Comparison of the Thrombogenicity of a Bare and Antithrombogenic Coated Flow Diverter in an In Vitro Flow Model.

BACKGROUND: Dual antiplatelet therapy is a pre-requisite for flow diverter (FD) implantation. The purpose of this study was to assess the thrombogenicity of the p48 FD, coated with the newly developed phenox Hydrophilic Polymer Coating (p48_HPC, phenox GmbH, Germany) in comparison with uncoated p48 FDs in an in vitro flow model (Chandler Loop). METHODS: p48 and p48_HPC FDs were implanted into silicon tubes filled with whole human blood and incubated at 37 °C under pulsating flow. After 120 min, platelet count was determined in the blood. Platelet activation markers (PAR1) and formation of microparticles were analyzed in a flow cytometer. Fluorescence microscopy of CD42a positive cells and scanning electron microscopy was used to detect adherent platelets on the wire surface. RESULTS: Platelets in contact with the uncoated p48 FDs are significantly more activated than those incubated with p48_HPC (73 ± 9% vs. 65 ± 6%, p < 0.05) and release more microparticles (1.8 ± 0.5 vs. 1.4 ± 0.4, p < 0.05). The platelet count after 120-min circulation in the Chandler Loop was significantly lower for the uncoated p48 compared to the p48_HPC indicating significantly greater adherence of the platelets to the p48 (71 ± 8% vs. 87 ± 5%, p < 0.05). SEM and fluorescent antibody imaging revealed minimal platelet adherence to the surface of the p48_HPC compared to the uncoated p48. CONCLUSION: The pHPC coating significantly reduces thrombogenicity of the p48 FD. This may help to reduce the risk of thromboembolic complications when using these devices. A reduction in antiplatelet therapy may be possible.

A novel microcatheter-delivered, highly-flexible and fully-retrievable stent, specifically designed for intracranial use. Technical note.

SUMMARY: A new microcatheter-delivered, highly-flexible, fully-retrievable intracranial stent has been developed in order to facilitate the endovascular treatment of wide-necked aneurysms, though it might also prove useful for other intracranial pathology. The nitinol stent has radiopaque proximal and distal markers, is available in a wide range of sizes and is as flexible as a micro-guidewire. It is electrolytically detached, allowing retrieval even after full deployment. The stent is compatible with all currently available embolic agents and does not degrade MR images.

Technical Note on VDS. A System for the Endovascular Electrolytical Detachment of Platinum Coils at Variable Length.

SUMMARY: A new system was deviced that allows the electrolytical detachment of platinum microcoils at variable lengths for the endovascular treatment of intracranial aneurysms. The detachment element consists of two short platinum coil segments, which are connected by a threat of stainless steel. The steel threat is interrupted by electrolysis, using a continuous current with 1-2 mA at a voltage of 4-8 Volt. The average detachment time in heparinized blood is about 30-40 sec. The detachment elements can be used to connect either an insertion wire with a platinum coil or to connect several segments of platinum coils with variable helices and lengths. If several detachment elements are integrated in a coil, electrolysis interrupts only the element, which is next beyond the distal tip of the catheter. The electrolytical process does not affect the detachment elements proximal and distal to the element adjacent to the tip of the catheter. Single or several coil segments can be pulled back into the microcatheter if necessary. The system is expected to allow a faster and more complete endovascular coil occlusion of intracranial aneurysms. The principles described in this paper are claimed by the German pending patent DE 100 10840 A1.

Torquability of microcatheter guidewires: the resulting torsional moment.

Guidewires for microcatheters used for the subselective catheterization of small vessels must meet high quality requirements in regard to handling, steerability, radiopacity and physical properties. The aim of this paper is to classify one of the factors that determine the physical and mechanical parameters of a number of existing microcatheter guidewires. A torsion-testing equipment for guidewires was devised. Nitinol wires were tested and compared with the austenitic stainless steel variants. 13 different commercial wires were tested. Tensile strength, shear modulus and wire diameter are the determining factors of the torsional rigidity of guidewires. By interpreting the measured torsional momentums various statements concerning the torsional rigidity of different wires can be made. The properties of guidewires are characteristic features of a system and friction and flexible strength examinations have to be carried out to design new variants of wires to meet the requirements of interventional physicians.

Accuracy of intravascular microcatheter pressure measurements: an experimental study.

Intravascular pressure measurements are considered useful for the monitoring and assessment of endovascular treatment effects in intracranial vascular malformations. Experimental data on the accuracy of these measurements are limited. A flow phantom with defined intraluminal pressures and pulsatility flow waveforms was used in this study. Microcatheters commercially available for neuroendovascular procedures (length 140-155 cm), with different outer (0.5-0.83 mm) and inner (0.3-0.53 mm) diameters, were introduced into the phantom in the direction of flow. In a static experiment, pressure values from 0 to 75 mmHg were applied, and in the dynamic part of the experiment mean pressure values from 25 to 65 mmHg, with a pulsatile amplitude from 70 to 170 mmHg were employed. In the static experiment, there was a linear relationship between the pressure values obtained through the microcatheters and the local transducer of the flow phantom. The pulsatile experiments showed increased damping of the pressure waveforms with decreasing inner diameter of the microcatheters. However, the mean pressure values remained accurate. This experimental study has shown that mean pressure values can be accurately measured through microcatheters from 0.3-0.5 mm inner diameter and more than 140 cm in length. In vivo pressure measurements during interventional procedures are therefore reproducible and can be used for monitoring of embolization effects in patients.

First experiences with a distractible titanium implant in ventral cervical disc surgery: report on 30 consecutive cases.

A new titanium implant for ventral cervical fusion after microsurgical discectomy via a conventional antero-lateral approach is presented. The implant consists of a ventral fixation plate and a distractible disc space graft whose extension can be changed by adjusting a set screw. Additional fixation is achieved by four monocortical spongiosa screws. Thirty patients (14 men, mean age 46.5 years; 16 women, mean age 46.8 years), in whom the implant was used, were the subjects of this investigation. Twenty-eight patients suffered from monosegmental cervical disc herniations (C4/5: n = 3; C5/6: n = 14; C6/7: n = 12; C7/T1: n = 1) and two patients showed traumatic discoligamental instability (C5/6: n = 1, C6/7: n = 1). The postoperative follow-up was at least 12 months (range 12-26 months, average 16.6 months). All patients underwent a clinical control including functional X-rays 6-8 weeks and again 10-14 months after surgery. All had benefitted from the procedure and the clinical results were comparable to other ventral cervical fusion techniques. We observed neither overdistraction or dislocation of the implant nor loosening or breaking of the screws. The advantages of the implant are: simple handling, controlled distraction of the intervertebral space and avoidance of a "second operation" to obtain an iliac crest bone graft for fusion.

Endovascular laser detachment of platinum alloy microcoils: principle and initial experimental experience.

The aim of the investigation was the technical realization and approval of a new method for insertion and detachment of platinum alloy microcoils and other vascular implants via standard microcatheters. Flexible lightconducting fibers, 105 microns in diameter were connected to platinum alloy microcoils. It was examined whether an insertion wire, a lightconducting fiber and a platinum alloy microcoil could be advanced through a Tracker-18 (Target) microcatheter. The detachment of the attached coil from the lightconducting fiber was investigated. Platinum alloy microcoils can be attached to available lightconducting fibers in a reliable and reproduceable manner. Together with the fiber they can be advanced via a Tracker-18 microcatheter. Only extremely tortuous vessels may increase the friction to critical values. A Ho-YAG laser source was used. This allowed the instantaneous detachment of microcoils from laser fibers. In contrast to electrolytical detachment, no foreign substances are released to the blood stream. The detachment does not require waiting time and does not activate thrombus formation. Due to specific technical features, injuries of the vessel wall are avoided. After further miniaturization and adaption of the lightconducting fibers to the required characteristics, laster detachment may have the potential to replace current methods such as electrolytical and mechanical coil detachment.