Transvenous Lead Extraction: From Simple Traction to Internal Transjugular Approach

In the last years, indications for defibrillators and cardiac resynchronization therapy have expanded enormously; for this reason, and also due to the extension of human life length, the number of patients with implanted cardiac devices have steadily increased. The leads implanted for the functioning of these devices, however, have a limited duration in time and more and more their extraction will be a frequent issue in clinical practice, in order to treat short- and long-term complications, such as infections and failures.

Aim of this book is to provide readers with a state-of-the-art on lead extraction techniques. The chapters deal with leads characteristics, indications to lead removal, patient preparation, tools and techniques for extraction, and prevention and management of complications. In addition, a series of tips and tricks on how to treat some particular conditions (tight cost-clavicular space, fractured leads, ICD leads, dangered leads…etc.), are given. A new extracting technique, according to which the extraction is performed through the internal jugular vein is described; several examples are included and many figures provide a thorough depiction of this innovative procedure.

The volume will be an excellent resource for all those involved in the management of cardiac patients: cardiologists, arrhythmologists, cardiac surgeons, GPs, pediatricians, and post-graduate students in these disciplines.

• Language: English
• Publisher: Springer
• Release date: Sep 6, 2011
• ISBN: 9788847014664

Book preview

Maria Grazia Bongiorni (ed.)Transvenous Lead ExtractionFrom Simple Traction to Internal Transjugular Approach10.1007/978-88-470-1466-4_1© Springer-Verlag Italia 2011

1. Importance of Knowing Lead and Patient Interaction

Raffaele De Lucia¹ , Giovanni Coluccia¹, Stefano Viani¹ and Luca Paperini¹

(1)

2nd Cardiovascular Department AOUP, Santa Chiara University Hospital, Pisa, Italy

Abstract

The implantable cardiac pacemaker (PM)/defibrillator is a technically sophisticated system composed of a generator connected to one or more leads. Pacemaker/defibrillator leads play a pivotal role for system function, delivering the output pulse or the endocardial shock from the generator to the myocardium and acquiring spontaneous intracardiac electrogram from the heart to the device. Leads are also the most frequently involved component in case of system malfunction, and when a generator-pocket infection is present, their extraction — always necessary to guarantee complete resolution — is a challenge. The success of lead extraction is highly influenced by lead characteristics; for that reason, this chapter is dedicated to lead technology, i.e., polarity, electrodes, fixation mechanisms, electrode-tissue interaction, conductors, insulators, and connectors, with particular attention to aspects that may interfere with the extraction procedure. We discuss separately cardiac PM and defibrillator leads to emphasize their different technology.

1.1 Structure, Function, and Clinical Aspects of Pacemaker and Defibrillator Leads

The implantable cardiac pacemaker (PM)/defibrillator is a technically sophisticated system composed of a generator connected to one or more leads. Pacemaker/defibrillator leads play a pivotal role for system function, delivering the output pulse or the endocardial shock from the generator to the myocardium and acquiring spontaneous intracardiac electrogram from the heart to the device. Leads are also the most frequently involved component in case of system malfunction, and when a generator-pocket infection is present, their extraction — always necessary to guarantee complete resolution — is a challenge. The success of lead extraction is highly influenced by lead characteristics; for that reason, this chapter is dedicated to lead technology, i.e., polarity, electrodes, fixation mechanisms, electrode-tissue interaction, conductors, insulators, and connectors, with particular attention to aspects that may interfere with the extraction procedure. We discuss separately cardiac PM and defibrillator leads to emphasize their different technology.

1.1.1 Pacemaker Leads

1.1.1.1 Lead Polarity

Transvenous lead polarity simply indicates the number of electrodes in contact with the heart. A unipolar lead has only one electrode, the cathode, on his tip. In this configuration, the PM case serves as the anode of the circuit (Fig. 1.1). A bipolar lead has two electrodes at the distal end separated by a short distance. The tip electrode is the cathode, and the proximal ring electrode serves as the anode (Fig. 1.2). In this configuration, the PM case is not involved in the electrical circuit. The distance between tip and ring electrode varies with manufacturer and design.

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Fig. 1.1

Typical unipolar, straight, passive-fixation lead

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Fig. 1.2

Typical bipolar, straight, passive-fixation lead

In the VDD-pacing lead, there are two bipolar systems. The distal one is used to pace and sense the ventricle chamber, whereas the proximal, floating one in the atrial chamber, with no contact with the endocardial surface, is only used to sense spontaneous atrial signals. These leads are called quadripolar, and distances from the four electrodes vary among manufacturer and lead design (Fig. 1.3). Bipolar may be superior to unipolar pacing/sensing because it is less prone to cause extracardiac stimulation at the pulse generator or to detect myopotentials, far-field signals, and electromagnetic interference. Moreover a bipolar lead can function in the unipolar mode, whereas the converse is obviously not possible. Historically, unipolar had a smaller external diameter than bipolar leads due to the presence of only one conductor and were therefore easier to manipulate during implantation than their counterpart. Otherwise, in a lead extraction procedure, the advantages of this design could be disadvantages: unipolar leads are smaller and usually more fragile than bipolar leads (with two or more conductors) because they are not as stiff.

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Fig. 1.3

AV Plus DX (St. Jude Medical, Model 1368). Vertical arrows show the different dimensions along the lead; horizontal arrows show the distance between the four electrodes. Measurements in millimeters (courtesy of St. Jude Medical)

1.1.1.2 Pacing Electrodes

The electrode is the portion of a pacing lead that acts as a long-term interface between the lead and the heart tissue providing functions of pacing and sensing, and these functions are influenced by the electrode’s surface area. To describe pacing, we use the following analogy from Ken Stokes (former Medtronic senior research fellow): The battery of the PM is like a bucket of water. There is a hole in the bucket, and that represents the current drain through the pacing system electrode. If the hole (electrode) is larger, the water (or current) drains out quickly. But if we can make the hole small, then it will drain more slowly. In the same manner, in a pacing lead system, if we reduce the electrode size (the bucket’s hole), we increase the pacing impedance and deliver energy more efficiently.

The earliest transvenous pacing leads had a stimulating electrode surface area greater than 100 mm². Such a broad area was associated with a very low pacing impedance and, consequently, excessive current drain which influenced negatively battery longevity. So, from the 1960s to the 1990s, the cathode area of most pacing leads had been reduced from 8 to 1.2 mm² (Figs. 1.4 and 1.5) [1]. Unfortunately, continued reduction of electrode size is undesirable because it increases the polarization phenomenon. But what is polarization?

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Fig. 1.4

Progressive variation in stimulating electrode surface area over the years (from [1], chap. 8 p. 69 (courtesy of Medtronic)

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Fig 1.5

This patient was referred to our institution for lead extraction using the internal transjugular venous approach. The fractured lead (*) was implanted in 1975. Note that the old lead has an electrode with a broader stimulating electrode surface area. Temporary pacing lead (°)

When there is no voltage difference between the cathode (tip) and the electrode (ring), ions are distributed randomly, but when the pacing pulse begins, ions move, which results in current flow from the electrode to the myocardium. As the current pulse continues, a charged layer surrounds the electrode tip and produces capacitive effect, which is the buildup of charge layers on the electrode, called polarization. When polarization is excessive, a substantial amount of lead current must be used to overcome it, which means that less current is available to stimulate the myocardium. As a consequence, output voltage must be increased, and more lead current is required to maintain adequate electrode-tip voltage and a safety margin. Nevertheless, if electrode size is reduced, sensing capability is also reduced, because decreasing the stimulation surface area, the area available for sensing is also reduced (Fig. 1.6).

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Fig 1.6

Correlation between stimulating surface area, impedance, polarization, and sensing

To guarantee a small geometric electrode radius maintaining a large surface area, the porous electrode was developed. By altering the surface structure to be more porous, the geometric surface area of the electrode increases and therefore lowers polarization. In this design, internal spaces within the electrode pores increase the surface area with the same radius. The porous electrodes initially consisted of a fine wire mesh of platinum-iridium fibers and were referred to as totally porous electrodes. Subsequently, manufactures moved to porous-surface electrodes created by sintering a metal powder or microspheres onto a solid metal substrate (Fig. 1.7) [2]. Summarizing, porous electrodes show lower stimulation threshold, better sensing properties, lower current drainage (higher impedance), and lower polarization [3–5]. Relatively few conductive materials have proven to be satisfactory for use in pacing electrodes.

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Fig. 1.7

Porous-surface electrodes (from [2], p. 38)

Ideal material should be biologically inert, resistant to degradation over time, and not elicit a marked tissue reaction at the electrode-myocardium interface. Today, materials most often used for electrode building are platinum-iridium, platinized-titanium-coated platinum, iridium oxide, and platinum. Carbon electrodes finally seem to be the least susceptible to corrosion. To increase their surface area, they can be treated with a process called activation, which roughens the lead surface. Carbon electrodes elicit only minimal tissue reaction compared with the reaction surrounding platinum-iridium electrodes [6–8].

1.1.1.3 Lead Fixation and Electrode-Tissue Interaction

Lead Fixation

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 the tip. In the latter case, screws are covered with a material that dissolves in the blood stream in a time period sufficient for lead positioning in the heart. Mannitol compounds, for example, have been used for this purpose. While covering the screw, mannitol prevents it from catching on tissue and allows easier lead advancement in the venous system. Fixing these leads is possible by rotating the entire lead. In this case, the helix is always out. Otherwise, in an extendable/ retractable design, is possible to activate the screw by applying a tool to the connector pin and rotating the inner conductor. In these leads, is possible to determine when the screw is out by apposite fluoroscopy markers, as shown in Fig. 1.9.

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Fig. 1.8

Types of passive fixation leads (from [2], p.36)

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Fig. 1.9

Extendable/retractable screw-in lead at fluoroscopy (courtesy of Medtronic)

Passive and active fixation mechanisms have both advantages and disadvantages. The clinical situation and operator preference dictate which kind of lead is chosen. Active fixation leads are preferred in cases of distorted anatomy (postsurgical or congenital heart disease), high right-sided pressure, after lead extraction procedure, or when an alternative site of pacing [i.e., atrial septum, right ventricular (RY) outflow tract] is deemed necessary.

Electrode-Tissue Interaction

After lead implantation, an inflammatory process develops at the electrode-tissue interface. This process causes an acute rise in stimulation threshold, but when the inflammatory process subsides and a fibrous capsule is formed, the stimulation threshold progressively falls to a chronic plateau level, which is reached about 4–6 months after implantation. Fibrous reaction and tissue ingrowth over tines and into porous and grooved electrodes consistently improve mechanical stability and intimate electrode-tissue contact but may also negatively influence chronic stimulation threshold.

The electric field strength at the cathode increases with current density but decreases as a function of the square of the distance between the electrode surface and the tissue, In the case of a thick, fibrous capsule developing at the tip of the electrode, the stimulation threshold inevitably increases, and sometimes it may be impossible to obtain myocardial electrical activation (exit block). For this reason, inflammation after lead implantation is the crucial factor that must be controlled to achieve a chronic, low-stimulation threshold.

The mechanical lead configuration can influence inflammatory reaction: for example, a lead design that allows excessive pressure to the distal electrode or an excessive lead stiffness can traumatize the endocardium resulting in accelerated inflammatory response, myocardial ischemia or even ventricular perforation [9]. To prevent traumatic contact at the electrode-tissue interface, softer forms of silicone or polyurethane may be used for the distal portion of the lead. Local pharmacologic agents were developed some years ago to reduce inflammatory reaction at the lead tip. Today, only glucocorticoids are used for this purpose. Dexamethasone sodium phosphate demonstrated the best performance compared with other glucocorticoids. The original design of drug-eluting leads was composed of a platinum-coated titanium electrode with an internal chamber behind it containing a plug of silicone rubber soaked with 1 mg or less of dexamethasone sodium phosphate; the internal chamber communicates with the outer electrode surface through a porous channel. The plug is referred to as a monolithic controlled release device (MCRD). This kind of electrode has demonstrated both acute and chronic very low stimulation thresholds, with elimination of the early postoperative peak. Steroid-eluting electrodes also show higher acute and long-term R- or P-wave amplitudes than their non-drug-eluting counterpart [10, 11]. Another type of drug-eluting lead is designed with a porous ceramic or silicone collar soaked with dexamethasone sodium phosphate positioned immediately proximal to tip electrode. This system is used in steroid-eluting, active fixation screw-in leads and shows similar performance as the MCRD. Steroid elution is available on atrial and ventricular leads and as well as coronary venous and epicardial leads.

Obviously, fixation mechanisms and electrode-tissue interaction have crucial implications for lead extraction also. Encasement of the tines of a passive fixation lead by fibrous reaction may make transvenous lead removal more difficult than that of an active-fixation isodiametric leads.

1.1.1.4 Pacing Conductors: Materials and Designs

The conductor of a pacing lead is basically a wire that conducts the electrical current from the pulse generator to the stimulating electrode and the sensed cardiac signals from the electrode to the sensing amplifier of the pulse generator.

Materials

The early conductor for unipolar pacing leads, developed by Elema-Schönander and Ericsson, consisted of four thin bands of stainless steel wound around a core of polyester braid (Fig. 1.10) [1]. This design was later abandoned because of possible corrosion. The same problem happened later with another conductor made with a drawnbrazed-strand (DBS) technique and insulated with polyurethane. In this design the silver occupies the central core and the spaces between the nickel alloy wires and also forms a thin coating around the wires. These leads had a high rate of insulation failure caused by internal oxidation from the DBS. Another early type of electrical conductor was the tinsel wire, but this design also showed later to be less than optimal. Separated from a central textile core (created to provide a high tensile strength), the individual strands or ribbons were relatively fragile (Fig. 1.11) [1]. Alloys such as MP35N (35% cobalt, 35% nickel, 20% chromium, and 10% molybdenum) and nickel-silver are the most frequently used materials for modern lead conductors. It is corrosion resistant, flexible and durable, and offers a low resistance to allow efficient transfer of energy from the PM to the lead tip. When the MP35N conductor is silver-cored, it also offers enhanced conductivity.

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Fig. 1.10

Elema-Schönander unipolar lead with conductor made of stainless steel bands. (from [1], Chap. 9, p. 1) (courtesy of Medtronic)

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Fig. 1.11

Platinum/iridium ribbons intertwined around polyester yarn (from [1], Chap. 9, p. 76) (courtesy of Medtronic)

Designs

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].

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Fig. 1.12

Unifilar conductor: a single wire coil is wound around a central axis in a spiral (from [1], Chap. 9, p. 37) (courtesy of Medtronic)

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Fig. 1.13

Multifilar conductor: each conductor strand is individually coated with a thin layer of insulator, and the entire helical coil is insulated again with a thicker conventional insulator (from [1], Chap. 9, p. 79) (courtesy of Medtronic)

This design reduces pacing impedance and the redundancy prevents pacing failure if a filar breaks. A third design is the cable. A cable conductor is obtained by two or more wires twisted together as a strand and then bundled with other strands around each other as a rope. Cable-leads have lower electrical resistance but are less prone to crush failure and smaller than coils (Fig. 1.14) [1].

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Fig. 1.14

Cable conductor: two or more wires twisted together as a strand and then bundled with other strands around each other like a rope (from [1], Chap. 9, p. 78) (courtesy of Medtronic)

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-radial or parallel wound, and a parallel or multiluminal design. Coaxial bipolar leads, standard in treating bradyarrhythmias, have an inner coil extending to the cathode and an outer coil terminating at the proximal electrode (anode). The inner coil is insulated from the outer coil by his own insulator. Coradial bipolar leads have two or more individually insulated coils wound next to each other in a single coil and a common outer insulation. With this configuration, the outside diameter of the polar lead is as small as that of a unipolar lead. Multiluminal leads, the standard for treating tachyarrhythmias, have conductor coils and cables parallel to each other, and are again separated by insulating materials. Coaxial, co-radial, and multi luminal designs are shown in Fig. 1.15 [1].

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Fig. 1.15

Many kinds of conductor designs (from [1], Chap. 9, pp. 79, 80) (courtesy of Medtronic)

1.1.1.5 Lead Insulation

Insulation is a nonconducting material that prevents electrical current from leaving the lead and entering the surrounding tissue. Usually, lead insulation extends from the lead connector to the cathode tip and, in bipolar leads, is interrupted by the anode ring. Insulation also prevents tissue stimulation, except at the electrode-myocardial interface, and protects the conductor from corrosion due to body fluids and exposure to tissue.

Insulation Materials

The story of insulation materials started in 1958 with polyethylene and silicone rubber, going through many changes — from polyurethane 80A to 55D — and is still in evolution, with emerging biomaterials such as fluoropolymer and copolymer. The most commonly used insulation materials in pacing leads are silicone and polyurethane, the advantages and disadvantages of which are shown in Table 1.1 and Fig. 1.16.

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Fig. 1.16

Metal ion oxidation is an oxidative degradation of polyurethane insulation, true for both kinds of polyurethane (80A and 550) (a). Environmental stress cracking is an oxidative condition that takes place on the surface of polyurethane leads (true for 80A) (b)

Table 1.1

Lead insulation: comparison of silicone rubber and polyurethane

Silicone rubber that was introduced as insulating material for pacing leads in 1958, is flexible, soft and continues to be used today. It is a reliable substance but has some disadvantages: it is relatively fragile and susceptible to abrasion and has low tear strength. To avoid this problem, it must be thick. This is acceptable in a unipolar lead in which there is only a conductor coil to insulate, but in bipolar leads, thickness increases the external diameter. For this reason, it has been recently upgraded to platinum-cured silicone rubber that, even though thinner, allows better mechanical performance. Silicone rubber also has a high coefficient of friction in blood, especially when two leads are implanted in the same vein. One method recently developed to avoid this problem is to use an insulating system with lubricious coatings.

Polyurethane is a stiffer and firmer material than silicone introduced in 1977 for its better tear strength and low coefficient of friction. Due to documented cases of stress cracking discovered a few years after implantation, some processing changes were made, increasing performance satisfaction. Compared with silicone, it allows for a thinner lead body and when moist is slippery. This represents an advantage in cases in which two leads are implanted in the same vein. Polyurethane is available in a softer and more flexible version, known as Pellethane (P) 80A, and a stiffer version, known as P55D. Most polyurethane leads now used in clinical practice have the P55D polymer insulation, which is far less prone to degradation than the P80A version.

Some currently used bipolar coaxial leads use both silicone (inner insulation) and polyurethane (outer insulation) coating, incorporating the durability of silicone with the ease of handling of polyurethane while maintaining a thinner external lead diameter.

Fluoropolymers are polytetrafluoroethylene (PTFE) and ethylene tetrafluoroethylene (ETFE). They can assist as redundant insulation and are primarily used as a coating to defend conductor wires from corrosion. The advantages of those materials are their inert and biocompatible behavior and high tensile strength. Otherwise, their stiffness, creep, and trend to metal ion oxidation during manufacturing represent important disadvantages.

Finally, new insulators for cardiac leads have recently been developed that are silicone rubber-polyurethane copolymer to combine the advantages of both materials [12]. The possibility of matching the biocompatibility and biostability of silicone with the processability and resistance of polyurethane is an appealing step toward a nearly ideal biomaterial. The first copolymer used on cardiac leads was the Optim™, which was actually used only on St. Jude Medical, Inc. pacing leads. As indicated by St. Jude Medical, Optim should have the following characteristics: improved flexibility and lubricity, increased abrasion resistance, and excellent biostability. Obviously insulator characteristics and integrity not only influence the reliability/failure of pacing leads (sometimes the indication for lead extraction) but deep ly influence the transvenous lead extraction procedure. A low resistance to tear or traction may predispose to insu lator fracture during attempts at lead removal, with potentially dangerous direct exposure of the bare metal coil to the venous system.

1.1.1.6 Connectors

The connector electrically binds the lead to the PM. Many types of connectors have been developed in the past, and this created considerable confusion among physicians and, in some cases, a potential hazard to the patient. Historically, unipolar leads were 5 or 6 mm in diameter, and bipo lar leads required a bifurcated