Insulation Failure with Bipolar Polyurethane Pacing Leads

Between October, 1981, and April, 1983, 200 pacemakers were inserted at Rhode Island Hospital. Forty-five bipolar polyurethane leads (Medtronic 6972) were positioned in the right ventricle. Three (6.6%) of these leads presented 15 to 18 months post-implant with insulation failure. The manifestation was inappropriate inhibition of the pacemaker. No obvious cracking was visible on X-ray or during surgery. All the leads had low impedance, indicative of insulation failure.     

Multicenter Experience With a Bipolar Tined Polyurethane Ventricular Lead

A multicenter study was undertaken to determine the failure rate of a specific bipolar tined polyurethane ventricular pacing lead, the Medtronic 4004/4004M pacing lead. Seven centers in the United States and Canada implanted 586 Medtronic 4004/4004M pacing leads. The study was designed to determine the probability and clinical manifestations of lead failure. Only failures compatible with an insulation problem were included. The Kaplan-Meier estimate of the percentage of 4004/4004M lead failures within 4 years after implantation was 14.1% (95% confidence interval: 8.5%–19.3%). Failures were manifested as sensing abnormalities, failure to capture, early battery depletion, and significant decrease in measured impedance compared with previous impedance measurements. The observed rate of failure is unacceptable, and strong consideration should be given to replacing the 4004/4004M pacing lead in pacemaker dependent patients and closely monitoring nondependent patients.     

A Multicenter Experience with a Bipolar Tined Polyurethane Ventricular Lead

A multicenter study was undertaken to determine the failure rate of a specific polyurethane bipolar tined pacing lead, the Medtronic 4012 pacing lead. Six centers in the United States and Canada implanted 1,190 Medtronic 4012 pacing leads. The study was designed to determine the probability and clinical manifestations of lead failure. Only failures compatible with an insulation problem were included. The probability of a 4012 lead failure by Kaplan-Meier analysis was 20.9% at 6 years after implantation. Failures were manifested as sensing abnormalities, failure to capture, early battery depletion, and significant decrease in measured impedance compared with the previous impedance measurements. Of the 95 definite lead failures, 16 (16.8%) were associated with symptoms similar to those experienced before pacemaker placement. The observed failure rate is unacceptable, and strong consideration should be given to replacing the 4012 pacing lead in pacemaker-dependent patients and closely monitoring nondependent patients.     

Sixteen Failures in a Single Model of Bipolar Polyurethane-insulated Ventricular Pacing Lead: A 44-Month Experience

During a 44-month period, 105 Medtronic model 6972-58 polyurethane-insulated, bipolar ventricular pacing leads were implanted, of which 16 failed clinically at a mean of 20.5 months post-implant. Pacing dysfunction presented as either intermittent or complete loss of sensing and/or capture and, rarely, oversensing. Thirteen of the 16 patients were asymptomatic, and problems were detected in 11 instances during routine telephonic surveillance. At the time of lead replacement, low or widely fluctuating lead resistance values and high current drain were uniformly observed. The single lead capable of total extraction revealed rupture of both internal and external insulation. A brief summary of the currently much-discussed "polyurethane controversy" is presented, and the issue of patient management is discussed.     

"In-Line" Bipolar, Steroid-Eluting, High Impedance, Epimyocardial Pacing Lead

Recent advances in electrode surface designs have eliminated traditional threshold differences between endo- and epicardial pacing leads. Since the epicardial approach offers the potential of direct left ventricular pacing and the transvenous approach may not be feasible or warranted in all instances, more advanced leads are being designed to optimize epicardial pacing capabilities. This study was conducted to evaluate a bipolar epimyocardial lead. Six immature canines (age 3 months) were instrumented. The lead (Medtronic mode! 10389) is a single-pass, "in-line" bipolar electrode with low current drain and high impedance, with an intramyocardial steroid-eluting cathode and nonsteroid epicardial anode. Twelve ventricular leads were implanted (two per animal) and the animals followed for 6 months with weekly analysis of pacing and sensing capabilities. Results at explant were compared with implant values and showed no significant differences between sensed R waves or in R wave slew rates in unipolar or bipolar modes. Explant lead impedances remained high in both modes: bipolar, 1658 ± 331; and unipolar, 1327 ± 308 Ω (P < 0.05). Chronic voltage (V) threshold at 0.5 ms showed no significant change from implant values during the study: unipolar, 0.3 ± 0.06 versus 1.0 ± 0.8; and bipolar, 0.4 ± 0.06 versus 1.6 ± 1.2. Histologic review showed negligible fibrous reaction at the electrode-tissue interface. This study introduces a high impedance, low threshold, "in-line" bipolar pacing lead design capable of stable chronic pacing with implant facilitated by a single suture technique.     

Bipolar Tined Polyurethane Ventricular Lead: A Four-Year Experience

With the advent of polyurethane as an insulating material for permanent pacemaker leads, concern has arisen over the integrity and long-term durability of polyurethane-insulated pacing leads. Specific concern has arisen over particular bipolar tined polyurethane ventricular leads. We have assessed our 4-year experience with this lead. This experience involves two groups of patients, those with leads manufactured before a certain date and those with leads manufactured at a later date. In the first group (judged to be at increased risk) the failure rate was 8.8%, and in the second group (judged not to be at increased risk) the rate was 3.9%. Lead failure occurred at an average of 17.5 months in the first group. Adequate follow-up on the second group is not available to determine whether or not the failure rate may eventually be as high as that in the early group. Actuarial analysis suggests that survivorship free of lead failure is probably not significantly different in the two groups. This experience points out the need for determining lead failure rates, identifying optimal lead design and configuration, and establishing a lead registry or mechanism by which the integrity of various pacing leads can be evaluated.     

Clinical Evaluation of a Thin Bipolar Pacing Lead

The main disadvantages of bipolar pacing leads have traditionally been related to their relative thickness and stiffness compared to unipolar leads. In a new "drawn filled tube" plus "coated wire" technology, each conductor strand is composed of MP35N tubing filled with silver core and coated with a thin ETFE polymer insulation material. This and parallel winding of single anode and cathode conductors into a single bifilar coil resulted in a bipolar lead (ThinLine, Intermedics) with a body diameter and flexibility similar to unipolar leads. The lead is tined. polyurethane. with the cathode and the anode made of iridium-oxide-coated titanium (IROX). The slotted 8-mm² cathode tip is coated with polyethylene glycol. a blood soluble material. We present the clinical evaluation results from four pacemaker clinics, where 47 leads (23 atrial-J model 432–04 and 24 ventricular model 430–10) were implanted in 25 patients and followed for up to 2 years. The lead handling characteristics were found to be very satisfactory. Electrical parameters of the leads were measured at implant and noninvasively on postoperative days 1, 2, 21, 42. and months 3, 6, 12, and 24. Mean chronic pulse width thresholds at 2.5 V were 0.14 ± 0.05 ms in the atrium and 0.10 ± 0.02 ms in the ventricle, pacing impedances 443 ± 104 Ω and 520 ± 241 Ω. while median electrogram amplitudes were ≥ 3.5 mV and ≥ 7 m V, respectively. Pacing impedances and thresholds were found to be slightly but statistically significantly higher in unipolar than in bipolar configuration—the findings are explainable bv the lead construction. One of 47 leads failed 3 weeks after implant; the conductors were short circuited due to an error during the manufacturing process. We conclude that the new lead thus far has demonstrated appropriate mechanical and electrical characteristics.     

Clinical Surveillance of an Active Fixation, Bipolar, Polyurethane Insulated Pacing Lead, Part II: The Ventricular Lead

Since 1989, 72 Telectronics 330–201 active fixation, polyurethane insulated ventricular leads (Accufix) have been implanted at the Mayo Clinic. There were four (5.6%) acute lead related complications (perforation, microdislodgment, and macrodislodgment), three of which led to early reoperation. Over a follow-up time of up to 2.7 years (median 9.4 months), there were six (8.3%) chronic lead related complications but no failures of lead material. Most of these complications developed during the first month, and half of them were transient, with documented improvement later. Two patients (2.6%) required reoperation for chronic complications. At follow-up examination of the pacing thresholds, usually performed about 3 months after implantation, 14.3% of the examined patients had high pacing thresholds necessitating high-output programming. The mechanisms and later evolution of this phenomenon should be further evaluated.     

Initial Experience with a Co-Radial Bipolar Pacing Lead

A new type of endocardial bipolar pacing lead has been designed to overcome the potential drawbacks of the conventional coaxial bipolar pacing had. We prospectively evaluated the new co-radial bipolar pacing leads (Intermedics Thin Line), which are thinner (5 Fr vs 6—8 Fr) than standard coaxial bipolar leads. X-ray visibility and lead handling were subjectively assessed (excellent, good, adequate, or poor) at implant; lead impedance, sensitivity threshold, and pacing threshold were measured at implant, then at 1, 3. 6, 12, and 18 months. The results were as follows: 103 patients (51 M; age 63.8 ± 17.4 years) received 71 atrial (A) and 89 ventricular (V) leads. X-ray visibility was excellent in 59/103; good in 23/103; adequate in 11/103; and poor in 10/103. Overall handling was excellent in 56/71 A and 69/89 V; good in 11/71 A and 18/89 V; adequate in 3/71 A and 1/89 V; poor in 1/71 A and 1/89 V. There were two perioperative complications. At implant: impedance in A and V were 370.1 ± 74.7 and 501.5 ± 124.4 Ω, sensing thresholds in A and V were 3.0 ± 1.5 and 9.9 ± 5.0 mV, pacing thresholds at 0.45 ms in A and V were 0.59 ± 0.21 and 0.41 ± 0.15 volt, respectively. At 1, 3, 6. 12, and 18 months of follow-up: no pacing lead related complications were reported; pacing lead characteristics remained outstanding and stable. This new lead appears to have significant clinical advantages over the conventional coaxial bipolar pacing lead. Long-term follow-up is required to confirm its reliability and chronic performance characteristics.     

Five-Year Follow-Up of a Bipolar Steroid-Eluting Ventricular Pacing Lead

Steroid-eluting pacing leads are known to attenuate the threshold peaking early after implantation. Long-term performance, however, is not yet settled. The lead design tested in this prospective study combines a 5.8-mm2 tip of microporous platinum-iridium with elution of 1.0 mg of dexamethasone sodium phosphate and tines for passive fixation (model 5024, Medtronic Inc.). In 50 patients (mean age 69 +/- 10 years), the electrode was implanted in the right ventricular apex. Follow-up was performed on days 0, 2, 5, 10, 28, 90, 180 and every 6 months thereafter for 5-years postimplant. At each visit, pacing thresholds were determined as pulse duration (ms) at 1.0 V and as the minimum charge (microC) delivered for capture. Lead impedance (omega) was telemetered at 2.5 V-0.50 ms, and sensing thresholds (mV) were measured in triplicate using the automatic sensing threshold algorithm of the pacemaker implanted (model 294-03, Intermedics Inc.). On the day of implantation, mean values were 0.10 +/- 0.03 ms, 0.12 +/- 0.03 microC, 758 +/- 131 omega, and 13.1 +/- 1.8 mV, respectively. Beyond 1-year postimplant, pacing thresholds did not vary significantly. Sensing thresholds and lead impedance values were stable during long-term follow-up. Five years after implantation, mean values were 0.23 +/- 0.11 ms, 0.24 +/- 0.07 microC, 670 +/- 139 omega, and 11.6 +/- 3.1 mV for pulse width and charge threshold, lead impedance, and sensing threshold, respectively, and all leads captured at 1.0 V with the longest pulse duration available (1.50 ms). It is concluded that the bipolar steroid-eluting tined ventricular lead showed stable stimulation thresholds, lead impedance values, and sensing thresholds for 5 years after implantation.     

Is Polyurethane Lead Insulation Still Controversial?

A controversy arose some 10 years ago over the reliability of polyurethane lead insulation. On the basis of one of the longest standing and largest databanks worldwide, the authors compare the cumulative survival of several thousand polyurethane, standard silastic, and high-performance silastic electrodes as it pertains to the failure criterion described as insulation degradation. With the possible exception of the Medtronic 6972 (Medtronic, Inc.) electrode, polyurethane electrodes have a 100% reliability at 84 months, which is similar to silastic electrodes.     

Ten-Year Experience with Implanted Polyurethane Lead Insulation

Polyurethane leads have been implanted in humans since 1977. Because of cases of stress cracking found in 1981, changes in the manufacturing process were made. Subsequent performance was excellent. There remains concern regarding the ability to predict accurately long-term performance. However, the advent of reliable, statistically accurate actuarial data coupled with accelerated tests predictive of human performance has restored confidence in the newer polyurethane lead technology.     

Oversensing from Electrode ''Chatter'' in a Bipolar Pacing Lead: A Case Report

An 81-year-old man was treated for high degree AV block and syncope with an AV universal (DDD) pacemaker. Bipolar active fixation atrial and ventricular leads were used. Intermittent oversensing from the ventricular lead was detected on Holter monitoring following implantation. This resulted in inappropriate inhibition of ventricular pacing. Ventricular electrogram showed spurious signals between 5 mV and 15 mV in magnitude coincident with ventricular lead inhibition. Treatment consisted of reprogramming the device to the VVT mode. Six weeks after implantation normal pacemaker function in the DDD mode was demonstrated on Holter monitoring and inappropriate pacer inhibition could not be demonstrated. We postulate that electrode 'chatter' between the cathodal ring electrode and the helix of the ventricular lead resulted in artifactual potentials sufficient to inhibit pacing. We hypothesize that fibrosis and fixation of the ventricular lead tip over a period of weeks eliminated these electromechanical artifacts and resulted in the oversensing problem being self-limited. Physicians should be aware of electrode 'chatter' as a cause of pacemaker oversensing.     

Crosstalk During Bipolar Pacing

Bipolar sensing pulse generators were thought to have eliminated crosstalk problems evident in unipolar systems. Crosstalk has been observed in the Model 284–02* bipolar sensing pacemakers. These intermittent problems were resolved by decreasing atrial output, decreasing ventricular sensitivity or increasing the ventricular blanking period. Three patients had pacemaker crosstalk, two experienced symptoms analogous to pacemaker syndrome.     

Unsatisfying Results in Long-Term Atrial Pacing with a Bipolar Active Fixation Atrial Lead

A high dislodgment rate during long-term atrial pacing using the unipolar sickle-shaped active fixation lead was recently reported; therefore, the long-term results of atrial pacing in 118 consecutive patients with the bipolar sickle-shaped active fixation lead (Biotronik FH60-BP) were evaluated. Between January 1989 and September 1993, 87 leads (74%) were inserted for dual chamber pacing and 31 leads (26%) for atrial pacing only. At the time of implantation, the bipolar atrial electrogram had a mean voltage of 4.4 ± 1.6 mV, whereas the acute atrial threshold was 0.72 ± 0.38 V and 1.46 ± 0.67 ml at 0.5-msec pulse duration and mean resistance 506 ± 79 Ω. Early lead dislodgment (< 1 month after implantation) occurred in 9 patients (7.6%). During a mean follow-up of 21.8 months (median 20.9 months), late dislodgment (> 1 month after implantation) occurred in 6 patients (5.1%) after a mean interval of 7.9 months (range 3–14 months). Due to the unacceptably high late dislodgment rate, which to date remains unexplained, new implants of this lead are not recommended.     

Long-Term Performance of Endocardial Pacing Leads

To assess the performance of endocardial pacemaker leads and to identify factors associated with structural lead failure, medical records of 2,611 endocardial pacing leads (in 1, 5W patients) implanted between 1980 and 1991, having at least 1 month of follow-up, were reviewed. Leads without structural failure had normal function at the last follow-up date, or were discontinued for reasons other than structural failure (patient death, infection, dislodgment, lead-pacemaker incompatibility, operative complication, or abandonment by telemetry not related to failure). Leads with suspected structural failures were invasively or noninvasively disconnected because of clinical malfunction (loss of capture or sensing, oversensing, elevated thresholds, or skeletal muscular stimulation). Leads with verified structural failures met the criteria for suspected lead failure and also had a visible defect seen in the operating room or on chest roentgenograms, a change in the impedance interpreted by the physician as lead disruption, or a manufacturer's return product report that confirmed structural failure. Variables analyzed included patients’ age and gender, paced chamber, venous access, insulation materials, fixation mechanism, coaxial design, polarity, and different lead models. The cumulative lead survival at 5 and 10 years were 97.4% and 92.9%, respectively, for suspected failures; and 98.7% and 97.3%, respectively, for verified failures. Leads in older patients (≥ 65 years old), and leads in atrial position had fewer verified failures (P = 0.014 and P = 0.007, respectively). Unipolar leads also tended to perform better according to the verified definition (P = 0.07). The lead Medtronic 4012 had more suspected (P < 0.05) and more verified failures (P < 0.01), the lead CPI 4010 had more verified failures (P < 0.05) than the entire group of ventricular leads. Conclusions: Endocardial pacing leads implanted in atrial position, and implanted in older patients (> 65 years old) seems to have better long-term survival. Some lead models (Medtronic 4012 and CPI 4010) had poor survival rates, that could not be explained by the analyzed variables. The expected performance of endocardial pacing leads varies according to how failure is defined.     

Long-Term Performance of Polyurethane Pacing Leads: Mechanisms of Design-Related Failures

Environmental stress cracking has been identified as a crack propagating mechanism in polyurethane-insulated, heart pacemaker leads, which is directly related to specific lead design parameters. Lead designs imposing excessive stress on the polyurethane insulation through an interference fit between the coil and polymer have demonstrated insulation failures. Conversely, low-stress designs have shown virtually no insulation problems. The higher-stress designs have used organic solvents to facilitate coil placement during manufacturing. which may result in lowering the polymer's ability to resist the higher stress. In addition, a specific silver-containing coil wire composition has been found to galvanically corrode upon body fluid intrusion info the lead, ionizing the silver. These ions interact with the polyurethane polymer resulting in the loss of polymer strength. All polyurethane lead failures to date have been specific to high stress and/or chemical interaction. Leads using low-stress designs and nonreactive coil wire compositions continue to demonstrate a positive clinical experience.     

Clinical Surveillance of an Active Fixation, Bipolar, Polyurethane Insulated Pacing Lead, Part I: The Atrial Lead

Since 1989, 168 Telectronics model 330–801 active fixation, polyurethane insulated atrial leads (Accufix) have been implanted at the Mayo Clinic. There were four (2.4%) acute lead related complications, (i.e., perforation, microdislodgment, and pericarditis). Over a median follow-up time of 7.6 months (up to 2.7 years), there were 14 (8.3%) chronic complications, including 1 instance (0.6%) of definite lead failure. Most of these complications were early (within the first month) and transient. Four patients (2.4%) required reoperation for chronic complications. During follow-up, 23% of the examined patients had high pacing thresholds, most at about 3 months after implantation, necessitating high-output programming. The exact mechanism and natural history of this phenomenon should be further investigated.     

Self-Inhibition of an AV Sequential Demand (DVI) Pulse Generator Due to Polyurethane Lead Insulation Disruption

Self-inhibi lion of bipolar DVIAV-sequentia I pacemakers has been attributed to eleclrode malposition, although the potential for self-inhibition due to current leakage has been recognized. Previous cases of current leakages due to insulation defects in bipolar VVI ventricular demand systems have usually presented as abnormal sensing or pacing function without a change to actual unipolar sensing and pacing. This article describes a case of disruption of the insulation of polyurethane bipolar atrial and ventricular leads by silk ligatures, resulting in unipolar atrial and ventricular pacing and self-inhibition of ventricular output of a DVI pulse generator. This case emphasizes the importance of avoiding any application of suture material directly to polyurethane leads. This case also emphasizes the importance of monitoring pacemaker artifact amplitude and axis in patient follow-up.     

Bipolar versus Unipolar Issues in DDD Pacing

Les mérites relatifs de la stimulation unipolaire et bipulaire sont discutés dans le contexte des stimulateurs DDD. Pour assurer le recueil du potentiel auricuiaire en présence de potentiel musculaire, l'utilisation d'un systéme bipolaire est préferable. Le recueil bipolaire ventriculaire réduira l'incidence d'inhibition par des myopotentiels et pourrait aussi réduire la possibilité de l'écoute croisée. Cependant, la stimulation est mieux obtenue par un systéme unipolaire. C'est pourquoi nous développons un nouveau stimulates qui fournira la slimulation en unipolaire et le recueil du potentiel en bipolaire. Ce stimulateur est conçu et basé sur un schéma unipolaire, avec la simplicité et la fiabilité inhéreutes à ce mode.