Active-fixation leads retractable/extendable screw

FIGURE 20.7 Close-up views of three pacemaker and/or cardioverter fi ior leads. The lead on the far left is an active fixation lead with a retractable screw embedded in the lead lip- It can be extend after implantation to attach the lead to the heart wall. The middle lead possesses a soluble ct that dissolves within a few minutes inside the body to reveal a hook or screw for tip fixation. A lined passive fixation lead is shown on the right The soft tines become lodged in the iiregular inside surface of the heart, preventing lead migratron. 

The major design available today is the retractable-extendable screw-in lead, which has become popular for both atrial and ventricular use. These designs use a variety of mechanisms to extend and retract the screw (31, 32) This includes an implanent to turn the connector pin, which in turn, is mechanically and electrically connected to the electrically active screw via the conductor. A screw driver stylet has also been used to extend and retract the screw. Unlike tined leads, aU active-fixation leads traumatize the... 

Fig. 1.20 Retractable-extendable active-fixation leads. Above Medtronic 5076 Capsure Fix Novus. Note the steroid-elntmg collar immediately behind the extended cathode screw. Below St Jnde 1488T Tendril . Both the lead tip and the extended screw are electrically active (cathode). The steroid-elntmg plug is housed at the tip of the lead through which the screw passes. (Permission for use Medtronic and St Jude.)...

Not all active-fixation leads have an extendable-retractable screw. Some models have a fixed screw coated in mannitol which dissolves in blood prior to fixation (Guidant, Sweet Tip ). As discussed previously, a thin diameter cabled lead inserted through a steerable catheter has a fixed screw which is essentially covered by the catheter until it is attached to the endocardium (Medtronic SelectSecure Medtronic Inc., Minneapolis MN) (Fig. 1.19). Active-fixation leads can also be attached to the endocardium using a steerable stylet (St Jude... 

The second type of common active fixation lead design employs a retractable/extendable screw that is mechanically activated (Fig. 4.37). This lead avoids the problem of hang-up and is much easier to work with. One merely maps a point of fixation and activates the fixation mechanism. 

Lead fixation provides lead-tip stabilization during the hours immediately following the procedure. Fixation may be passive or active. Passive means that no part of the lead itself is actually embedded in the endocardium. After first experiences with flanged or helicoidal-shaped tips, endocardial leads now incorporate different numbers and kinds of tines at the tip that ensnare in trabeculated tissue of the right atrium or ventricle, providing stabilization (Fig. 1.8) [2]. Active fixation means that part of the lead actually embeds in the heart tissue for fixation. These leads utilize screw-based mechanisms to adhere to the myocardium to provide lead stability. Some leads incorporate screws that are electrically active, whereas others are inactive. Therefore, some screws are extendable and retractable from the lead tip and others are fixed on... 

Fig 1.35 Passive lined fixation lead (a). Active fixation extendable/retractable screw-in lead (b)... 

---

See also in sourсe #XX -- [ ]

---