A New Low Threshold Platinized Epicardial Pacing Electrode: Comparative Evaluation in Immature Canines

A prospective comparison of pacing and sensing capabilities between the conventional Medtronic Model 4951 platinum-iridium epicardial pacing electrode and a new modified "platinized" version of the same electrode was performed in immature canines to determine if the new electrode design improves pacing in the immature myocardium. The conventional electrode was modified by electroplating platinum black particles onto the surface to increase the effective or true microscopic surface area, yet essentially maintain the same overall geometric electrode size. Both epicardial electrodes were inserted into the right ventricular myocardium with the lead pad sutured to the epicardium, and externalized to the scruff in five puppies (age 3 months). An additional left ventricular lead was implanted to permit chronic pacing following epicardially-induced atrioventricular block. Acute and chronic sensing and pacing capabilities of each externalized electrode were performed at implant and weekly up to 4 months. Histologic examination of each electrode implant site was performed at the end of the study period. At implant, both electrodes exhibited comparable values for sensed R waves, lead impedances, and pacing thresholds. During the study, the platinized electrode exhibited lower pacing thresholds. Analysis of all postimplant data demonstrated this threshold difference to be significantly lower (P less than .01) for the platinized version. Lead impedance and sensing capabilities remained comparable between the two designs. Histologic study demonstrated less fibrotic infiltration at the platinized electrode site. This preliminary evaluation indicates that for the duration of the postimplant study period, the platinized epicardial electrode design was associated with significantly lower thresholds and less fibrosis as a function of time compared to the conventional smooth electrode surface design. The new platinized electrode limits exit block in the developing immature myocardium and permits safe pacing at lower pulse widths and voltages to increase battery life.     

Steroid-Eluting Epicardial Pacing Electrodes: Six Year Experience of Pacing Thresholds in a Growing Pediatric Population

Indications for pacemaker implantation in the pediatric population often include sinus or atrioventricular node dysfunction following surgery for congenital heart defects. However, patient size, cardiac defects, and vascular and valvular concerns may limit transvenous lead utilization. Since the epicardial surface of these patients often exhibits variable degrees of fibrosis from scar tissue formation or pericardial adhesions, chronic low output (2.5/1.6 V, 0.3 ms) epicardial pacing from implant is not currently recommended in children due to frequent threshold changes and electrode exit block. As a result, pacing in children is often viewed as a less efficient system than in adults. The addition of steroid combined with newer low threshold electrode designs however stabilizes the electrode-tissue interface and eliminates postimplant changes seen with standard smooth surface electrodes potentially permitting efficient chronic pacemaker application to all patient ages. The stability of chronic low output epicardial pacing with steroid-eluting electrodes was prospectively studied in 22 patients (ages 2 days-18.5 years, median 3.5 years) for up to 6 years. Chronic pulse width thresholds were compared according to implant site and association of prior cardiac surgery. A total of 26 pacing leads were implanted. The acute implant mean pulse width threshold (2.5 V) for all the electrodes studied was 0.10 ms ± 0.05 ms. Stable low thresholds were maintained for up to 6 years without significant variation from implant. Mean ventricular pulse width thresholds (0.12 ms ± 0.05 ms) were significantly higher (P < 0.001) than atrial thresholds (0.06 ms ± 0.03 ms) at implant and throughout the study period. The thresholds in the patients following cardiac surgery were comparable to those without previous cardiac surgery (P = NS). Stable low thresholds may be chronically maintatined for up to 6 years for epicardial steroid-eluting electrodes irrespective of pacing site or associated cardiac surgery.     

Do Steroid-Eluting Electrodes Really Have Better Performance Than Other State-of-the-Art Designs?

A multicenter study evaluated the performance of atrial and ventricular unipolar leads with porous steroid-eluting and platinized grooved electrodes. A total of 563 leads were implanted in 451 patients. These included 311 ventricular and 97 atrial steroid-eluting electrodes; and 112 ventricular and 43 atrial leads with platinized electrodes. Mean follow-up was ± 1 year. At implant there were no significant differences in threshold parameters in either chamber. Chronically, however, the steroid eluting lead consistently had significantly lower pacing thresholds in both chambers. For example, after 360 days implant, steroid-eluting electrodes had 0.23 ± 0.10 msec ventricular thresholds at 0.8 V compared to 0.45 ± 0.3 msec in the platinized group (P < 0.0001). In the atrium, the steroid-eluting lead's 6-month thresholds at 0.8 V were 0.15 ± 0.06 msec compared to 0.9 ± 0.8 msec for the platinized electrode (P < 0.01). The chronic ventricular QRS amplitudes were significantly greater for the steroideluting electrode (P < 0.0005). There were no significant differences in atrial sensing and no incidence of atrial undersensing in the study. The low and consistent thresholds of the steroid-eluting electrodes would have permitted pacing in the ventricle at ± 2.5 V without compromising safety factor in 99.4% of the patients. The other 0.6% required 5 V temporarily. In the atrium, 100% of the patients could have been paced safely at reduced output. In spite of this, 63% of the implanters lacked the confidence to use reduced outputs.     

Preliminary Studies on a New Steroid Eluting Epicardial Electrode

Acute and chronic canine atrial and ventricular thresholds and sensing were compared for a steroid eluting epicardial plaque electrode, a similar steroid free plaque electrode and two standard leads. The steroid eluting electrode had low, stable thresbolds in atrium and ventricle compared to the steroid free plaque and standard leads. This new electrode also provided improved atrial sensing. Thus, the concept of a steroid eluting epicardial electrode shows promise for further evaluation.     

The Porous Titanium Steroid Eluting Electrode: A Double Blind Study Assessing the Stimulation Threshold Effects of Steroid

A transvenous pacing lead with a porous electrode which slowly elutes the steroid, dexamethasone sodium phosphate, has been developed. Previous investigations show low and constant stimulation thresholds persisting over at least the first two years post-implantation. As it is not known whether this low threshold results from the steroid or electrode configuration, a double blind study was designed to compare the same electrode configuration with and without steroid over a 2-year follow-up period. There were ten patients in each group with similar age, sex, indications for pacing and implantation data. Regular measurements of postoperative pulse duration thresholds were performed using a customized VVIM pulse generator programmed to 1.5 V output. For the first two days post-implantation, there were no statistical differences in the pulse duration thresholds between the two pacing leads. From 2 weeks to 2 years the pulse duration thresholds for the steroid leads remained almost constant, whereas the leads without steroid showed a typical rise. The difference in pulse duration thresholds between the two groups of leads from two weeks onwards confirmed that it was the steroid rather than the electrode configuration which prevented the rise in chronic stimulation threshold.     

Chronic Performance of a Transvenous Steroid Pacing Lead Used as an Epi-Intramyocardial Electrode

Excessive surface fibrosis or fat limits effective electrode insertion in patients requiring epicardial pacing. We present chronic performance of a modified transvenous steroid lead used as an epi-intramyocardial electrode in a patient following repair of a univentricular heart after failure of both standard and steroid-eluting epicardial leads. Low implant threshold values remained stable during a 3-year postimplant interval demonstrating an effective and innovative approach to epicardial pacing.     

Composite Electrode Tips Containing Externally Placed Drug Releasing Collars

We have developed a composite electode tip based on a new concept whereby the electrode is combined with a polymeric collar containing dexamethasone sodium phosphate (DSP). The collar is positioned immediately adjacent to the electrode. Initial evaluation of this concept employed the Telectronics Laserpor electrode and a collar containing approximately 1.8 mg of DSP (LPD). Conventional Telectronics Laserpor (LP) electrodes were used as controls. Further evaluation was performed using a DSP (< 0.5mg) eluting collar and a new 4 mm² mushroom shaped electrode with a high microsurface Pt/Ir coating (MD). Data for conventional Telectronics Laserdish (LD) electrodes were used for comparison. Unipolar ventricular leads were implanted transvenously in the right ventricular apex of sheep. Voltage thresholds, pacing (5V, 0.5ms) and sensing (50/100 mVRMS, 50 Hz) impedances were measured during the subchronic phase (< 6 weeks) and in the case of LD and MD for 6 months. The steroid eluting electrodes were elective in eliminating (2 weeks vs. Impl., N.S.) the 2 week threshold peaking seen with the control leads (2 weeks vs. Impl., P < 0.005). The small area MD electrode thresholds remained stable and low for up to 6 months (0.38 ± 0.09 (10) c.f. 0.46 ± 0.11(6); 14 and 180 days, respectively, N.S.). The composite electrode tips with steroid releasing collars thus show great potential for a substantial reduction in stimulation energy.     

High impedance low energy pacing leads: long-term results with a very small surface area steroid-eluting lead compared to three conventional electrodes

We evaluated the handling performance at implant, and the long-term atrial and ventricular electrical performance of a new generation using a very small surface area (1.2 mm2) steroid-eluting electrode (Medtronic CapSure Z). We compared the performance of CapSure Z to that of traditional passive fixation leads, with and without steroid elution. The study was conducted during 2 years of follow-up. We studied 188 patients (105 males and 83 females; mean age 71 +/- 7 years). All of the patients were implanted with a dual chamber pacemaker and the same type of lead in both chambers. Forty-one patients received CapSure Z leads, 25 patients received Target Tip leads (8-mm2 surface area; no steroid elution), 63 patients received CapSure leads (8-mm2 surface area; steroid elution), and 59 patients received CapSure SP leads (5.8-mm2 surface area; steroid elution). The four groups were homogeneous in regards to sex, age, cardiac disease, and reason for implant. At follow-up, the CapSure Z lead showed sensing values comparable to the other leads, with lower pacing thresholds and higher pacing impedance in both chambers. We evaluated the mean current drained from the pacemaker by the different types of leads when using safe, low energy output settings. We found that by using CapSure Z leads, the mean current was significantly lower than that of the other types of leads (0.42 microA for CapSure Z ventricular lead vs 0.85 for CapSure SP, 1.42 for CapSure, and 1.54 for Target Tip). Thus, the use of the CapSure Z lead, combined with low energy output programming, will increase pacemaker longevity compared to the use of traditional leads and standard output programming.     

Unusual pacing observed in a biventricular pacemaker with epicardial pacing leads

In this case report, we describe inappropriate pacing in a patient with a newly implanted biventricular pacing system with three epicardial leads. Very high pacing thresholds resulted from the use of nonsteroid eluting leads, and unusual pacing behavior was due to the chosen implant locations for the right atrial and right ventricular epicardial leads. The interplay between the programmed pacemaker parameters, the very late ventricular sensing in the setting of intrinsic right bundle branch block, and atrial lead oversensing led to ineffective biventricular pacing. The persistently elevated pacing thresholds and sensing problems led to very early battery depletion and the need to replace the epicardial system with three new endocardial leads.     

Pacing Threshold Spikes Months and Years After Implant

To determine patterns of variation in chronic pacing thresholds, we made 4,942 threshold measurements in 257 patients with 312 leads, at times from implant to 295 months (median 17 months) including 1,053 determinations in 46 children < 12 years old. Motivation was late sudden death in two single-ventricle pacemaker-dependent children with multiple possible death causes. At stimulus duration 0.5 ± 0.04 msec, mean of the thresholds, measured 1 month or more after implant, was 1.3 ± 0.66 volts (V) for endocardial electrodes and 2.8 ± 1.39 V for epicardially applied electrodes. Highest mean thresholds were in the 6 to 12-year-old age group. In 34 leads studied at implant, again within a month and for at least three years thereafter, time of maximum threshold occurred after one month in 59%, independent of lead type or patient age. Of 107 leads with five or more measurements after 3 months use, gradual increase in threshold continued after 3 months in 24%. An additional 21% had at least one threshold that exceeded the post-three-months individual patient lead mean by three standard deviations. Most striking was the occurrence of transient several-volt increases and decreases in threshold as late as 8 years after lead implantation in at least three children. These temporary changes were detected initially transtelephonically by the vario method of threshold measurement. They occurred during minor illnesses such as summer colds, yet similar illnesses also occurred without threshold elevation. We suggest further study of pacing threshold variations in highly pacemaker-dependent children whose cardiac anatomy makes use of epicardial electrodes necessary.     

Comparison of Titanium-Mesh and Porous Disc Electrodes for Epicardial Defibrillation

The object of this study was to compare the effectiveness of chronically implanted porous electrodes with that of smooth mesh titanium electrodes of the same diameter but smaller effective surface area. The criteria used in evaluating the electrodes were (1) acute, subacute, and chronic resistance and (2) acute, subacute, and chronic defibrillation thresholds. Electrode pairs 2.5 cm in diameter were implanted in each of 17 dogs (ten mesh and seven porous). One electrode of each pair was sutured to the right ventricle and one to the left ventricle near the cardiac apex. Defibrillalion threshold energy and total resistance were measured at the time of implantation and again 6 and 12 weeks after implantation. The mean initial resistance of the titanium electrodes was 131.7 Ω; the mean defibrillation values /or the porous electrode implant were 96.9 Ω and 7,5 joules, respectively. Three to 6 weeks after implantation, the values for the titanium mesh electrode were 88.9 Ω and 12.0 joules, while those for the porous electrode were 59.9 Ω and 8.0 joules. In the chronic state, the figures for the titanium mesh electrode were 78.1 Ω and 13.0 joules, while those for the porous electrode were 64.3 Ω and 8.3 joules. We conclude that defibrillation can be achieved successfully with small epicardial electrodes. The findings suggest that a porous electrode, with its larger effective surface area, has lower electrode/tissue interface resistance in the acute and chronic phases, and, therefore, provides lower defibrillation threshold energy.     

Chronic Animal Testing of New Cardiac Pacing Electrodes

ADLER, S., ET AL.: Chronic Animal Testing of New Cardiac Pacing Electrodes. To evaluate the electrical performance of new electrode technologies, 24 leads containing either carbon coated porous titanium (BIOPORE, (Intermedics, Inc., Freeport, TX)), iridium oxide (IROX), or iridium oxide coated with polyethylene glycol (IROX-PEG) electrodes (eight of each) were implanted into the ventricles of 12 canines. Stimulation threshold data was measured at regular intervals for 24 weeks. Low acute values were observed for all leads (0.32 ± 13 V at 0.6 msec pulse width), but the IROX-PEG electrode demonstrated lower subchronic, peak, and chronic values. Compared to implant, the IROX-PEG electrodes' stimulation thresholds rose only 0.23 V when chronic conditions occurred. There were no significant differences between the electrodes in pacing impedance or R wave amplitude measurements. We conclude that both IROX and IROX-PEG technologies represent a promising approach to the design of more efficient cardiac pacing leads.     

"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.     

A New Steroid-Eluting Epicardial Lead: Experience with Atrial and Ventricular Implantation in the Immature Swine

The first study with investigational steroid epicardial leads was carried out in mature canine with prototype leads. Because the demand for epicardial leads is highest in small infants and the prototype steroid-eluting lead has been redesigned, this study was carried out in immature swine to evaluate the newly designed lead. Six immature swine (2 at 5 weeks of age and 4 at 6 weeks) underwent epicardial implantation of four porous platinized tip leads: one steroid and one nonsteroid on the right atrium; one steroid and one nonsteroid on the right ventricle. At implantation, the lead terminals were connected to a percutaneous access device subcutaneously placed in the right lateral neck. This allowed chronic measurements by using an insulated needle connected with a cable to the pacing systems analyzer. Measurements were obtained at implantation and weekly for 3 weeks. Compared to the nonsteroid atrial leads, the steroid atrial leads had lower mean thresholds (P less than 0.01) at 1, 2, and 3 weeks after implantation. The mean threshold values from ventricular steroid leads were also lower and exhibited little increase from implant with the highest mean threshold of only 1.02 V, however, a statistically significant difference between steroid and nonsteroid was not reached. This newly designed steroid epicardial lead provided favorable results for continual human clinical study.     

In Vivo Elution Rate of Drug Eluting Ceramic Leads with a Reduced Dose of Dexamethasone Sodium Phosphate

MATHIVANAR, R., ET AL.: In Vivo Elution Rate of Drug-Eluting Ceramic Leads with a Reduced Dose of Dexamethasone Sodium Phosphate. We have evaluated the in vivo elution rate and the threshold voltage performance of a new lead incorporating a controlled delivery device based on a porous ceramic collar. The drug, dexamethasone sodium phosphate (DSp < 0.2 mg), was contained within the pores of a ceramic collar that was positioned externally and adjacent to a 4 mm² Pt/Ir coated electrode. Thirty-three leads comprising a porous ceramic drug eluting collar (DEC) were implanted in the right ventricle of 12 sheep. In vivo elution was determined by analyzing the drug remaining in the collar after 1, 3, 11, and 28 days. Voltage thresholds were measured at implant and then weekly for 28 days on three sheep. Results were compared to leads with identical electrodes but with silicone DEC (DSp < 0.5 mg). The in vivo elution rate of the ceramic DEC leads was fast with approximately 90% of the drug content eluted on the first day. By comparison, the silicone DEC released approximately 50% of the drug content on the first day. Although the drug content and elution rates were different for the ceramic and silicone DEC leads, the threshold performance of the leads was similar. For ceramic and silicone DEC leads, threshold voltages at implant and at 4 weeks were 0.29 ± 0.09 compared to 0.37 ± 0.08 and 0.42 ± 0.08 compared to 0.44 ± 0.13, respectively. The results show that a relatively rapid release of a reduced dose of DSP from a DEC is still effective in reducing threshold peaking.     

Characteristles of Advanced Porous and Textured Surface Pacemaker Electrodes

Reduced stimulation thresholds, improved sensing and betler attachment have been claimed for totally porous and porous surfaced electrodes. In this study, the potential for clinical use of two new types of porous electrodes and a non-porous, textured high microsurface area electrode, has been evaluated by comparison with equivalenf sized, smooth non-porous controls. Eighteen sintered and seven laser drilled porous electrodes, seven non-porous textured electrodes, and sixteen controls, were implanted singly in fhe right ventricles of sheep. Measurements of threshold, pacing, sensing and bulk impedances were taken at regular intervals for up to 180 days. At sacrifice, only three of the thirteen non-porous confrols were attached. AU laser porous electrodes, apart from two which were dislodged, were attached, as were eieven of fifteen sintered porous, and five of seven textured non-porous electrodes. Tissue ingrowth was found for both porous electrode types. Stimulation threshoJds were not statistically different for all electrode types (p < 0.05). Pacing and bulk impedances of the two porous and surface textured electrodes were significantly higher (p < 0.10, p < 0.05, respectively) than those of controls. The three new electrodes exhibited similar chronic sensing impedance vaJues, 30% less than equivalent non-porous electrodes. The similar sensing performance of the porous and high microsurface area non-porous electrodes indicates that the nature of the external surface, rather than internal porosity, determines sensing impedance. All three new electrode types showed improved attachment and sensing compared with similar smooth eJectrodes. The laser porous electrode, which permits fixation by tissue ingrowth and maintainssimplicity of construction, is promising for routine clinical use.     

Stable electrical performance of high efficiency pacing leads having small surface, steroid-eluting pacing electrodes

Previous experience with steroid-eluting small electrode designs have described their increased pacing efficiency, yet some reports have questioned their electrical stability. We report our experience with a new pacing lead design incorporating small surface (i.e. 1.2 mm2), high impedance pacing electrodes. Medtronic Model 5034 ventricular pacing leads were implanted by a single physician in 167 patients. Of those, 96 patients had an additional Model 5534 atrial lead implanted. All patients were followed for at least 9 months. Microdislodgment, as defined by a sudden increase in pacing threshold accompanied by radiographic stability, was observed in 6 of 263 (2.3%) leads implanted. Of the 4/167 (2.4%) ventricular leads that exhibited electrical instability, only 2 were sustained. Importantly, neither was significant enough to result in loss of capture. The other two cases of ventricular electrode instability manifested as a transient threshold rise with eventual return to near the original values. By comparison, the atrial lead model exhibited a sudden and sustained pacing threshold rise 5 which was evident in two patients (2.1%) with neither requiring invasive intervention. For all remaining chronic leads, clinically acceptable electrical performance profiles were demonstrated. We conclude that low microdislodgment rates and stable electrical performance profiles can be achieved with the small electrode steroid-eluting pacing electrodes as long as careful lead positioning and securing techniques are followed during implantation. We further suggest that successful high impedance lead design is critically dependent on its stiffness and mass characteristics.     

A Randomized Comparison of a Bipolar Steroid-Eluting Electrode and a Bipolar Microporous Platinum Electrode: Implications for Long-Term Programming

Differences in acute and chronic pacing thresholds were compared in patients receiving either the Medtronic Model 4004 steroid-eluting lead or the Medtronic Model 4012 microporous platinum lead. Patients (n = 35) were randomized at the time of implant to receive either a steroid-eluting (n = 17) or a microporous (n = 18) lead. Pacing thresholds were determined within 24 hours and at 2, 4, 6, 12. 24, and 52 weeks postimplant. By 2 weeks postimplant. pacing thresholds measured at 0.8, 1.6, 2.5, 3.3, and 4.2 V were significantly lower in the steroid lead group compared to the microporous Jead group (P < 0.05). At 24 weeks, the voltage threshold at 0.3 msec was 0.8 V in 88% of patients with a steroid lead whereas this threshold was only observed in 33% of patients with the microporous lead (P < 0.01). At 52 weeks the pacing energy measured at 1.6 V, twice pulse duration threshold, was significantly lower in the steroid lead group (0.81 ± 0.59 μJ) compared to the microporous lead group (1.25 ± 0.60 μJ, P < 0.05). Thirteen patients in the steroid lead group and 9 patients in the microporous lead group have been programmed at a pulse amplitude of 1.6 V since the 24-week follow-up visit. These patients have been followed for a minimum of 6 months without documented failure to capture. This study shows that pacemaker/lead systems with stable chronic low thresholds can be safely programmed to low pulse amplitude settings. This practice will prolong the longevity of pulse generators.     

The Mythology of Threshold Variations as a Function of Electrode Surface Area

It has been established that the chronic thresholds of cardiac pacing leads vary as a function of the (spherical) electrode's radius or (geometric) surface area and the thickness of fibrotic encapsulation.^1,2 Where the radius of the electrode is equal to the thickness of the fibrous capsule (about 0.7 to 1 mm for polished surfaces), threshold should be at a minimum.¹ Where the radius of the electrode is larger or smaller than the thickness of the fibrous capsule, then thresholds should increase since the electric field strength required to stimulate decreases as the square of the distance between the electrode's surface and stimulatable tissue.¹ In addition, it has become (incorrectly) accepted that small electrodes do not sense well.³ About 8-mm² electrodes, therefore, became the "standard" surface area, providing the best tradeoffs between pacing and sensing. Analysis of 18 years of canine data in our laboratory, however, suggest that these relationships may be overemphasized for the surface areas of clinical interest. In fact, new small porous and steroid-eluting electrodes do not have high thresholds, are efficient, and their sensing is excellent.     

Inadvertent Atrial Location of a Sutureless Epicardial Pacemaker Electrode

A 70-year-old woman had an epicardial pacing system implanted after transvenous right ventricular endocardial pacing resulted in cardiac perforation. At the time of revision of the epicardial system for pacing failure, it was noted that one of the bipolar epicardial electrodes was pacing atrial tissue. The differential diagnosis of this unusual finding is discussed and recommendation urged for systematic analysis of pacing system function at the time of implant, in order to avoid inadvertent electrode plpcement.