ICD
Covering sleeves can shield the high-voltage coils from lead chatter in an integrated bipolar ICD lead
1 University of Pennsylvania Health System, 9 Founders Pavilion, 3400 Spruce Street, Philadelphia, PA 19104, USA; 2 Guidant Inc. (Boston Scientific), St Paul, MN, USA
Manuscript submitted 4 September 2006. Accepted after revision 10 November 2006.
* Corresponding author. Tel: +215 6154332; fax: +215 615 4350. E-mail address: joshua.cooper{at}uphs.upenn.edu
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Abstract |
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Aims Integrated bipolar implantable cardioverter-defibrillator (ICD) leads use the distal high-voltage coil as both the ventricular sensing anode and the distal shocking electrode. Mechanical interactions between the distal ICD coil and other intracardiac leads have been reported to result in electrical oversensing and inappropriate ICD therapies. We sought to determine whether covering sleeves over the high-voltage coils of an integrated bipolar ICD lead could prevent sensed artefact from mechanical lead interactions.
Methods and results Endotak Reliance® 0157 and Endotak Reliance-G® 0185 leads, the latter with expanded polytetrafluoroethylene (ePTFE) sleeves covering the high-voltage coils, were connected to ICD generators and the leads were submerged in saline. Device programmers were used to communicate with the ICD generators, providing real-time electrogram recording throughout testing. A series of mechanical interactions were performed with the ICD leads, including sliding and striking each distal coil against metal and non-metal components of other ICD and pacemaker leads. All direct metal–metal interactions resulted in sensed electrical artefact, including interactions between the bare ICD coil and another bare ICD coil or metal pacemaker ring. Identical mechanical interactions where metal–metal contact was prevented due to an interposed ePTFE covering sleeve were electrically silent with no sensed artefact.
Conclusions A covering sleeve over the distal high-voltage coil of an integrated bipolar ICD lead can mechanically shield the lead from metal–metal interactions, which might otherwise result in sensed artefact and inappropriate ICD therapies or withholding of pacing output. This finding has implications for lead selection when a new ICD lead is to be implanted adjacent to abandoned intracardiac leads or lead fragments.
Key Words: Implantable cardioverter-defibrillator, ICD lead, Artefact, Sensing, Electrogram, Shock
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Introduction |
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Transvenous pacemaker and implantable cardioverter-defibrillator (ICD) leads become adherent to the inner walls of the great veins, right atrium, and right ventricle over time, due to scar tissue binding.1
,2 The high-voltage coils of ICD leads provide a large surface area for scar ingrowth, and typically represent sites for significant binding, increasing the difficulty and risk of subsequent lead extraction, should that be needed for mechanical or infective complications.3,4 The Endotak® 0185 Reliance-G® ICD lead (Guidant, Inc., St Paul, MN, USA) was designed to incorporate two sleeves of expanded polytetrafluoroethylene [(ePTFE) Goretex®] that cover the proximal and distal high-voltage coils (Figure 1), with the goal of preventing tissue ingrowth between the coil filars and thereby improving the success and safety of future lead extraction. The presence of the ePTFE sleeves was demonstrated by Guidant, Inc. to have no significant impact on the sensing, pacing, cardioversion, and defibrillation capabilities of the lead when compared with standard ICD leads, and the Endotak Reliance-G® lead was therefore approved by the US Food and Drug Administration for clinical use (PMA P910073/S043, 2 March 2004).
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Current dual-coil ICD leads have either a true bipolar or an integrated bipolar ventricular sensing configuration. True bipolar leads have two dedicated electrodes that form a sensing dipole at the lead tip, while integrated bipolar leads share the distal high-voltage coil as both the ventricular sensing anode and the distal shocking electrode. Advantages of the true bipolar lead include reduced far-field oversensing, but disadvantages are related to the increased complexity of the lead, which may increase the chance for failure of one of its components. The integrated bipolar lead, because of the large surface area of the sensing anode, as well as the much larger interelectrode spacing of the sensing bipole, is more prone to oversensing non-QRS electrical events such as the T-wave, P-wave, and diaphragmatic myopotentials.5
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An integrated bipolar lead is also more prone to oversensing non-physiological electrical signals that are generated during interactions with other intracardiac leads. The large surface area of the distal high-voltage coil is more likely to come in contact with adjacent abandoned pacing or ICD leads than is the ring electrode of a true bipolar ICD lead. These mechanical interactions can lead to sensed electrical artefact and delivery of spurious ICD shocks.7,8 Because the cardiac defibrillation threshold tends to be lowest with the RV coil positioned as apically as possible,9,10 optimal sites for implantation of the new ICD lead may be limited in patients who have existing leads in place (Figure 2). Occasionally, extraction of the abandoned lead hardware may be necessary for effective implantation of the new ICD lead, due to mechanical lead interactions,11 and it is a Class I indication to remove a lead that interferes with the operation of another implanted device, according to the most recently published guidelines.12
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We hypothesized that the presence of a covering sleeve over the distal high-voltage coil might reduce or prevent electrical noise artefact in an integrated bipolar lead by mechanically shielding the coil from metal-on-metal interactions with adjacent hardware. This potential benefit of the covering sleeve would be serendipitous and not related to the original design intent, as outlined above.
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Methods |
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Endotak Reliance® Model 0157 and Endotak Reliance-G® Model 0185 integrated bipolar ICD leads were attached to ICD generators. The two lead models are identical in every respect, except that the former lead model has bare metal high-voltage coils, and the latter has ePTFE sleeves covering the coils (leads and ICD generators manufactured by Guidant, Inc.; both Vitality® AVT and Contak Renewal 3® ICD generators were used). The leads were submerged in a bath of 0.9% NaCl. Programming wands were placed over each ICD generator, so that real-time electrograms could be continuously and simultaneously obtained during all testing manoeuvres. The ICDs were arbitrarily programmed for backup pacing at VVI 30 ppm, with nominal ventricular sensitivity, a single ventricular fibrillation (VF) zone >160 bpm, and tachycardia therapies were turned off. The programmed tachycardia rate cutoff was irrelevant, as the parameter to be followed was the presence or absence of sensed artefact; the cycle length of the noise transients that were produced was directly related to the type and rate of the mechanical manoeuvre being implemented.
Mechanical manoeuvres were performed by an operator wearing latex gloves, who did not look at the leads that were presented in the saline bath. With the elimination of visual and tactile cues, the operator was unaware of which type of ICD lead, one with covered or uncovered coils, was being tested, and mechanical manoeuvres could thereby be freed from performance bias. As an initial control, each type of lead was initially subjected to vigorous agitation in saline, during continuous strip recordings from the ICD programmer. Subsequent manoeuvres involved physical contact between different segments of each ICD lead and various components of other ICD and pacemaker leads. Sliding and repeated striking manoeuvres were performed using both the distal coil and an insulated portion of each tested ICD lead, as each was sequentially paired with the distal coil of other ICD leads and the distal electrodes and insulated segments of other pacemaker and ICD leads. Both sliding and striking manoeuvres were performed with each pairing of lead components.
In all scenarios, the ICD lead being tested was connected to an ICD generator, with the programming wand in place so that real-time programmer strip recordings at 25 mm/s could be made throughout the manoeuvres. When mechanical manoeuvres were performed using two ICD leads, both leads were connected to ICD generators so that simultaneous electrogram recordings could be made and compared. Each manoeuvre and lead pairing was repeated three times to demonstrate reproducibility. Five different leads were used to demonstrate that observed phenomena were not a function of the specific lead being tested.
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Results |
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All manoeuvres that involved direct contact between a bare metal distal ICD coil (acting as the sensing anode) and any other metal ICD or pacemaker lead component were able to produce noise artefact with ICD oversensing. These included sliding and striking interactions between two bare metal distal ICD lead coils, as well as interactions between a bare metal ICD lead coil and metal pacemaker and ICD ring electrodes. Figure 3A shows the electrogram recordings generated during a sliding interaction between the metal ring anode of a pacemaker lead (Fineline® Model 4457, Guidant, Inc.) and the bare metal distal coil of an 0157 ICD lead. Figure 4 shows the simultaneous electrogram recordings that were generated when the bare metal distal coils of two 0157 ICD leads were repeatedly struck against one another. Both of these interactions are shown consistently to generate electrograms that are inappropriately sensed as ventricular events by the ICD generators.
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Vigorous lead agitation was initially performed with each ICD lead to ensure that it was the physical interaction with another lead, rather than the motion itself, that was responsible for any sensed electrical noise. No oversensing occurred with isolated lead motion, however vigorous. When sliding or striking interactions were performed between lead components that involved either lead insulation or ePTFE covered ICD coils of one or both leads, no appreciable electrogram artefact was generated, and no oversensing occurred. Figure 3B shows the ICD electrogram recording generated during a sliding manoeuvre between the metal ring anode of a pacemaker lead and the ePTFE covered distal coil of an 0185 ICD lead, in a manner identical to that performed over the bare metal coil of the 0157 lead (Figure 3A). Figure 5 shows the simultaneous electrogram recordings generated when the distal coils of the 0185 ICD lead (ePTFE-covered coil) and the 0157 ICD lead (bare metal coil) were repeatedly struck against one another, in a manner identical to the striking manoeuvre performed using two bare metal 0157 coils (Figure 4). In each case where there was interposed lead insulation or a sleeve of ePTFE that prevented metal–metal interactions, no sensed artefactual electrograms could be generated.
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Discussion |
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This study addresses the potential risk for spurious ICD tachyarrhythmia detection and inappropriate therapy delivery that have been reported to occur from interactions between an active ICD lead and other intracardiac leads or lead fragments.7
,8 As ICD implantation is performed in an ever-growing population of patients, including younger patients, the problem of accumulation of intracardiac lead hardware will increase. The findings of this study suggest that only metal–metal lead interactions are able to generate electrical artefact that may result in ICD oversensing, and that mechanical shielding with a sleeve of ePTFE can prevent the generation of artefactual sensed electrograms. This finding is specific to integrated bipolar leads, as the distal high-voltage coil is not part of the sensing circuit in a true bipolar lead. The 0185 lead that was used in this study is currently in clinical use, and the ePTFE sleeves were added to prevent scar growth into the high-voltage coils over time, thereby improving the success and safety of subsequent lead extraction, should that be necessary. The finding that covering sleeves over the high-voltage coils may reduce the incidence of mechanically-induced artefact is serendipitous, and might be an additional advantage of implantation of such a lead into a patient with abandoned leads, considering both issues of future extraction and lead interactions. While new leads are purposefully implanted in a location to minimize contact with abandoned hardware, the physical relationship between new and old leads during implantation is only evaluated with the patient in the supine position, and lead geometry may change over time as scar tissue gradually and progressively binds each lead to the endovascular and endocardial walls, and to each other, at points of contact.
In addition to shielding the integrated bipolar coil from metal interactions with other leads, covering sleeves should also prevent similar interactions with metallic guide wires, which have been reported to result in mechanically-induced oversensing, inappropriate ICD firing, and irreversible damage to the ICD high-voltage circuitry.13 The possibility that metal–metal contact between a high-voltage coil and other intracardiac leads at the moment of shock delivery could result in current shunting and a change in defibrillation efficacy was not investigated in this study, but a study performed in a canine model did not show a change in the 50% effective dose (ED50%) for successful ventricular defibrillation when an active intracardiac lead was in contact with an adjacent non-active lead electrode.14
The main limitation of this study is its in vitro design, with the question of how closely the mechanical interactions that were created replicate the possible lead interactions that could occur in a contracting ventricle. Mechanically-induced oversensing is a real clinical phenomenon, but its occurrence is rare and unpredictable, making it difficult to design and implement an in vivo trial. A lead complication registry might provide some insights into the best way to manage patients with multiple intracardiac leads, including the evaluation of strategies that incorporate early lead extraction of abandoned leads and the use of ICD leads with covering sleeves over the high-voltage coils. Another limitation of this study is that ICD generators from other companies were not used to record the lead chatter artefact. The electrical artefact that was generated was sensed at nominal sensitivity in the ICD models that were used, and was therefore likely to be of sufficient amplitude to be sensed by any ICD generator, regardless of the subtleties of company-specific auto-gain algorithms and signal processing.
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Conclusions |
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Metal–metal interactions are responsible for lead chatter artefact. An interposed layer of material, such as the ePTFE covering sleeve on the metal high-voltage coils in the 0185 ICD lead, can eliminate this artefact during mechanical lead interactions. If an integrated bipolar ICD lead is to be implanted in a patient with abandoned intracardiac leads, consideration should be given to using a lead with ePTFE sleeves covering the high-voltage coils to minimize the chance for mechanically-induced oversensing and inappropriate ICD therapies. New strategies for preventing lead-related complications will likely be needed in this era of rapid expansion of our ICD patient population, including younger patients who will likely receive multiple intracardiac leads over their lifetime.
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Acknowledgements |
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JMC and RJV participate in industry-sponsored clinical research trials sponsored by Medtronic, Guidant, and St Jude Medical, and have given lectures at educational conferences sponsored by Medtronic and Guidant. WHS and FCG have no disclosures to make. MJK is an employee of Guidant Inc.
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References |
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