Detection of high incidence of Riata lead breaches by systematic postero-anterior and lateral chest X-ray in a large cohort

Abstract

Aims

Insulation breaches with externalization of conductor cables have been described for St-Jude Medical Riata™ defibrillation leads. Published data on the incidence of Riata lead abnormalities are quite heterogeneous. The objective of this study was to estimate systematically the prevalence of lead abnormalities using a postero-anterior (PA) and lateral chest X-ray (CXR).

Methods and results

From 2002 to 2008, 552 Riata defibrillation leads were implanted at our centre. We evaluated patients for potential insulation breaches. A PA and lateral CXR was obtained. Chest X-rays were reviewed by two electrophysiologists using a zooming function with magnification up to factor 7.5 and were classified as normal or abnormal for the presence of conductor externalization. A total of 284 patients were included. Riata lead models were 1570, 1580, 1582, 1590, 1592, 7000, 7002, and 7022. The total frequency of radiological lead defects was 24.3%. Insulation breaches occurred at zones of major lead curvature. Mean maximal spacing between extruding lead components was 3.6 ± 1.9 mm (range 2.0–12.4). Abnormal CXRs were more frequent in 8F leads (31.4% vs. 6.3%; P < 0.001). Most defects occurred with lead models 1582 (41.2%) and 1580 (31.4%). Mean time since implantation was longer in abnormal leads (6.7 vs. 5.9 years; P < 0.001). Abnormal leads had higher pacing thresholds (1.1 ± 0.8 V vs. 0.9 ± 0.4 V; P = 0.02).

Conclusion

The incidence of insulation breach in Riata leads is much higher than quoted by the manufacturer or reported by most of the literature. A PA and lateral CXR with zooming appears adequate to identify lead breaches when reviewed by an electrophysiologist. Riata lead breaches without electrical abnormalities present a management dilemma and will require further studies.

Introduction

Breakdown of lead insulation with secondary externalization of conductor cables has been described for the St-Jude Medical Riata™ and Riata ST™ defibrillation leads.^1–8 Among the 227 000 Riata™ leads, which have been sold worldwide between 2002 and 2010, ∼5300 leads were implanted in Canada.⁹ In 2010, Riata leads were withdrawn from the market by the manufacturer. Subsequently, the United States Food and Drug Administration (FDA) released a class I recall and at the end of 2011 the Canadian Heart Rhythm Society (CHRS) gave Canadian recommendations.⁹

The insulation defects of the Riata leads are the result of inside-out abrasions, which are favoured by relative movements of the conductor cables in the multilumen silicone leads.¹⁰ There is still uncertainty about the true incidence of insulation defects and published data are quite heterogeneous reporting prevalences reaching from 0.21 to 27.4%.^11–13 Many of those reports were based on return products or cine fluoroscopy. So far, most studies used fluoroscopy for the detection of lead breaches. This approach is relatively expensive, time consuming, and exposes patients to more radiation.

We hypothesized that the true prevalence of radiological lead abnormalities in an unselected cohort of patients with Riata leads could be higher than the aforementioned reported prevalences if a systematic approach was applied. A standard PA and lateral chest X-ray (CXR) could then be sufficient to accurately and simply diagnose radiological lead abnormalities.

Methods

From 2002 to 2008, 552 Riata defibrillation leads were implanted at the Quebec Heart and Lung Institute, the only single tertiary university centre inserting implantable cardioverter-defibrillators (ICD) for a catchment population of 2.5 million people. We performed an observational study for potential insulation defects as the problem was first reported and prospectively evaluated all patients of our study population. Most patients alive were seen at our ICD clinic and for every patient a new PA and lateral CXR was obtained. Patients with Riata leads were identified using our EP database. The digitized CXRs were analyzed with a commercially available program for post-image processing (IMPAX™ 6.5.1.501; AGFA Healthcare, Ontario, Canada). All CXRs were reviewed by two electrophysiologists using the zooming function of the software, which permitted a magnification by a factor of ∼7.5. The software options for contrast enhancement or contrast inversion were also used if necessary. On the basis of this approach, Riata leads were classified as normal (including equivocal) or abnormal. Abnormal leads included those with either a clear conductor externalization or an abnormal conductor spacing. We defined abnormal conductor spacing as a localized non-parallel conductor separation that was wider than the distal coil of the analyzed lead and measured using the caliper function of the software program. Equivocal leads were defined as leads with a doubtful localized non-parallel conductor separation that was less than the distal coil of the analyzed lead. Equivocal leads were classified as normal for the data analysis to avoid overestimation of insulation breaches. Owing to the technical principles of CXR imaging, there is a 10% overestimation of measured lead diameters. The maximal diameter of the inner and outer spacing of conductor elements was measured in all abnormal leads. Patients who had died since the lead implantation as well as patients who had undergone heart transplantation or were lost to follow-up were excluded from the final analysis.

The primary objective of this study was to estimate the prevalence of Riata cable externalization by a PA and lateral CXR alone. The secondary objective was to correlate the structural abnormalities with electrical abnormalities and lead failure. We also tried to identify predictors of insulation breaches. The definition of electrical lead abnormality included the presence of at least one of the following electrical findings: noise on the Riata lead, a right ventricular pacing lead impedance <200 Ω or >1000 Ω, a right ventricular high-voltage impedance <20 Ω or >100 Ω, a right ventricular pacing threshold ≥2.0 V at 0.4 ms. Noise was defined as oversensing of any non-physiological electrical activity on the Riata lead, excluding oversensing of physiological electrical activity such as T-wave oversensing. Data from the ICD interrogation at the time of implantation, 6 months after implantation and follow-up visits in 2011 and 2012 were used for the analysis of electrical parameters.

Statistics

Qualitative data are presented as percentages and were analyzed using Fisher's exact test. Quantitative data are expressed as mean ± standard deviation (SD) and were analyzed using Student's t-test. Univariate and multivariate analysis were performed to identify predictors associated with insulation breaches and potential lead dysfunction. The univariate normality assumptions were verified with the Shapiro-Wilk tests. For multivariate analysis, a logistic regression analysis was performed to identify variables independently associated with the dependent variable ‘incidence of lead abnormalities’. Variables with univariate logistic regression with probability value <0.20 were candidate for the multivariate regression model building. The selection variables were performed using the Akaike's and Sawa's Bayesian information criterions. Statistical significance was defined as a P value of <0.05. All analyses were conducted using the statistical package SAS, version 9.2 (SAS Institute Inc., Cary, NC, USA).

Results

From 2002 to 2008, a total of 552 Riata and Riata ST leads were implanted at our centre. Riata lead models were 1570, 1580, 1582, 1590, 1592, 7000, 7002, and 7022. Among the initial 552 patients with Riata leads, 24 patients were excluded because of early explantations, which were performed within the first 3 years after implantation. One hundred forty-six patients (27.7%) had died since implantation, another 15 patients (2.8%) underwent heart transplantation, and 83 patients (15.7%) were excluded because of a missing PA and lateral CXR, including 14 patients who were followed at another centre. The remaining 284 patients were included for the final analysis (Figure 1). Sixty-nine of 284 patients presented cable externalization on the CXR, resulting in an overall prevalence of insulation breaches of 24.3%. There were only three equivocal leads, which were classified as normal leads for the data analysis. Insulation defects mostly occurred at zones of major lead curvatures (Figure 2A). The mean spacing between extruding cables and the lead body was 3.6 ± 1.9 mm (range 2.0–12.4 mm). It is noteworthy that the process of cable externalization progressed over time (Figure 2B).

Patients were then classified into two groups based on the presence or not of cable externalization. The baseline clinical characteristics for both groups are shown in Table 1. Patients with abnormal Riata leads were slightly younger than patients with normal leads (66 ± 11 vs. 68 ± 10 years; P = 0.05). There was no difference between a subclavian or a cephalic venous access. The mean left ventricular ejection fraction was similar in both groups (32 ± 13% vs. 31 ± 13%; P = 0.56). The percentage of patients with defibrillation safety margin testing at implantation was similar in both groups with a comparable mean energy of ∼15 J. The mean time since implantation was significantly longer in abnormal leads (6.7 ± 1.2 vs. 5.9 ± 1.4 years; P < 0.001). Lead models 1580, 1582, 1590, and 7002 were most implanted, accounting for 48, 6, 15, and 25% of all leads, respectively. The highest frequency of cable externalization occurred in the lead models 1582 (8 F, single-coil) (41.2%) and 1580 (8 F, dual-coil) (31.4%) followed by 21.4% in lead model 1590 (8 F, single-coil). The high overall prevalence of lead breaches was mostly driven by the 1580 leads, which accounted for 62.3% of all insulation defects (Table 2). There was no case of conductor externalization in patients with a 7F dual-coil lead or Riata 7022 leads with Optim™ insulation; however, those patients represented only 3.2% of the total study cohort.

Univariate analysis showed that 8F leads had a significant higher risk of conductor externalization and abnormal CXRs were almost five times more frequent in 8F leads than in 7F leads (31.4% vs. 6.3%; P < 0.001) (Table 3). Also, single-coil leads were at higher risk for conductor externalization than dual-coil leads. Among the 8 F leads 43.5% of single-coil leads compared with 29.8% of dual-coil leads presented insulation breaches (Table 3).

Insulation defects started to occur several years after implantation. More than 90% of all abnormal Riata leads had been implanted >5 years ago and 66% of all abnormal leads had been implanted >6 years ago (Figure 3). This shows that the externalization of conductors is a time-dependent process. On multivariate analysis, the 8F lead over time was identified as a combined independent predictor of insulation defects (odds ratio, OR, 3.48; 95% confidence interval, CI, 0.86–14.10; P = 0.08) with the time since implantation being the strongest single independent predictor (OR 1.64; 95% CI 1.18–2.28; P = 0.003).

Abrasion defects were associated with subtle, but significantly higher pacing capture thresholds (1.1 ± 0.8 V vs. 0.9 ± 0.4 V; P = 0.02) (Table 4). The overall frequency of electrical lead abnormalities was 21.7% (15 of 69) in patients with abnormal leads compared with 9.8% (21 of 215) in patients without lead breaches (P = 0.01) (Figure 4). This was mostly due to very high pacing thresholds in some patients. More patients with cable externalization had a pacing threshold ≥2.0 V at 0.4 ms compared with the other group (8.7% vs. 1.4%; P < 0.001). There was no difference between the incidence of noise, abnormal lead impedances or inappropriate shocks between groups.

So far, no patient with any of the abnormal Riata leads underwent lead extraction at our centre. However, three patients with abnormal Riata leads had lead revision with addition of a new right ventricular defibrillation lead at the time of elective changes of their pulse generator.

Discussion

This is the first study using systematic PA and lateral CXR for the detection of conductor externalization in a large unselected cohort of patients with Riata leads. Using this approach, we found an overall prevalence of 24.3% of Riata lead breaches and as high as 31.4% in 8F leads, which is the highest prevalence reported so far in the literature. The large number of unselected patients with Riata leads and the standardized approach make our strategy clinically relevant and unbiased. A previous study reported a structural lead failure in 33.3% seen on fluoroscopy. However, their patients were highly selected on the basis of referral for lead extraction.¹⁴ The recently published data from Shen et al.¹³ reporting 27.4% abnormal leads were also based on cine fluoroscopy evaluation in a limited population of 84 patients and investigated exclusively 8F leads.

The key element of our radiological approach is the use of a zooming function with a 7.5-fold magnification applied to a standard CXR (PA and lateral) to search for cable externalization or abnormal conductor spacing. Even subtle cable extrusion can be detected using this approach. Otherwise, lead abnormalities could be missed during routine CXR interpretation without a zooming function.

So far, almost all studies used fluoroscopy for the detection of conductor externalization.^11–14 This approach is time consuming, costly, and exposes the patient to more radiation than a standard CXR. According to calculations by the biomedical engineering service in our institution, the total radiation dose of a standard PA and lateral CXR at our centre is 0.09 milliSievert (mSv), whereas a three-view fluoroscopy (PA, right anterior oblique 20–45° and left anterior oblique 20–45°) at 15 frames per second and 15 cm magnification would expose the patient to a total dose of 0.23 mSv. A cine fluoroscopy with image acquisition would even mean a 2- to 3-fold higher dose. Our results are encouraging, but a systematic direct comparison of PA and lateral CXR with fluoroscopy in a larger cohort has not been realized so far.

The lead models 1580 (8F, dual-coil) and 1582 (8F, single-coil) were identified as high-risk lead models in our study with insulation breaches of 31.4 and 41.2%, respectively. This finding is of clinical importance as it might influence future decisions concerning prophylactic lead revision.

This study also shows that insulation breaches and cable extrusion are a time-dependent process with a longer time as implantation increasing the risk of insulation breakdown. More than 90% of all abnormal Riata leads had been implanted >5 years ago and two-thirds of all abnormal leads >6 years ago. This is similar to a recent study, which found a cut-off for time since implantation around 5 years before lead abnormality.¹⁴ The presence of an 8F lead over time was identified as an independent predictor of structural lead failure, which is consistent with the findings of another recent study.¹⁵

One of the reasons, why 8F leads have significantly higher rates of conductor externalization than 7F leads, is probably the lead design. While both, 8F and 7F leads have the same outer insulation thickness, the smaller lead diameter of 7F leads makes that the conductors are lying closer to the lead centre. Therefore, centrifugal forces are less in 7F leads (communication from St. Jude Medical).

The principal concern about conductor externalization is potential lead dysfunction. Failure of therapy delivery or inappropriate shocks could have fatal consequences. Data from a recent study suggested that a series of death could be attributed to insulation defects resulting in electrical shorts between high-voltage components, including can abrasions.¹⁶ In that study no high-voltage failure appeared to be caused by externalized conductors. Little is known about the prevalence of electrical abnormalities in Riata leads with conductor externalization. Our study demonstrates that cable externalization is associated with electrical abnormalities. Right ventricular capture thresholds were slightly higher in abnormal Riata leads. This was not only a finding during a single measure, but a consistent trend over time. Although statistically significant, those subtle differences would usually not raise concerns during a routine follow-up visit and their clinical impact is questionable. However, it could be possible that those subtle electrical abnormalities represent an early sign of a Riata insulation defect. Subtle, but significant electrical abnormalities have also been reported by the Liu et al.¹⁵ who found a decreased R-wave sensing in abnormal Riata leads. However, those subtle electrical differences would not be sufficient alone to guide decisions about the further management of a Riata lead. Moreover, it should be kept in mind that the long-term impact of extruded lead wires is still not well known and we should be very cautious about extraction or replacement of radiologically abnormal, but electrically normal leads considering the potential complications of lead revision (reference CHRS).^17,18

According to our definition, the cumulative incidence of electrical abnormalities was significantly higher in abnormal Riata leads (21.7%) compared with normal Riata leads (9.8%). While non-physiologic noise was the most common electrical abnormality in normal Riata leads (7.4%), abnormal Riata leads mostly presented very high pacing thresholds (8.7%) followed by noise (5.8%). The higher right ventricular pacing thresholds in abnormal Riata leads should nevertheless be interpreted with caution, as they could also be attributed to other reasons such as lead age, older lead design, differences in lead maturation or exit blocks. Our results differ from the electrical abnormalities seen in other recent studies. A study by Sung et al.¹⁹ analyzed electrical lead failure of different defibrillator leads including Riata and Riata ST leads from a database of remote monitoring of US veterans. In this study, Riata leads showed an annual incidence of electrical failure 0.67% and a cumulative electrical lead failure rate of 3.4%. Interestingly, Riata ST leads had a higher rate of electrical failure than Riata leads. Isolated electrical noise was the most frequent abnormality and found in 28%, followed by noise with inappropriate shocks in 26%. A pathological rise in the right ventricular pacing threshold was found in 23%. The Independent Multicenter Study of Riata and Riata ST leads found an annual incidence of 1.47% per patient-year for a combined electrical and/or radiological abnormality in Riata leads.²⁰ In this study, isolated noise was also the most observed electrical abnormality (51%), followed by elevated pacing thresholds requiring lead replacement (33%). Different study populations, definitions of electrical lead abnormalities and follow-up periods could at least partially explain for these differences. There was no difference in the frequency of inappropriate shocks between groups in our study, but the incidence was very low in both groups and our study was underpowered to detect any difference in inappropriate shocks. To our knowledge, there was no case of lead-related death in our cohort so far. Although the true long-term impact of asymptomatic conductor externalization is still unknown, recent retrospective studies suggest a significantly worse lead survival of Riata/Riata ST leads compared with other frequently implanted defibrillator leads.^19,20

One of the unsolved questions is the follow-up of patients with Riata leads. The fact, that official recommendations are quite heterogeneous reflects the necessity of better data to guide decision management. Some authorities and expert committees including the United States FDA recommend systematic x-rays or alternative imaging of all patients with Riata/Riata ST leads.^21,22 Others, like the German Cardiac Society, do not recommend systematic imaging in asymptomatic patients without evidence of electrical dysfunction of the Riata lead and point out the potential risk of harmful overtreating by lead revision or lead extraction.²³ Further studies are required to answer those questions.

Limitations

Our study has some limitations. First, the limitations of any observational study should be considered. This is a single centre study and the true prevalence of insulation breakdowns in Riata leads might be even higher. Not equal proportions of lead models have been implanted and some lead models are underrepresented in our study. The choice of lead model at time of implantation may have been influenced by clinical parameters and may have influenced the rate of lead dysfunction.

Cable externalization or abnormal conductor spacing represent advanced and visible manifestations of insulation defects in Riata leads due to inside-out abrasion. However, it has been shown that those abrasions can also occur under the shocking coils, which would not result in visible cable externalization. Other forms of insulation defects include direct contact between cables or coils or can abrasions.¹⁰ All those other forms of insulation defects are not detectable by simple CXR or fluoroscopy. We cannot exclude that these possible insulation defects contributed to the electrical abnormalities seen in our cohort.

Another limitation of our study is the lack of a direct comparison to cine fluoroscopy, which is considered by some to be the gold standard for the detection of structural lead abnormalities, so we do not know the real sensitivity and specificity of our approach. Even using fluoroscopy, it is sometimes difficult to identify subtle lead abnormalities. This is also true for an approach using a PA and lateral CXR including a zooming function and contrast adjustment. We cannot exclude that we missed some abnormal Riata leads. Nevertheless, the prevalence of abnormal Riata leads in our cohort is consistent with the results of the existing literature, which is mostly based on fluoroscopy.

Although we looked at several electrical parameters, we did not systematically perform DFT testing in all our population as it was not clinically justified at that time. The question of performing or not performing DFT-testing at the time of generator change and during regular follow-up is a subject of ongoing controversy and has not yet been sufficiently answered.^24,25 In the context of the Riata recall, this issue becomes even more important and we have to question if patients with a conductor externalization but normal electrical parameters are still protected by their ICD.

Conclusions

Insulation defects with externalized conductors are frequent in Riata leads. Using a standard CXR, we found an overall prevalence of 24.3% of lead breaches in a large unselected cohort with a prevalence as high as 31.4% in 8F leads. Conductor externalization is associated with electrical abnormalities. This study also shows that a systematic PA and lateral CXR with zooming has a high diagnostic yield to detect insulation defects and should be considered in all patients with Riata leads. Fluoroscopy may eventually not be required if a standardized CXR is performed. Riata lead breaches without electrical abnormalities present a management dilemma and require further investigation.

Acknowledgements

The authors thank Serge Simard for his help with the statistical analysis and Jean Arsenault for the calculation of the radiation exposure.

Conflict of interest: none declared.

References