Performance of the Linox implantable cardioverter defibrillator leads: A single‐center experience

Background: An early failure of Biotronik Linox implantable cardioverter defibrillator (ICD) leads has been reported from several centers. Aim: To compare the performance of Linox ICD leads with different other ICD leads as a report of the Sheba Medical Center experience. Methods: All patients who had implantation of Linox ICD leads between 2007 and 2016 were included in this study. ICD lead failure was defined as low‐ or high‐voltage impedance; failure to capture, sense, or defibrillate; or the presence of nonphysiological signals not due to external interference. The survival probability of Linox leads was determined and compared to Medtronic Sprint Quattro ICD leads. Results: A total of 340 patients (age 64.4 ± 1.8 years) were included in this analysis. They were followed up to 105 months (mean 45.7 ± 7, median 44 (Interquartile range (IQR) 26‐63) months). Twelve patients (3.5%) met the criteria for lead failure within 61.2 ± 22.9 months (median 66.5 [IQR 48–85 months]) post implantation. Noise with inappropriate ventricular arrhythmias detection, with or without therapy, was seen in 10 patients (83%). High pacing thresholds and high impedances were detected in two patients (17%). The survival probability of Linox leads at 60 months (97.3%) was similar to the survival probability of Sprint Quattro leads (98.2%) (P = .58). Nevertheless, the survival probability at 105 months was much lower (81% vs 97%, Linox ICD lead and Sprint Quattro lead, respectively, P = .0039). Conclusion: Linox ICD leads have higher late failure rates compared to Sprint Quattro leads. These findings need to be confirmed in larger scale studies.

Keywords: lead failure; Linox; Sprint Quattro

Implantable cardioverter defibrillators (ICDs) are increasingly used for primary and secondary prevention of sudden cardiac death.[[1]] Unfortunately, ICD leads are prone to technical failures, which at times could be early failures as reported for the Riata and Fidelis leads.[[3]] Riata ICD leads are actually prone to a specific insulation abrasion characterized by externalization of conductor cables,[3] the majority of which are not detectable with standard ICD interrogation. Sprint Fidelis leads were reported to show an increased rate of fracture, resulting in failure to sense/pace or inappropriate or inefficient shocks.[4]

The Linox ICD leads (Biotronik SE & Co. KG, Berlin, Germany) were introduced in 2006. Early failures were reported by several centers. The aim of this study was to assess the performance of the Linox ICD leads in a single referral center and compare it to the Medtronic Sprint Quattro leads.

All patients who underwent implantation of Linox ICD leads (performed by four experienced operators) between 2007 and 2016 were included in this study. They all underwent routine office interrogations during implantation, a day after implantation, at 3 months, and thereafter every 6 months. Patients underwent additional interrogations per physician discretion. ICD lead failures were defined as abnormally low‐ or high‐voltage impedances, failure to capture, failure to sense or defibrillate, or the presence of nonphysiological signals that are not due to external interference.[5]

The rates of Linox lead failure were compared to the rates of Medtronic Sprint Quattro (6944 or 6947 models) ICD leads failures that were implanted and followed up during the study period.

All patients gave written informed consent according to the local institutional guides.

Continuous variables are reported as mean ± standard deviation and median. Nominal and ordinal variables are reported as frequencies and proportions. Chi‐square test was used to compare the failure rates of Linox and Sprint Quattro ICD leads. Kaplan–Meir survival curve was used to calculate the probability of survival of ICD leads. Log‐rank test was used to compare the probability of survival of Linox ICD leads and Sprint Quattro ICD leads.

Three hundred and forty patients (mean age 64.37 ± 11.79 years, ejection fraction 27.3 ± 9.3%) who underwent ICD or cardiac resynchronization therapy‐defibrillator (CRT‐D) implantation with Linox ICD leads were followed up to 105 months (mean 45.7 ± 7, median 44 [IQR 26‐63] months). Twelve patients (3.5%) had failure of the Linox lead within 61.2 ± 22.9 months (median 66.5 months) following implantation (Table ). Nonphysiological signals not due to external interferences with inappropriate detection of ventricular tachycardia and or fibrillation, with or without inappropriate therapy, were detected in 10 of these patients (83.3%). The other two patients had high pacing thresholds and high impedances (16.7%).

Details of Linox leads failure

1 Abbreviations: CRT‐D = cardiac resynchronization therapy‐defibrillator; P/S = pace sense.

Nine patients underwent new ICD lead implantation without extraction of the old lead, whereas two patients had new ICD lead implantations with extraction of the old leads. Finally, one patient had a new implantation of CRT‐D system from the opposite side without extracting the old leads.

Three hundred and eighty‐two patients who had ICD/CRT‐D implantation with Sprint Quattro ICD leads were followed up to 105 months (mean 66.5 ± 24 months, median 66.5 [IQR 48‐85 months]). The failure rate of Sprint Quattro detected in 1.8% of the patients during the study period was not statistically different compared to the Linox ICD lead (P = .15 for comparison to Linox ICD). This was also true at 5 years, with similar failure rates (1.47% of Linox and 1.57% of Sprint Quattro failed, P = .9). Kaplan‐Meier survival curves showed similar survival probability at 5 years, with 97.3% and 98.2% for Linox and Sprint Quattro leads, respectively (P = .58). However, after 5 years, the Kaplan‐Meier curves started to divert and the survival probability at 105 months of Linox ICD leads was much lower compared to Sprint Quattro leads (81% vs 97%, respectively, P =.0039) (Figure ).

The Linox family of ICD leads includes the Linox and Linox Smart models. Linox model was used in 148 (43.5%) patients and Linox Smart model in 192 (56.5%) patients. Follow‐up period for the Linox model was much longer compared to the Linox Smart model (63.7 ± 24.1 vs 31.8 ± 14.7 months, respectively; P < .0001). The survival probability at 63 months (Linox Smart model was followed up to 63 months) was not statistically different (98.6% for Linox Smart vs 95.8% for Linox; P = .4) (Figure ). Sex and age were not associated with increased risk for lead failures.

In our cohort, Linox ICD lead failure was noted in 3.5% of cases over 105 months follow‐up. This failure was usually presented as noise and inappropriate detection of ventricular arrhythmias, with or without inappropriate therapy. The survival probability of the Linox ICD lead at 5 years was within the industry reported standards (survival rate within a range of 85%‐95% at 5 years) and was similar to the Sprint Quattro lead. However, after 5 years, its survival probability declined and at 105 months it was much lower compared to the Sprint Quattro ICD lead. Albeit previously reported,[[8]] we found no associations between lead failures, sex, or age.

Several studies reported that the Linox ICD leads are safe. Good and colleagues[7] reported 96.3% survival probability at 5 years, a clinically acceptable rate. Conversely, many others showed early failure of the Linox ICD leads. In a prospective ICD registry, 5.9% of Linox, 1.5% Endotak, and 1.5% Durata leads failed during a follow up of 5.1 years. The majority of failures were attributed to noise (62.5%) and abnormal impedances (33.3%).[5] In another study, the reported Linox lead survival was 94.9% at 3 years and 88% at 5 years.[8] Also, Padfield and colleagues[9] reported findings from the British Columbia cardiac registry, and showed that over a median of 39 months the Linox failed more frequently compared to the Durata lead (3.4% vs 0.4%, P < .001}, and had a significantly lower estimated cumulative survival (91.6% vs 99.4% at 5 years; P < .0001). Similarly, Kawada and colleagues[10] reported that the 5‐year survival rate of the Linox lead was 85.3%, and the 7‐year survival rate was 81.0%. Actually, the survival probability of Linox leads was significantly lower than that of Endotak leads and comparable to that of Sprint Fidelis leads.

Recently, Lam et al[11] compared lead failure manifestation and lead performance of the Biotronik Linox lead with the St. Jude Medical Riata and Medtronic Sprint Fidelis defibrillator leads, which are known to have high early failure rates.[[3]] Lead survival at 5 years was 88%, 92%, and 71% for Linox, Riata, and Fidelis group, respectively. Nonphysiological high rate signals were frequently observed in Linox and Fidelis lead failures, whereas in Riata lead failures, a damaged lead integrity was the predominant finding.

Hence, several studies reported early failure of the Linox ICD leads. In fact, long term follow up is lacking. In our study, we found late failure rather than early failure of the Linox lead. Similar results were recently reported.[12] In this study, the 4‐, 6‐, and 8‐year survival for Linox leads was 97%, 93%, and 76%, respectively. Linox lead failure was associated with a younger age of patient.

It is important to note that the Linox family of ICD leads is comprised of the Linox and the Linox Smart models. Biotronik first received FDA approval for the Linox ICD lead in 2006 and for the Linox Smart ICD lead in 2010. Most of the studies investigated the survival of the Linox model. Good and colleagues[7] reported similar estimated cumulative survival probability rates for both Linox models. In our cohort, the follow up of Linox model (63.7 ± 24.1 months) was significantly longer than Linox Smart model (31.8 ± 14.7 months), and the survival probability of Linox model ICD was not different compared to Linox Smart model during 63 months follow up.

However, the survival probability of the Linox Smart group (88% at 5 years) was found to be significantly lower than that of the Endotak (Boston Scientific) and Sprint Quattro (Medtronic).[13] Nonphysiological signals not due to external interference were observed in all Linox Smart leads, with normal parameters and without visible anomalies on chest X‐ray. In other study, estimates of 5‐year lead failure rates for Linox Smart SD were 14.0% compared to 1.3% for contemporary leads (log‐rank P = .028).[14] Most of lead failures were due to nonphysiological high‐rate sensing or impedance abnormalities.

The majority of lead failures were presented as noise and inappropriate detection. High pacing thresholds and high impedances were also detected but less frequently. Similar sorts of failures were observed in other studies.[[5], [9], [11]] Of note, in contrast to some reports, conductor externalization was not seen in our cohort.[8]

This is a single‐center experience with its inherent biases. In addition, the follow up of Linox smart model was limited and therefore late survival probability could not be determined.

In summary, Linox ICD lead has late but not early low survival probability compared to Sprint Quattro lead. More studies with long‐term follow up are needed to confirm our findings.

The authors have declared no conflict of interest.