The Sprint Fidelis lead fracture story: time to come to our senses?

Primary prevention of sudden cardiac death by means of implantation of a cardioverter/defibrillator is an accepted treatment strategy in high-risk patients. Practitioners in this field have been aware of pacemaker lead failure for several decades.¹ More than ten years ago, it was noted that ICD leads had a higher risk of failure during prolonged patient follow-up than initially appreciated.² At that time, a 20 to 30% rate of lead-related complications was noted after almost five years of follow-up, but the risk of lead failure has decreased recently.³ However, the recent experience with lead and generator recalls and market withdrawals has led to a highly critical examination of lead and generator performance, and questions about device reliability have become much more frequent from patients. In October 2007, Medtronic voluntarily stopped selling its Sprint Fidelis ICD lead after observing an abnormally high rate of lead failure. A total of approximately 268,000 Fidelis leads have been implanted in patients throughout the world, the majority in the United States. Since the initial removal of the Sprint Fidelis lead from the market, the body of literature documenting the problems with the Fidelis lead has grown.^4-6 Three recent reports and accompanying editorials in Heart Rhythm have added to our understanding of the problem.^5,7-10 An accelerating risk of lead fracture has consistently been found and is also borne out in the current study by Beukema et al. in this issue of Netherlands Heart Journal.¹¹

Relevance of the current study

Beukema et al. document a rate of Fidelis lead failure which appears to be less than that of the recently published study by Farwell et al.⁵ In the latter study, Fidelis leads were examined and it was found that the risk of lead failure increased by an exponential function of 2.74 per year. In a recent study, Hauser and Hayes found an 88% three-year survival rate for Fidelis leads, whereas two Medtronic studies found three-year survival rates of 97% (CareLink remote follow-up) and 95% (System Longevity Study).^8,12 As further studies of lead reliability are developed, strict definitions of lead failure are important. In the current study, Beukema et al. define lead failure as an increase in lead impedance, decrease in signal amplitude or frequent short sensed intervals. There were only pace-sense conductor fractures, and in contrast to earlier reports no high-voltage conductor fractures. As further data on Fidelis leads accumulate, it will become ever more important to standardise definitions of ‘lead failure’.

Interestingly, until now the major studies on Fidelis reliability could be grouped into two categories, and the results appeared to cluster with the type of study. Both the study by Hauser et al.¹⁰ and the study of Farwell et al.⁵ were based at one or two high-volume centres, with implant and performance data collected in a prospective manner into an ‘ICD database’. Both of these studies showed three-year failure rates in the 10 to 12% range. However, the Medtronic studies (System Longevity Study, CareLink)¹² and the Device Advisory Committee of the Canadian Heart Rhythm Society (CHRS)⁸ were multicentre efforts with a large number of implanters, were subject to voluntary reporting, and found three-year failure rates in the 3 to 5% range. The discrepancy in failure rates between these groups of studies was presumably thought to be multifactorial, but the reasons were most likely considered to include closer follow-up and more vigorous examination for evidence of lead failure in the singleor two-site studies, including possible false-positive diagnosis of lead failure, and, conversely, less rigorous follow-up and underreporting of lead failure in the multicentre studies. In addition, the time urgency of these data leads to submission and publication before follow-up is complete, which may lead to overinterpretation of the data in the previously reported studies.5,6,9,10 Lastly, given the small number of events in these studies, some of the observed variation may be due to random chance rather than meaningful differences in lead performance.

An important finding comes from the currently presented study by Beukema et al. They report a single high-volume centre study, but the 32-month failure rate of 5.7% is more similar to annual failure rates reported by the Medtronic studies. A strong point of the current study is that of the 619 patients at risk in the study, 558 were still at risk at three years, and therefore this almost complete follow-up precludes the above-mentioned underestimation of failure risk at three years due to unequal follow-up. Even so, they also predict an ever increasing failure lead of the Sprint Fidelis conductor.

Management of patients with Fidelis leads

The question of interest for all electrophysiologists is the appropriate management of Fidelis leads. Beukema et al. looked at the relative merit of additional alerts such as the Lead Integrity Alert [LIA] and remote monitoring tools such as CareLink. Current recommendations from the manufacturer include the following: (1) routine follow-up with full interrogation of the lead on a typical three-month schedule; (2) utilisation of a software patch (LIA) in an attempt to provide early notice of impending Fidelis lead fractures, although this is of uncertain value, and (3) at the first sign of lead failure, prompt evaluation and intervention to ensure continued proper device function. Once a Fidelis lead has fractured and must be replaced, proceeding to extraction certainly makes sense in some patients. The findings of the study by Beukema et al. do not warrant any substantial change in the current management of Fidelis leads. Functioning Fidelis leads should continue being used with the LIA activated, even if it is imperfect. At the time of generator change, some consideration for replacement and possibly removal of a Fidelis lead is warranted, especially if the acceleration of risk of lead failure is borne out in future prospective studies. These decisions should be made on an individual patient basis, with prior history of ventricular arrhythmias, prior device therapy, pacemaker dependence, and psychological patient factors all playing a role. Currently at least one prospective study tracking the outcomes of these leads is under way, and such studies should provide greater insight into long-term management of these leads.

ICDs and primary prevention

Implantable cardioverter defibrillators (ICDs) are established therapy for the prevention of death from ventricular arrhythmias.^13-15 However, conventional ICDs rely on transvenous leads for cardiac sensing and defibrillation. The recent focus on implantable cardioverter-defibrillator (ICD) lead failure is not a new problem. ICD leads present new challenges and more complex modes of failure than pacemaker leads. Furthermore, removal of an ICD lead is associated with a higher risk than is pacemaker lead extraction.¹⁶ The risk of ICD lead failure is probably at least an order of magnitude greater than the risk of ICD generator failure.

Due to the nature of its stochastic approach in tackling the major health care problem of sudden cardiac death, many patients receive an ICD implant without ever experiencing appropriate shocks. In the most recently published large randomised ICD prophylaxis trials, the annual shock rate was 5.1%. In contrast, the procedure-related complication rate was 5%, whereas a 9% chronic complication rate was reported.¹⁴ None of the current primary prevention trials extended follow-up beyond the device battery (or transvenous lead) lifetime. Since most primary prevention patients ‘survive’ their first ICD, long-term benefit should be re-addressed with regard to device replacement related complications, device recalls and hardware failure rates. It is conceivable that the currently perceived benefits of prophylactic ICD implantation may have to be mitigated in that perspective.

Lead failure is a prominent consideration for young patients in whom ICD therapy may be needed for decades. Consequently, young patients may well experience at least one lead failure over their life time and have transvenous complication rates occurring at a rate of 8.9%/year even with simple single lead systems.¹⁴ In such patients, a novel concept of entirely subcutaneously placed ICD system (S-ICD) may provide the best balance between protection from sudden cardiac death and minimising long-term, device-related morbidity. Unlike transvenous leads, which are required to be soft and compliant so as to not perforate the heart with cardiac motion, the S-ICD electrode, by virtue of its location, can have a sturdier design. Furthermore, the S-ICD lead is exposed to less repetitive motion while also being free from the potential for crush injury in the subclavian space. With these considerations, the S-ICD lead should prove less susceptible to failure. That said, should an S-ICD electrode failure occur, removal from a subcutaneous space should be a comparatively simple and safe procedure. Although promising in nature, these potential benefits still need to be proven.