Recoil following Wiktor stent implantation for restenotic lesions of coronary arteries

The impact of plaque type on strut embedment/protrusion and shear stress distribution in bioresorbable scaffold

AIMS

Scaffold design and plaque characteristics influence implantation outcomes and local flow dynamics in treated coronary segments. Our aim is to assess the impact of strut embedment/protrusion of bioresorbable scaffold on local shear stress distribution in different atherosclerotic plaque types.

METHODS AND RESULTS

Fifteen Absorb everolimus-eluting Bioresorbable Vascular Scaffolds were implanted in human epicardial coronary arteries. Optical coherence tomography (OCT) was performed post-scaffold implantation and strut embedment/protrusion were analysed using a dedicated software. OCT data were fused with angiography to reconstruct 3D coronary anatomy. Blood flow simulation was performed and wall shear stress (WSS) was estimated in each scaffolded surface and the relationship between strut embedment/protrusion and WSS was evaluated. There were 9083 struts analysed. Ninety-seven percent of the struts (n = 8840) were well-apposed and 243 (3%) were malapposed. At cross-section level (n = 1289), strut embedment was significantly increased in fibroatheromatous plaques (76 ± 48 µm) and decreased in fibrocalcific plaques (35 ± 52 µm). Compatible with strut embedment, WSS was significantly higher in lipid-rich fibroatheromatous plaques (1.50 ± 0.81 Pa), whereas significantly decreased in fibrocalcified plaques (1.05 ± 0.91 Pa). After categorization of WSS as low (<1.0 Pa) and normal/high WSS (≥1.0 Pa), the percent of low WSS in the plaque subgroups were 30.1%, 31.1%, 25.4%, and 36.2% for non-diseased vessel wall, fibrous plaque, fibroatheromatous plaque, and fibrocalcific plaque, respectively (P-overall < 0.001).

CONCLUSION

The composition of the underlying plaque influences strut embedment which seems to have effect on WSS. The struts deeply embedded in lipid-rich fibroatheromas plaques resulted in higher WSS compared with the other plaque types.

Predictors and outcomes of acute recoil after ultrathin bioresorbable polymer sirolimus-eluting stents implantation: an intravascular ultrasound in native coronary arteries

BACKGROUND

Ultrathin bioresorbable polymer sirolimus-eluting stents (BP-SESs) may easily lead to acute recoil. This study investigated acute recoil after BP-SES implantation on the basis of intravascular ultrasound (IVUS).

METHODS

We enrolled 40 consecutive stents. Absolute acute recoil by quantitative coronary angiography was defined as the difference between the mean diameter of the last inflated balloon (X) and mean lumen diameter of the BP-SES immediately after balloon deflation (Y). Percent (%) acute recoil was defined as (X-Y)×100/X. IVUS was performed within the culprit lesion. Plaque eccentricity, % plaque burden and calcification grade score were assessed using IVUS. Calcification grade was scored on the basis of quadrants. On the basis of the median acute recoil value of 5.0%, the stents were divided into two groups: low (LAR, n = 20) and high % acute recoil (HAR, n = 20).

RESULTS

Mean % acute recoil was 5.8 ± 5.3%. Plaque eccentricity, % plaque burden and stent/artery ratio were significantly higher in the HAR group than in the LAR group. Significant differences in % acute recoil were not observed regarding the types of stent diameter. In multivariate logistic regression and multiple linear regression analysis, plaque eccentricity and % plaque burden in the culprit plaque were significant positive predictors for the occurrence of % acute recoil. No significant differences, including clinical outcomes, were found between both groups at follow-up.

CONCLUSION

Acute recoil of BP-SESs may be influenced by an eccentric plaque with a large burden, which did not affect long-term outcomes. However, the present study might suggest the proper strategy (e.g. a more exhaustive plaque preparation) before BP-SES implantation in a case with these IVUS characteristics.

Predictors of acute scaffold recoil after implantation of the everolimus-eluting bioresorbable scaffold: an optical coherence tomography assessment in native coronary arteries

This study investigated the predictors of acute recoil after implantation of everolimus-eluting BRS based on optical coherence tomography (OCT). Thirty-nine patients (56 scaffolds) were enrolled. Acute absolute recoil by quantitative coronary angiography was defined as the difference between the mean diameter of the last inflated balloon (X) and the mean lumen diameter of BRS immediately after balloon deflation (Y). Acute percent recoil was defined as (X - Y) × 100/X. Plaque eccentricity (PE) and plaque composition (PC) were assessed by OCT. PC was classified into two different types: calcific (score = 1), fibrous and lipid (score = 0). Based on the mean acute scaffold recoil value of the present study, scaffolds were divided into two groups: the low acute recoil group (LAR, n = 34) and the high acute recoil group (HAR, n = 22). Acute percent and absolute recoil were 6.4 ± 3.0 % and 0.19 ± 0.11 mm. PE, PC score and scaffold/artery ratio were significantly higher in HAR than in LAR. In multivariate logistic regression analysis, PE > 1.49, PC score (score 1) and scaffold/artery ratio >1.07 were significant positive predictors for the occurrence of acute scaffold recoil (OR 10.7, 95 % CI 2.2-51.4, p < 0.01; OR 5.6, 95 % CI 1.9-22.0, p = 0.04; OR 12.4, 95 % CI 2.6-65.4, p < 0.01, respectively). Acute recoil of BRS is influenced by BRS sizing as well as OCT-derived plaque characteristics.

In vivo assessment of stent recoil of biodegradable polymer-coated cobalt-chromium sirolimus-eluting coronary stent system

INTRODUCTION

Immediate and acute stent recoil has been observed following balloon deflation in normal and diseased coronary arteries, and the degree varies by stent design.

METHODS

A total of 19 patients, who underwent elective stent implantation for single de novo native coronary artery lesions, were enrolled: all patients treated with the biodegradable polymer-coated sirolimus-eluting cobalt-chromium coronary stent system (Supralimus-Core(®)). The immediate, acute and cumulative stent recoil was assessed by quantitative coronary angiography. The cumulative stent recoil was measured at 24 h of stent implantation.

RESULTS

The absolute late loss due to recoil was found 0.08 ± 0.19 mm for Immediate Stent Recoil (ISR), 0.05 ± 0.21 mm for Acute Stent Recoil (ASR) and 0.11 ± 0.25 mm for Cumulative Stent Recoil (CSR) respectively.

CONCLUSIONS

In vivo acute stent recoil of the Supralimus-Core(®) has higher radial strength compared to other available standard drug-eluting stents.

MAHOROBA, first-in-man study: 6-month results of a biodegradable polymer sustained release tacrolimus-eluting stent in de novo coronary stenoses

AIMS

To report the 4-month angiographic and 6-month clinical follow-up in first-in-man study using the tacrolimus-eluting bioabsorbable polymer-coated cobalt-chromium MAHOROBA stent.

METHODS AND RESULTS

A total of 47 patients with either stable angina or unstable angina, or silent myocardial ischaemia, based on a de novo coronary stenosis that could be covered by a single 18 mm stent in a native coronary artery with a diameter between 3.0 and 3.5 mm were enrolled at three sites. The primary endpoint was in-stent late loss at 4 months. The secondary endpoints include %volume obstruction of the stents assessed by intravascular ultrasound (IVUS) at 4 months and major adverse cardiac events (MACE) at 6 months. Forty-seven patients were enrolled. Procedural success was achieved in 97.9%. At 4-month follow-up, in-stent late loss was 0.99 +/- 0.46 mm, whereas in-stent %volume obstruction in IVUS was 34.8 +/- 15.8%. At 6 months, there were no deaths, but 2 patients suffered from a myocardial infarction and 11 patients required ischaemia-driven repeat revascularization. The composite MACE rate was 23.4%.

CONCLUSION

This tacrolimus-eluting stent failed to prevent neointimal hyperplasia, despite the theoretical advantages of the tacrolimus, which has less inhibitory effects on endothelial cells than smooth muscle cells.

Design criteria for the ideal drug-eluting stent

The deployment of drug-eluting stents (DESs) is an integral treatment option for patients with coronary artery disease. Although the development and testing of the first-generation DESs focused to a considerable degree on efficacy parameters, including restenosis, recent concerns over late clinical events have prompted a refinement of the design criteria for succeeding generations of these devices. This review assesses design criteria for the ideal DES from 3 complementary perspectives: deliverability, efficacy, and safety. Most new investigational balloon-expandable DES systems have lowered crossing profiles by thinning stent struts using a cobalt chromium alloy, while investigational self-expanding DESs often use nitinol as the platform material. Stents designed to be fully biodegradable are also being developed, with deliverability and performance to be determined in future clinical trials. Refinements in bifurcation-dedicated stents will secure branch accessibility to offer better deliverability in complex lesion morphologies. Experimentation in stent design is already realizing multiple-lesion stenting and the in situ customization of stent length. Rather than simply targeting further reductions in restenosis rates, efforts to improve efficacy are shifting toward a lesion-specific approach, including the design of stents dedicated to bifurcation lesions. Another future direction is a disease-specific approach, or an approach using DESs as local drug-delivery devices. The identification of long-term safety issues with the first-generation DESs has reignited clinical interest in the development of stents that are more biologically based, including fully biodegradable stents and stents using biomimetic and biodegradable polymers. Important performance criteria for future DES agents include more cell-type specificity, broader safety margins, and greater facility at promoting endothelialization and healing.

Comparison of in vivo acute stent recoil between the bioabsorbable everolimus-eluting coronary stent and the everolimus-eluting cobalt chromium coronary stent: Insights from the ABSORB and SPIRIT trials

OBJECTIVES

This study sought to evaluate and compare in vivo acute stent recoil of a novel bioabsorbable stent and a metallic stent.

BACKGROUND

The bioabsorbable everolimus-eluting coronary stent (BVS) is composed of a poly-L-lactic acid backbone, coated with a bioabsorbable polymer containing the antiproliferative drug, everolimus, and expected to be totally metabolized and absorbed in the human body. Because the BVS is made from polymer, it may have more acute recoil than metallic stents in vivo.

METHODS

A total of 54 patients, who underwent elective stent implantation for single de novo native coronary artery lesions, were enrolled: 27 patients treated with the BVS and 27 patients treated with the everolimus-eluting cobalt chromium stent (EES). Acute absolute recoil, assessed by quantitative coronary angiography, was defined as the difference between mean diameter of the last inflated balloon at the highest pressure (X) and mean lumen diameter of the stent immediately after the last balloon deflation (Y). Acute percent recoil was defined as (X - Y)/X and expressed as a percentage.

RESULTS

Acute absolute recoil of the BVS and EES was 0.20 +/- 0.21 mm and 0.13 +/- 0.21 mm, respectively (P = 0.32). Acute percent recoil was 6.9% +/- 7.0% in the BVS group and 4.3% +/- 7.1% in the EES group (P = 0.25).

CONCLUSIONS

In vivo acute stent recoil of the BVS is slightly larger but insignificantly different from that of the EES, implying that the BVS may have good radial strength similar to the metallic stent.

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.

Coronary stenting in diabetic patients: Results from the ROSETTA registry

OBJECTIVE

Diabetes mellitus is associated with high rates of restenosis and adverse outcomes after percutaneous transluminal coronary angioplasty (PTCA). It is unclear whether coronary stenting reduces adverse events in diabetic patients after PTCA. Our purpose was to determine whether coronary stenting improves clinical event rates in diabetic patients after PTCA.

METHODS

The Routine Versus Selective Exercise Treadmill Testing After Angioplasty (ROSETTA) registry was a prospective multicenter observational study examining functional testing and adverse outcomes after successful PTCA.

RESULTS

Among the 791 patients enrolled, 180 were diabetic. A total of 90 diabetics received stents while the remaining 90 patients did not. Baseline clinical characteristics were similar between the 2 groups of patients. However, patients with stents were more likely to have complex lesions, whereas those without stents were more likely to undergo atherectomy and have greater residual coronary stenosis. At 6-month follow-up, the composite end point defined as cardiac death, unstable angina, myocardial infarction, need for repeat PTCA, or coronary artery bypass graft surgery (CABG) occurred in 25.0% of stented and 22.2% of nonstented diabetic patients (P not significant [NS]). A multivariate logistic regression analysis showed that coronary stenting was not associated with a reduced incidence of the composite end point among diabetic patients (odds ratio 0.97, 95% CI 0.46-2.05, P NS).

CONCLUSION

Coronary stenting does not improve clinical event rates in diabetic patients after PTCA.

Mechanical properties of coronary stents determined by using finite element analysis

The mechanical function of a stent deployed in a damaged artery is to provide a metallic tubular mesh structure. The purpose of this study was to determine the exact mechanical characteristics of stents. In order to achieve this, we have used finite-element analysis to model two different type of stents: tubular stents (TS) and coil stents (CS). The two stents chosen for this modeling present the most extreme mechanical characteristics of the respective types. Seven mechanical properties were studied by mathematical modeling with determination of: (1) stent deployment pressure, (2) the intrinsic elastic recoil of the material used, (3) the resistance of the stent to external compressive forces, (4) the stent foreshortening, (5) the stent coverage area, (6) the stent flexibility, and (7) the stress maps. The pressure required for deployment of CS was significantly lower than that required for TS, over 2.8 times greater pressure was required for the tubular model. The elastic recoil of TS is higher than CS (5.4% and 2.6%, respectively). TS could be deformed by 10% at compressive pressures of between 0.7 and 1.3 atm whereas CS was only deformed at 0.2 and 0.7 atm. The degree of shortening observed increases with deployment diameter for TS. CS lengthen during deployment. The metal coverage area is two times greater for TS than for CS. The ratio between the stiffness of TS and that of CS varies from 2060 to 2858 depending on the direction in which the force is applied. TS are very rigid and CS are significantly more flexible. Stress mapping shows stress to be localized at link nodes. This series of finite-element analyses illustrates and quantifies the main mechanical characteristics of two different commonly used stents. In interventional cardiology, we need to understand their mechanisms of implantation and action.

Acute stent recoil: in vivo evaluation of different stent designs

This study sought to investigate the degree of acute recoil of four different stents by means of quantitative coronary angiography. Four hundred and six patients underwent stent implantation for single discrete coronary artery lesion: 105 received a 16 mm Paragon stent, 112 an 18 mm Multilink Duet, 97 a 16 mm NIR Primo stent, and 92 a 15 or 18 mm NIR Royal Advance. Elastic recoil was defined as the difference between mean balloon cross-sectional area (CSA) at the highest pressure and mean CSA after PTCA. The mean stent recoil was 13% +/- 10% CSA (P < 0.001), being statistically greater for the nitinol Paragon stent (21% +/- 11%), intermediate for the multicellular Multilink Duet stent (14% +/- 7%), and minimum for the NIR family (9% +/- 6% and 8% +/- 7%, respectively). The recoil was not homogeneously distributed along the stent length but was lower at the two ends (11% +/- 12% and 13% +/- 11%) and highest in the central part (15% +/- 12%)(P < 0.001). Thus, acute recoil is a significant phenomenon regardless of the mechanical properties and design of new-generation tubular stents.

Procedural and late outcomes following MULTI-LINK DUET coronary stent deployment

The MULTI-LINK DUET is the next generation MULTI-LINK stent with modified strut geometry. Safety and efficacy of the MULTI-LINK DUET were evaluated in a prospective multicenter registry and were compared with prior MULTI-LINK stent experience from the ASCENT randomized trial. A total of 270 patients received 302 MULTI-LINK DUET stents and were evaluated using a composite primary end point of major cardiac events (death, Q-wave and non-Q-wave myocardial infarction, and requirement for coronary revascularization) attributable to the target stenosis cumulative to 30 days following enrollment. Quantitative coronary angiography was performed at a mean follow-up of 6 +/- 2 (+/-SD) months. No difference in primary end point or in angiographic restenosis to 6 months was observed between MULTI-LINK DUET and MULTI-LINK experiences. The MULTI-LINK DUET demonstrated improved device and procedural success, less postprocedural in-stent stenosis, larger postprocedural minimal lumen diameter, and fewer postprocedural marginal dissections compared with the MULTI-LINK stent. Multivariate regression modeling identified stent length, diabetes mellitus, poststent minimal lumen diameter, lesion eccentricity, and current smoking as independent predictors of in-stent restenosis. Thus, the MULTI-LINK DUET Registry demonstrates enhanced procedural performance with clinical and angiographic outcomes similar to those previously observed for the MULTI-LINK stent in the ASCENT randomized trial.

Effect of stent design on reduction of elastic recoil: a comparison via quantitative intravascular ultrasound

The increase in minimum lumen diameter achieved by coronary stent placement can be further enhanced by reducing the immediate recoil that occurs after stent deployment. The effect of various stent designs-flexible coils, slotted tubes, and a locking stent-on minimization of postdilation stent recoil was evaluated using an in vitro model of circumferential compression. The stents were expanded to 7 atm (3.82 +/- 0.02 mm); as pressure was reduced, lumen diameter and cross-sectional area (CSA) were determined by on-line intravascular ultrasound imaging (30 MHz) positioned inside the dilating balloon (n = 10-15 inflation-deflation cycles). Stent recoil was assessed by calculation of percent change in CSA from 7 atm to negative balloon pressure: -33.1 +/- 5.6% (GR-II) and -22.4 +/- 3.8% (Wiktor) in the coil stents; -20.0 +/- 4.2% (JJIS coronary), -8.4 +/- 2.6% (JJIS biliary), and -6.9 +/- 1.5% (Multilink) in the slotted tube stents; and -1.9 +/- 3.2% in the Navius ZR1 locking stent (P < 0.05 vs. Multilink, P < 0.0001 vs. others). A range of resistances to recoil is demonstrated by this model, with coil stent designs undergoing greater elastic recoil than slotted tube stent designs. The locking stent design demonstrated the greatest radial strength and the most reduction in elastic recoil.

Mechanisms of residual lumen stenosis after high-pressure stent implantation: a quantitative coronary angiography and intravascular ultrasound study

BACKGROUND

Intravascular ultrasound (IVUS) studies have demonstrated that stents are frequently suboptimally expanded despite the use of high pressures for deployment. The purpose of this study was to identify the mechanisms responsible for such residual lumen stenosis.

METHODS AND RESULTS

Fifty-seven lesions from 50 patients treated with high-pressure (median+/-interquartile range, 14+/-2 atm) elective (44 de novo, 13 restenotic lesions) stenting were prospectively studied (29 Wiktor, Medtronic; 28 Palmaz-Schatz, Cordis Corp). Balloon subexpansion was calculated as the difference between maximal and minimal balloon cross-sectional areas at peak pressure measured by automatic edge detection; elastic recoil was calculated as the difference between minimal measured balloon size and IVUS-derived minimal lumen area within the stent. Angiographic residual diameter stenosis was 10+/-13% (reference diameter, 3.1+/-0.7 mm; balloon to artery ratio, 1.12+/-0.23) and IVUS-derived stent expansion was 80+/-28%. However, although balloon nominal size was 9.6+/-1.3 mm2 and maximal balloon size measured inside the coronary lumen was 12.5+/-3.2 mm2, final stent minimal lumen area was only 7.1+/-2.2 mm2. Balloon subexpansion of 4.0+/-1.8 mm2 (33%) and elastic recoil of 1.6+/-2.3 mm2 (20%) (both P<0.0001) were the two mechanisms responsible for residual luminal stenosis. Wiktor stent and peak inflation pressure correlated with balloon subexpansion, whereas Wiktor stent, de novo lesion, and minimal lumen area at baseline correlated with elastic recoil.

CONCLUSIONS

Despite high-pressure deployment, lumen dimensions after stenting are only 57% of maximal achievable. Inadequate balloon expansion and elastic recoil are responsible for residual lumen stenosis, suggesting that plaque characteristics and stent resistance deserve further investigation.

Wiktor stent for treatment of chronic total coronary artery occlusions: short- and long-term clinical and angiographic results from a large multicenter experience

OBJECTIVES

This study reports the first multicenter experience with the Wiktor coil stent for treatment of chronic total coronary artery occlusions (CTOs).

BACKGROUND

Percutaneous transluminal coronary angioplasty (PTCA) of CTO is associated with very high restenosis and reocclusion rates. Coronary stenting has been proposed as a means of improving outcome. However, the Wiktor device for CTOs has never been tested in a large patient sample.

METHODS

From January 1993 to December 1996, 89 patients with 91 CTOs underwent Wiktor stent implantation after successful PTCA. The post-stenting regimen consisted of warfarin (Coumadin) plus aspirin in the initial 49 patients (55%) and aspirin plus ticlopidine in 40 patients (45%).

RESULTS

Stenting was successful in 87 patients (98%). At 1 month, 6% of patients had subacute stent thrombosis, 3% had a major bleeding event, and 1% had access-site complications. Subacute stent thrombosis showed univariate association with warfarin therapy (p = 0.009). Angiographic follow-up was obtained in 76 (93%) of 82 eligible patients. The restenosis rate was 32%, including 4% reocclusions. By multiple logistic regression analysis, restenosis was independently associated with multiple stents (adjusted odds ratio [OR] 27.67, 95% confidence interval [CI] 4.25 to 79.95, p = 0.0008) and increasing values of occlusion length (adjusted OR 1.23, 95% CI 1.09 to 1.39, p = 0.001). Freedom from death, myocardial infarction or stented vessel revascularization was 87% and 72% at 1 and 3 years, respectively.

CONCLUSIONS

Short- and long-term clinical and angiographic outcomes are favorable in patients undergoing Wiktor stent implantation in CTO. Further technical improvement is needed to reduce the restenosis rate in patients with long lesions and multiple stents.