Mechanical Sheaths

Mechanical sheaths sheaths composed of metal. Teflon, polypropylene, or other materials they require manual advancement over the lead and rely on the mechanical properties of the sheath to disrupt fibrotic adhesions. 

Stylet wires (Fig. 4.2) are used to stiffen leads for removal. Moreover, stylet wires can be used to debride foreign matter inside the lead body, confirm patency, and measure lead length. Stylet wires improve the effectiveness of lead removal when using either direct traction or mechanical sheaths. 

Reports in the literature suggest that powered sheaths are more effective than mechanical sheaths [10] in some experiences, their use is associated with a higher incidence of major complications and is undoubtedly more expensive. In the near future, the cost/benefit ratio of both techniques will require careful evaluation probably, most procedures could be performed by mechanical techniques, whereas powered sheath techniques should be reserved for select cases. 

Tears in the venous wall of the innominate vein and SVC have been reported with the Excimer sheath [34-39], as has cardiac tamponade due to lasing into the heart [22]. The inability of the laser technique to overcome calcified scar tissue and to perform dilation near the tip of the lead are major limitations [19]. Laser sheaths have a larger diameter compared with mechanical sheaths, and advancing them through the costoclavicular space is often difficult. Another limitation is the consistently higher cost of equipment and sheaths. Despite these disadvantages, this technique spreads rapidly and is today the most commonly used technique in the USA [9, 11]. Whereas earlier studies addressed the efficacy and safety of the initial laser sheath models [36], the recent Lead Extraction in the Contemporary Setting (LExICon) Study [40]... 

The concern about ICD extraction using conventional equipment was averted by clinical results. Even if extraction procedures were complex and time consuming, the final outcome showed no outstanding differences in comparison with results of PM lead extraction. Results of ICD lead extraction using mechanical sheaths were included in the US Lead Extraction Database published in 1999 [17], and early trials on laser-assisted sheaths were performed for both PM and ICD leads [21, 23, 45]. In 2000, Kantharia et al. reported their experience with transvenous extraction of 47 transvenous high-voltage leads implanted in 42 patients [46]. All leads were extracted - 11 by traction and 36 by mechanical dilatation - in the absence of serious complications. Extraction time was related to time from implant and degree of... 

The predominant extraction approach was via the implant vein in all three periods. The major method of extraction via the superior approach was by use of the locking stylets and sheaths together. In the third period, during which several centers participated in the clinical trial for the excimer laser sheath, laser sheaths were used in combination with locking stylets and mechanical sheaths for 30% of the leads. 

In the Philippines, the principal suppHer of abaca fiber, the fibrous layer ia the sheath is separated with a knife between the layers, and the strips of fiber-containing layers, called tuxies, are pulled off and cleaned by hand to remove the pulp. In Indonesia and Central America these operations are performed mechanically. Hand- and spiadle-stripped fiber is graded for braids, fine textiles, and cordage decorticated fiber is another class. A cross-sectional view is shown ia Figure 4a. The abaca fiber has a large lumen and the presence of siUcified plates is not unusual. 

Lead—tin (1.8—2.5 wt %) is used both as a cable sheathing ahoy (BS 801 ahoy A and DIN 17640) and as a battery connector ahoy ia sealed lead—calcium—tin batteries (15). Tia is generahy added to lead—arsenic cable ahoys ia smah amounts. The arsenic ahoys have excehent creep resistance and mechanical properties, but are unstable and lose arsenic readily by oxidation. The addition of smah amounts of tin (0.10—0.20 wt %) eliminates arsenic loss. Lead ahoys having 0.4 wt % tin and 0.15 % cadmium, which are used for cable sheathing, do not age harden, show excehent corrosion and creep resistance, and are very ductile. 

Electroless copper solutions underwent similar development during the same period (10). Early printed circuit boards used mechanically attached eyelets to provide electrical conductivity between the copper sheathing laminated on two sides of a plastic board. Electroless copper plating provided a less expensive, better conductive path, allowing much greater numbers and smaller sizes of holes. Later, electroless coppers even replaced the laminated bulk copper sheathing in the semiadditive and additive processes (see Copper). 

A single or multicored plastic-coated cable of the type NYY or NYY-O is used as the connecting cable between a protected object and an anode in soils and fresh water, and particularly in seawater, medium heavy or heavy rubber-sheathed connections of an NSHou or NSSHou type are used. Heavy welded connections of type NSLFSou are used for severe mechanical loading. In addition to these, for ships, marine cable of type MGCG or watertight cables must be considered. 

In the tidal zone and the spray zone (known as the splash zone), cathodic protection is generally not very effective. Here thick coatings or sheathing with corrosion-resistance materials (e.g., based on NiCu) are necessary to prevent corrosion attack [4]. The coatings are severely mechanically stressed and must be so formed that repair is possible even under spray conditions. Their stability against cathodic polarization (see Section 17.2), marine growths, UV rays and seawater must be ensured [4,5]. 

An alternative route to obtain NbS2-sheathed carbon nanotubes (CNT) has been proposed by Zhu et al. [71] with this sonochemical method. In this study, CNTs act as templates to produce the uniform and well-crystallized bS2 nanotubes and the formation of such nanotubes has been explained by means of multi-point nuclei site growth mechanism. 

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