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By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco is a consultant for Novartis, and does research for Medtronic and Guidant.
Source: Kleemann T, et al. Annual rate of transvenous defibrillation lead defects in implantable cardioverter-defibrillators over a period of >10 years. Circulation 2007; 115:2474-2480
Kleemann and his colleagues from Ludwigshafen, Germany, report on survival of transvenous defibrillation leads during long-term follow-up. A total of 990 consecutive patients who received transvenous ICD defibrillation leads were included in this report. A spectrum of lead models from five different manufacturers was included, but most leads were manufactured by either St. Jude Medical or Medtronic.
Most of the transvenous leads were implanted using a subclavian puncture approach. Patients visited a defibrillator outpatient clinic every three months. At the time of the clinic visit, the ICD was interrogated and intracardiac real-time electrograms, pacing and sensing thresholds, lead impedance values, and stored electrograms were analyzed. Routine defibrillation threshold testing was not performed during follow-up. A lead defect was defined as "severe lead failure" if it required surgical intervention. This included failures that resulted in oversensing, lead impedance rises or falls, fractures, or abnormal electrical testing.
During a median follow-up of 934 days (interquartile range 368 to 1870) 15% of the 990 ICD leads failed. Patients with lead failures tended to be younger, more often female and had better preserved left ventricular function. Actuarial analysis of lead survival showed survival rates at 5 years of 85% and at eight years of 60%. Of note, the annual failure rate increased over time. In the first four years after implant, failure, annual failure rates remained low in the 2% to 3% range. However, in the eighth, ninth and tenth years of follow-up, failure rates ranged from 11% to 20%.
The major lead complications included insulation defects (56%), lead fractures (12%), loss of ventricular capture (11%), abnormal lead impedance (10%), and sensing failure (10%). Insulation failure became more prominent over time accounting, for 70% of lead failures detected in leads older than 6 years. Newer leads did not show improved survival. In fact, there was a trend towards better lead survival in the first five years after implant with older model Medtronic 6936 and 6966 leads compared with a pooled group of models implanted from 1997 onwards. Lead defects became manifest either by inappropriate shocks (33% of patients) or by abnormal electrical testing during routine device evaluation (65% of patients). One lead failure was known to have occurred at the time of a spontaneous clinical cardiac arrest. In this case, the patient had to be resuscitated by external defibrillation. In the entire series, there were 207 deaths, but only 4 sudden deaths. In addition, 34 patients (3%) were lost to follow-up.
The authors concluded that transvenous ICD lead failure is a significant problem which becomes more prominent with longer lead implant durations. Careful long-term follow-up is required particularly in patients with longer implant durations.
In 2005, considerable attention was focused on the problem of ICD generator component failure. However, the failure rate for generators was quite low, even in the most severely affected models. Electrophysiologists have long known that the lead is the weakest part of an ICD system. However, unlike a generator failure where the failure may not become apparent until a critical time, lead failures often present with inappropriate shocks, or signs of dysfunction which can be picked up during a routine analysis. As a result, death due to lead failure is rare.
As we have shifted more to implants for primary prevention of sudden death and are implanting devices in younger patients with cardiomyopathy or inherited arrhythmia syndromes, the consequences of long-term lead deterioration will become more important. Lead extractions in very old leads can often be difficult and risky and associated with significant risk even in experienced hands. This is particularly true with defibrillator leads since they have two coils, one of which sits in the superior vena cava. With dual chamber or CRT devices, fibrosis between the other leads and this coil is common and the risk of vascular injury with extraction increases.
The data presented by Kleemann et al illustrate how important it is for manufacturers to seek better technology to improve lead longevity. Current ICD leads represent impressive technology, but continued research to enhance their long-term safety is needed.