Active-fixation leads

Once a lead has been implanted, it must remain stable (or fixated). The fixation device is either active or passive. Active-fixation leads incorporate corkscrew mechanisms, barbs, or hooks to attach themselves to the myocardium. Passive-fixation leads are held in place with tines that become entangled in the net-like lining (trabeculae) of the heart. Passive-fixation leads generally have better acute pacing and sensing performance but are difficult to remove chronically. Active-fixation leads are easier to remove chronically and have the advantage of unlimited placement sites. Some implanters prefer to use active-fixation leads in the atrium and passive-fixation leads in the ventricle. 

As with pacing leads, the ICD lead cathode is a platinum, iridium, and titanium combination the electrode structure depends on whether fixation mechanism is passive with tines or active with a screw. In an active-fixation lead, the platinum-iridium screw is usually electrically active, but there are also models with both electrically active collar and helix or others with electrically silent helix and active carbon cathode collar. A platinum-iridium anode lies immediately behind the cathode in a true bipolar system. All models now elute steroids to reduce chronic threshold and prevent pacing threshold rise or exit block. 

Fixation mechanism Active fixation leads seem to have advantages and disadvantages. On the one hand, once the screw is retracted, the tip can be easily detached from the endocardium, and the lead, being isodiametric, can be removed more easily than the others [6, 7]. On the other hand, an unscrewed lead is more difficult than a tined one. Fixation mechanisms that cannot be unscrewed, such as the Vitatron Helifix, make the procedure more complex, increasing the risks of myocardial perforation and cardiac tamponade. 

Fig. 3 2 Posteroanterior (a) and lateral (b) chest X-ray showing a patient with four screw in leads, including a coronary sinus (CS) active fixation lead (Medtronic Starfix). RA, right atrium, RV, right ventricle, ICD, implantable cardioverter-defibrillator, PS, pericardial space...

Before starting the extraction procedure, the operator must identify the type and manufacturer of leads submitted to removal. One must identify lead fixation mechanism and type of fixation in case of an active fixation lead in some active fixation leads, special stylets are needed in order to unscrew the screw. After lead identification, the procedure of lead extraction consists of lead preparation and sheath application when gentle manual traction is unsuccessful. 

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. 

Transvenous leads may be attached to the endocardium either actively or passively. Active-fixation leads incorporate devices that invade the endomyo-cardium, whereas passive-fixation leads promote fixation by indirect means. When correctly implanted, both fixation mechanisms result in an extremely low incidence of lead dislodgment. 

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. 1.19 Thin (4.1Fr) bipolar active-fixation lead with a fixed screw and no Inmen for a stylet. (Medtronic 3830 SelectSecure ). The screw is coated with beclomethasone. The lead is delivered by a steerable catheter. (Permission for nse Medtronic.)...

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... 

Fig. 1.27 A steer able stylet (Locator , St Jude), operated with one hand, for positioning an active fixation lead in the heart. The stylet can be used to continually and temporarily alter the curvature of the distal part of the lead without the necessity to remove or replace the stylet. Above The lead pin is attached to the guiding stylet by a setscrew attached to the bulbous clamp of the stylet handle. For a straight stylet, the arrow indicates the position of the slide next to this clamp. Below Moving the shde along the handle away from the lead gradually curves the stylet and hence the lead. The amount of movement each way determines the curvature of lead. Turning the whole handle also turns the distal curved lead within the heart. The clamp can be released from the handle and rotating the detached clamp turns the lead pin, which extends or retracts the serew mechanism. (Permission for use St Jude.)...

There are essentially two types of active fixation leads both involve a helix or screw as a fixation mechanism. The first and simplest design incorporates a continuously exposed screw. Because the screw is exposed, problems may be encountered as the exposed screw seemingly catches on every endocardial stracture. Usually, the lead tip is freed by counterclockwise rotation of the lead body. In an attempt to avoid this problem, some manufacturers have eoated the exposed screw with some form of sugar that dissolves, ultimately exposing the screw (Fig. 4.36). The problem with this remedy is that, once the eoating dissolves, the exposed screw once again can hook on any endocardial stmcture. 

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. 

The second technique involves atrial placement of an active fixation lead that is straight. In this case, desired lead position is achieved by preforming the stylet into a shape that will achieve the desired position. Such leads... 

Unlike the ventricular lead, good fixation is not documented by retraction. Good position is documented by fluoroscopy and acceptable threshold meas-uranents. This is particularly hue with active fixation leads where pulling should be avoided, because it may result in easy dislodgment. 

The floppy-tip technique may be used for achieving unusual atrial lead placement with a shaight active fixation lead. This is particularly useful for placement along the right lateral atrial wall. With the curved stylet retracted 1 to 2 in., the lead tip assumes a more lateral position. By simply advancing the lead to a point of contact, the fixation mechanism can be activated and threshold measurements carried out. 

Zei PC, Eckart RE, Epstein LM. Modified temporary cardiac pacing using transvenous active fixation leads and external resterihzed pulse generators. J Am Coll Cardiol 2006 47 1487-1489. 

Fig. 15.1 Typical transvenous active-fixation lead placement in a 5-year-old child with complete congenital AV block. Note the large amount of extra lead that was introduced to allow for future growth, as well as the placement of the ventricular lead high in the ventricle to minimize the effect of future growth.

Lead dislodgment occurs in approximately 2% of cases despite the use of active fixation leads, and myocardial penetration or perforation occurs in approximately 1% of cases (58). Movement of the lead tip is detected by changes in lead performance and by changes in the paced QRS complex morphology on the surface ECG. The typical paced QRS complex has a left BBB-hke pattern with either a superior (with a right ventricular apex position) (Fig. 16.5) or an inferior (with a right ventricular outflow tract position) (Fig. 16.6) mean frontal plane axis. A right BBB-like pattern may indicate perforation of the lead into the left... 

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