Crossing Total Occlusions: Navigating Towards Recanalization

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.

Crossing Total Occlusions Using a Hydraulic Pressure Wave: Development of the Wave Catheter

With the ongoing miniaturization of surgical instruments, the ability to apply large forces on tissues for resection becomes challenging and the risk of buckling becomes more real. In an effort to allow for high force application in slender instruments, in this study, we have investigated using a hydraulic pressure wave (COMSOL model) and developed an innovative 5F cardiac catheter (L = 1,000 mm) that allows for applying high forces up to 9.0 ± 0.2 N on target tissues without buckling. The catheter uses high-speed pressure waves to transfer high-force impulses through a slender flexible shaft consisted of a flat wire coil, a double braid, and a nylon outer coating. The handle allows for single-handed operation of the catheter with easy adjusting of the input impulse characteristic, including frequency (1–10 Hz), time and number of strokes using a solenoid actuator, and easy connection of an off-the-shelf inflator for catheter filling. In a proof-of-principle experiment, we illustrated that the Wave catheter was able to penetrate a phantom model of a coronary Chronic Total Occlusion (CTO) manufactured out of hydroxyapatite and gelatin. It was found that the time until puncture decreased from 80 ± 5.4 s to 7.8 ± 0.4 s, for a stroke frequency of 1–10 Hz, respectively. The number of strikes until puncture was approximately constant at 80 ± 5.4, 76.7 ± 2.6, and 77.7 ± 3.9 for the different stroke frequencies. With the development of the Wave catheter, first steps have been made toward high force application through slender shafts.

A method of characterising the complex anatomy of vascular occlusions and 3D printing biomimetic analogues

Chronic total occlusions (CTOs) occur in approximately 40% of individuals with symptomatic peripheral arterial disease and are indicative of critical limb ischaemia. Currently, few medical devices can effectively treat CTOs long-term, with amputation often required. This is due to a lack of knowledge of CTO anatomy, making device design and testing difficult. This study is a proof-of-concept study, which aimed to develop a workflow for further characterising the complex multi-material anatomy of CTOs and creating 3D models of CTO components, which may be useful in producing a vascular CTO biomimetic for device testing. Here, we establish such a workflow using samples of atheromatous plaques. We focus on a high-resolution, non-destructive microcomputed tomography (μCT) technique which enables visualisation of occlusion anatomy at a greater resolution than computed tomography angiography (CTA), which is the typical modality used for CTO clinical visualisation. Four arteries (n = 2 superficial femoral; n = 2 popliteal) with evidence of atheromatous plaques were cut into 8 cm segments, which were then stained with iodine and scanned at low resolution, with calcified regions rescanned at high resolution. Resulting files were manually segmented to generate 3D models, which were then 3D printed in resin using a stereolithography printer to produce parts suitable for creating a biomimetic. In total, μCT files from three arterial segments (n = 2 high resolution, n = 1 low resolution) were deemed suitably calcified for segmentation, and thus were segmented to produce 3D models. 3D models of the arterial wall, intima and atheromatous calcium deposits from a high-resolution popliteal artery scan were successfully 3D printed at several scales. While this research is at an early stage, it holds great promise. The workflow for segmentation and 3D printing various components of an atheromatous plaque established here is replicable and uses software and equipment which are accessible to research laboratories in both academia and industry. The ability to print detailed models on a desktop 3D printer is unprecedented and can be improved further, which is promising for future development of biomimetics with multi-material detail of both soft tissue and calcified components of a vascular occlusion. Indeed, this workflow provides a solid foundation for future studies of CTO anatomy and the creation of true, multi-material CTO biomimetics. Such biomimetics may enable the development of improved interventional devices, as they would mimic the general in vivo CTO environment. As this method cannot be applied in vivo, we cannot yet produce patient-specific biomimetics, however, these analogues would still be important in device development, which would improve patient outcomes in critical limb ischaemia.

Five-year outcomes after revascularization of superficial femoral artery occlusion using Ocelot catheter

Introduction

The population of patients with lower limb atherosclerosis includes a considerable proportion of individuals with long superficial femoral artery (SFA) lesions. Chronic total occlusions (CTOs) represent the "last frontier" of percutaneous interventions. While open strategies are considered earlier as standard management for these lesions, the results of a number of trials indicate that endovascular management might become an effective alternative to surgery.

Material and methods

This paper presents 5-year outcomes of a first-in-man (FIM) study (before CE mark) and the registry of OCT Guided Ocelot Catheter (Avinger) for chronic total occlusions of the superficial femoral artery. The study group comprised 10 patients with Rutherford 3 lower limb ischemia including nine men and one woman.

Results

The efficacy of the primary intervention was 90%. Angiography performed at 6 months of the procedure, according to the study protocol, revealed 3 and 1 cases of restenosis and reocclusion, respectively, repaired using PTA and open common and deep femoral artery patch plasty. Doppler ultrasound performed at 1, 2 and 5 years after the primary intervention did not reveal significant target vessel restenosis. The primary and primary-assisted patency was 89%. During a 5-year follow-up, four peripheral percutaneous interventions and one femoropopliteal bypass surgery were performed in non-target limbs. There were no cardiovascular deaths, myocardial infarction or stroke and no amputation was required.

Conclusions

This is a first-in-man study reporting long-term follow-up after SFA CTO revascularization using the Ocelot catheter. The catheter proved to have a satisfactory safety profile and a high proportion of CTO crossings. A 5-year follow-up revealed high primary and primary-assisted patency rates.

Flexible impulse transfer using a Newton's Cradle-inspired catheter: A feasibility study

A major challenge during minimally invasive surgery is transfer of high forces through small, flexible instruments, such as needles and catheters, because of their low buckling resistance. In this study, we determined the feasibility of using a Newton's Cradle-inspired catheter (patented) to transfer high-force impulses. Exerting a high-force impulse on the tissue increases the critical buckling load and can prevent buckling. The system comprised an input plunger onto which the impulse is given, a (flexible) shaft filled with Ø2 mm stainless steel balls, and an output plunger to transfer the impulse to the target tissue. In the proof-of-principle experiment, the effect on efficiency of clearance (0.1, 0.2, and 0.3 mm), length (100, 200, and 300 mm), shaft type (rigid vs. flexible), curve angle (0, 45, 90, 135, and 180°), and curve radius (20, 40, 60, and 100 mm) was determined. The catheter delivered forces of 6 N without buckling. The average impulse efficiency of the system was 35%, which can be further increased by optimizing the design. This technology is promising for high-force delivery in miniature medical devices during minimally invasive surgery.

Novel treatment of a totally occluded venous outflow tract of an arteriovenous graft

INTRODUCTION

Conventional guidewire techniques are not always sufficient to restore arteriovenous graft patency in patients with challenging vascular scenarios. We discuss a novel approach to the treatment of chronic total occlusion of the venous outflow tract to enable successful arteriovenous graft thrombectomy.

CASE PRESENTATION

A 28-year-old female with end-stage renal disease on chronic hemodialysis and recurrent arteriovenous graft thromboses presented with a clotted thigh graft. An existing ipsilateral common femoral vein stent was found to be chronically occluded, causing persistent venous outflow obstruction and rendering an initial attempt at thrombectomy unsuccessful due to wire buckling and the inability to navigate through the stent chronic total occlusion.

RESULTS

After establishing femoral vein access, a vibrational recanalization device was used to cross the occluded stent. The device was then removed, permitting routine angioplasty. Post-angioplasty angiogram revealed persistent intra-stent stenosis, so a covered stent was deployed with good angiographic results. Routine pharmaco-mechanical thrombectomy of the arteriovenous graft was then performed. Two additional stents were placed due to stenotic recoil in the venous limb of the graft. Angioplasty was also performed at the arteriovenous graft arterial anastomosis. Repeat imaging demonstrated marked improvement in the graft blood flow.

DISCUSSION

Total occlusion of the venous outflow tract prevents adequate blood flow through an arteriovenous graft and undermines successful thrombectomy. We describe the use of the Crosser vibrational recanalization device for the safe and effective treatment of a chronic total occlusion of the venous outflow tract, thus extending the life of the patient's vascular access for hemodialysis.

Endovascular Crossing of Chronic Total Occlusions Using an Impulse: An Explorative Design Study

In this study we investigated whether exerting an impulse on a Chronic Total Occlusion (CTO) improves the success rate of CTO crossing as compared to the currently used method of statically pushing the guidewire against the CTO. A prototype (Ø2 mm) was developed that generates translational momentum using a spring-loaded indenter and converts it to an impulse during impact. Mechanical performance was evaluated by measuring the peak force and momentum for different spring compressions and strike distances in air and blood-mimicking fluid. Puncture performance, in terms of number of punctures, number of strikes to puncture, and energy transfer from the indenter to the CTO, was assessed for six tip shapes (stamp, wedge, spherical, pointed, hollow spherical, and ringed) on three CTO models with different weight percentages of gelatin and calcium. As a control, a Ø0.4 mm rigid rod was tested. A maximum indenter momentum of 1.3 mNs (velocity of 3.4 m/s), a peak force of 19.2 N (vs. 1.5 N reported in literature and 2.7 N for the control), and CTO displacement of 1.4 mm (vs. 2.7 mm for the control) were measured. The spherical and ringed tips were most effective, with on average 2.3 strikes to puncture the most calcified CTO model. The prototype generated sufficient peak forces to puncture highly calcified CTO models, which are considered most difficult to cross during PCI. Furthermore, CTO displacement was minimized, resulting in a more effective procedure. In future, a smaller, faster, and flexible clinical prototype will be developed.

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.