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Editorial
Transvenous Implantable Cardioverter-Defibrillator Leads
The Weakest Link
William H. Maisel, MD, MPH
T
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turned to the manufacturer, returned product analysis tends to
be a poor predictor of failure mode and failure rate.6 Assessment of potential lead failure, therefore, often depends on
circumstantial evidence rather than direct visualization or
confirmation of a lead abnormality. Definitions of verified
and suspected pacemaker lead failure have been proposed and
are applicable to ICD leads7 (TABLE).
Although lead reliability is affected by a number of
bioengineering factors, including lead design, insulation durability, and manufacturing processes, lead performance is
also impacted by patient and operator characteristics, such as
implant route and implanting physician skill. These factors
collectively make lead performance much more challenging
than assessment of ICD generator performance. Because
leads are rarely returned for postfailure analysis, assessment
of lead reliability is most accurately assessed by prospective
device registries.6 Passive lead-malfunction reporting (ie,
relying on physicians to report lead failures when they occur),
as used by most ICD manufacturers when reporting product
performance, is subject to significant underreporting and,
therefore, significant overestimation of device reliability.
In this issue of Circulation, Kleemann et al8 report on the
reliability of ICD leads in 990 consecutive patients who
underwent first implantation of an ICD between 1992 and
2005. Lead defect was defined as a severe lead failure that
required surgical correction. Overall, 148 (15%) of ICD leads
failed during follow-up, with estimated survival rates of 85%
and 60% at 5 and 8 years after implant, respectively.
Insulation defects were the most common cause of lead
failure, with lead fracture, loss of ventricular capture, abnormal lead impedances, and sensing failure accounting for most
of the other failure modes.
Importantly, the study results were not attributable to 1 or
2 “bad” leads. Although the investigation was not designed to
compare the performance of different lead models, and
although some underperforming leads were included in the
study (eg, the Medtronic Transvene Model 6936/6966 ICD
lead, which is known to be prone to premature failure), the
report includes leads from 5 manufacturers, involving more
than 20 lead models. The long-term follow-up is a strength of
the study, but it does result in a cohort with a substantial
number of older lead models. Therefore, the relevance of the
results to modern ICD leads that have not yet been followed
up on for extended periods is uncertain. In addition, most
leads were implanted via the subclavian vein, an implant
route known to be associated with a higher lead-complication
rate.9 Nevertheless, the study findings are consistent with
prior reports demonstrating similar failure rates and
mechanisms.10 –13
ransvenous implantable cardioverter-defibrillator
(ICD) lead development was an important advance in
arrhythmia management. Their evolution has been
critical to the wide acceptance of ICDs for the treatment of
ventricular arrhythmias and the prevention of sudden cardiac
death. Indeed, it is unlikely that the 20-fold increase in annual
ICD implants observed during the past 15 years would have
occurred without the advent of these leads.1 Compared with
their epicardial predecessors, transvenous ICD leads are
easier to implant, are less costly, and result in substantially
decreased morbidity and mortality.2
Article p 2474
Modern ICD leads consist primarily of electrodes, conductors, and insulation, with a fixation mechanism and a connector to attach the lead to the myocardium and the ICD
generator, respectively. ICD leads must withstand hundreds
of millions of repetitive cardiac cycles, survive in the hostile
environment of the human body, and allow high-voltage
energy delivery for defibrillation at a moment’s notice. In
total, the demands placed on ICD leads are unparalleled
among implantable medical devices. Successful resuscitation
of a potentially lethal ventricular arrhythmia by an ICD
system depends on successful arrhythmia detection and
timely delivery of therapy. Both the ICD generator and the
lead are critical components of this system. Although ICD
generator malfunctions have recently garnered much attention, failure of an ICD lead also can result in significant
clinical events.1,3,4 Oversensing can cause inhibition of pacing or inappropriate shocks, and failure to capture, premature
battery depletion, or failure to defibrillate also can occur.5
Unlike ICD generators, which can be explanted and returned for manufacturer analysis when malfunction is suspected, ICD leads cannot be easily removed, because of the
extensive scarring and fibrosis that occurs around the lead in
the vasculature and heart. Verification of suspected lead
malfunction is uncommon because of the substantial risks of
lead extraction and the attendant electrode damage that may
obscure malfunction analysis. Even when removed and reThe opinions expressed in this article are not necessarily those of the
editors or of the American Heart Association, nor do they necessarily
represent the opinions, policies, practices, or positions of the US Food
and Drug Administration.
From the Cardiovascular Division, Beth Israel Deaconess Medical
Center and Harvard Medical School, Boston, Mass.
Correspondence to William H. Maisel, MD, MPH, Cardiovascular
Division, Beth Israel Deaconess Medical Center, 185 Pilgrim Rd, Baker
4, Boston, MA 02465. E-mail [email protected]
(Circulation. 2007;115:2461-2463.)
© 2007 American Heart Association, Inc.
Circulation is available at http://www.circulationaha.org
DOI: 10.1161/CIRCULATIONAHA.107.698597
2461
2462
Circulation
May 15, 2007
Definitions of ICD Lead Failure
Lead Failure Category
Definition
No structural failure
Lead functions normally, or has been discontinued for reasons unrelated to lead failure (eg, patient death or infection)
Suspected structural failure*
One of the following clinical findings of malfunction without verified lead structural failure:
Loss of capture or markedly elevated thresholds
Loss of sensing, oversensing, or skeletal muscular stimulation
Verified structural failure*
One of the following findings of malfunction
A visible conductor fracture or insulation defect seen at surgery
A change in the lead impedance, judged to be caused by conductor or insulation failure
(abnormally low in those cases with insulation breakdown and ⬙infinite⬙ in those cases with conductor fracture)
An evident fracture seen on chest roentgenogram
Manufacturer’s returned product report confirming the failure
*Abnormality led to discontinued use (either surgically or noninvasively).
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Hundreds of thousands of pacemaker leads have been
recalled by the US Food and Drug Administration during the
past 2 decades, with the majority of these recalls attributable
to failure of the leads’ insulation.5 ICD leads have been
plagued similarly by insulation failures,5 so it is not surprising
that insulation defects were the most common abnormality
observed in the study by Kleemann et al.8 Polyurethane and
silicone are the 2 most widely used electrical insulators in
ICD leads. Despite reports during the early 1980s that
polyurethane pacemaker leads might experience premature
degradation in vivo, many of the physical characteristics of
this insulation remain attractive to manufacturers and implanting physicians, and polyurethane insulation is still used
in many ICD transvenous leads.5 Its tensile and tear strength
are greater than those of silicone, allowing for thinner
insulation and smaller diameter leads. However, cracks on the
inner insulation surfaces of polyurethane insulation, caused
by metal oxidation, can markedly accelerate the failure
process.5 To achieve the same durability and strength as
polyurethane, silicone insulation must be thicker. This results
in larger-diameter leads, which some implanting physicians
do not favor. Some modern ICD leads use both silicone and
polyurethane insulation. No matter what insulation or combination of insulations a manufacturer chooses, no two
models of ICD leads are alike. The physical properties of a
specific insulation vary with chemical structure, and lead
reliability can be affected not only by the specific insulation
used but also by the insulation-manufacturing process, lead
manufacturing, and lead design.5
One third of patients with lead failure presented with
inappropriate shocks in the report by Kleemann et al.8
Methods to identify lead failure before clinical presentation
are necessary, both to reduce the risk of inappropriate shocks
and to prevent fatal events. Novel algorithms, such as the
recognition of numerous short, nonphysiological ventricular
intervals, or the recognition of a “mismatch” between farfield and intracardiac electrograms after signal processing,
may identify lead malfunctions earlier and minimize clinical
consequences.14,15 Notably, two thirds of lead defects are
identified on routine device follow-up; this underscores the
importance of routine care for ICD patients. Wireless technologies that permit automated, more frequent device checks
should identify lead failures earlier and warn patients sooner.
The high rate of ICD lead failure and the need for invasive
surgical procedures to correct many of the observed defects
could challenge the tenet that ICDs are cost-effective. For
example, a cost-effectiveness analysis of the Sudden Cardiac
Death in Heart Failure Trial concludes that ICDs were
cost-effective in that trial’s study population (New York
Heart Association Class II or III heart failure with left
ventricular ejection fraction no greater than 35%) “as long as
the benefits of ICD therapy observed in the Sudden Cardiac
Death in Heart Failure Trial persist for at least 8 years,” but
this was based on the assumption that costs and complication
rates observed during the first 5 years remain stable throughout the patient’s life.16 Although numerous ICD costeffectiveness analyses have been performed, all underestimate the ICD lead–malfunction rate and fail to account for the
substantial observed rates of ICD lead failure that necessitate
costly lead revisions and alter the calculus of ICD costeffectiveness. Future ICD cost-effective analyses must account for the observed moderate ICD lead–failure rates.
ICD lead reliability decreases over time and varies from
model to model. As such, clinicians need more accurate and
timelier lead-performance data, to clinically manage their
patients appropriately. Although manufacturers have significantly improved product performance reporting for ICD
generators in the wake of recent unfavorable press,4 ICD
lead–performance reporting remains inadequate. For example, in their most recent product performance report, one
manufacturer supplies only 6-month postimplant reliability
data on fewer than 300 patients for an ICD lead that was
approved for the US market in 2004 and that has been
implanted in close to 100 000 patients.17 Other manufacturers
fail to prospectively study lead reliability in a sufficient
number of patients to adequately and accurately inform users
of actual device performance.18,19 In short, better-designed
lead-monitoring programs and more timely reporting of ICD
lead performance must be required of manufacturers by the
US Food and Drug Administration.
Even a thorough preapproval testing process cannot reproduce the real-life stress that a transvenous lead experiences
during its years of service. Advances in lead technology
require changes in lead design and manufacturing practices
that may be met with unexpected increases in failure rates.
Important ICD lead improvements have occurred and have
Maisel
benefited many patients. However, these modifications must
be accompanied by more robust postimplant lead surveillance
so that unanticipated high failure rates may be detected as
early as possible. The National Cardiovascular Data Registry
ICD Registry may offer the opportunity to better monitor
individual lead performance, although modifications to the
registry would be required; these modifications could be
accomplished at relatively little cost.
More than a decade ago, a consensus report on pacemaker
lead performance suggested target lead survival of more than
95% at 5 years after implantation and noted that the “better”
leads demonstrated better than 95% survival at 10 years.7
Although these are realistic and reasonable goals for ICD lead
performance, significant improvements in lead design, premarket testing, and postmarket surveillance will be required
to attain these target rates. Until then, ICD leads will remain
the weakest link in an ICD patient’s chain of survival.
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Disclosures
Dr Maisel is the chair of the US Food and Drug Administration’s
Circulatory System Medical Device Advisory Panel.
References
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Transvenous ICD Leads
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KEY WORDS: Editorials
䡲 tachyarrhythmias
䡲
death, sudden
䡲
defects
䡲
defibrillation
Transvenous Implantable Cardioverter-Defibrillator Leads: The Weakest Link
William H. Maisel
Circulation. 2007;115:2461-2463
doi: 10.1161/CIRCULATIONAHA.107.698597
Downloaded from http://circ.ahajournals.org/ by guest on June 14, 2017
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