Proximal Cap Research Articles

Characterisation of a novel porcine coronary artery CTO model

To create a large animal coronary chronic total occlusion (CTO) model. Presence of microvessels within the CTO lumen facilitates guidewire crossing. The patterns and time profiles of matrix changes and microvessel formation during coronary CTO maturation are unknown. CTO were created in 15 swine by percutaneous deployment of a collagen plug. Matrix changes were assessed by histology. Intraluminal neovascularisation was assessed by histology and several imaging modalities, including conventional and 3D spin angiography, micro-computed tomography (micro-CT) imaging, and contrast-enhanced magnetic resonance imaging (MRI), at six and 12 weeks following CTO creation. Matrix changes included an intense inflammatory reaction at six weeks which had partially abated by 12 weeks. A proteoglycan-rich matrix at six weeks was partially replaced with collagen by 12 weeks. Similar changes were noted in the proximal cap which was acellular. Three patterns of microvessel formation were identified and defined based on the presence and extent of a "lead" neovessel. No major differences in pattern or extent of neovascularisation were noted between six and 12 weeks. Heterogeneity in neovascularisation patterns occurs during coronary CTO development in a porcine model. Non-invasive imaging to determine the predominant type of neovascularisation prior to and during CTO revascularisation may improve guidewire crossing success rates. This model may be useful for further exploration of CTO pathophysiology, and may aid in further refinements of in vivo imaging of CTO and development of novel therapeutic approaches to revascularisation of CTO, such as manipulations of the proximal cap, matrix composition, neovessel induction, and device testing.

A Novel Approach to Facilitating Balloon Crossing Chronic Total Occlusions: The “Wire‐Cutting” Technique

Following successful guidewire passage, inability to cross the occluded lesion with a balloon is the most common cause of procedural failure for percutaneous recanalization of chronic total occlusions (CTOs). We sought to evaluate the efficacy of "wire-cutting" technique for facilitating the balloon passage through the lesion during CTO-percutaneous coronary intervention. Sixteen consecutive patients with CTOs were treated by "wire-cutting" technique when a lubricious balloon could not be passed through the lesion after successful guidewire crossing. The main process of the "wire-cutting" technique involved: inserting 2 percutaneous transluminal coronary angioplasty (PTCA) guidewires (A and B) into the distal true lumen; advancing a balloon over guidewire A to the site of the occlusion abutting the proximal cap, the balloon was then inflated and guidewire B was pressed between the balloon and the proximal cap; rapidly withdrawing guidewire B produced a cutting power that crushed the proximal cap thus facilitating balloon crossing. Technique success was defined as balloon having crossed CTO lesions successfully after performing wire-cutting procedure. Both technical success and procedural success were obtained in 10 (62.5%) cases. Technique failure occurred in 6 (37.5%) cases, of which 2 were due to the inability to place a second guidewire into the distal true lumen and the other 4 were due to severe coronary calcification. Of these 4 failures, 2 have final procedure success with the use of Rotablator and the remaining 2 patients were referred for bypass surgery. Major complication included severe coronary dissection that occurred in 1 (6.3%) patient, which was successfully treated by stenting. No other complications were observed. The wire-cutting technique may be considered as a simple and effective approach for facilitating balloon crossing resistant CTO lesions.

Percutaneous Coronary Intervention for Intra-stent Chronic Total Occlusion Assisted by Stent Visualization Enhancement Technology

A 50-year-old female patient with a history of prior acute inferior myocardial infarction successfully treated 2 years earlier by primary percutaneous coronary intervention (PCI) with thrombus aspiration and implantation of a 3x30 mm bare-metal stent in the proximal right coronary artery (RCA) was submitted to coronary angiography after reappearance of effort angina. An initial coronary angiogram showed a chronic total occlusion (CTO) intra-stent with Rentrop III collateral filling of the RCA originating from distal left anterior descending (LAD). A mid LAD 60% stenosis and a 60% mid circumflex stenosis were considered non-significant since fractional flow reserve (FFR) was measured at 0.84 and 0.90 respectively. After demonstrating inferior wall viability by cardiac magnetic resonance imaging (MRI), a PCI was programmed two months after the initial coronary angiogram. The intra-stent CTO was ≥ 30 mm long, with no blunt stump and at least 2 small branches originating at its proximal cap level. Mid and distal RCA antegrade filling existed due to bridging collaterals. The crossing technique by guidewire exchange and use of a microcatheter is described. After balloon predilatation the RCA was recanalized. The use of a stent visualization enhancement technology (StentViz) helped understand the most probable procedure-related restenosis mechanisms (stent undersizing and underexpansion) and guided the subsequent successful implantation of two drug-eluting stents. The use of this technology is described step by step for this intervention.

Cd doping of AlN via ion implantation studied with perturbed angular correlation

AbstractAlN with a wide bandgap of 6.2 eV is a promising candidate for ultraviolet light‐emitting diodes and laser diodes. However, the production of the required p‐type AlN is still challenging. As a possible dopant Cd was suggested among other Group II atoms (Be, Mg, and Zn). In this study the annealing condition of implanted Cd in AlN was investigated with the method of the perturbed angular correlation (PAC). Therefore radioactive 117Cd or 111mCd ions were implanted into thin AlN films on sapphire substrate with an energy of 30 keV and fluences in the range of 1011 ions/cm2.After thorough annealing with a proximity cap of the same material most of the Cd‐probes occupy substitutional lattice sites and almost all implantation damage can be annealed. This results in a distinct frequency in the PAC spectra which increases with temperature. In contrast to the formation of an indium nitrogen‐vacancy complex observed with the probe 111In on substitutional Al‐sites no defects are bound to substitutional Cd impurities. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

141 Effectiveness of modern techniques and the transradial approach for the recanalization of chronic total occlusions; early canadian experience

141 Effectiveness of modern techniques and the transradial approach for the recanalization of chronic total occlusions; early canadian experience

330 A simplified 4-wire strategy to cross chronic total occlusions; early canadian experience

330 A simplified 4-wire strategy to cross chronic total occlusions; early canadian experience

Multicentre experience with the BridgePoint devices to facilitate recanalisation of chronic total coronary occlusions through controlled subintimal re-entry

The major challenge for the interventional treatment of chronic total coronary occlusion (CTO) is a low primary success rate. A common problem is the passage of the recanalisation wire into a subintimal position. New devices, which were evaluated in the first multicentre study in CTOs resistant to a conventional wire approach, may help to facilitate a controlled re-entry into the true lumen. The aim of this study was to assess the safety and efficacy of this approach, with successful true lumen distal wire passage as the primary endpoint. Forty-two patients were enrolled in four centres with high expertise in PCI for CTOs. All CTOs were of at least three months duration, and were initially attempted with dedicated recanalisation wires. After failure to pass or creation of a subintimal dissection, the BridgePoint devices were applied, consisting of a ball-tipped catheter (CrossBoss) to pass the proximal occlusion cap, and a flat-shaped balloon catheter (Stingray catheter) to be inflated within the subintimal space to guide the re-entry into the true vessel lumen with a special wire (Stingray guidewire). The primary endpoint was met in 67% of all patients. A higher success rate seemed to be possible when all devices were used in sequenced beginning with the CrossBoss, and in the case of a subintimal passage, followed by the Stingray. True lumen re-entry failed because of the loss of distally contrast filling and thus loss of a target for re-entry, and by a failure to advance the Stingray balloon far enough distal and parallel to the distal lumen. There were no severe device related complications. In patients with complex CTOs referred to dedicated centres with high experience in CTOs, these results demonstrate the potential of a guided re-entry from a subintimal wire position by use of the BridgePoint devices.

A novel method for the measurement of proximal fibrous cap puncture force in chronic total occlusions: the effect of increasing age

The composition of CTO lesions changes significantly as they age. These changes may adversely affect PCI outcome. We present a robust ex vivo technique to measure the force required to puncture the proximal cap of CTOs, and to determine whether the puncture force differs according occlusion age to examine the effects of compositional changes over time on lesion stiffness. Occlusions were created in 44 rabbit femoral arteries by thrombin injection. Between two and 15 weeks following induction, vessels were harvested and tested in a custom setup to determine the force required to puncture the proximal cap. The puncture force mean values at 2, 6, 12, and 15 weeks were 0.61N, 0.78N, 1.21N and 1.52N, respectively. The puncture force required in occlusions of ≤6 weeks was significantly lower those≥12 weeks (0.72±0.10N versus 1.45±0.13N, p<0.01). Using a cutoff point of 1N, 86% of lesions≤6 weeks of age required<1N compared to 30% of those≥12 weeks. We have shown an objective and reproducible testing system for measuring CTO puncture force. Puncture force is correlated with occlusion age. This technique would be useful to evaluate therapies that alter CTO composition/compliance, as well as guidewire testing.

Annealing Effects on Impurity Band Conduction of ZnSnAs2 Epitaxial Films

Un-doped II-IV-V2 ZnSnAs2 thin films have been grown epitaxially on semi-insulating InP(001) substrates by molecular beam epitaxy using a substrate temperature of Ts=300°C. In-situ reflection high-energy electron diffraction observations during the growth revealed streaky patterns indicating an atomically flat surface. After verification of the resulting stoichiometry by electron probe microanalysis and the crystalline structure by high-resolution X-ray diffraction studies, three samples were cleaved from the as-grown sample and subsequently annealed at temperatures of 300, 320, and 340°C for two hours with face-to-face proximity capping by GaAs wafers to simulate an arsenic atmosphere. The temperature dependence of the Hall coefficient of the as-grown sample and the samples annealed at 300 and 320°C showed equal carrier concentration at the exhaustion and freeze-out ranges, suggesting the validity of the impurity band model for these samples. The measured temperature dependence of the Hall coefficient and resistivity, analyzed within the framework of the impurity band model proposed by Isomura, revealed decreasing total carrier concentration p and impurity band carrier mobility μa, increasing acceptor activation energy Ea and maximum valence band mobility μv with increasing annealing temperature.

The BridgePoint devices to facilitate recanalization of chronic total coronary occlusions through controlled subintimal reentry

In view of the improved long-term patency with drug-eluting stents, the challenge with chronic total coronary occlusion remains a low primary success rate. Modes of failure to open a chronic total coronary occlusion are mainly related to the inability to pass a wire through the proximal occlusion cap, and the most difficult part of the procedure is to guide the wire into the distal true lumen. A frequent situation is a subintimal wire position. The BridgePoint (BridgePoint Medical, MN, USA) family of devices is designed to cope with both of these problems. First, the CrossBoss™ catheter aims at passing through the proximal cap by manual rotation of a blunt proximal tip, and second, in case of a subintimal position, the Stingray™ balloon enables guided reentry from the subintimal space into the true lumen. Certain features of an occlusion might favor the CrossBoss device, while the reentry approach may also be used as a standalone bailout method. The aim is to provide a means to resolve otherwise failed attempts and to make it unnecessary to resort to the more complex and time-consuming retrograde wire techniques through collateral channels with the associated potential higher procedural risks.

Open Sesame Technique for chronic total occlusion

Angioplasty for chronic total occlusion (CTO) of the coronary artery is still technically challenging. New techniques to improve the success rate are still required. The inability to penetrate guidewires into the CTO lesion through the proximal cap is one of the most difficult situations. When any guidewire cannot penetrate into the CTO lesion, and if the lesion has both a hard proximal cap and a side branch ramifying at the proximal end of the lesion, the insertion of stiff guidewires and/or balloon inflation in the side branch may induce a geometrical shift of the hard plaque. This in turn enables the entry of a guidewire into the CTO lesion. This procedure has been termed the "Open Sesame Technique."

Intraplaque therapies for facilitating percutaneous recanalization of chronic total occlusions

Chronic total occlusions (CTOs) are found in up to 30% of angiograms performed on patients with coronary disease. The technical difficulty of performing percutaneous coronary interventions (PCIs) in CTOs, primarily because of the inability to cross CTOs with a guide wire, is reflected in low rates of PCI for CTo (approximately 9% of PCI procedures). The main barrier to successful CTO crossing is the dense collagenous extracellular matrix, particularly at the entrance, known as the 'proximal fibrous cap'. Current interventional strategies to overcome this barrier are based primarily on forceful penetration of the CTO plaque by the use of dedicated CTO guide wires. These extra-stiff wires are designed to transfer maximal force to the tip to create a path within the plaque. However, these wires can also cause vascular complications such as dissections; overall procedural success rates remain modest. Several groups are working on new approaches to actually alter the biology and structural characteristics of the CTO plaque to facilitate guide wire crossing. Preliminary data suggest that plaque-directed therapies aimed at 'priming' it for wire crossing may increase PCI success in these challenging cases. New techniques for plaque modification, either by 'softening' the collagenous matrix (collagenase) or by exposing and enlarging existing microvessels (intravascular thrombolysis, contrast injection) or by inducing new microvessels (angiogenic growth factor[s]) are described in the present review.

Effect of thermal annealing on the properties of narrow-bandgap ZnSnAs2 epitaxial films on InP(001) substrates

ZnSnAs2 epitaxial film has been grown on epi-ready semi-insulating InP(001) substrates by low-temperature molecular beam epitaxy (LT-MBE) technique. The MBE-grown sample was then cleaved into pieces, three of which were subjected to lowtemperature annealing at different temperatures of 300 ∘C, 320 ∘C and 340 ∘C which are equal or slightly higher than growth temperature using face-to-face proximity capping by GaAs wafers to simulate arsenic atmosphere. HR-XRD measurements showed that increasing annealing temperature decreases the lattice constant towards the bulk value. This suggests that indeed the relatively higher lattice constant of ZnSnAs2 epitaxial films is partly, if not wholly, due to defects consequence of low temperature growth. For the as-grown control sample, resistivity of 4.31×10−2 Ω cm, mobility of 17.7 cm2/V −s and hole concentration of 8.18×1018 cm−3 were obtained at room temperature. After annealing at 340 ∘C, the resistivity was increased to 21.0×10−2 Ω cm, the mobility increased to 60.9 cm2/V −s, and the hole concentration was decreased to 4.88×1017 cm−3.

TCT-247: Determining the Hardness of the Proximal and Distal Caps of Chronic Total Occlusions by 64-slice CT for the Retrograde Approach

TCT-247: Determining the Hardness of the Proximal and Distal Caps of Chronic Total Occlusions by 64-slice CT for the Retrograde Approach

Natural History of Experimental Arterial Chronic Total Occlusions

We sought to perform the first systematic study of the natural history of chronic total arterial occlusions (CTOs) in an experimental model. Angioplasty of CTOs has low success rates. The structural and perfusion changes during CTO maturation, which may adversely affect angioplasty outcome, have not been systematically studied. Occlusions were created in 63 rabbit femoral arteries by thrombin injection. Histology, contrast-enhanced magnetic resonance imaging, relative blood volume (RBV) index, and micro-computed tomography imaging were analyzed at 2, 6, 12, and 18 to 24 weeks. Early changes were characterized by an acute inflammatory response and negative arterial remodeling, with >70% reduction of arterial cross-sectional area (CSA) from 2 to 6 weeks. Intraluminal neovascularization of the CTO occurred with a 2-fold increase in total (media + intima) microvessel CSA from 2 to 6 weeks (0.014 +/- 0.002 mm2 to 0.023 +/- 0.005 mm2, p = 0.0008) and a 3-fold increase in RBV index (5.1 +/- 1.9% to 16.9 +/- 2.7%, p = 0.0008). However at later time periods, there were significant reductions in both RBV (3.5 +/- 1.1%, p < 0.0001) and total microvessel CSA (0.017 +/- 0.002 mm2, p = 0.011). Micro-computed tomography imaging demonstrated a corkscrew-like recanalization channel at the proximal end at 6 weeks that regressed at later time points. These vascular changes were accompanied by a marked decrease in proteoglycans and accumulation of a collagen-enriched extracellular matrix, particularly at the entrance ("proximal fibrous cap"). This study is the first to systematically analyze compositional changes occurring during CTO maturation, which may underlie angioplasty failure. Negative remodeling, regression of intraluminal channels, and CTO perfusion, together with the accumulation of dense collagen, may represent important targets for novel therapeutic interventions.

A p-type-doped quantum dot superluminescent LED with broadband and flat-toppedemission spectra obtained by post-growth intermixing under a GaAs proximitycap

Broadband superluminescent light emitting diodes are realized by a post-growth annealingprocess, on modulation p-doped multiple InAs/InGaAs/GaAs quantum dot layerstructures, under a GaAs proximity cap. The device exhibits a large and flat emission withspectral width up to 132 nm at 2 mW. This is mainly attributed to the reduction of theenergy separation between the ground state and the excited state, in addition to the opticalquality of the intermixed modulation p-doped quantum dot materials being comparable tothat of the as-grown sample.

Wire trapping technique combined with retrograde approach for recanalization of chronic total occlusion

Wire trapping technique combined with retrograde approach for recanalization of chronic total occlusion

CTO recanalization by intraocclusion injection of contrast: The microchannel technique

To assess the utilization of microinjection of contrast for the recanalization of chronic total occlusions (CTO). Microchannels in CTOs have been considered important conduits for CTO crossing, utilizing dedicated guidewires. We postulated that microinjection of contrast immediately distal to the proximal cap of the CTO could identify and enlarge these microvessels, creating a passage for crossing the CTO with a floppy guidewire. A total of 32 patients with a CTO were treated with this technique. Following few millimetres penetration of the proximal fibrous cap of the occlusion with a dedicated CTO guidewire, the over-the-wire balloon was advanced into the proximal portion of the occlusion, and 50-100 microg of nitroglycerine followed by 1 ml of contrast was gently injected into the occluded segment. Technical success of the microchannel technique was defined as the ability to visualize the distal true lumen with microinjection of contrast and thereafter cross the CTO with a floppy guidewire in the absence of any dissection. Overall, technical success of the microchannel technique was obtained in 20 (63%) with angiographic success in 19. In 12 (37%) cases there was a technical failure because of dissection, and we obtained recanalization of the artery in 7 of these 12 cases with another technique. There was only one case of periprocedural myocardial infarction in an unsuccessful procedure and no major adverse cardiac events or subacute stent thromboses were observed. Microinjection of contrast immediately distal to the proximal fibrous cap of a CTO may be an additional technique to facilitate recanalization of CTO.

The role of proximity caps during the annealing of UV-ozone oxidized GaAs

This study provides a deeper insight into the chemistry and physics of the common engineering practice of using a proximity cap, while annealing compound semiconductors such as GaAs. We have studied the cases of a GaAs proximity cap, a Si proximity cap, and no proximity cap. Using x-ray photoelectron spectroscopy, it has been found that annealing increases the gallium to arsenic ratio in the oxide layer in all cases. During the annealing of UV-ozone oxidized GaAs, it has been observed that GaAs proximity caps also serve as a sacrificial layer to accelerate the desorption of oxide species. In all cases surface deterioration due to pit formation has been observed, and the depth of pits is found to depend on the effective role played by the capping material. Energy dispersive x-ray analysis provides additional evidence that pits mainly consist of elemental As and gallium oxide, with most of the elemental As situated at the pit-substrate interface. Deposition of a thin layer of gold and subsequent annealing to 500°C for 300s under different capping conditions shows the use of a proximate cap to be practically insignificant in annealing Au deposited films.

In-vitro study of medial strain distribution in the femur during impaction grafting

Impaction bone grafting (IBG) is widely used for revision hip surgery to compensate for bone stock loss. It is performed by impacting morsellized allograft into the femoral canal and acetabulum prior to cementing new total hip components. Per- and post-operative femoral fractures and post-operative implant subsidence are major complications in IBG. The aim of this study was to investigate the strain distribution on the medial side of the femur during impaction grafting and the subsequent stability of the stem under uniaxial cyclic loading. The Exeter IBG technique was used in conjunction with Howmedica X-change instrumentation. Sawbones composite femora were used. An impactometer, which provides a known impaction energy and momentum, was used to standardize the impaction process. Three drop heights, 130, 260, and 390 mm, were used for proximal impaction. In-vitro medial hoop strains and the number of impacts were recorded. A drop height of 260 mm was found to provide sufficient energy for impaction without introducing excessive strains to achieve implant stability. Furthermore, a feasibility study was performed on the use of a proximal impaction cap (PIC) to restrain extrusion of the graft during impaction. Although no significant difference in impaction strains or stem stability in uniaxial cylic loading was found by using a PIC, it is postulated that the design of a proximal impactor could be improved to assist with proximal stem alignment and graft containment.