Intracoronary brachytherapy: past, present, and future

Biodegradable self-expanding poly-L/D-lactic acid vascular stent: a pilot study in canine and porcine iliac arteries

PURPOSE

To report results of an in vivo pilot study to evaluate the biocompatibility and delivery system of a new biodegradable vascular stent and validate the study design.

METHODS

Two self-expanding intravascular stents, a biodegradable poly-D/L-lactic acid (PLA) and a medical stainless steel stent (Wallstent) were implanted in the common iliac arteries of 2 postpuberal female pigs and 3 laboratory-bred beagle dogs. Specimens were harvested after 45 days in the dogs and 32 days in the pigs for histomorphometry of the stented iliac artery segments. Preliminary measurements were made to assess the reliability of the quantitative histomorphometric measurements before final measurements.

RESULTS

Histomorphometry analyses showed that mean luminal diameter and area were decreased in the PLA stent group (1.97+/-0.48 mm and 14+/-6.4 mm2, respectively) compared to the control stent group (4.28+/-0.83 mm and 61+/-19 mm2, respectively). The intimal thickness was higher in the PLA stent group (0.65+/-0.07 mm) than in the control group (0.44+/-0.21 mm). The mean injury score was 0.19+/-0.12 in the PLA stent group and 0.78+/-0.39 in the controls. In the PLA stent group, the mean inflammation score was 1.46+/-0.78 compared to 0.58+/-0.40 in the control group. There were no differences observed between the animal models.

CONCLUSIONS

The PLA stent showed increased neointimal formation and reduced patency during early follow-up. Mechanical properties of the new biodegradable vascular stents are still inadequate, and the stent and the delivery device require modifications. The study methods were assessed as reliable and reproducible.

The Use of Brachytherapy to Treat Renal Artery In‐Stent Restenosis

The percutaneous treatment of renal artery stenosis has become the accepted revascularization strategy by most physicians treating this disorder. Unfortunately, as renal artery angioplasty and stent implantation become increasingly prevalent the Achilles heel of angioplasty, in-stent restenosis, also rises. There are currently no data suggestive of the optimal treatment strategy for renal artery in-stent restenosis. However, given the similarities in the pathophysiology between renal artery and coronary artery in-stent restenosis, brachytherapy is considered a reasonable option. This is the strategy that has been suggested and used by a number of operators. This case report describes two examples of renal artery in-stent restenosis treated with angioplasty and brachytherapy.

Intracoronary β-irradiation prevents excessive in-stent neointimal proliferation in de novo lesions of patients with high plasma ACE levels. The BetAce randomized trial

BACKGROUND

This study evaluated vascular brachytherapy (VBT) as a potent antiproliferative treatment to prevent in-stent restenosis (ISR) after coronary angioplasty of de novo lesions in patients carrying the D allele of the I/D polymorphism of the ACE gene and high ACE plasma levels (>34 U/l).

METHODS AND MATERIALS

A prospective randomized trial was designed to detect a 30% improvement in the minimal lumen diameter (MLD) of the stenotic artery, as measured by quantitative coronary analysis (QCA), 6 months following VBT at the time of stented angioplasty. All patients were carriers of the D allele of the ACE gene, with plasma ACE levels >34 U/l.

RESULTS

Thirty-one patients (33 stenoses) were allocated to stent implantation (control group) and 30 patients (31 stenoses) to VBT and stented angioplasty. After angioplasty, in-stent MLD was similar in the two groups. At 6 months in the control group, in-stent MLD had decreased to 1.74+/-0.8 versus 2.25+/-1.05 mm in the VBT group (P=.04). The mean in-stent diameter was 2.3+/-0.8 mm in the control group versus 2.9+/-1.05 mm after VBT (P=.02), and the restenosis rate was 37.5% versus 17.9%, respectively (P=.08). At 6 months, a higher need for target vessel revascularization (TVR) was observed in the control group: 35.5% versus 13.3% (P=.04).

CONCLUSIONS

This randomized study confirms that patients with high plasma ACE concentrations are exposed to an increased risk for ISR after coronary stenting. The preventive use of VBT in these patients reduced neointimal formation by 65% such that the MLD at follow-up was increased by 29% compared with the control group.

New devices for percutaneous coronary intervention are rapidly making bypass surgery obsolete

PURPOSE OF REVIEW

This review summarizes recent and cumulative progress in the success, safety, applicability, and durability of percutaneous coronary intervention.

RECENT FINDINGS

Improvements in basic percutaneous coronary intervention (PCI) equipment and the availability of bare metal stents in the mid-1990s improved acute procedural success to 98%, reduced the emergency surgery rate to 0.2%, and reduced the incidence of recurrent symptoms due to restenosis at the treated site to 15 to 20%. The recent availability of drug-eluting stents has reduced the in-stent neointimal proliferation that causes restenosis and reduced the incidence of symptomatic recurrence to less than 5%, rivaling that of bypass surgery. The work on better antithrombotic pharmacology, distal embolic protection, and devices for crossing chronic total occlusions will further add to the armamentarium for catheter-based revascularization.

SUMMARY

Based on progress over the past decade, PCI has grown to represent about two-thirds of all coronary revascularization (800,000 PCI vs 350,000 bypass surgeries). Recent and ongoing progress will make bypass surgery largely obsolete within the next several years.

Requirements for quantitative analysis of intimal reaction in arteries treated with intraluminal stents

PURPOSE

To assess the reliability of quantitative histomorphometry measurements for the intimal reaction that occurs after intraluminal stenting in an animal model.

METHODS

Two self-expanding intravascular stents, a biodegradable poly-D/L-lactic acid (PLA) stent and a stainless steel Wallstent, were implanted in the common iliac arteries of a beagle dog. After 45 days, the histomorphometry of the stented iliac artery segments was quantitatively measured. The relative standard error (RSE) of the estimate was calculated, and the reliability of measurements for maximal (LDmax) and minimal (LDmin) luminal diameters and internal (IELT) and external (EELT) elastic lamina thicknesses was assessed.

RESULTS

The PLA stent required more measurements of variables from a single slide to ensure reliable (RSE<10%) results (1 for LDmax, 1 for LDmin, 8 for IELT, and 4 for EELT) compared to the Wallstent (1 for LDmax, 1 for LDmin, 2 for IELT, and 2 for EELT 2). The measured results were reliable for both stent materials when variables were measured from 2 slides of each segment (proximal/central/distal) of the stent.

CONCLUSIONS

We conclude that these preliminary measurements to estimate the reliability of quantitative histomorphometry measurements should be made and reported before final results are given.

Vascular brachytherapy using a beta emitter source in diabetic patients with in-stent restenosis: angiographic and clinical outcomes

PURPOSE

The management of diabetic patients with restenosis after percutaneous coronary intervention remains a significant challenge. Diabetic patients remain at significant risk of restenosis despite stent implantation. This retrospective analysis was performed to determine the extent to which vascular brachytherapy improves late clinical and angiographic outcomes in diabetic patients compared to conventional therapy and compared to patients' nondiabetic counterparts.

METHODS

Pooled data from two studies (START [Stents and Radiation Trial] and START-40 trials) of patients (204 diabetic, 477 nondiabetic) receiving vascular brachytherapy (VBT) with a (90)Sr/(90)Y source after conventional percutaneous coronary intervention for in-stent restenosis comprise the study population. The radiation delivery system used in both studies was the Beta-Cath system. The prescribed dose at 2 mm from the centerline of the source axis was 18.4 Gy or 23 Gy, depending on vessel diameter. The reference vessel diameter, minimal lumen diameter, and percent diameter stenosis were measured before the intervention, at the conclusion of the procedure, and at the 8-month follow-up examination. The Breslow-Day test was used to formally assess the similarity of treatment effect between diabetic and nondiabetic patients.

RESULTS

Target lesion and target vessel revascularization rates and angiographic restenosis rates in diabetic and nondiabetic patients treated with beta radiation or placebo were analyzed. Diabetic patients were more likely to have longer and more complex coronary lesions. In-hospital outcomes in diabetic and nondiabetic patients were similar, irrespective of treatment status. At 8 months, patients treated with beta radiation exhibited less target lesion revascularization (diabetic: 10.9% vs. 22.7%, p = 0.02; nondiabetic: 12.8% vs. 22.3%, p = 0.007) and less target vessel revascularization (diabetic: 14.7% vs. 25.3%, p = 0.06; nondiabetic: 16.6% vs. 23.6%, p = 0.06) compared to placebo. In-stent binary angiographic restenosis was lower in irradiated patients (diabetic: 19.4% vs. 37.3% for placebo, p = 0.01; nondiabetic: 12.9% vs. 43% for placebo, p < 0.001). However, restenosis beyond the stent site reduced the impact of VBT, regardless of diabetic status. The magnitude of the treatment effect for target lesion and target vessel revascularization rates was similar between diabetic and nondiabetic patients.

CONCLUSIONS

Previously published institutional experiences have suggested that diabetic patients benefit from the use of VBT in the management of in-stent restenosis. This analysis now provides direct evidence to support the role of beta radiation VBT in this patient population. Diabetic patients undergoing this therapy are just as likely to benefit from it as their nondiabetic counterparts.

Endovascular brachytherapy for treatment of bilateral renal artery in-stent restenosis

Percutaneous transluminal angioplasty of renal artery stenosis is an attractive alternative to surgical therapy. However, even with endovascular stenting, the overall rate of restenosis is 21%. While brachytherapy for coronary in-stent restenosis has proven efficacy, its use for renal artery in-stent restenosis has not been formally evaluated. We report a case of bilateral in-stent renal artery restenosis treated with endovascular brachytherapy.

[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.