Nicolas Foin

Incomplete Stent Apposition Causes High Shear Flow Disturbances and Delay in Neointimal Coverage as a Function of Strut to Wall Detachment Distance Implications for the Management of Incomplete Stent Apposition

Background—Lack of re-endothelialization and neointimal coverage on stent struts has been put forward as the main underlying mechanism leading to late stent thrombosis. Incomplete stent apposition (ISA) has been observed frequently in patients with very late stent thrombosis after drug eluting stent implantation, suggesting a role of ISA in the pathogenesis of this adverse event. The aim of this study was to evaluate the impact of different degrees of ISA severity on abnormal shear rate and healing response with coverage, because of its potential implications for stent optimization in clinical practice. Methods and Results—We characterized flow profile and shear distribution in different cases of ISA with increasing strut-wall detachment distance (ranging from 100 to 500 &mgr;m). Protruding strut and strut malapposed with moderate detachment (ISA detachment distance <100 &mgr;m) have minimal disturbance to blood flow as compared with floating strut that has more significant ISA distance. In vivo impact on strut coverage was assessed retrospectively using optical coherence tomography evaluation on 72 stents (48 patients) sequentially at baseline and after 6-month follow-up. Analysis of coverage revealed an important impact of baseline strut-wall ISA distance on the risk of incomplete strut coverage at follow-up. Malapposed segments with an ISA detachment <100 &mgr;m at baseline showed complete strut coverage at follow-up, whereas segments with a maximal ISA detachment distance of 100 to 300 &mgr;m and >300 &mgr;m had 6.1% and 15.7% of their struts still uncovered at follow-up, respectively (P<0.001). Conclusions—Flow disturbances and risk of delayed strut coverage both increase with ISA detachment distance. Insights from this study are important for understanding malapposition as a quantitative, rather than binary phenomenon (present or absent) and to define the threshold of ISA detachment that might benefit from optimization during stent implantation.

Kissing balloon or sequential dilation of the side branch and main vessel for provisional stenting of bifurcations: lessons from micro-computed tomography and computational simulations

OBJECTIVES This study sought to evaluate post-dilation strategies in bifurcation stenting. BACKGROUND In bifurcation stenting practice, it is still controversial how post-dilation should be performed and whether the kissing balloon (KB) technique is mandatory when only the main vessel (MV) receives a stent. METHODS A series of drug-eluting stents (DES) (n = 26) were deployed in a coronary bifurcation model following a provisional approach. After the deployment of the stent in the MV, post-dilation with the KB technique was compared with a 2-step, sequential post-dilation of the side branch (SB) and MV without kissing. RESULTS The percentage of the SB lumen area free of stent struts was similar after KB (79.1 ± 8.7%) and after the 2-step sequence (74.4 ± 11.6%, p = 0.25), a considerable improvement compared with MV stenting only without dilation of the stent at the SB ostium (30.8 ± 7.8%, p < 0.0001). The rate of strut malapposition in the ostium was 21.3 ± 9.2% after KB and 24.9 ± 10.4% after the 2-step sequence, respectively, a significant reduction compared with a simple SB dilation (55.3 ± 16.8%, p < 0.0001) or MV stenting only (47.0 ± 8.5%, p < 0.0005). KB created a significant elliptical overexpansion of the MV lumen, inducing higher stress concentration proximal to the SB. KB also led to a higher risk of incomplete stent apposition at the proximal stent edge (30.7 ± 26.4% vs. 2.8 ± 9.6% for 2-step, p = 0.0016). CONCLUSIONS Sequential 2-step post-dilation of the SB and MV may offer a simpler and more efficient alternative to final KB technique for provisional stenting of bifurcations.

Baseline Instantaneous Wave-Free Ratio as a Pressure-Only Estimation of Underlying Coronary Flow Reserve Results of the JUSTIFY-CFR Study (Joined Coronary Pressure and Flow Analysis to Determine Diagnostic Characteristics of Basal and Hyperemic Indices of Functional Lesion Severity–Coronary Flow Reserve)

Background—Coronary flow reserve has extensive validation as a prognostic marker in coronary disease. Although pressure-only fractional flow reserve (FFR) improves outcomes compared with angiography when guiding percutaneous coronary intervention, it disagrees with coronary flow reserve classification 30% of the time. We evaluated whether baseline instantaneous wave-free ratio (iFR) could provide an improved pressure-only estimation of underlying coronary flow reserve. Methods and Results—Invasive pressure and flow velocity were measured in 216 stenoses from 186 patients with coronary disease. The diagnostic relationship between pressure-only indices (iFR and FFR) and coronary flow velocity reserve (CFVR) was compared using correlation coefficient and the area under the receiver operating characteristic curve. iFR showed a stronger correlation with underlying CFVR (iFR–CFVR, &rgr;=0.68 versus FFR–CFVR, &rgr;=0.50; P<0.001). iFR also agreed more closely with CFVR in stenosis classification (iFR area under the receiver operating characteristic curve, 0.82 versus FFR area under the receiver operating characteristic curve, 0.72; P<0.001, for a CFVR of 2). The closer relationship between iFR and CFVR was found for different CFVR cutoffs and was particularly marked in the 0.6 to 0.9 FFR range. Hyperemic FFR flow was similar to baseline iFR flow in functionally significant lesions (FFR ⩽0.75; mean FFR flow, 25.8±13.7 cm/s versus mean iFR flow, 21.5±11.7 cm/s; P=0.13). FFR flow was higher than iFR flow in nonsignificant stenoses (FFR >0.75; mean FFR flow, 42.3±22.8 cm/s versus mean iFR flow, 26.1±15.5 cm/s; P<0.001). Conclusions—When compared with FFR, iFR shows stronger correlation and better agreement with CFVR. These results provide physiological evidence that iFR could potentially be used as a functional index of disease severity, independently from its agreement with FFR.

Maximal expansion capacity with current DES platforms: a critical factor for stent selection in the treatment of left main bifurcations?

AIMS Left main stenting is increasingly performed and often involves deployment of a single stent across vessels with marked disparity in diameters. Knowing stent expansion capacity is critical to ensure adequate strut apposition after post-dilatation of the stent has been performed. Coronary stents are usually manufactured in only two or three different model designs with each design having a different maximal expansion capacity. Information about the different workhorse designs and their maximal achievable diameter is not commonly provided by manufacturers but, in the absence of this critically important information, stents implanted in segments with major changes in vessel diameter have the potential to become grossly overstretched and to remain incompletely apposed. METHODS AND RESULTS We examined the differences in workhorse designs of six commercially available drug-eluting stents (DES): the PROMUS Element, Taxus Liberté, XIENCE Prime, Resolute Integrity, BioMatrix Flex and Cypher Select stents. Using micro-computed tomography, we tested oversizing capabilities above nominal pressures for the different workhorse designs of the six DES using 4.0, 5.0 and 6.0 mm post-dilatation balloons inflated to 14 atmospheres. MLD could be increased significantly in all stents, only restricted by workhorse design limitations. Minimal inner lumen diameter (MLD) achieved after two successive 6.0 mm post-dilatations of the largest design (4.0 mm stent) was 5.7 mm for the Element, 5.6 mm for the XIENCE Prime, 6.0 mm for the Taxus, 5.4 mm for the Resolute Integrity, 5.9 mm for the BioMatrix and 5.8 mm for the Cypher stent. Significant deformations were observed during stent oversizing with large changes in terms of cell opening and crowns expansion. These are affected by design structure and reveal important differences among all stents tested. Such extensive deformations may alter the functional ability of an individual stent to scaffold a lesion and prevent restenosis. CONCLUSIONS Stent selection based on stent model design may be critical, particularly for treatment of large artery and left main bifurcations where overexpansion is normally required to optimise results and ensure full expansion of the stent.

Optical coherence tomography: from research to practice

Optical coherence tomography (OCT) is a high-resolution imaging technique with great versatility of applications. In cardiology, OCT has remained hitherto as a research tool for characterization of vulnerable plaques and evaluation of neointimal healing after stenting. However, OCT is now successfully applied in different clinical scenarios, and the introduction of frequency domain analysis simplified its application to the point it can be considered a potential alternative to intravascular ultrasound for clinical decision-making in some cases. This article reviews the use of OCT for assessment of lesion severity, characterization of acute coronary syndromes, guidance of intracoronary stenting, and evaluation of long-term results.

Pre-angioplasty instantaneous wave-free ratio pullback provides virtual intervention and predicts hemodynamic outcome for serial lesions and diffuse coronary artery disease.

OBJECTIVES The aim of this study was to perform hemodynamic mapping of the entire vessel using motorized pullback of a pressure guidewire with continuous instantaneous wave-free ratio (iFR) measurement. BACKGROUND Serial stenoses or diffuse vessel narrowing hamper pressure wire-guided management of coronary stenoses. Characterization of functional relevance of individual stenoses or narrowed segments constitutes an unmet need in ischemia-driven percutaneous revascularization. METHODS The study was performed in 32 coronary arteries with tandem and/or diffusely diseased vessels. An automated iFR physiological map, integrating pullback speed and physiological information, was built using dedicated software to calculate physiological stenosis severity, length, and intensity (ΔiFR/mm). This map was used to predict the best-case post-percutaneous coronary intervention (PCI) iFR (iFRexp) according to the stented location, and this was compared with the observed iFR post-PCI (iFRobs). RESULTS After successful PCI, the mean difference between iFRexp and iFRobs was small (mean difference: 0.016 ± 0.004) with a strong relationship between ΔiFRexp and ΔiFRobs (r = 0.97, p < 0.001). By identifying differing iFR intensities, it was possible to identify functional stenosis length and quantify the contribution of each individual stenosis or narrowed segment to overall vessel stenotic burden. Physiological lesion length was shorter than anatomic length (12.6 ± 1.5 vs. 23.3 ± 1.3, p < 0.001), and targeting regions with the highest iFR intensity predicted significant improvement post-PCI (r = 0.86, p < 0.001). CONCLUSIONS iFR measurements during continuous resting pressure wire pullback provide a physiological map of the entire coronary vessel. Before a PCI, the iFR pullback can predict the hemodynamic consequences of stenting specific stenoses and thereby may facilitate the intervention and stenting strategy.

Impact of stent strut design in metallic stents and biodegradable scaffolds

Advances in the understanding of healing mechanisms after stent implantation have led to the recognition of stent strut thickness as an essential factor affecting re-endothelialization and overall long term vessel healing response after Percutaneous Coronary Interventions (PCI). Emergence of Drug-eluting stents (DESs) with anti-proliferative coating has contributed to reducing the incidence of restenosis and Target Lesion Revascularization (TVR), while progress and innovations in stent materials have in the meantime facilitated the design of newer platforms with more conformability and thinner struts, producing lesser injury and improving integration into the vessel wall. Recent advances in biodegradable metal and polymer materials now also allow for the design of fully biodegradable platforms, which are aimed at scaffolding the vessel only temporarily to prevent recoil and constrictive remodeling of the vessel during the initial period required, and are then progressively resorbed thereby avoiding the drawback of leaving an unnecessary implant permanently in the vessel. The aim of this article is to review recent evolution in stent material and stent strut design while understanding their impact on PCI outcomes. The article describes the different metallic alloys and biodegradable material properties and how these have impacted the evolution of stent strut thickness and ultimately outcomes in patients.

Optical coherence tomography for guidance in bifurcation lesion treatment.

Optical coherence tomography (OCT) has higher resolution than IVUS (approximately 10 times), with the potential to precisely measure lumen diameters in the variable geometry of a bifurcational lesion and to identify superficial lipid laden plaques and calcium, relevant to confirm the severity of the lumen obstruction before treatment and guide location and diameter of the stent. In addition, OCT produces fewer strut-induced artifacts and offers precise evaluation of strut apposition in a real-life clinical setting. The increase in the speed of image acquisition consequent to the introduction of frequency domain OCT allows rapid pull-back at a speed of 2 cm/sec, minimising the amount of contrast required to clear blood during image acquisition, with an average injection of 10-18 ml required for the maximal length currently available of 5.6 cm. This allows serial OCT acquisitions, typically before treatment if the lesion is not very severe and flow is expected to be present around the OCT catheter, after predilatation and to assess and guide stent expansion. Repeated OCT examinations at follow-up may help to detect presence and characteristics of strut coverage, a potential predictor of late stent thrombosis. These applications are of particular interest in the context of bifurcational lesion treatment because this condition is still associated with a higher number of malapposed stent struts and frequent impairment of stent expansion, explaining the higher incidence of stent thrombosis and restenosis. In this article, all potential applications of OCT for bifurcational lesion treatment are explored. The use of OCT to characterise plaque components, and to optimise stent expansion and strut apposition are first discussed in detail. The conclusion of the article highlights some future research and technological developments that promise to expand the role of OCT further still.

Increase in J-CTO lesion complexity score explains the disparity between recanalisation success and evolution of chronic total occlusion strategies: insights from a single-centre 10-year experience

Objective To investigate whether treatment of lesions of greater complexity is now undertaken and to assess the rates of procedural success per class of lesion complexity. Design Observational study. Setting Despite impressive progress in treatment strategies and equipment, the success rate of percutaneous coronary intervention for chronic total occlusion (CTO) has remained relatively stable. Participants 483 patients consecutively treated with CTO from 2003 to 2012. Main outcome measures The Multicenter CTO Registry of Japan (J-CTO) score was used to classify lesion complexity. The study population was subdivided into an early (period 1, n=288) and a late (period 2, n=195) period according to the routine implementation of novel techniques and advanced equipment. Results Period 2 was marked by more ‘difficult’ and ‘very difficult’ lesions (J-CTO grades 2 and 3) being attempted, with procedural success increasing from 68.4% to 88.1% (p<0.001) and from 42.0% to 78.9% (p<0.001), respectively. ‘Easy’ and ‘intermediate’ lesions (J-CTO grades 0 and 1) were less common, but with similarly high success rates (89.1% vs 96.6% (p=0.45) for easy, and 86.3% vs 86.1% (p=0.99) for intermediate). Period 2 was characterised by a trend for more successful procedures overall (by 6.1%, p=0.09). Procedural complications were similarly low in both periods. J-CTO score and technical era were identified as independent correlates of success in the total population by logistic regression analysis. Conclusions Advanced CTO techniques and equipment have resulted in an increase in the successful treatment of highly complex lesions. Total success rate did not substantially improve, as it was counterbalanced by the increased rate at which complex lesions were attempted.

Frequency domain optical coherence tomography for guidance of coronary stenting

OBJECTIVE To evaluate the role of Frequency domain optical coherence tomography (FD-OCT) in guiding stent implantation procedures. METHODS Dragonfly-imaging catheter was used pre-intervention, after pre-dilatation or at various stages of stent deployment/post-dilatation to assess lesion severity, characteristics and guide stent expansion/apposition. RESULTS We performed 398 OCT pull-backs in 108 consecutive patients. The 371 pull-backs analysable, had an average length of 35 mm and encompassed 193 lesions (1.8 lesions per patient). Seventy-six percent of patient had AHA-ACC-class B-C lesions. In the pre-intervention group deferral of treatment was decided for 13/68 pullbacks (19.1%), whereas strategies different from conventional predilatation (e.g. thrombectomy, rotablator, cutting-balloon) were decided in 23 cases (33.8%). After full lesion dilatation 96 pullbacks (25.9%, pre-stenting group) were performed, 46 (47.9%) of which suggested proceeding directly with stenting while 50 (52.1%) suggesting further treatment. Out of the 207 pullbacks in post-stenting group, 29 (14%) suggested new stent implantation because of dissection or residual stenosis; 64 (30.9%) suggested further optimization with high pressure/larger-sized balloon. Average number of pull-backs per patient was 3.4 requiring 75.8 ± 19.3 ml of iopamidol. No major complications were observed. Five cases (4.6%) of contrast-induced nephropathy were reported. CONCLUSIONS Repeated examinations with FD-OCT can be safely used to guide stent selection and improve stent expansion and apposition.