Intravascular ultrasonic assessment of stent diameters derived from manufacturer's compliance charts

Polymer Coating Integrity, Thrombogenicity and Computational Fluid Dynamics Analysis of Provisional Stenting Technique in the Left Main Bifurcation Setting: Insights from an In-Vitro Model

Currently, the provisional stenting technique is the gold standard in revascularization of lesions located in the left main (LM) bifurcation. The benefit of the routine kissing balloon technique (KBI) in bifurcation lesions is still debated, particularly following the single stent treatment. We compared the latest-generation drug-eluting stent (DES) with no side branch (SB) dilatation “keep it open” technique (KIO) vs. KBI technique vs. bifurcation dedicated drug-eluting stent (BD-DES) implantation. In vitro testing was performed under a static condition in bifurcation silicone vessel models. All the devices were implanted in accordance with the manufacturers’ recommendations. As a result, computational fluid dynamics (CFD) analysis demonstrated a statistically higher area of high shear rate in the KIO group when compared to KBI. Likewise, the maximal shear rate was higher in number in the KIO group. Floating strut count based on the OCT imaging was significantly higher in KIO than in KBI and BD-DES. Furthermore, according to OTC analysis, the thrombus area was numerically higher in both KIO and KBI than in the BD-DES. Scanning electron microscopy (SEM) analysis shows the highest degree of strut coating damage in the KBI group. This model demonstrated significant differences in CFD analysis at SB ostia with and without KBI optimization in the LM setting. The adoption of KBI was related to a meaningful reduction of flow disturbances in conventional DES and achieved results similar to BD-DES.

Longitudinal stent elongation or shortening after deployment in the coronary arteries: which is dominant?

Background

Stent manufacturers always record stent shortening data while they do not record stent elongation data. The aim of this study is to identify both stent shortening and elongation occurring after deployment in the coronary arteries and know their percentage.

Results

The length of coronary stents was measured by intravascular ultrasound (IVUS) by (1) edge-to-edge (E-E) length, measured from the appearance of the first distal strut to the last proximal strut, and (2) area-to-area (A-A) length, measured from the first distal struts seen at more than one IVUS quadrant to the last proximal struts seen at more than one IVUS quadrant. Stent shortening was defined as both E-E and A-A lengths were shorter than the manufacturer box-stated length (shortened group). Stent elongation was defined as both E-E and A-A lengths were longer than the manufacturer box-stated length (elongated group), otherwise unchanged group. Consecutive 102 stents deployed in ischemic patients were included. Stent elongation was detected in 67.6% (69 stents), and shortening was detected in 15.7% (16 stents), while unchanged stents were detected in 16.7% (17 stents). Although the 3 groups had similar box-stated length and predicted foreshortened length, they had significantly different measurements by IVUS, p<0.001 for each comparison. Differences from box-stated length were 1.9±1.4mm, −1.4±0.4mm, and 0.4±0.3mm, respectively, p<0.001. The elongated group had significantly longer differences from the corresponding box-stated and predicted foreshortened lengths, while the shortened group had significantly shorter differences from the corresponding box-stated length and similar foreshortened length. By multinomial regression analysis, the plaque-media area and stent deployment pressure were the independent predictors of the stent length groups, p=0.015 and p=0.026, respectively.

Conclusions

Change in stent length is not only shortening—as mentioned in the manufacturer documents—but also stent elongation. Stent elongation is dominant, and the most important predictors of longitudinal stent changes are plaque-media area and stent deployment pressure.

Procedural effectiveness with a focused force scoring angioplasty catheter: Procedural and clinical outcomes from the Scoreflex NC trial

BACKGROUND

The Scoreflex NC scoring angioplasty catheter is designed with a short rapid-exchange tip distal to a non-compliant, high-pressure balloon and an integral wire outside of the balloon, such that the guidewire and the integral wire act as scoring elements during balloon inflation. The external scoring elements enable a focal stress pattern facilitating expansion of resistant lesions at lower pressures using a focused force angioplasty effect.

METHODS

Patients undergoing elective percutaneous coronary intervention (PCI) were enrolled in a prospective, single-arm study conducted at 12 centers in the United States. The primary endpoint was device procedural success, defined as the composite of successful device delivery to the target lesion with balloon inflation and deflation; absence of vessel perforation, flow-limiting dissection or reduction in TIMI flow from baseline; and achievement of final TIMI 3 flow.

RESULTS

Among 200 patients (234 lesions), lesion complexities included: bifurcation disease (37.6%), moderate/severe calcification (36.6%), and total occlusions (5.0%). Successful delivery to the target lesion, inflation and removal of the balloon catheter was achieved in 95.5% of patients (191/200). Procedural success was achieved in 93.5% (187/200) of patients, and final TIMI 3 flow was observed in 99.0% of cases (198/200). No unanticipated device-related events occurred. In-hospital major adverse events were reported in 4.5% of patients (9/200), related to periprocedural myocardial infarction (8/200, 4.0%) and target lesion revascularization (1/200, 0.5%).

CONCLUSIONS

Among patients undergoing elective PCI and with varied lesion complexity, these results support the safety and effectiveness of a dilation strategy using the Scoreflex NC scoring catheter.

Comparison of overexpansion capabilities and thrombogenicity at the side branch ostia after implantation of four different drug eluting stents

Interventions in bifurcation lesions often requires aggressive overexpansion of stent diameter in the setting of long tapering vessel segment. Overhanging struts in front of the side branch (SB) ostium are thought to act as a focal point for thrombi formation and consequently possible stent thrombosis. This study aimed to evaluate the overexpansion capabilities and thrombogenicity at the SB ostia after implantation of four latest generation drug-eluting stents (DES) in an in-vitro bifurcation model. Four clinically available modern DES were utilized: one bifurcation dedicated DES (Bioss LIM C) and three conventional DES (Ultimaster, Xience Sierra, Biomime). All devices were implanted in bifurcation models with proximal optimization ensuring expansion before perfusing with porcine blood. Optical coherence tomography (OCT), immunofluorescence (IF) and scanning electron microscope analysis were done to determine thrombogenicity and polymer coating integrity at the over-expanded part of the stents. Computational fluid dynamics (CFD) was performed to study the flow disruption. OCT (p = 0.113) and IF analysis (p = 0.007) demonstrated lowest thrombus area at SB ostia in bifurcation dedicated DES with favorable biomechanical properties compared to conventional DES. The bifurcated DES also resulted in reduced area of high shear rate and maximum shear rate in the CFD analysis. This study demonstrated numerical differences in terms of mechanical properties and acute thrombogenicity at SB ostia between tested devices.

In vivo measurement of stent length by using intravascular ultrasound

Background

What happens to stent length when deployed in a coronary artery? It is the aim of this study.

Results

Consecutive 95 balloon-expandable stents (BES) were studied by intravascular ultrasound (IVUS) imaging. The stent length was measured from the longitudinal view in two ways: (1) edge-to-edge length (E-E) measured between distal and proximal stent frames located at one IVUS quadrant and (2) area-to-area length (A-A) measured between distal and proximal stent frames located at two or more IVUS quadrants. IVUS measurements were compared with the manufacturer-stated length (M-L). The median E-E length was significantly longer than M-L, 18.76 mm [interquartile range (IQR) 15.65–23.60] versus 18.00 mm (IQR 15.00–23.00), respectively, p < 0.0001. Also, the median A-A length was significantly longer, 18.36 mm (IQR 15.19–23.47), p < 0.0001, than M-L. Moreover, the E-E length was significantly different from A-A length, p < 0.0001. Among the stent groups, the differences were significantly present in all drug-eluting stent and bare metal stent (BMS) comparisons, p < 0.0001, except the A-A length versus M-L in BMS only. By multivariate analysis, the predictors of difference in stent length were as follows: lesion length, p = 0.01; pre-intervention minimal diameter of the external elastic membrane (EEM), p = 0.03; lesions present in the left anterior descending branch, p = 0.03; and M-L, p = 0.04.

Conclusions

In the present study, the length of BES measured by IVUS was significantly different from the manufacturer-stated length. In addition to the manufacturer length, other important factors such as lesion length, pre-intervention diameter of EEM, and affected vessel determine the stent length.

Imaging during percutaneous coronary intervention for optimizing outcomes

Angiography is the current gold standard for imaging during percutaneous coronary interventions but has significant limitations. Catheter-based intravascular imaging techniques such as intravascular ultrasound and the more recent optical coherence tomography have the potential to overcome these limitations and thus optimize clinical outcomes. In this update, we discussed the current applications of the available imaging techniques, existing evidence, continuing unmet needs, and potential areas for further research.

Novel ultrahigh molecular weight amorphous PLLA bioresorbable coronary scaffold upsized up to 0.8 mm beyond nominal diameter: An OCT and histopathology study in porcine coronary artery model

OBJECTIVES

The aim of the study was to evaluate the biomechanical properties and healing pattern of novel sirolimus-eluting, ultrahigh molecular weight amorphous poly-L-lactic acid bioresorbable scaffolds (S-BRS) that have been postdilated by 0.55 and 0.8 mm beyond the nominal diameters within the pressure-diameter compliance chart range.

BACKGROUND

Due to the inherent limitations of bioabsorbable polymeric materials, overexpansion/upsizing may be very limited for some BRS such as the benchmark Absorb BVS. The unique biomechanical properties of the novel S-BRS may allow it to be safely upsized.

METHODS AND RESULTS

12 coronary arteries of 4 healthy Yucatan mini-swine underwent implantation of a novel S-BRS. Upsizing by postdilation was performed up to 0.55mm (PLUS 0.55, n = 6) or 0.8 mm (PLUS 0.8, n = 6) in a manner maintaining consistent 1:1.1 stent-to-artery, thus ensuring not only the overexpansion of the scaffold but consistent level of arterial injury. Optical coherence tomography (OCT) follow-up was performed at 28 and 90-days follow-up. There was no statistical difference between the tested groups in terms of acute recoil. OCT analysis after 28 days showed numerically lower levels of neointimal formation in PLUS 0.8 compared to PLUS 0.55 group. These results were sustained at 90-days follow-up. There was no difference in late recoil between studied groups. No scaffold discontinuation, deformation or overlapping of the struts were observed.

CONCLUSIONS

Overexpansion up to 0.8 mm of novel, high strength S-BRS is not associated with worse angiographic outcomes, neointimal formation or biomechanical issues such as scaffold discontinuation, deformation or overlapping of the struts, neither acutely nor chronically. © 2017 Wiley Periodicals, Inc.

Finite Element Analysis of the Implantation Process of Overlapping Stents

Overlapping stents are widely used in vascular stent surgeries. However, the rate of stent fractures (SF) and in-stent restenosis (ISR) after using overlapping stents is higher than that of single stent implantations. Published studies investigating the nature of overlapping stents rely primarily on medical images, which can only reveal the effect of the surgery without providing insights into how stent overlap influences the implantation process. In this paper, a finite element analysis of the overlapping stent implantation process was performed to study the interaction between overlapping stents. Four different cases, based on three typical stent overlap modes and two classical balloons, were investigated. The results showed that overlapping contact patterns among struts were edge-to-edge, edge-to-surface, and noncontact. These were mainly induced by the nonuniform deformation of the stent in the radial direction and stent tubular structures. Meanwhile, the results also revealed that the contact pressure was concentrated in the edge of overlapping struts. During the stent overlap process, the contact pattern was primarily edge-to-edge contact at the beginning and edge-to-surface contact as the contact pressure increased. The interactions between overlapping stents suggest that the failure of overlapping stents frequently occurs along stent edges, which agrees with the previous experimental research regarding the safety of overlapping stents. This paper also provides a fundamental understanding of the mechanical properties of overlapping stents.

Expert Opinion: Optimising Stent Deployment in Contemporary Practice: The Role of Intracoronary Imaging and Non-compliant Balloons

Final stent dimensions remain an important predictor of restenosis, target vessel revascularisation (TVR) and subacute stent thrombosis (ST), even in the drug-eluting stent (DES) era. Stent balloons are usually semi-compliant and thus even high-pressure inflation may not achieve uniform or optimal stent expansion. Post-dilatation with non-compliant (NC) balloons after stent deployment has been shown to enhance stent expansion and could reduce TVR and ST. Based on supporting evidence and in the absence of large prospective randomised outcome-based trials, post-dilatation with an NC balloon to achieve optimal stent expansion and maximal luminal area is a logical technical recommendation, particularly in complex lesion subsets.

Fluoroscopy Assisted Scoring of Myocardial Hypoperfusion (FLASH) ratio as a novel predictor of mortality after primary PCI in STEMI patients

BACKGROUND

The aim of this study was to investigate whether Fluoroscopy Assisted Scoring of Myocardial Hypoperfusion (FLASH) enabled a more accurate assessment of coronary blood flow and prediction of cardiac mortality after primary PCI (pPCI), than the presently used angiographic scores of reperfusion.

METHODS

We included 453 STEMI patients who received pPCI at our hospital. Using the novel FLASH algorithm, based on contrast passage time and quantitative coronary analysis, FLASH flow was measured after pPCI and was used to calculate FLASH ratio of culprit and reference artery. In 28 of the 453 patients, FLASH flow was compared to Doppler-derived-flow.

RESULTS

FLASH flow had a good correlation with Doppler derived flow (Pearson's R=0.65, p<0.001) and had a high inter-observer agreement (ICC=0.83). FLASH flow was significantly lower in patients that died of cardiac death within six months (25.9±17.7 ml/min vs. 38.2±18.8 ml/min, p=0.004). FLASH ratio had a high accuracy of predicting cardiac mortality with a significant higher area under the curve as compared with CTFC and QuBe (p=0.041 and p=0.008). FLASH ratio was an independent predictor of mortality at 6 months (HR=0.98 per 1% increase, p=0.014).

CONCLUSION

FLASH is a simple non-invasive method to estimate coronary blood flow and predict mortality directly following pPCI in STEMI patients, with a higher accuracy compared to the presently used angiographic scores.

Two-in-one aortic valve sizing and valvuloplasty conductance balloon catheter

BACKGROUND

Inaccurate aortic valve sizing and selection is linked to paravalvular leakage in transcatheter aortic valve replacement (TAVR). Here, a novel sizing valvuloplasty conductance balloon (SVCB) catheter is shown to be accurate, reproducible, unbiased, and provides real-time tool for aortic valve sizing that fits within the standard valvuloplasty procedure.

METHODS AND RESULTS

The SVCB catheter is a valvuloplasty device that uses real-time electrical conductance measurements based on Ohm's Law to size the balloon opposed against the aortic valve at any given inflation pressure. Accuracy and repeatability of the SVCB catheter was performed on the bench in phantoms of known dimension and ex vivo in three domestic swine aortic annuli with comparison to computed tomography (CT) and dilator measurements. Procedural workflow and safety was demonstrated in vivo in three additional domestic swine. SVCB catheter measurements had negligible bias or error for bench accuracy considered as the gold standard (Bias: -0.11 ± 0.26 mm; Error: 1.2%), but greater disagreement in ex vivo versus dilators (Bias: -0.3 ± 1.1 mm; Error: 4.5%), and ex vivo versus CT (Bias: -1.0 ± 1.6 mm; Error: 8.7%). The dilator versus CT accuracy showed similar agreement (Bias: -0.9 ± 1.5 mm; Error: 7.3%). Repeatability was excellent on the bench (Bias: 0.02 ± 0.12 mm; Error: 0.5%) and ex vivo (Bias: -0.4 ± 0.9 mm; Error: 4.6%). In animal studies, the device fit well within the procedural workflow with no adverse events or complications.

CONCLUSIONS

Due to the clinical relevance of this accurate, repeatable, unbiased, and real-time sizing measurement, the SVCB catheter may provide a useful tool prior to TAVR. These findings merit a future human study.

Efficacy of non-compliant balloon post-dilation in optimization of contemporary stents: A digital stent enhancement study

Background

There is no evidence from randomized trials for the benefit of routine non-compliant balloon (NCB) post-dilation after stent deployment. Despite being the gold standard, intravascular ultrasound is infrequently performed due to time and cost constraints and a suitable alternative technology is required for routine assessment of stent expansion. The purpose of this study was to assess the contribution of NCB post-dilation in optimizing contemporary stents by using digital stent enhancement (DSE).

Methods

We treated 120 patients with stent insertion and assessed the stents with DSE before and after NCB use. Optimal expansion was defined as the minimum stent diameter (MSD) ≥ 90% of the nominal stent diameter, an adaptation of the MUSIC and POSTIT trial criteria. Stent deployment was performed at 12 atm pressure followed by routine NCB post-dilation at ≥ 14 atm.

Results

The mean reference diameter on QCA was 2.75 mm (SD 0.63) and mean stent diameter was 3.15 mm (SD 0.46). At a mean stent deployment pressure of 11.7 atm (SD 2.4), only 21% of stents were optimally expanded. After NCB inflation at a mean of 16.9 atm (SD 2.8), MSD increased by 0.26 mm (SD 0.24), optimal stent expansion increased from 21% to 58% and mean stent symmetry ratio increased from 0.83 to 0.87 (p < 0.0001).

Conclusions

Contemporary stents are sub-optimally expanded in the majority of cases after standard deployment compared with nominal sizes. Adjunctive NCB post-dilation optimized an additional 37% of stents. DSE analysis can assist in qualitative and quantitative stent assessments and can potentially facilitate a selective NCB post-dilation strategy to achieve optimal stent expansion.

A new method for real-time co-registration of 3D coronary angiography and intravascular ultrasound or optical coherence tomography

We present a new clinically practical method for online co-registration of 3D quantitative coronary angiography (QCA) and intravascular ultrasound (IVUS) or optical coherence tomography (OCT). The workflow is based on two modified commercially available software packages. Reconstruction steps are explained and compared to previously available methods. The feasibility for different clinical scenarios is illustrated. The co-registration appears accurate, robust and induced a minimal delay on the normal cath lab activities. This new method is based on the 3D angiographic reconstruction of the catheter path and does not require operator's identification of landmarks to establish the image synchronization.

Conductance sizing balloon for measurement of peripheral artery minimal stent area

BACKGROUND

Because stent underdeployment occurs frequently, accurate minimal stent area (MSA) measurement during postdilatation is necessary. This study investigated the accuracy and repeatability for MSA determination using a novel conductance balloon (CB) catheter for peripheral vessels.

METHODS

The CB catheter is a standard balloon catheter that measures electrical conductance (ratio of current/voltage drop) in real-time during inflation, which directly relates to the balloon cross-sectional area through Ohm's law. CB measurements were made in 4- to 10-mm phantoms on the bench, ex vivo in stents fully deployed in diseased human peripheral arteries, and in vivo in stents fully deployed in peripheral vessels in six swine. CB measurement accuracy and repeatability were calculated and compared with the known dimension (bench phantoms) or with intravascular ultrasound (IVUS) measurement after stent deployment (ex vivo and in vivo).

RESULTS

CB measurements were highly accurate (error: 1.8% bench, 5% ex vivo, and 5% in vivo) and repeatable (error: 0.9% bench, 1.8% ex vivo, and 1.3% in vivo), with virtually no bias (average difference in measurements: -0.05 mm bench CB vs known phantom diameters, -0.06 mm ex vivo CB vs IVUS, and -0.11 mm in vivo CB vs IVUS).

CONCLUSIONS

The CB sizing capability can be integrated within a standard balloon catheter (two-in-one function) to provide accurate, real-time assessment of MSA to ensure full stent apposition rather than the use of pressure as a surrogate for size.

Compliance charts to guide non-complex small artery stenting: validation by quantitative coronary angiography

OBJECTIVE

To determine whether stent sizing derived from manufacturers' compliance charts provides a reasonable in vivo estimate of final minimum lumen diameter (MLD) when compared with quantitative coronary angiography (QCA).

DESIGN

Single-centre measurement comparison study.

SETTING

Tertiary referral university hospital.

PATIENTS

Fifty cases receiving a single stent for non-complex de novo stenosis were randomly selected from the percutaneous coronary intervention database of our high-volume centre. Restenosis, stent thrombosis, bifurcational disease, rotablation, left main or graft stenting, intravascular ultrasound or kissing balloon inflations were exclusion criteria.

MAIN OUTCOME MEASURES

Equality and limits of agreement (LOA) between compliance chart and QCA measurements of final MLD, especially focusing on patients with small stents<3 mm. The paired t test and Bland-Altman plots were used to compare measurements.

RESULTS

There was no significant difference between compliance chart-derived and QCA final MLD (n=50; mean -0.034 mm, SD 0.35, 95% CI -0.132 to +0.064; p=0.49), with reasonable Bland-Altman LOA between the two methods of assessing final MLD in the overall group (LOA -0.72 to +0.66 mm), as well as in the group of particular interest with Derived final MLD <3 mm (n=30; mean 0.019 mm, SD 0.27, 95% CI -0.082 to +0.119; p=0.71; LOA -0.52 to +0.56 mm).

CONCLUSIONS

Compliance charts provide an acceptable estimate of final MLD and are a reasonable guide to sizing during non-complex stenting, especially in small vessels <3 mm.

Effect of stent inflation pressure and post-dilatation on the outcome of coronary artery intervention. A report of more than 90,000 stent implantations

Background

Percutaneous coronary intervention (PCI) stent inflation pressure correlates to angiographic lumen improvement and stent expansion but the relation to outcome is not clarified. Using comprehensive registry data our aim was to evaluate how stent inflation pressure influences restenosis, stent thrombosis and death following PCI.

Methods

We evaluated all consecutive coronary stent implantations in Sweden during 46 months from 2008 using data from the Swedish Coronary Angiography and Angioplasty Registry (SCAAR). We used logistic regression and Cox proportional hazard modeling to estimate risk of outcomes with different balloon pressures.

Results

In total, 93 697 stents were eligible for analysis and divided into five different pressure interval groups: ≤15 atm, 16–17 atm, 18–19 atm, 20–21 atm and ≥22 atm. The risks of stent thrombosis and restenosis were significantly higher in the ≤15 atm, 18–19 atm and ≥22 atm groups (but not in the 16–17 atm group) compared to the 20–21 atm group. There were no differences in mortality. Post-dilatation was associated with a higher restenosis risk ratio (RR) of 1.22 (95% confidence interval (CI) 1.14–1.32, P<0.001) but stent thrombosis did not differ statistically between procedures with or without post-dilatation. The risk of death was lower following post-dilatation (RR 0.81 (CI 0.71–0.93) P = 0.003) and the difference compared to no post-dilatation was seen immediately after PCI.

Conclusion

Our retrospective study of stent inflation pressure identified a possible biological pattern—the risks of stent thrombosis and of restenosis appeared to be higher with low and very high pressures. Post-dilatation might increase restenosis risk.

Angiographically confirmed stent thrombosis in contemporary practice: insights from intravascular ultrasound

OBJECTIVE

We hypothesized that patients presenting with stent thrombosis (ST) have a high prevalence of stent underexpansion and malapposition when assessed by intravascular ultrasound (IVUS).

BACKGROUND

IVUS can provide mechanistic insight into mechanical factors, including stent underexpansion, malapposition, and fracture that may predispose to ST.

METHODS

All consecutive cases of angiographically confirmed ST from a multicenter registry (from 2005 to 2010) were reviewed. All IVUS images were reviewed off-line for the presence of stent underexpansion, malapposition, and fracture. Kaplan-Meier analysis was used to determine whether use of IVUS at the time of ST was associated with long-term mortality and major adverse cardiovascular events.

RESULTS

IVUS was performed in 32 of 173 subjects with ST (18%). Stent underexpansion was present in 82% of cases and in all cases of early ST, with a mean stent expansion of 0.7 ± 0.23 by MUSIC criteria. Stent malapposition was most frequently observed in very late ST (40%). In-hospital mortality was similar between subjects who had IVUS performed at the time of ST when compared with the non-IVUS group (3.2% vs. 4.3%, P = 0.8). Subjects who had IVUS performed at the time of ST had lower rates of mortality (HR 0.4, 95% CI 0.1-1.6, P =0.2) and major adverse cardiovascular events (HR 0.5, 95% CI 0.2-1.4, P =0.2) at follow-up, but these values were not statistically significant.

CONCLUSIONS

There is a high prevalence of stent underexpansion in early ST, while the prevalence of malapposition is higher in very late ST. Use of IVUS during treatment for ST may identify mechanisms underlying the development of ST.

Expansion of the Multi-Link Frontier™ coronary bifurcation stent: micro-computed tomographic assessment in human autopsy and porcine heart samples

BACKGROUND

Treatment of coronary bifurcation lesions remains challenging, beyond the introduction of drug eluting stents. Dedicated stent systems are available to improve the technical approach to the treatment of these lesions. However dedicated stent systems have so far not reduced the incidence of stent restenosis. The aim of this study was to assess the expansion of the Multi-Link (ML) Frontier™ stent in human and porcine coronary arteries to provide the cardiologist with useful in-vitro information for stent implantation and selection.

METHODOLOGY/PRINCIPAL FINDINGS

Nine ML Frontier™ stents were implanted in seven human autopsy heart samples with known coronary artery disease and five ML Frontier™ stents were implanted in five porcine hearts. Proximal, distal and side branch diameters (PD, DD, SBD, respectively), corresponding opening areas (PA, DA, SBA) and the mean stent length (L) were assessed by micro-computed tomography (micro-CT). PD and PA were significantly smaller in human autopsy heart samples than in porcine heart samples (3.54±0.47 mm vs. 4.04±0.22 mm, p = 0.048; 10.00±2.42 mm(2) vs. 12.84±1.38 mm(2), p = 0.034, respectively) and than those given by the manufacturer (3.54±0.47 mm vs. 4.03 mm, p = 0.014). L was smaller in human autopsy heart samples than in porcine heart samples, although data did not reach significance (16.66±1.30 mm vs. 17.30±0.51 mm, p = 0.32), and significantly smaller than that given by the manufacturer (16.66±1.30 mm vs. 18 mm, p = 0.015).

CONCLUSIONS/SIGNIFICANCE

Micro-CT is a feasible tool for exact surveying of dedicated stent systems and could make a contribution to the development of these devices. The proximal diameter and proximal area of the stent system were considerably smaller in human autopsy heart samples than in porcine heart samples and than those given by the manufacturer. Special consideration should be given to the stent deployment procedure (and to the follow-up) of dedicated stent systems, considering final intravascular ultrasound or optical coherence tomography to visualize (and if necessary optimize) stent expansion.

Intravascular ultrasound assessment of cobalt chromium versus stainless steel drug-eluting stent expansion

It is not clear whether the thin struts and different alloy of a cobalt chromium stent will cause greater acute stent recoil compared to conventional stainless steel stents. We used postintervention intravascular ultrasound (IVUS) examinations to study 99 patients with 116 stented lesions: 61 Xience/Promus stents (cobalt chromium stent group) and 27 Taxus Liberté and 28 Cypher stents (stainless steel stent group). The IVUS images were obtained before and immediately after stent implantation with only the stent-delivery balloon. The ratio of the IVUS-measured to manufacturer-predicted stent diameter and area was the measure of acute stent recoil and expansion. The baseline patient characteristics, lesion morphology, and procedural details were comparable between the 2 groups. The ratio of the IVUS-measured to manufacturer-predicted stent diameter and area was 0.74 versus 0.73 (p = 0.57) and 0.63 versus 0.63 (p = 0.69), respectively, for the cobalt chromium and stainless steel stents. In conclusion, the acute performance of Xience/Promus was similar to that of previous stainless steel stents, and the thinner cobalt chromium metallic platform did not compromise the radial strength of the stent.

Intravascular ultrasound-guided percutaneous coronary interventions in contemporary practice

Intravascular ultrasound imaging has been pivotal in the understanding of coronary artery disease and the development of percutaneous coronary intervention. The ability to analyse vessel walls and measure atherosclerotic lesions more accurately has enabled the field of invasive cardiology to overcome the limits of angiography. In fact, intravascular ultrasound measurements correlate with functional measurement of coronary blood flow, as a result interest in their use for the diagnosis of lesion severity in ambiguous lesions and for left main trunk analysis has grown. On the interventional side, intravascular ultrasound is used to determine the major predictors of restenosis and stent thrombosis, which are the main pitfalls of percutaneous coronary intervention. In the bare-metal stent era, intravascular ultrasound-guided percutaneous coronary intervention was associated with a reduction in restenosis rates because it enabled identification and treatment of the risk factors for complications. Although drug-eluting stents have provided a great technological advance in percutaneous coronary intervention, further reducing the rate of in-stent restenosis, they have not abolished restenosis completely; intravascular ultrasound has also been used in this setting to identify the mechanisms responsible for drug-eluting stent restenosis. As in the bare-metal stent era, identification of the predictors of restenosis and stent thrombosis and their subsequent treatment may offer the promise of improved outcome in the drug-eluting stent era. This review focuses on the potential benefit of intravascular ultrasound-guided percutaneous coronary intervention with regard to restenosis and stent thrombosis in the bare-metal stent and drug-eluting stent eras.

Intravascular ultrasound assessment of expansion of the sirolimus-eluting (cypher select) and paclitaxel-eluting (Taxus Express-2) stent in patients with diabetes mellitus

Patients with diabetes have a higher risk for in-stent restenosis after coronary stent implantation. Drug-eluting stents (DES) are highly effective in reducing in-stent restenosis. Once neointimal hyperplasia is suppressed with DES, the impact of stent underexpansion becomes magnified. The aim of this study was to evaluate DES expansion in patients with diabetes. Ninety-five patients with diabetes were randomized to Cypher Select (n = 48) or Taxus Express-2 (n = 47) stent implantation. Intravascular ultrasound was performed after stent implantation. Stent expansion was defined as the ratio of measured to predicted minimum stent diameter. There was a trend for lower stent expansion in the Cypher Select stent group (0.74 +/- 0.08 vs 0.78 +/- 0.11 in the Taxus Express-2 stent group, p = 0.061). Cypher Select stents achieved a final minimal stent cross-sectional area of 5.5 +/- 1. 8 mm2, compared with 6.4 +/- 1.9 mm2 for Taxus Express-2 stents (p = 0.015). For stents with nominal diameters > or =2.75 mm (Cypher Select n = 40, Taxus Express-2 n = 38), 42.5% of the Cypher Select stents and 10.5% of the Taxus Express-2 stents did not achieve a final minimum stent area of 5 mm2 (p = 0.002). Insulin treatment (relative risk 0.31, 95% confidence interval 0.10 to 0.95, p = 0.041) and stent type (relative risk 0.15, 95% CI 0.04 to 0.53, p = 0.003) were independent predictors of not achieving a minimum stent area >5.0 mm2. In conclusion, an important percentage of DES in patients with diabetes fail to achieve the manufacturers' predicted final minimal stent diameter. Cypher Select stent and insulin treatment were independent predictors of not achieving a minimum stent area >5.0 mm2.

Numerical Study of the Uniformity of Balloon-Expandable Stent Deployment

Stents are small tubelike structures, implanted in coronary and peripheral arteries to reopen narrowed vessel sections. This endovascular intervention remains suboptimal, as the success rate is limited by restenosis. This renarrowing of a stented vessel is related to the arterial injury caused by stent-artery and balloon-artery interactions, and a local subsequent inflammatory process. Therefore, efforts to optimize the stent deployment remain very meaningful. Several authors have studied with finite element modeling the mechanical behavior of balloon-expandable stents, but none of the proposed models incorporates the folding pattern of the balloon. We developed a numerical model in which the CYPHER™ stent is combined with a realistic trifolded balloon. In this paper, the impact of several parameters such as balloon length, folding pattern, and relative position of the stent with respect to the balloon catheter on the free stent expansion has been investigated. Quantitative validation of the modeling strategy shows excellent agreement with data provided by the manufacturer and, therefore, the model serves as a solid basis for further investigations. The parametric analyses showed that both the balloon length and the folding pattern have a considerable influence on the uniformity and symmetry of the transient stent expansion. Consequently, this approach can be used to select the most appropriate balloon length and folding pattern for a particular stent design in order to optimize the stent deployment. Furthermore, it was demonstrated that small positioning inaccuracies may change the expansion behavior of a stent. Therefore, the placement of the stent on the balloon catheter should be accurately carried out, again in order to decrease the endothelial damage.

Nonrandomized comparison of coronary stenting under intravascular ultrasound guidance of direct stenting without predilation versus conventional predilation with a semi-compliant balloon versus predilation with a new scoring balloon

This study was conducted to determine the influence of lesion preparation using the AngioSculpt balloon on final stent expansion. Stent expansion remains an important predictor of restenosis and subacute thrombosis, even in the drug-eluting stent (DES) era. In these patients, the role of different predilation strategies has yet to be established. Two hundred ninety-nine consecutive de novo lesions treated with 1 >2.5-mm DES (Cypher or Taxus) under intravascular ultrasound guidance without postdilation, using 3 implantation strategies, were studied: (1) direct stenting without predilation (n = 145), (2) predilation with a conventional semi-compliant balloon (n = 117), and (3) predilation with the AngioSculpt balloon (n = 37). Stent expansion was defined as the ratio of intravascular ultrasound-measured minimum stent diameter and minimum stent area to the manufacturer's predicted stent diameter and area. These ratios were larger after AngioSculpt predilation, and a greater percentage of stents had final minimum stent areas >5.0 mm(2) (another commonly accepted criterion of adequate DES expansion). Lesion morphology, stent and lesion length, and reference vessel size did not affect DES expansion. In conclusion, in this observational, nonrandomized study, pretreatment with the AngioSculpt balloon enhanced stent expansion and minimized the difference between predicted and achieved stent dimensions.

Intravascular ultrasound assessment of drug-eluting stent expansion

BACKGROUND

In the drug-eluting stent (DES) era, stent expansion remains an important predictor of restenosis and subacute thrombosis. Compliance charts are developed to predict final minimum stent diameter (MSD) and area (MSA). The objectives of the study were (1) to assess DES expansion by comparing intravascular ultrasound (IVUS)-measured MSD and MSA against the values predicted by compliance charts and (2) to compare each DES against its bare-metal stent (BMS) equivalent.

METHODS

We enrolled 200 patients with de novo coronary lesions treated with single, >2.5-mm Cypher (Cordis, Johnson & Johnson, Miami Lakes, FL) (sirolimus-eluting stent [SES], 133 patients) or Taxus (Boston Scientific, Natick, MA) (paclitaxel-eluting stent [PES], 67 patients) stent under IVUS guidance without another postdilation balloon. We used a comparison cohort of 65 equivalent BMS (Express 2 [Boston Scientific], 37 patients; Bx Velocity [Cordis, Johnson & Johnson], 28 patients) deployed under similar conditions.

RESULTS

The DES achieved only 75% +/- 10% of predicted MSD and 66% +/- 17% of predicted MSA; this was similar for SES and PES. Furthermore, 24% of SES and 28% of PES did not achieve a final MSA of 5 mm(2), a consistent predictor of DES failure. The SES achieved 75% +/- 10% of predicted MSA versus 75% +/- 9% for Bx Velocity (P = .9). The PES achieved 79.9% +/- 14% of predicted MSA versus 79% +/- 10% for Express 2 (P = .8). Lesion morphology, arc and length of calcium, stent diameter and length, and implantation pressures did not affect expansion.

CONCLUSIONS

Compliance charts fail to predict final MSD and MSA. A considerable percentage of DES does not achieve minimum standards of stent expansion. The SES and PES achieve similar expansion to their BMS platform, indicating that the polymer coating does not affect DES expansion in vivo. However, stent expansion cannot be predicted from preintervention IVUS lesion assessment.

IVUS makes important strides in 2005

Researchers utilized intravascular ultrasound in unique ways in 2005, from assessing transplant vasculopathy to evaluating long-term drug-eluting stent outcomes to identifying predictors of stent thrombosis. These and other applications signify key developments in the field of intravascular imaging.

Adjunctive Balloon Postdilatation after Stent Deployment: Is It Still Necessary with Drug-Eluting Stents?

Deployment of bare metal stents (BMS) with current stent delivery systems is often associated with suboptimal stent expansion. Adjunctive postdilatation with noncompliant balloons has improved stent expansion with BMS and has been associated with less need for target vessel revascularization (TVR). Drug-eluting stents (DES) have proven highly effective in reducing restenosis and TVR and are now being used in the great majority of percutaneous coronary interventions. Because of the very low rates of TVR with DES, many operators have felt that postdilatation may no longer be necessary. In this review, we present data showing that stent expansion of DES (like BMS) using current stent delivery systems is frequently suboptimal. Furthermore, smaller mimimal stent area (MSA) and stent underexpansion following deployment of DES are strong predictors of stent thrombosis and TVR. Adjunctive postdilatation with noncompliant balloons can increase MSA and decrease the frequency of suboptimal stent deployment and potentially can reduce the frequency of stent thrombosis and TVR. Despite the lack of evidence from randomized clinical trials, we believe the observational data support the use of adjunctive balloon postdilatation following deployment of DES in the great majority of patients.