Endoluminal beta-radiation therapy for the prevention of coronary restenosis after balloon angioplasty. The Dose-Finding Study Group

Coronary stent traversed volume during the cardiac cycle defined as a target for high-precision radiotherapy by using biplane angiograms

Three-dimensional reconstructions of 19 coronary artery stents from biplane angiograms were used for measurement of the volume through which the stents traversed during the cardiac cycle. This volume, less than 0.8% of the whole heart volume in all patients, represents a target volume for high-precision radiotherapy to treat coronary artery in-stent restenosis.

High-dose intravascular beta-radiation after de novo stent implantation induces coronary artery spasm

BACKGROUND

Intracoronary brachytherapy is effective in preventing restenosis after coronary interventions. However, in vitro and animal studies have shown that irradiation produces immediate and sustained endothelial dysfunction. This study assesses the clinical relevance of impaired vasomotoric function induced by brachytherapy.

METHODS AND RESULTS

We analyzed the occurrence of postradiation coronary artery spasms in 1 animal study and 2 clinical trials investigating the effects of high-dose intracoronary beta-radiation after de novo coronary artery stenting. Irradiated segments (IRSs) proximal and distal to the stent were studied by quantitative coronary angiography after stenting, after radiation, and at the end of the procedure. There was an 67% overall incidence of coronary artery spasm in the IRSs immediately after beta-radiation compared with 9% after sham treatment (P<0.001). Whereas in most cases this phenomenon was only minor or moderate, in 12 cases, 4 (22%) animals and 8 (28%) patients, severe coronary spasm (>90% diameter stenosis) with significant ECG-changes or hemodynamic instability was observed. Relief of spasms was protracted (mean time until complete relief of spasm 423+/-122 seconds) and required repetitive intracoronary administration of nitroglycerin (mean dose: 1.2+/-0.6 mg).

CONCLUSIONS

Vasoconstriction is a frequent reaction of coronary arteries after high-dose intracoronary beta-radiation, necessitating repetitive administration of vasodilators.

Clinical and angiographic outcomes after use of 90Strontium/90Yttrium beta radiation for the treatment of in-stent restenosis: results from the Stents and Radiation Therapy 40 (START 40) registry

PURPOSE

To evaluate the safety and efficacy of a 40-mm 90Strontium/90Yttrium source train in the management of in-stent restenosis within native coronary arteries.

MATERIALS AND METHODS

This multicenter, prospective registry was designed to compare the results of patients with in-stent restenosis treated with a 40-mm source train to the placebo arm of the previously reported randomized Stents and Radiation Trial (START). All patients entered in the registry were treated with repeat balloon angioplasty followed by intravascular brachytherapy. Radiation dose was prescribed based on vessel size. 18 Gy was delivered at 2 mm for vessel diameters between 2.75 and 3.35 mm, and 23 Gy was used for vessels between 3.36 and 4.0 mm. The efficacy endpoints for the START 40 registry included a reduction in the target lesion revascularization (TLR) rate, target vessel revascularization rates, and target vessel failure (TVF) at 8 months. Secondary angiographic efficacy endpoints were binary restenosis at 8 months, in-stent minimum luminal diameter (MLD), and late loss. The safety endpoints included major adverse cardiac events as well as late aneurysm formation. The registry was designed to allow a statistically valid comparison of these results to the placebo group of the START 30 trial. Quantitative angiographic analysis was performed on the 8-month follow-up examination. Rates of restenosis were evaluated for various segments of the treated vessel. A separate analysis was performed to evaluate the relationship between vessel injury length and the radiated segment.

RESULTS

A total of 207 patients were entered into the START 40 registry. The postprocedure angiographic results, including the postprocedure MLD and percent diameter stenosis, were similar between the START 40 patients and the placebo group from the START trial in the stented segment of the treated vessel. Eight-month angiographic follow-up was available on 150 patients from the registry. The TLR rate was significantly reduced when compared to the placebo group (11% vs. 22.4% respectively, p = 0.008). A similar reduction was seen in terms of target vessel revascularization (15.9% vs. 24.1%, p = 0.03). The 8-month MLD was found to be significantly larger in the START 40 patients (1.85 mm vs. 1.47 mm, p < 0.0001). The difference seen in the clinical endpoint of TVF (19.3% vs. 25.9%) did not reach statistical significance (p = 0.1). Analysis of the procedural angiograms revealed mismatch between the length of vessel injured and the location of the 90% isodose in 46% of the treated cases. Angiographic analysis revealed that geographic miss was associated with a higher rate of binary restenosis (32% vs. 18% p = 0.04) in the analysis segment.

CONCLUSIONS

This multicenter registry demonstrates the safety and efficacy of a 40-mm 90Strontium/90Yttrium source train in the management of patients with in-stent restenosis. Restenosis rates were lowered with the use of this longer source train when compared to the placebo arm of the START trial for lesions with a maximum vessel injury length of 20 mm. Angiographic analysis identified the importance of the accurate delineation of injury length and correct source positioning. These results support the continued use of beta radiation for the treatment of this disease process.

Long genuine coronary artery lesions treated with stiff tubular or flexible coiled stents. A randomized angiographic follow-up study

OBJECTIVE

To investigate effects of stent flexibility on 6 months' clinical and angiographic outcome in long stented lesions.

DESIGN

A total of 44 genuine coronary artery lesions (lesion length >20 mm and < or =30 mm) were randomized to implantation with a 30 mm long flexible coiled stainless steel stent (Freedom Force, Global Therapeutics) (n = 23) or a 30 mm long stiff tubular stainless steel stent (Crown, Johnson & Johnson) (n = 21).

RESULTS

Target vessel revascularization was performed in 10 patients (45%) in the Freedom Force stent group, and in 7 patients (33%) in the Crown stent group (ns). No significant differences concerning minimum lumen diameter (MLD), early gain, late loss or binary restenosis rate were seen. In the Freedom Force stent group all restenoses were located within the stent. In the Crown stent group three (27%) of the restenoses were located at the edge of the stent (ns).

CONCLUSION

In a limited number of patients no significant differences could be detected in clinical or angiographic parameters between patients treated with long tubular or long coiled stents.

Use of localised intracoronary beta radiation in treatment of in-stent restenosis: the INHIBIT randomised controlled trial

BACKGROUND

In-stent restenosis is a major limitation of intracoronary stenting. Ionising gamma radiation has been shown to reduce recurrence of restenosis after stent placement. We aimed to compare the effects of intracoronary beta radiation treatment with those of placebo for clinical and angiographic outcomes of patients with diffuse in-stent restenosis.

METHODS

332 patients with in-stent restenosis underwent successful coronary intervention, and were then randomly allocated to intracoronary beta radiation with a phosphorus-32 source (n=166) or placebo (166) delivered into a centreing balloon catheter through an automatic afterloader. Longer lesions (>22 mm of dilated length) were treated with tandem positioning of the study wire. The primary safety endpoint was major adverse cardiac events, defined as death, myocardial infarction, and repeat target-lesion revascularisation at 9 months. The primary efficacy endpoint was binary angiographic restenosis rate in the analysis segment during 9-months' follow-up. Analysis was by intention to treat.

FINDINGS

Procedural success, and in-hospital and 30-day complications were similar among the two groups. 24 (15%) patients in the radiated group had the primary safety endpoint of death, myocardial infarction, or repeat target-lesion revascularisation over 290 days compared with 51 [corrected] (31%) in the placebo group (difference 16% [95% CI 7-25], p = 0.0006). Binary angiographic restenosis rate was lower in the radiated group than the placebo group for the entire analysed segment (difference 25% [14--37], p < 0.0001).

INTERPRETATION

Vascular brachytherapy using pure beta-emitter 32P delivered into a centreing catheter via an automatic afterloader can be used to reduce overall revascularisation in patients undergoing treatment for diffuse in-stent restenosis.

Definition of a moving gross target volume for stereotactic radiation therapy of stented coronary arteries

PURPOSE

To measure the effect of cardiac motion on coronary artery stent position during the cardiac cycle as a first step toward exploring the feasibility of stereotactic external beam radiation therapy targeted at restenotic stented coronary arteries.

METHODS AND MATERIALS

The three-dimensional (3D) position of eight coronary artery stents in 8 patients immobilized in a stereotactic body frame was studied noninvasively by single-breathhold ECG-gated multislice spiral computed tomography (MSCT) during 10 retrospectively selected phases, equally distributed throughout the R-R interval of consecutive cardiac cycles. The volume encompassing all measured 3D positions of the stent was measured.

RESULTS

Stent volumes measured by MSCT closely agreed with measurements by quantitative coronary angiography (r > 0.99). The mean of the maximum 3D stent center of mass displacement between any two phases during the cardiac cycle for all eight coronary arteries was 7.5 mm (range 3.3-20.5 mm) in the lateral direction, 8.6 mm (range 2.7-21.6 mm) in the ventrodorsal direction, and 8.2 mm (range 2.5-19.7 mm) in the craniocaudal direction. As was anticipated, the volume encompassing all measured 3D positions of the stent represented only a fraction of the whole heart volume in all patients, i.e., less than 0.6%.

CONCLUSIONS

ECG-gated MSCT allowed the measurement of the volume encompassing multiphase 3D positions of coronary artery stents during the cardiac cycle. This volume, a measure of the cardiac motion effect on coronary artery stent position during the cardiac cycle, represents a moving gross target for stereotactic external beam radiation therapy.

Repeated intracoronary beta radiation for recurrent in-stent restenosis

More than 70% of percutaneous coronary interventions are followed by a stent implantation. In-stent restenosis still occurs in 20-30% of patients and remains a therapeutic challenge. At present only vascular brachytherapy has been shown to be an effective treatment option. We report here one case of recurrent in-stent restenosis after vascular brachytherapy that was successfully treated by a second beta radiation treatment.

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.

Intravascular brachytherapy for peripheral vascular disease

BACKGROUND

International treatment of atherosclerotic narrowed and blocked arteries involves either bypassing the blockage using a graft, widening it 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 (IVBT) 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.

OBJECTIVES

The objective of this review was to assess the efficacy and complications of intravascular brachytherapy on maintaining patency after angioplasty or stent insertion in native vessels or bypass grafts of the iliac or infrainguinal arteries.

SEARCH STRATEGY

The reviewers searched the Cochrane Peripheral Vascular Diseases Group Trials Register (last searched 5 July 2002), the Cochrane Controlled Trials Register (last searched Issue 2, 2002), MEDLINE, EMBASE and reference lists of relevant articles.

SELECTION CRITERIA

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

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed trial quality and extracted data. Adverse events information was collected from the trials.

MAIN RESULTS

One trial was identified which met the inclusion criteria, involving 117 patients, mean age 71 years (43-89). The trial compared PTA versus PTA and IVBT in patients with long-segment de novo or restenotic lesions or occlusions of any length in the femoropopliteal artery. Results were provided at six month follow up in 107 patients (54 PTA alone, 53 PTA+IVBT). The results favoured adjuvant IVBT in preventing restenosis/occlusion with an odds ratio (OR) of 0.35 (95% CI 0.24 to 0.53). Analysis of subgroups showed a significant benefit of IVBT in non-diabetics, OR 0.22 (95% CI 0.07 to 0.69), in those undergoing IVBT in restenotic lesions, OR 0.32 (95% CI 0.10 to 1.01), occlusive lesions, OR 0.19 (95% CI 0.06 to 0.62) and lesions in which the PTA length was greater than 10cm, OR 0.24 (95% CI 0.09 to 0.62).

REVIEWER'S CONCLUSIONS

Results from the only trial available would suggest that IVBT is effective at improving the patency of femoropopliteal arteries undergoing PTA in the short-term, particularly in non-diabetics with long occlusions (>10cm).

Coronary artery radiation therapy for the prevention of restenosis after percutaneous coronary angioplasty, II: Outcomes of clinical trials

Coronary artery radiation therapy (CART) has become the standard of care for the treatment of coronary in-stent restenosis after repeat angioplasty. More than 5,000 patients have been enrolled into various clinical trials using 3 major systems. Based on the results of GAMMA I and START trials, both the Checkmate system using (192)Ir and the Betacath system using (90)Sr/Y have been approved for routine clinical use in the treatment of in-stent restenosis. The Galileo system using (32)P with data from INHIBIT trial is pending premarketing approval. With a better understanding and application of radiation oncology concepts to vascular brachytherapy, problems such as geographic miss and/or edge failure should be overcome. The complication of late thrombosis should also become less notable by eliminating restenting at the brachytherapy procedure and the prolonged use of antiplatelet therapy. Although there are other competing modalities in the very early phases of clinical trials, the future of CART appears bright. The durability of results, lack of any important complications, and confirmation of the efficacy in other sites will further consolidate the role of CART in preventing vascular restenosis.

Intracoronary beta-radiation of de novo coronary lesions using a (186)Re liquid-filled balloon system: six-month results from a clinical feasibility study

Vascular brachytherapy has shown to be effective for in-stent restenosis, but efficacy in de novo lesions remains uncertain. We evaluated feasibility and outcome of intracoronary beta-radiation therapy in de novo coronary lesions using a (186)Re liquid-filled balloon system. Thirty-three patients received 20 Gy (186)Re beta-radiation immediately after balloon angioplasty. The 6-month restenosis rate was 41% (12/29) and restenosis was located within the target lesion in eight patients and at the edges of the injured and irradiated segment, outside the target lesion, in four patients. At 6 months, four patients (12%), all stented during the initial procedure, had experienced a late (> 30 days) total occlusion. Intracoronary beta-radiation therapy of de novo coronary lesions using (186)Re is technically feasible. No reduction in restenosis was observed. The high incidence of late total occlusions may have been prevented by avoiding new stent implantation and prolonging double antiplatelet therapy.

Targeting the adventitia with intracoronary beta-radiation: comparison of two dose prescriptions and the role of centering coronary arteries

PURPOSE

To compare by intravascular ultrasound (IVUS) the efficacy of delivering the prescribed dose to the adventitia between two commonly used dose prescriptions for intracoronary radiotherapy.

METHODS AND MATERIALS

In 59 human postangioplasty coronary vessels, one IVUS cross-section (1 mm thick) with the highest plaque burden was used for creating dose-volume histograms with different hypothetical positions of the source.

RESULTS

On average, prescription to 1 mm beyond lumen surface resulted in delivery of the prescribed dose (20 Gy +/- 20%) to a higher fraction of adventitial volume than with the prescription to 2 mm from the source, with source placed in vessel center, lumen center, or in the IVUS catheter position. Source placement in the lumen center resulted in a low dose heterogeneity to the adventitia and the least dose heterogeneity to the intima.

CONCLUSIONS

Prescription to 1 mm beyond lumen surface appeared more effective in delivering the prescribed dose to the adventitia than the American Association of Physicists in Medicine (AAPM) recommended prescription to 2 mm from the source center. Moreover, centering the source in the lumen provides the better balance of effective adventitial targeting and intimal dose homogeneity. Modification of the current AAPM recommendation for dose prescription for intracoronary radiotherapy should be considered.

Clinical outcomes of patients treated with the cutting balloon and Sr-90 beta-irradiation for instent restenosis

BACKGROUND

The cutting balloon (CB) is an emerging therapy for the treatment of instent restenosis (ISR), but its impact on the clinical outcomes of patients treated with intracoronary radiation therapy (IRT) with Sr-90 compared with conventional PTCA and IRT is not clearly defined.

METHODS

We compared the baseline demographics, angiographic characteristics and clinical outcomes of 102 consecutive patients with ISR treated either with CB+IRT (n=45) or with conventional PTCA+IRT (n=57). The combined endpoint was the occurrence of major adverse cardiac events (MACE), which was defined as a composite of death, myocardial infarction (MI) or target vessel revascularization (TVR) at 6 months.

RESULTS

The CB+IRT group had a shorter mean lesion length (14.3+/-6.5 vs. 21.1+/-15.7, P=.009), and greater utilization of glycoprotein IIb/IIIa inhibitors during the procedure (48.9% vs. 26.3%, P=.02) compared to the PTCA+IRT group. There were no significant differences in the baseline demographics, angiographic and procedural results, or subsequent MACE at 6 months between the two groups.

CONCLUSION

The strategy of CB+IRT using Sr-90 for ISR is associated with similar procedural and clinical outcomes compared to conventional PTCA+IRT. Further study is warranted to determine which patient subgroups would derive the most benefit from this approach.

Endovascular gamma-irradiation to prevent recurrent femoral in-stent restenosis. A case report

We report about a patient with twice recurrence of femoral in-stent restenoses. Centered endoluminal gamma-irradiation with 192 iridium was performed immediately after the second stent recanalization. The irradiation dose was 14 Gy calculated at 2-mm depth of vessel wall. One-year follow-up demonstrates neither clinical nor angiographic evidence of restenosis.

Encapsulation of isotope on novel beta-emitting poly(ethylene terephthalate) surfaces

Recent data indicate that intravascular betaa-irradiation from centrally located sources at the time of balloon angioplasty or stenting reduces proliferation of smooth muscle cells, neointima formation, and restenosis. In an effort to simplify radiation delivery, a novel beta-radiation source was developed based on the adsorption of 32P (phosphoric acid) by pH-sensitive chitosan hydrogel on a poly(ethylene terephthalate) balloon surface. To prevent the 32P-isotope desorption in the patient's blood, the adsorbed phosphoric acid was precipitated as CaHPO4 on the surface by a saturated Ca(OH)2/5% CaCl2 solution. Various polyurethanes were applied to seal the radioactive surface by the dip-coating method. The isotope off-rate results were determined. Optimal results were obtained by serially coating with two polyurethane solutions. This approach holds promise for simplifying and improving the safety, and minimizing the cost of intravascular brachytherapy.

Coronary artery disease in uremia: Etiology, diagnosis, and therapy

Cardiovascular disease is a major challenge to nephrologists, whether we deal with patients with pre-end-stage renal failure, on dialysis or after successful renal transplantation. It is the most common cause for death in patients with a functional allograft, and prevents many dialysis patients from being engrafted. Coronary artery disease is a diagnostic and therapeutic challenge, as it differs in some respects from that seen in non-uremic cohorts, and lacks much of the evidence-base on which therapeutic intervention rests. This review examines the experimental and clinical literature on cardiovascular disease in uremia, focusing on coronary artery disease. We focus on the incidence, presenting syndromes, screening tools, and interventions in the context of acute and chronic coronary syndromes. Recent evidence comparing coronary angioplasty, coronary artery stenting, and bypass surgery in subjects with renal failure is also reviewed. Coronary artery disease is more prevalent in uremia, more difficult to diagnose and less rewarding to treat compared to non-uremic subjects. Many more randomized trials are needed. In the absence of information from such trials, we advocate aggressive control of conventional and novel cardiovascular risk factors, and early intervention for symptomatic coronary disease.

Non-flow limiting dissection leading to late coronary restenosis following intracoronary brachytherapy

We report a coronary dissection detected during routine repeat angiography 6 months following balloon angioplasty and intracoronary radiation. No dissection was seen immediately following the initial procedure. Subsequent late healing of the dissection led to marked restenosis and the development of angina 14 months after the index procedure.

High-dose external beam irradiation inhibits neointima formation in stented pig coronary arteries

PURPOSE

To evaluate high-dose external beam irradiation (EBRT) in a pig coronary stent preparation because low and intermediate-dose EBRT failed to show inhibition of neointima formation in stented animal models.

METHODS AND MATERIALS

Thirty-five stents were implanted in the coronary arteries of 17 pigs. Seven pigs were exposed to a single dose of 21 Gy EBRT immediately after stenting. Ten stented, nonirradiated pigs served as controls. After 4 weeks, the study arteries and myocardium were examined by light and scanning electron microscopy.

RESULTS

Compared with controls, 21 Gy EBRT resulted in a larger lumen area (7.57 +/- 1.67 mm2 vs. 4.00 +/- 1.63 mm2, p <0.001), a smaller neointima area (0.47 +/- 0.43 mm2 vs. 3.36 +/- 2.26 mm2, p <0.001) and a smaller maximal intimal thickness (0.16 +/- 0.09 mm vs. 0.68 +/- 0.31 mm, p <0.001). Unresorbed intramural hemorrhages and adherent mural thrombi were present in the irradiated vessels, which also showed incomplete re-endothelialization. The irradiated hearts demonstrated diffuse interstitial and perivascular inflammation and fibrosis.

CONCLUSIONS

EBRT at 21 Gy to the entire heart significantly inhibited neointima formation in stented pig coronary arteries but also resulted in incomplete re-endothelialization, myocardial inflammation, and fibrosis. Improvements in localization and delivery techniques are required to allow clinical implementation of this technique.

Intravascular radiation accelerates atherosclerotic lesion formation of hypercholesteremic rabbits

OBJECTIVES

The purpose of the present study is to evaluate the effect of intravascular radiation (IR) on the arterial wall of uninjured vessels in the hypercholesteremic rabbit model.

METHODS

Aortas of 24 New Zealand white rabbits were treated with either intravascular 192-Ir gamma-radiation (15 Gy at 2 mm from the center of the source) or were exposed to the source catheter without radiation (sham controls). Following the radiation treatment, the animals were fed a 2% cholesterol diet until euthanasia at 2 (n=8) or 6 (n=16) weeks. Arteries were analyzed using light and scanning electron microscopy (SEM); transforming growth factor beta (TGF-beta) 1, a promoter of connective tissue deposition, was also monitored.

RESULTS

At 2 weeks, SEM analysis showed well-aligned endothelial cells in nonradiated segments, whereas irradiated arteries consistently contained adherent and subendothelial macrophages with focal areas of endothelial disruption. Further radiated segments at 2 weeks showed a 7-fold increase in active TGF beta-1 over nonradiated segments. At 6 weeks, there was a significant increase in plaque and vessel wall area relative to control arteries, however, no differences were noted in the density of actin-positive smooth muscle cells (SMCs) or macrophages. Similarly, no differences were noted in cell proliferation between groups as evidenced by the marker bromodeoxyuridine (BrdU). In contrast, nonirradiated segments frequently contained cellular areas with extracellular lipid.

CONCLUSION

Exposure of previously uninjured vessels to IR and hypercholesterolemia is associated with increased plaque burden and leads to more advanced plaque types. Special care should be taken to minimize radiation exposure in normal vascular segments in hypercholesterolemic patients undergoing radiation therapy.

The influence of guiding equipment and stents on the beta dose distribution in the brachytherapy of in-stent restenosis

BACKGROUND

Intracoronary devices such as stents or guide wires may disturb the dose distribution of beta sources in cardiovascular brachytherapy. As clinical observations indicate that underdosage increases the risk of restenosis, accurate measurements are mandatory to investigate these effects.

METHODS AND RESULTS

Dose perturbation effects of different interventional equipment were systematically determined. Dose distributions of 90Sr-beta line sources were measured by means of a special set-up employing plastic scintillator dosimeters in a water phantom. Shielding effects were found to be 2-5% for single stents and 5-10% for graft stents, stent-in-stent geometries, and guiding catheters. Guide wires close to the source reduced the dose by 25-30%.

CONCLUSIONS

Beta dose perturbation effects of typical stent types are almost negligible and can be corrected by an increased source dwell time if necessary. Guide wires produce effects which are clinically much more important and should therefore be retracted from the irradiation area.

Comparison of different methods to define a target volume for external beam radiation therapy of restenotic coronary arteries

PURPOSE

Different methods have been described to define a target volume for the treatment of restenotic (stented) coronary arteries by external beam radiation therapy (EBRT). The purpose of this study was to explore two methods to define a target for such therapy, and to compare these with previously investigated methods.

MATERIALS AND METHODS

The 3-D position of a stent throughout the cardiac cycle in the three major epicardial coronary arteries was measured in three patients by single-breathhold multislice spiral CT and breathhold biplane conventional X-ray angiography, both indexed in time with the ECG. The volume through which the stent traversed (STV) during the cardiac cycle was determined by use of displacement measurements.

RESULTS

For multislice CT and biplane angiography, respectively, the mean STV was 1.23 cm(3) (range 0.65-2.22 cm(3)) and 2.81 cm(3) (range 1.60-4.99 cm(3)). The STV represented only a fraction of the whole heart volume in all patients, that is, equal to or less than 0.4%.

CONCLUSIONS

Multislice CT and biplane angiography allowed the measurement of a relatively small potential target, that is the STV, for EBRT of restenotic stented coronary arteries. Both studied imaging modalities are instrumental for targeting the STV by highly conformal radiation therapy in case of restenotic stented coronary arteries.

[Current status of intracoronary brachytherapy]

Intracoronary radiation therapy or intracoronary brachytherapy has been developed as an attempt to decrease restenosis after percutaneous coronary interventions. Two parallel technologies, one employing radioactive stents, the other catheter-based radiation (using either beta- or gamma- emitters), have been the subject of numerous animal and human studies. In vivo intravascular ultrasound imaging studies have played a major role in determining the possible mechanism of action of intracoronary radiation therapy and the pathogeny of many of the complications related to the use of this technique. This manuscript is aimed at revising the potential and limitations of intracoronary brachytherapy, as well as at summarizing the results of the currently reported clinical trials.

Dose-response study of intracoronary beta-radiation with 32P in balloon- and stent-injured coronary arteries in swine

PURPOSE

A dose-response study was performed in swine to investigate the vascular effects of 32P over a broad range of doses in order to define the therapeutic window of intracoronary radiotherapy (ICR) with 32P.

METHODS AND MATERIALS

A total of 131 porcine arteries were subjected to balloon injury or stenting followed by 0-36 Gy of ICR from a centered 32P source wire to 1 mm beyond lumen surface or a sham ICR procedure. Animals were euthanized at 4 weeks, and vessels were harvested for histomorphometry.

RESULTS

In the balloon-injured arteries, doses of 7 and 9 Gy did not impact restenosis. At doses of 14-36 Gy, neointima was markedly reduced, with mild dilatation at the highest dose, 36 Gy. In the stent-injured arteries, the lowest dose of 9 Gy failed to reduce neointimal growth, while 14-26 Gy showed the most favorable response.

CONCLUSIONS

ICR with 32P features a broad therapeutic window. Doses of 14-26 Gy to 1 mm beyond lumen surface provided an optimal combination of efficacy and safety. Doses of 7 and 9 Gy were generally ineffective, suggesting a minimum threshold for ICR with 32P to effectively inhibit restenosis.

Experimental and clinical evaluation of the PARIS centering catheter for delivery of endovascular gamma-irradiation of femoropopliteal stenoses

PURPOSE

To investigate the effect of aortic bifurcation and iliac geometry on centered endovascular irradiation (CEI) of femoropopliteal arteries and evaluate procedure-related complications.

MATERIALS AND METHODS

In an experimental tubing model, crossover delivery of the dummy wire by an afterloader using different sheaths (Type I: noncrossover; Type II: crossover, length 40 cm; Type III: crossover, length 65 cm) was examined at simulated angles between 20 degrees -100 degrees (aortic bifurcation) and 0 degrees -100 degrees (iliac vessels). In the clinical phase, 28 heparin-anticoagulated patients underwent percutaneous transluminal angioplasty (PTA) for femoropopliteal stenoses followed by CEI (192-iridium, 14 Gray at 2 mm depth of the vessel wall) delivered with the centering catheter (crossover from contralateral leg using a 65-cm-long 8F sheath in 13 patients, noncrossover from ipsilateral leg using a 10-cm 8F sheath in 15 patients). Measurement of the aortic bifurcation angle before advancement of the crossover sheath and rating of iliac artery tortuosity on both sides was retrospectively performed on angiograms. Fifteen controls received no post-PTA CEI.

RESULTS

Experimental delivery of the dummy wire was not possible at aortic angles less than 40 degrees with Type I, 60 degrees with Type II, and 30 degrees with Type III sheaths. Advancement of the centering catheter was possible in all patients. CEI failed in two patients with crossover (aortic angle <40 degrees ) and in one obese patient with antegrade approach because advancement of the dummy wire was impossible. Thromboembolism rate was 4.6% during irradiation (2.3% after PTA alone).

CONCLUSIONS

CEI in femoropopliteal arteries has a risk of procedure-related thromboembolic complications. Efficacy is affected by vessel geometry.

Dosimetry of a 188rhenium-labeled self-expanding stent for endovascular brachytherapy in peripheral arteries

PURPOSE

Radioactive stents have been proposed as endovascular irradiation device to prevent in-stent restenosis by inhibiting neointimal proliferation. 32P-stents have been used in several studies so far, but require large-scale labeling procedures and endovascular barotrauma for stent expansion supporting the development of edge restenosis. Purpose of this study was to establish dosimetry of a self-expanding nitinol stent for peripheral vascular disease, which was radiolabeled with 188rhenium (188Re) by a dip coating technique.

METHODS AND MATERIALS

The surface of nitinol Memotherm FLEXX stents was polymer-coated providing functional NH(2) groups for diethylenetriaminepentaacetic acid (DTPA) binding, providing the ligand for the complexation of 188Re onto the stent surface. Stability of radiolabeling was tested over 48 h using an in vitro blood circulation (Chandler Loop). Radial and longitudinal dose distributions of a radiolabeled stent were obtained with a plastic scintillator dosimetry system.

RESULTS

Stents with a length of 30 mm and a diameter of 8 mm were labeled with up to 33 MBq 188Re. A total of 69+/-4% of the labeled 188Re remained stable on the stent surface after 48 h. Ninety-five percent of the infinitely accumulated dose was supplied to the target tissue within 72 h. Including correction for radioactivity washout from the stent, the infinitely accumulated dose at 1 mm radial distance from the stent surface was 1.85+/-0.19 Gy/MBq 188Re/cm stent length.

CONCLUSIONS

We developed a technique for radiolabeling of self-expanding nitinol stents with 188Re by dip coating and formation of 188Re chelate complexes. We provide dosimetry data useful for application of this beta-emitting stent for endovascular brachytherapy in peripheral vascular occlusive disease.

Clinical and quantitative coronary angiographic predictors of coronary restenosis: a comparative analysis from the balloon-to-stent era

OBJECTIVES

We sought to assess whether coronary stents have modified the predictive value of demographic, clinical and quantitative coronary angiographic (QCA) predictors of coronary restenosis.

BACKGROUND

A systematic analysis in a large cohort of registries and randomized trials of the percutaneous transluminal coronary angioplasty (PTCA) and stent era has never been performed.

METHODS

A total of 9,120 treated lesions in 8,156 patients included in nine randomized trials and 10 registries, with baseline, post-procedural and six-month follow-up QCA analyses, were included in this study. Predictors of restenosis were identified with univariate and multivariate logistic regression analyses. Interaction terms were introduced in the regression equation to evaluate whether the predictors of restenosis were common to both eras or specific for either one of the revascularization techniques.

RESULTS

The restenosis rate was 35% after PTCA and 19% after angioplasty with additional stenting. In the univariate analysis, favorable predictors were previous coronary artery bypass graft surgery (CABG), stent use, stent length and a large pre-procedural minimal lumen diameter (pre-MLD); unfavorable predictors were weight, body mass index, diabetes mellitus, multi-vessel disease, lesion length and a high residual post-procedural diameter stenosis (post-DS). Predictors specific for the PTCA population were a large post-procedural MLD (post-MLD) as favorable and a severe pre-procedural DS (pre-DS) as unfavorable. Favorable predictors specific for the stent population were a large post-MLD and a large pre-procedural reference diameter (pre-RD). In the multivariate analysis, the best model included the following favorable predictors: stent use, a large post-MLD, previous CABG and the interaction term between stent use and a large post-MLD; unfavorable predictors were lesion length and diabetes mellitus.

CONCLUSIONS

There are no major differences in demographic and clinical predictors of coronary restenosis between PTCA and stent populations. In the modern (stent) era, a severe pre-DS is no longer an unfavorable predictor of restenosis. Still important, but more so in the stent population, is a large post-MLD (optimal result). Finally, a larger pre-RD became a favorable predictor with the advent of stenting.

Mechanisms of angioplasty and stent restenosis: implications for design of rational therapy

Restenosis after angioplasty or stenting remains the major limitation of both procedures. A vast array of drug therapies has been used to prevent restenosis, but they have proven to be predominantly unsuccessful. Recent trends in drug therapy have attempted to refine the molecular and biological targets of therapy, based on the assumption that a single biological process or molecule is critical to restenosis. In contrast, both stenting and brachytherapy, which are highly nonspecific, can successfully reduce restenosis after angioplasty or stenting, respectively. This review examines the biology of both angioplasty and stent stenosis, focussing on human studies. We also review the landmark human trials that have definitively proven successful therapies, such as stenting and brachytherapy. We suggest that the successful trials of stenting and brachytherapy and the failure of other treatments have highlighted the shortcomings of conventional animal models of arterial intervention, and gaps in our knowledge of human disease. In contrast to arguments advocating gene therapy, these studies suggest that the most likely successful drug therapy will have a wide therapeutic range, targeting as many of the components or biological processes contributing to restenosis as possible.

Intravascular radiation therapy after balloon angioplasty of narrowed femoropopliteal arteries to prevent restenosis: results of the PARIS feasibility clinical trial

PURPOSE

To conduct a feasibility study to assess the feasibility, safety, and outcome of endoluminal gamma radiation therapy after balloon angioplasty of superficial femoral artery (SFA) lesions.

MATERIALS AND METHODS

Forty patients with claudication were enrolled in the study and underwent percutaneous transluminal angioplasty (PTA) of SFA lesions with a mean lesion length of 9.8 cm +/- 3.0 and a mean reference vessel diameter of 5.2 mm +/- 3.1. After successful PTA, a segmented centering balloon catheter was positioned to cover the PTA site. The patients were then transported to the radiation oncology suite and treated with a microSelectron HDR afterloader with use of an Ir-192 source with a prescribed dose of 14 Gy, 2 mm into the vessel wall. Ankle-brachial index (ABI) and Rutherford score were evaluated at 1, 6, and 12 months after the procedure and angiographic follow-up was conducted at 6 months.

RESULTS

Radiation was delivered successfully to 35 of 40 patients. There were no procedural complications. Exercise and rest ABI were higher at 1 year (0.72 +/- 0.26 and 0.89 +/- 0.18, respectively) compared to baseline (0.51 +/- 0.25 and 0.67 +/- 0.17, respectively). Maximum walking time on a treadmill increased from 3.41 min +/- 2.41 to 4.43 min +/- 2.49 at 30 days and was 4.04 min +/- 2.8 at 12 months. The angiographic binary restenosis rate at 6 months was 17.2% and the clinical restenosis rate at 12 months was 13.3%. There were no angiographic or clinical adverse events related to the radiation therapy.

CONCLUSIONS

Intraarterial radiation after PTA of SFA lesions with use of high-dose rate gamma radiation is feasible and safe. The angiographic and clinical improvements are sustainable at 1 year and represent a potent antirestenotic therapy for the treatment of narrowed peripheral arteries.

Endovascular and surgical revascularization for patients with intermittent claudication

Intermittent claudication (IC), the most common symptom of peripheral arterial disease (PAD), most often results from flow-reducing lesions in the arteries of the lower extremity that cause exercise-induced muscle ischemia. Intermittent claudication has a significant impact on quality of life and calls attention to PAD, which is secondary to systemic atherosclerosis and a major marker for cardiovascular morbidity and mortality. Most IC patients improve with a regimen that includes aggressive risk-factor modification, exercise, platelet inhibition, and pharmacotherapy to improve walking distance. Selected patients may require endovascular or surgical intervention if it can be offered with low risk. Endovascular procedures, most often percutaneous balloon angioplasty with or without stenting, are recommended for short-segment stenotic lesions in the aortoiliac and infrainguinal arterial segments. Combined platelet inhibition and endoluminal radiation are under study and may be useful to improve long-term outcome with these procedures. Percutaneous hemostatic puncture closure devices can also be used to reduce bleeding complications and allow more aggressive and immediate antithrombotic therapy, further improving results. Operative revascularization is recommended for patients with long-segment and multisegment disease, especially if obstruction is present. Aortofemoral reconstruction is associated with a low operative mortality and an 80% to 85% 5-year patency rate. Iliac reconstruction is recommended for isolated unilateral iliac arterial disease. Infrainguinal arterial reconstruction is associated with a 60% to 80% 5-year patency rate, with better outcomes noted for autogenous conduits than for prosthetic devices. Mechanical modification and pharmacotherapy with platelet inhibitors and anticoagulants improve long-term patency.

Coronary pressure and FFR predict long-term outcome after PTCA

Although coronary stents have been the most important improvement in percutaneous coronary interventions in the last 10 years, it is well known to interventionalists that many patients after percutaneous transluminal coronary angioplasty (PTCA) have a favourable outcome without stenting. Coronary angiography, however, is not sensitive enough to identify those particular patients and it has been suggested that a combination of angiographic and functional criteria would be more suitable to distinguish patients with a low restenosis chance after plain balloon angioplasty. In the present study, the authors investigated the value of coronary pressure measurement for conditional stenting in 85 patients. It was demonstrated that in patients in whom a high fractional flow reserve (FFR) was present (> 0.90), the incidence of coronary events at two-year follow-up was almost three times lower than in those patients with an FFR below 0.90. Such high FFRs could be obtained in approximately 45% of all patients. In an additional group of patients, it was demonstrated by intravascular ultrasound (IVUS) studies that the mechanism of a high FFR after plain balloon angioplasty is most likely the result of a larger lumen compared with patients with a suboptimal FFR. This means that, in patients in whom both the angiographic and the functional result after PTCA is optimal, a restenosis rate is achieved similar to that achieved by stenting. Obviously, in such patients, additional stenting and a number of problems in the long-term possibly related to stenting can be avoided. Therefore, coronary angiography and coronary pressure measurement have a complementary value in the evaluation of PTCA results and such information can be easily obtained by using a pressure wire instead of a regular guidewire.