Conductor coil

Using these Bi-2212 and 2223 tapes, large current conductors, coils and magnets, and other products have been successfully made. 

For an inductor, a center electrode, ferrite layer and conductor coil are printed. The inductance could be varied by changing the number of turns of the printed coil. 

Conductor coils are commonly of a multifilament or cable structure instead of unifilar to make them more flexible and resistant to fracture. Unifilar conductor is a single wire wound spirally around a central axis (Fig. 1.12), whereas a multifilar cable consists of two or more wires wound together in parallel spirally around a central axis (Fig. 1.13) [1]. In a multifilar coil, each conductor strand is individually coated with a thin layer of insulator, and the entire helical coil is then insulated again with a thicker conventional insulator (Fig. 1.13) [1]. 

Unipolar leads obviously have only one conductor coil, whereas bipolar leads require two -one for the proximal and the other for the tip electrode. Bipolar leads may have a coaxial, a co-radi-al or parallel wound, and a parallel or multiluminal design. Coaxial bipolar leads, standard in treating... 

Wilkoff locking stylet (Cook Vascular Inc., Leechburg, PA, USA) (Fig. 4.3) this stylet has a small flange at the tip that is locked into the conductor coil when a thin, preloaded cylinder... 

There are some limitations to the use of a locking stylet. Once it is inserted into the lead, it may sometimes be difficult or impossible to reverse the locking mechanism and remove the device. Furthermore, if the inner conductor is broken or distorted, it is impossible to introduce or pass the stylet. Excessive force can dislocate the stylet, or the distal conductor coil can still unwind or even disconnect from the electrode. 

High quality fluoroscopy a high-quality fluoroscopy system is a mainstay for lead extraction. Visualization of small lead components (such as stretched conductor coils, screws and embolized lead fragments) is fundamental to the safe performance of lead extraction. The equipment may be a fixed fluoroscopic system or a mobile high quality C-arm. Personnel specifically able to operate and troubleshoot this equipment are also required. 

Inspect the entire length of the lead for lack of integrity, such as fracture, compression, or crimp. Intermittent or complete failure to capture or sense or output could be secondary to lead conductor coU fracture or loss of insulation integrity. Attempt to follow each lead along its course, assessing the conductor coil. Also, inspect for any crimping of the lead as it passes under the clavicle. 

If no abnormality is appreciated radiographically but there is a clinical abnormality, reassess the chest radiograph in a problem-oriented fashion. For example, if the patient has intermittent failure to output, the differential diagnosis includes a problem with the connector pin, such as a loose set screw or fracture of the conductor coil. Go back once again and inspect these elements of the pacing system. 

In Fig. 18.27, placement of the atrial lead is too shallow, and close observation reveals that the conductor coil of the atrial lead has separated. Atrial pacing was not possible, but surprisingly, atrial sensing remained intact, probably... 

Fig. 18.27 Posteroanterior chest radiograph (A) and close-up view (B) in a patient with a dual-chamber pacemaker and separation of the atrial conductor coil.

Fig. 18.29 Posteroanterior chest radiograph (A) demonstrating complete separation of the conductor coil of the ventricular lead as it passes helow the clavicle (upper arrow). (Lower arrow, a suhoptimaUy positioned atrial lead that is too shallow.) In the close-up view (B), the arrow again denotes the separation of the conductor coil.

Fig. 19.11 A cone-down view of two leads passing between the inferior margin of the clavicle and the first rib. An x-ray obtained at 6 months postimplant demonstrated totally intact leads. The patient presented at 18 months postimplant with oversensing and a very low telemetered lead impedance (< 250 Q) consistent with a breach of the internal insulation of the coaxial bipolar lead. While the insulation is radiolucent, there is a deformity of the conductor coil which is seen best on the view on the right. The lead was subsequently replaced and was able to be extracted. The deformity identified on the chest x-ray corresponded to a visible deformity on the explanted lead and the manufacturer confirmed this to the location of the insulation failure between the proximal and distal conductor coils.

The weak link in the pacing system is the thin insulated wire connecting the pulse generator to the heart. It is subjected to a multiplicity of extrinsic stresses which may predispose to either a breach in the insulation or fracture of the conductor coil. While this can occur with any pacing lead, there are some which are less than forgiving of these external stresses and have been identified by their manufacturer as having a relatively high incidence of problems... 

Fig. 5 Examples of various types of lead conductors and their insulation A. a unipolar single-filar conductor coil, B. parallel single-filar conductor cods, C. coaxial multifilar conductor cods, and D. a multifilament microcable...

Fig. 6 A 0.5 -inch-long grooved cobalt mandrel is inserted into tubing, which is sealed on both ends with medical adhesive. The grooves are intended to simulate the spaces between pacemaker lead conductor coils. A 1-mm-diameter hole is made in one end to assure ingress of exudate/transudate. Samples are tied together in strings, identified with a colored glass bead, and implanted in the subcutis of rabbits as shown in Fig. 3. After optical microscopic examination, the samples may be analyzed by FTIR, HPLC molecular weight, SEM, and other suitable techniques...

Still a third failure mechanism was not seen in animal studies, but was discovered clinically. Explanted and returned leads with crushed, flattened, and fractured conductor coils began to show up in the mid 1980s (Fig. 7) [17]. When polyurethane leads were introduced for human use, a new implant technique was developed. Instead of inserting the leads through a cephalic or jugular vein cut down, they were... 

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