Microvessels in Chronic Total Occlusions: Pathways for Successful Guidewire Crossing?

Wire-based antegrade dissection re-entry technique for coronary chronic total occlusions percutaneous revascularization: Experience from the ERCTO Registry

BACKGROUND

The recent development and widespread adoption of antegrade dissection re-entry (ADR) techniques have been underlined as one of the antegrade strategies in all worldwide CTO consensus documents. However, historical wire-based ADR experience has suffered from disappointing long-term outcomes.

AIMS

Compare technical success, procedural success, and long-term outcome of patients who underwent wire-based ADR technique versus antegrade wiring (AW).

METHODS

One thousand seven hundred and ten patients, from the prospective European Registry of Chronic Total Occlusions (ERCTO), underwent 1806 CTO procedures between January 2018 and December 2021, at 13 high-volume ADR centers. Among all 1806 lesions attempted by the antegrade approach, 72% were approached with AW techniques and 28% with wire-based ADR techniques.

RESULTS

Technical and procedural success rates were lower in wire-based ADR than in AW (90.3% vs. 96.4%, p < 0.001; 87.7% vs. 95.4%, p < 0.001, respectively); however, wire-based ADR was used successfully more often in complex lesions as compared to AW (p = 0.017). Wire-based ADR was used in most cases (85%) after failure of AW or retrograde procedures. At a mean clinical follow-up of 21 ± 15 months, major adverse cardiac and cerebrovascular events (MACCEs) did not differ between AW and wire-based ADR (12% vs. 15.1%, p = 0.106); both AW and wire-based ADR procedures were associated with significant symptom improvements.

CONCLUSIONS

As compared to AW, wire-based ADR is a reliable and effective strategy successfully used in more complex lesions and often after the failure of other techniques. At long-term follow-up, patient's MACCEs and symptoms improvement were similar in both antegrade techniques.

Magnetically assisted soft milli-tools for occluded lumen morphology detection

Methodologies based on intravascular imaging have revolutionized the diagnosis and treatment of endovascular diseases. However, current methods are limited in detecting, i.e., visualizing and crossing, complicated occluded vessels. Therefore, we propose a miniature soft tool comprising a magnet-assisted active deformation segment (ADS) and a fluid drag-driven segment (FDS) to visualize and cross the occlusions with various morphologies. First, via soft-bodied deformation and interaction, the ADS could visualize the structure details of partial occlusions with features as small as 0.5 millimeters. Then, by leveraging the fluidic drag from the pulsatile flow, the FDS could automatically detect an entry point selectively from severe occlusions with complicated microchannels whose diameters are down to 0.2 millimeters. The functions have been validated in both biologically relevant phantoms and organs ex vivo. This soft tool could help enhance the efficacy of minimally invasive medicine for the diagnosis and treatment of occlusions in various circulatory systems.

Identification of micro-channels within chronic total occlusions using contrast-enhanced ultrasound

BACKGROUND

Vascular micro-channels within chronic total occlusions (CTO) have been identified in histopathology and animal studies. They have been proposed as a potential path for achieving endovascular crossing via the lumen. There are currently no noninvasive means of imaging these structures. The aim of this study was to investigate whether contrast-enhanced ultrasound (CEUS) examination can identify micro-channels within CTO in humans.

METHODS

CTO within the femoropopliteal arteries were imaged with CEUS examination in 38 patients. Segments containing micro-channels were identified and their length measured. The proportion of occlusion length containing micro-channels was assessed for each case. Micro-channel appearances including linear or tortuous configuration, crossing of occlusion caps, and connections to vasa vasorum were recorded.

RESULTS

The median CTO length was 17.0 cm (interquartile range [IQR], 6.9-27.9 cm) and median age of CTO was 12 months (IQR, 6-16 months). Micro-channels were identified in 92.1% of cases (35/38). The median length within a lesion containing micro-channels was 6.4 cm (IQR, 2.4-14.3 cm) and median proportion of CTO containing micro-channels was 47.9% (IQR, 1.7%-28.5%). A linear micro-channel configuration was seen in 84.2% of cases and a tortuous configuration was seen in 57.9% of cases. Micro-channel connections through the cap were seen in 50% (19/38 cases) and connections to the vasa vasorum in 71.1% (27/38 cases). No association was found between the proportion of each lesion containing micro-channels and CTO age, lesion length or calcification severity. There were no adverse effects related to contrast use.

CONCLUSIONS

CEUS can be used to detect micro-channels in CTO in human femoropopliteal arteries. This imaging technique is safe and minimally invasive and may represent a practical method for selection of occlusion crossing method. Further work is required to determine whether identification of micro-channels can be used to improve treatment decision-making and provide a better understanding of the natural history of femoropopliteal CTO.

The Canadian Contribution to Science, Techniques, Technology, and Education in Chronic Total Occlusion Percutaneous Coronary Intervention

Chronic total occlusions are considered the most complex coronary lesions in interventional cardiology. This article reviews the Canadian clinical and academic contributions to this field, including innovative procedural techniques, teaching and proctoring, clinical research, and the development of novel tools and therapies.

Native Microchannel Recanalization with Orbital Atherectomy as a Viable Alternative to Failed Standard Recanalization of TASC II D Aortoiliac Occlusive Disease

BACKGROUND

Endovascular treatment of Trans-Atlantic Inter-Society Consensus (TASC) II D aortoiliac lesions is now an accepted form of revascularization. We sought to demonstrate that native microchannel recanalization and orbital atherectomy is a successful recanalization method of TASC II D aortoiliac lesions refractory to standard recanalization techniques.

METHODS

Four consecutive patients from 2016 to 2018 with symptomatic TASC II D aortoiliac occlusive disease prohibitive for open bypass and failed traditional prodding guidewire or device recanalization technique were identified and underwent advanced native microchannel selection and subsequent orbital atherectomy (Cardiovascular Systems, Inc, St Paul, MN). Native microchannels of the calcified lesions were probed and traversed with a 0.014″ wire. The atherectomy crown was tracked over the wire, and orbital atherectomy was initiated with a 1.25 mm crown starting at the lowest revolution and continued until the microchannel is sufficiently large to track a 1.2 mm-balloon for angioplasty. Serial microchannel angioplasty with exchange for stiffer and/or larger profile wires and balloons was achieved until a covered stent could be safely deployed across the target lesion. The kissing stent technique was then used to recreate the aortic bifurcation. A ViperSlide lubricant solution was used in all cases per indication for use. Patients were all heparinized to maintain an activated clotting time of 250. Lesion characteristics, survival, limb salvage, patency, and change in clinical symptoms were also analyzed.

RESULTS

All 4 patients underwent successful native microchannel recanalization and orbital atherectomy of the common iliac artery (CIA). There were no intraoperative ruptures, embolizations, or dissections. All 4 patients presented with unilateral CIA occlusion with contralateral CIA stenosis. The average occlusion lesion length of the CIA was 6.0 cm. The average contralateral stenosis length was 2.3 cm. The kissing stent technique was used in all patients for reconstruction of the aortic bifurcation. At 30 days, all patients had improvement in pain and primary patency of 100%. Long-term follow-up at 21.6 months noted continued improvement in symptoms and primary patency of 75%. The fourth patient died at 4 months from lung cancer with occluded iliac stents by imaging at that time.

CONCLUSIONS

Native microchannel recanalization with subsequent orbital atherectomy is an option in high-risk patients with TASC II D aortoiliac disease who have failed traditional recanalization techniques. Further work in proper patient selection and safe utilization of atherectomy devices in the CIA is needed.

Determination of predictors of successful recanalization of the chronic occlusions of coronary arteries by means of CT-coronarography method

The review illuminated actual issues of the diagnostic efficiency of computed tomography (CT) of the coronary arteries in the planning of the procedure percutaneous coronary intervention (PCI) in patients with chronic occlusion of coronary arteries (CTO). The results of researches of detection of predictors of unsuccessful recanalization according to traditional coronary angiography (CAG) and CT angiography were presented. The major CT characteristics of the CTO, which can supplement the coronary angiography data to predict outcomes of the PCI were discussed.

Coronary chronic total occlusion intervention: A pathophysiological perspective

Percutaneous coronary intervention (PCI) of chronic total occlusion (CTO) is the last frontier in coronary intervention. PCI of CTO carries multiple advantages, such as significant improvement in symptoms, improvement in abnormal wall motion and left ventricular function and, possibly, increased long-term survival. As of today the procedural success is markedly improved because of technical innovations and is limited to highly experienced operators. To enhance the overall success rate from a worldwide perspective, a thorough understanding of its pathophysiology is critical to further development of newer techniques and technologies. In this review, the author outlines in-depth the evidence that underpins our understanding of CTO pathophysiology and its insight into CTO intervention that incorporates various steps and techniques to cross the lesion.

Recanalization of Chronic Total Occlusion Lesions: A Critical Appraisal of Current Devices and Techniques

Chronic Total Occlusion (CTO) has been considered as one of the "final frontier" in interventional cardiology. Until recently, the patients with CTO are often managed surgically or medically due to lack of published evidence of clinical benefits and lower success rate of percutaneous recanalization of CTO. However, the introduction of enhanced guidewires, microcatheters combined with novel specialized devices and techniques reduce the number of unapproachable CTO. In this review article, current techniques and devices of percutaneous recanalization of CTO have been systematically summarized, which may help budding interventional cardiologists to theoretically understand these complex procedures and to deliver safe and effective percutaneous management of CTO to the patients.

CTO pathophysiology: how does this affect management?

Chronic total occlusion (CTO) pathophysiology has been described in a few, small studies using post mortem histology, and more recently, in vivo intravascular ultrasound (IVUS) to analyse the constituents of occluded segments. Recent improvements in equipment and techniques have revealed new insights into physical characteristics of occluded coronaries, which in turn enable predictable procedural success. The purpose of this review is to consider the published evidence describing CTO pathophysiology from the perspective of the hybrid algorithm approach to CTO PCI.

Methods: Literature searches using “Chronic Occlusion”, “angioplasty”, and” pathology” as keywords. Further searches on “coronary” “collateral”, “Viability”. Bibliographies were scrutinised for further key publications in an iterative process. Papers describing animal models were excluded.

Infrapopliteal arterial recanalization: A true advance for limb salvage in diabetics

The world is facing an epidemic of diabetes; consequently in the next years, critical limb ischemia (CLI) due to diabetic arterial disease, characterized by multiple and long occlusions of below-the-knee (BTK) vessels, will become a major issue for vascular operators. Revascularization is a key therapy in these patients as restoring adequate blood supply to the wound is essential for healing, thus avoiding major amputations. Endoluminal therapy for BTK arteries is now a key part of the vascular specialist armamentarium. Tibial artery endovascular approaches have been shown to achieve high limb salvage rates with low morbidity and mortality and endovascular interventions one should now consider to be the first line treatment in the majority of CLI patients, especially in those with associated medical comorbidities. To do so, the vascular specialist requires detailed knowledge of the BTK endovascular techniques and devices. The first step decision in tibial endovascular therapy is access. In this context, the anterograde ipsilateral approach is generally preferred. The next critical decision is the choice of the vessel(s) to be approached in order to achieve successful limb salvage. Obtaining pulsatile flow to the correct portion of the foot is the paramount for ulcer healing. As such, a good understanding of the current angiosome model should enhance clinical results. The devices used should be carefully selected and optimal choice of guide wire is also extremely important and should be based on the characteristics of the lesion (location, length, and stenosis/occlusion) together with the characteristics of the guide wire itself (tip load, stiffness, hydrophilic/hydrophobic coating, flexibility, torque transmission, trackability, and pushability). Passing through chronic total occlusions can be quite challenging. The vascular interventional radiologist needs therefore to master the techniques that have been recently described: anterograde approaches, including the drilling technique, the penetrating technique, the subintimal technique and the parallel technique; subintimal arterial flossing with anterograde-retrograde procedures (Safari); the pedal-plantar loop technique and revascularization through collateral fibular artery vessels.

New percutaneous approaches for chronic total occlusion of coronary arteries

Successful recanalization and percutaneous revascularization of coronary arteries with chronic total occlusion (CTO) is one of the 'last frontiers' in coronary interventions. Conquering this obstacle will enable complete percutaneous revascularization in an increasing number of patients. The introduction within the last few years of enhanced guidewires combined with increasing operator experience and creative procedural techniques, such as the retrograde approach and the re-entry subintimal tracking technique (STAR), have significantly reduced the number of CTOs that should now be considered unapproachable. In addition, novel devices have been developed over recent years that may increase the success rate, as well as the safety, of the procedure. The Safe-Cross radiofrequency combines optical coherence reflectometry that warns the operator when the wire tip moves to within 1 mm of the outer vessel wall, combined with radiofrequency energy pulses to facilitate the passage. The CROSSER catheter mechanically vibrates against the face of the CTO at 20 kHz at a stroke depth of approximately 20 microm, creating a channel through the CTO. The most novel approach is the biologic one, in which proteolytic enzymes that digest the CTO cap to facilitate mechanical passage. The success rates for otherwise refractory CTOs will continue to improve with the development and validation of new imaging modalities and active energy source catheters.

The use of ultrasound-stimulated contrast agents as an adjuvant for collagenase therapy in chronic total occlusions

AIMS

To investigate the effectiveness of combining collagenase and ultrasound-stimulated microbubble (USMB) treatments in reducing the mechanical force required for crossing a guidewire through CTOs.

METHODS AND RESULTS

Experiments were conducted on ex vivo specimens of a rabbit femoral artery CTO model (n=45 total samples). Four primary groups were employed: control (n=6), collagenase only (n=15), USMB only (1 MHz frequency) (n=5), and collagenase+USMB (n=19). In one set of experiments the force required to puncture through CTO samples was measured and it was found that the puncture force was 2.31-fold lower for the combined treatment group relative to the comparable collagenase-only group (p<0.05). In a second set of experiments, the total protein and hydroxyproline content of the supernatant solution adjacent to the CTO was analysed. Significantly higher hydroxyproline levels were measured in collagenase+USMB treated CTOs (0.065 g/mL) compared to collagenase (0.030 g/mL), USMB (0.003 g/mL) and control (0.004 g/mL) (p<0.05), indicating that the combined treatment augmented collagenase degradation.

CONCLUSIONS

Ultrasound-stimulated microbubbles improved the effectiveness of collagenase in reducing the force required to cross experimental CTOs. This new approach may have the potential to reduce treatment times and improve the success rates of emerging collagenase-based treatments of CTO.

Therapeutic angiogenesis with VEGF164 for facilitation of guidewire crossing in experimental arterial chronic total occlusions

AIMS

Percutaneous revascularisation of chronic total occlusions (CTO) is limited by failure of guidewire crossing. Neovascularisation within the proximal CTO segment may be important for guidewire crossing and dramatically declines in CTO beyond six weeks of age. The aims of the current study were to determine whether local delivery of a pro-angiogenic growth factor increases neovascularisation in mature CTO and facilitates guidewire crossings.

METHODS AND RESULTS

CTO (n=51) were created in the femoral arteries of 44 New Zealand white rabbits using the thrombin injection model. At 12 weeks, CTO were treated with poly-lactic-glycolic-acid (PLGA) microspheres containing either bovine serum albumin (BSA) (n=15) or recombinant mouse VEGF164 (n=14), or received no intervention (controls, n=12). Contrast-enhanced magnetic resonance angiography (CEMRA) was performed prior to treatment and at three weeks post treatment. Animals were sacrificed at three weeks post treatment and arterial samples were excised for micro-computed tomography imaging (µCT) and histologic morphometric analysis. Guidewire crossing was assessed at three weeks post treatment in an additional 10 VEGF164-treated CTO. In comparison to BSA-treated and control non-intervened CTO, VEGF164-treated CTO showed a significant increase in relative blood volume index in the proximal segment of the CTO lesion as determined by CEMRA and by µCT. Histologic measurements of microvessel area were also higher in VEGF164-treated CTO. Guidewire crossing across the proximal fibrous cap was successful in eight out of 10 VEGF164-treated CTO.

CONCLUSIONS

Angiogenic therapy appears to be a promising strategy to improve neovascularisation and guidewire crossing rates in CTO.

Coronary total occlusion lesions: linear intrathrombus enhancement at CT predicts better outcome of percutaneous coronary intervention

PURPOSE

To evaluate the presence of linear intrathrombus enhancement in coronary total occlusion (CTO) lesions observed at coronary computed tomographic (CT) angiography and its correlation with the outcome of percutaneous coronary intervention (PCI).

MATERIALS AND METHODS

All patients gave written informed consent, and the study protocol was approved by the hospital ethics committee. Consecutive patients with CTO confirmed at initial conventional coronary angiography were prospectively chosen to undergo a coronary CT angiography examination prior to their staged PCI. Linear intrathrombus enhancement was defined as a linear area of enhanced opacity traversing the nonopacified occluded segment with attenuation higher than 120 HU. Angiographic features, including lesion length, linear intrathrombus enhancement length, and calcification score, were measured at coronary CT angiography. Univariate and multivariate statistical tests were performed to identify variables associated with successful PCI.

RESULTS

Eighty patients with 88 CTO lesions were included in this study. Fifty-one lesions were successfully recanalized at PCI. Lesion length was longer in the PCI failure group (P = .043). Linear intrathrombus enhancement was observed in 30 (59%) of the 51 lesions successfully treated with PCI. However, linear enhancement was found in seven (19%) of 37 patients with failed PCI (P < .001 as compared with patients with successful PCI). Tortuous course was revealed to be the only angiographic parameter associated with unfavorable PCI outcome (P = .008). The presence of linear intrathrombus enhancement proved at multivariate analysis to be the only independent predictor of PCI success (odds ratio: 4.926; 95% confidence interval: 1.646, 14.74; P = .004).

CONCLUSION

The presence of coronary CT angiography-visible linear intrathrombus enhancement within the occluded segment predicts better outcome of PCI in CTOs.

The representative porcine model for human cardiovascular disease

To improve human health, scientific discoveries must be translated into practical applications. Inherent in the development of these technologies is the role of preclinical testing using animal models. Although significant insight into the molecular and cellular basis has come from small animal models, significant differences exist with regard to cardiovascular characteristics between these models and humans. Therefore, large animal models are essential to develop the discoveries from murine models into clinical therapies and interventions. This paper will provide an overview of the more frequently used large animal models, especially porcine models for preclinical studies.

Intravascular and extravascular microvessel formation in chronic total occlusions a micro-CT imaging study

OBJECTIVES

The purpose of this study was to characterize the 3-dimensional structure of intravascular and extravascular microvessels during chronic total occlusion (CTO) maturation in a rabbit model.

BACKGROUND

Intravascular microchannels are an important component of a CTO and may predict guidewire crossability. However, temporal changes in the structure and geographic localization of these microvessels are poorly understood.

METHODS

A total of 39 occlusions were created in a rabbit femoral artery thrombin model. Animals were sacrificed at 2, 6, 12, and 24 weeks (n > or =8 occlusions per time point). The arteries were filled with a low viscosity radio-opaque polymer compound (Microfil) at 150 mm Hg pressure. Samples were scanned in a micro-computed tomography system to obtain high-resolution volumetric images. Analysis was performed in an image processing package that allowed for labeling of multiple materials.

RESULTS

Two distinct types of microvessels were observed: circumferentially oriented "extravascular" and longitudinally oriented "intravascular" microvessels. Extravascular microvessels were evident along the entire CTO length and maximal at the 2-week time point. There was a gradual and progressive reduction in extravascular microvessels over time, with very minimal microvessels evident beyond 12 weeks. In contrast, intravascular microvessel formation was delayed, with peak vascular volume at 6 weeks, followed by modest reductions at later time points. Intravascular microvessel formation was more prominent in the body compared with that in the proximal and distal ends of the CTO. Sharply angulated connections between the intravascular and extravascular microvessels were present at all time points, but most prominent at 6 weeks. At later time points, the individual intravascular microvessels became finer and more tortuous, although the continuity of these microvessels remained constant beyond 2 weeks.

CONCLUSIONS

Differences are present in the temporal and geographic patterns of intravascular and extravascular microvessel formation during CTO maturation.

The pre-clinical animal model in the translational research of interventional cardiology

Scientific discoveries for improvement of human health must be translated into practical applications. Such discoveries typically begin at "the bench" with basic research, then progress to the clinical level. In particular, in the field of interventional cardiology, percutaneous cardiovascular intervention has rapidly evolved from an experimental procedure to a therapeutic clinical setting. Pre-clinical studies using animal models play a very important role in the evaluation of efficacy and safety of new medical devices before their use in human clinical studies. This review provides an overview of the emerging role, results of pre-clinical studies and development, and evaluation of animal models for percutaneous cardiovascular intervention technologies for patients with symptomatic cardiovascular disease.

Doppler optical coherence tomography for interventional cardiovascular guidance: in vivo feasibility and forward-viewing probe flow phantom demonstration

We demonstrate the potential of a forward-looking Doppler optical coherence tomography (OCT) probe for color flow imaging in several commonly seen narrowed artery morphologies. As a proof of concept, we present imaging results of a surgically exposed thrombotic occlusion model that was imaged superficially to demonstrate that Doppler OCT can identify flow within the recanalization channels of a blocked artery. We present Doppler OCT images in which the flow is nearly antiparallel to the imaging direction. These images are acquired using a flexible 2.2-mm-diam catheter that used electrostatic actuation to scan up to 30 deg ahead of the distal end. Doppler OCT images of physiologically relevant flow phantoms consisting of small channels and tapered entrance geometries are demonstrated.

Development of animal model for calcified chronic total occlusion

Chronic total coronary occlusion (CTO) remains a major problem for percutaneous revascularization, with relatively low primary success rates and a high incidence of restenosis and reocclusion compared with those of subtotal stenoses. No reproducible animal model simulating human CTOs has previously been developed. We hypothesized that an apatite-coated bioabsorbable polymer sponge could be implanted to produce calcified CTO lesions in animal coronary arteries/peripheral arteries. A total of 10 swine and six rabbits were used for this study. The apatite-coated bioabsorbable polymer sponges were implanted into a preselected segment of coronary and peripheral arteries. Four weeks after implantation, both angiography and histopathology were performed to document the presence or absence of CTO lesions. We could reproducibly develop CTO lesions in animal coronary/peripheral arteries that mimic human CTO lesions. These lesions were found to have microvascular channels and microcalcification similar to those of human older CTO lesions and demonstrate the development of adventitial arterioles, a consistent finding in human CTO. This CTO model might provide a platform for evaluating future CTO technologies as well as contributing to a better understanding of CTOs in both educational and practical terms.

Natural history of experimental arterial chronic total occlusions

OBJECTIVES

We sought to perform the first systematic study of the natural history of chronic total arterial occlusions (CTOs) in an experimental model.

BACKGROUND

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.

METHODS

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.

RESULTS

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").

CONCLUSIONS

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.

Forward-looking intravascular orthogonal-solenoid coil for imaging and guidance in occlusive arterial disease

Recent intravascular imaging coil configurations have focused on side-viewing catheters capable of imaging the vessel wall of a patent vessel. These designs suffer from the presence of signal nulls and the inability to image in front of a device when it is oriented along the main static field. This is of particular importance when a device is being navigated through an occlusive lesion. To address these limitations we propose a new intravascular coil design consisting of two independent orthogonal solenoids located at the catheter tip. The two coils are oriented in such a way that signal nulls are eliminated and imaging is possible in planes located directly in front of the catheter. Complete characterization of the spatial signal-to-noise ratio (SNR) distribution of the design is presented. The coil configuration was fabricated on a 6F guide catheter, and its use is demonstrated in phantoms and in vivo.

Investigation of micro-ultrasound for microvessel imaging in a model of chronic total occlusion

The aim of the current study is to investigate the ability of micro-ultrasound (microUS) to identify microvasculature in CTOs in vivo. Results are compared with MRI studies. CTOs were developed in nine porcine superficial femoral arteries (SFA) by percutaneous insertion of a dissolvable polymer plug. This model is characterized by acute thrombosis that later organizes into a fibrotic CTO containing abundant microchannels. 3D microUS images with Power Doppler (PD) overlays from the arteries were acquired at two timepoints: one and eight weeks after placement ofthe polymerplug. Phase contrast MRI and contrast enhanced MRI was also performed. Imaging was performed transcutaneously. Microvessels were identified in vivo in six of eight CTOs using microUS, and in three of seven CTO vessels with MRI, compared with five of seven seen histologically. PW Doppler profiles showed pulsatile blood velocities of approximately 2 cm/s. Intraluminal microvessels within CTOs can be consistently identified by 3D microUS. This technique appears to be more sensitive than MRI. MicroUS may play a role in guiding CTO interventions.

Ex vivo imaging of chronic total occlusions using forward-looking optical coherence tomography

BACKGROUND AND OBJECTIVES

Percutaneous coronary interventions (PCI) of chronic total occlusions (CTOs) of arteries are more challenging lesions to treat with angioplasty and stenting than stenotic vessels due primarily to the difficulty in guiding the wire across the lesion. Angiography alone is unable to differentiate between the occluded lumen and the vessel wall and to characterize the content of the occlusion. New technologies to aid in interventional guidance are therefore highly desirable. We sought to evaluate tissue characterization in arterial (CTOs) by imaging ex vivo peripheral arterial samples with optical coherence tomography (OCT).

STUDY DESIGN/MATERIALS AND METHODS

Ex vivo arterial samples were obtained from patients undergoing peripheral limb amputation. Samples were imaged in an enface orientation using an OCT system, enabling sequential acquisition of longitudinal images and volumetric reconstruction of cross-sectional views of the occluded arteries. Histology was performed for comparison.

RESULTS

OCT imaging reliably differentiated between the occluded lumen and the underlying arterial wall in peripheral CTOs. OCT correctly identified tissue composition within the CTO, such as the presence of collagen and calcium and was also able to identify intraluminal microchannels.

CONCLUSIONS

OCT imaging of CTO anatomy and tissue characteristics may potentially lead to substantial improvements in PCI interventions by providing novel guiding capabilities.