoronay beta radiation for ISR seems to yield low rates of subsequent target vessel revascularization and adverse cardiac events. In addition, pullback beta radiation using the Beta Cath (Novoste) 30 mm system is safe and can be used to treat long ISR lesions effectively. Further randomized trials are needed to confirm these findings.