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.     

Comparison of Electrical Characteristics Between a Steroid-Eluting Single-Pass VDD Lead and a Standard Steroid-Eluting Ventricular Lead

Compared to regular ventricular leads, single-pass VDD leads have two additional floating electrodes proximal to the ventricular tip, which enables them to detect atrial signals. Because of the latter, VDD leads are thicker than ventricular leads, which could affect ventricular pacing. The purpose of the present study was to compare ventricular pacing of a steroid-eluting single-pass VDD lead (CapSure VDD, Medtronic; n = 107) with the same steroid-eluting regular lead (CapSure SP, Medtronic; n = 39) implanted in the ventricle; both leads were connected to the same types of pacemakers. At implantation, pacing thresholds were measured at 0.5-ms pulse duration and impedance by means with the PSA. At discharge, as well as after 1 and 3 months, pulse duration thresholds were determined at 2.5 V pulse amplitude and impedance by telemetry. At implantation, pacing thresholds and impedance were not different in the VDD (0.38 ± 0.16 V; 691 ± 122 Ω) and ventricular lead group (0.44 ± 0.17 V; 648 ± 150 Ω). During follow-ups, no differences in pulse duration threshold were detected between the two groups neither at discharge (VDD = 0.05 ± 0.03 ms; ventricular 0.05 ± 0.02 ms), nor after 1 (VDD = 0.05 ± 0.02 ms; ventricular 0.08 ± 0.07 ms) and 3 months (VDD = 0.06 ± 0.03 ms; ventricular 0.09 ± 0.10 ms). There were also no significant differences for impedance at discharge (VDD = 675 ± 113 Ω; ventricular = 594 ± 113 Ω), after 1 (VDD = 678 ± 131 Ω,; ventricular = 627 ± 112 Ω) and 3 months (VDD = 652 ± 99 Ω; ventricular = 628 ± 105 Ω). Pacing thresholds and impedance were neither significantly different at implantation nor during follow-ups between patients with steroid-eluting VDD leads and patients with an equivalent ventricular lead indicating that the thicker VDD lead does not affect ventricular pacing.     

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.     

Clinical Experience with Steroid-Eluting Unipolar Electrodes

In continuing search of low chronic threshold leads, a new concept of electrode design which is capable of delivering corticosteroids at the myocardial tissue interface has been made available by Medtronic. Twenty-three patients, 17 females and 6 males, were either implanted with 4003 (n = 21) or 5023 (n - 2) steroid-eluting electrodes in the ventricular chamber. Pacing modes utilized were WIM (n = 13) or DDD (n = 10). Pulse generators used were Medtronic (7005. 8317, 8329) Pacesetter (285) and Intermedics (283). Thresholds at the time of implantation at 0.50 msec pulse width were 0.40 ± 0.02 volts at 0.66 ± 0.05 milliamps. Resistance and R wave measured were 565.43 ± 22.07 ohms and 9.24 ± 1.06 mv, respectively. Chronic thresholds were checked on routine follow-up visits by either decreasing pulse width and for pulse amplitude. Data is being reported between 1 and 88 (23.22 ± 4.35) weeks. Pulse width threshold at 2.5 volts were 0.10 msec (n = n) and 0.05 msec or lower (n = 12). At 5.0 volts no loss of capture was seen at 0.05 msec (n = 22) except in one patient at 0.10 msec. Pulse width thresholds in the first 24 weeks were lower than 0.20 msec at 2.5 volts (n = 15) and less than 0.70 msec, at 0.8 volts (n = 6). No loss of sensing was seen by electrocardiographic analysis at the time of threshold checks with the pulse generator at standard setting of the R wave. Thus, in this initial report, the steroid-eluting electrodes have demonstrated very low thresholds both in the early and chronic follow-up phase. Demonstration of consistently low thresholds, avoiding initial peaking, will permit routine low output setting without compromising safety and thus prolong the life of the pulse generators.     

Improved Epimyocardial Pacing: Initial Experience with a New Bipolar, Steroid-Elnting, High Impedance Lead Design

Epicardial pacing typically is associated with decreased pacing and sensing capabilities compared with the endocardial approach. Since endocardial pacing is neither appropriate nor possible in all instances, this study was conducted to evaluate a new concept in a chronic epimyocardial lead design in six 3-month-old growing dogs. The new bifurcated lead (Medtronic model 10401) is a low current drain, high impedance, steroid-eluting, bipolar design. The implant is facilitated by a suture attached with an atraumatic needle. Twelve ventricular leads were implanted (2 per animal) and followed for 6 months with weekly analysis of pacing and sensing capabilities. Results at explant were compared with implant values. There were no significant differences between implant and explant in sensed R waves, or in the slew rate of the R wave in unipolar or bipolar modes. Lead impedances at explant remained high in both modes: bipolar, 1550 ± 223; unipolar, 1234 ± 262 Ω (P < 0.05). Chronic voltage (v) threshold at 0.5 msec showed no significant change from implant values during the study: unipolar, 0.4 ± 0.2 vs 0.7 ± 0.3; bipolar, 0.5 ± 0.4 vs 1 ± 0.5. Histologic evaluations of the electrode tissue interface demonstrated negligible fibrotic capsule formation. This study introduces a new, easily implanted, high impedance, low threshold, bipolar epimyocardial pacing lead design with excellent chronic pacing and sensing characteristics.     

"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.     

Stimulation Characteristics of a Steroid-Eluting Electrode Compared with Three Conventional Electrodes

Stimulation thresholds of a steroid-eluting electrode (Medtronic CapSure 4003, 9 patients) were compared with three conventional electrodes (carbon-tipped lead, Siemens-Elema 423 S/60, 10 patients; Elgiloy-tipped lead, Cordis Encor, 10 patients; platinum-tipped lead, Telectronix Laserdish 030-276, 9 patients). Voltage thresholds were determined during implantation, 1-3 days, 6 weeks, and 6 months postimplantation. No significant difference among the four electrodes was found in regard to stimulation and sensing behavior during implantation. Compared to intraoperative measurements, mean increase in voltage threshold and absolute voltage thresholds were substantially less for the steroid-eluting electrode than for the other tested electrodes 6 weeks and 6 months after implantation. The rheobasechronaxie product, a parameter of the stimulation performance of electrodes, underlined the superior pacing characteristics of the steroid-eluting electrode. To achieve low chronic stimulation threshold by pharmacological means is an attractive direction for future electrode technology.     

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 New Efficient NanoTip Lead

STOKES, K., ET AL.: A New Efficient NanoTip Lead. The ideal lead has low, stable acute and chronic thresholds, high pacing impedance, and good sensing. Leads with low, stable thresholds have been developed, but pacing impedance has been in the 600 Ω region. One way to increase pacing impedance is to decrease the electrode's surface area. The threshold performance and sensing ability of < 5 mm² electrodes have been considered questionable, up to now. We have developed α 1.5 mm² porous, platinized, steroid-eluting electrode and have demonstrated in canine studies that it has excellent performance. Chronic thresholds are low at about 0.65 ± 0.28 V (ventricular) and 0.42 ± 0.12 V (atrial) at 0.5 msec. Chronic pacing impedance is in the 1200–1300 Ω region, but mean chronic R and P wave source impedance is ≤ 1500 Ω. Sensing is excellent, with almost double the P wave amplitudes usually measured in the canine.     

Precipitous Exit Block with Epicardial Steroid-Eluting Leads

Between fanuary 1990 and October 1992, we implanted 16 steroid-eluting ventricular epicardial pacing leads (Medtronic 10295A and 10295B/4965) in 12 patients. There were 8 males and 4 females ranging in age from 3 months to 49 years (mean 8.7 ± 13.2, median 6.0years). Structural cardiac disease was present in 11 of 12 patients. Follow-up ranged from 3–73 months postimplant (mean 35.7 ± 22.3, median 28.5 months). Lead fracture (10295A) occurred in 1 of 12 patients. Of the remaining 11 patients, 8 of 11 have very low long-term pacing thresholds. Unexpectedly, 3 patients demonstrated precipitous threshold increases from 3 months to 3.5 years postimplant. Although no deaths resulted in these exit block patients, 1 of 3 exit block patients developed marked worsening of congestive heart failure. We reviewed and analyzed the data obtained at 4 weeks postimplant for all of the 10295A and 4965 patients in the entire Medtronic clinical study database. Using the criterion of a 4 week postimplant pacing threshold ≥ 0.12 ms (5 V), we found that the long-term risk of eventual exit block was 27.3% for the 10295A lead (P = 0.005) and 7.5% for the 10295B/4965 lead (P = 0.03). We, therefore, recommend that in patients implanted with the 4965 steroideluting epicardial lead, ventricular pacing thresholds ≥ 0.12 ms (5 V) measured at 4 weeks postimplant should prompt frequent threshold testing to detect late and potentially sudden ventricular pacing threshold increases.     

Clinical Experience with a New Lead Comhining Active Fixation with Steroid Elution

The Medtronic lead engineering model number 10335A represents a new concept in lead design combining active fixation with steroid elution. It aims for immediate stability and low chronic thresholds. Twenty-one leads, 9 atrial and 12 ventricular, were implanted in 13 patients (10 males, mean age 68; range 22–91 years). The atrial leads showed no rise in pulse width threshold at a voltage of 1.6 volts (mean thresholds at implant, 1, and 26 weeks; 0.1 ± 0.09 msec, 0.15 ± 0.04 msec, and 0.1 ± 0.03 msec, respectively). The ventricular leads had a small but significant rise between implant and 1 week at an output of 1.6 volts (0.07 ± 0.03 msec increasing to 0.11 ± 0.04 msec; P < 0.02) but no significant later rise (0.1 ± 0.04 msec at 2 weeks and 0.1 ± 0.05 msec at 6 months). These low chronic thresholds would allow early reprogramming of the unit to low voltages resulting in a battery saving with prolongation of the unit's life. There were no significant changes in the P and R wave amplitudes, but there was a fall in lead impedance in the ventricular leads between implantation and 1 week (P < 0.02) but none subsequently, and there was no significant change in atrial impedance. There were no sensing failures and no lead displacements. Despite impressive pacing characteristics, the study was suspended because of a high level of mechanical complications. Of the 96 patients implanted worldwide with 136 leads there were eight helix deformations, which will require redesign. However, the concept of steroid elution combined with active fixation appears to be an attractive and valid concept and is supported by this data; further studies are planned.     

Chronic Steroid-Eluting Lead Performance: A Comparison of Atrial and Ventricular Pacing

It is generally believed that atrial pacing leads have higher stimulation thresholds and long-term complication rates than ventricular leads, and this is one of the factors limiting the use of dual chamber pacing. A study was undertaken to compare atrial and ventricular bipolar tined steroid-eluting leads in two designs: the Medtronic CapSure SP and the Telectronics Encor Dec. There were 123 pairs of leads: 81 CapSure SP and 42 Encor Dec. Bipolar atrial and ventricular stimulation thresholds, electrograms. and pacing impedance were measured using the Telectronics META DDDR pulse generator immediately postimplantation, and at 1, 3, and 6 months for all leads and at 12, 18, and 24 months for the CapSure SP. The only major lead complication was a 2% atrial lead dislodgment rate. All leads demonstrated low stimulation thresholds, with the CapSure SP leads having lower values than comparable Encor Dec leads. All leads had a mean range of 0.53–0.89 V at all testing periods with P < 0.05 for atrial leads only. There were no differences in electrogram size between manufacturers and no instances of atrial and ventricular undersensing. Pacing impedance was about 100 Ω higher for the Encor Dec leads (P < 0.05, atrial leads only), suggesting that these leads will result in lower pacing energy losses provided the pulse generators are at identical settings. More than 90% of patients could be paced chronically in the atrium and ventricle at 2.5 V, but for chronic 1.6-V pacing, the CapSure SP leads were superior. In conclusion, atrial and ventricular steroid-eluting leads of both manufacturers gave excellent stimulation threshold results allowing low energy dual chamber pacing.     

Acute and Long-Term Ventricular Stimulation Thresholds with a New, Iridium Oxide-Coated Electrode

Efforts have been made to design electrodes that significantly reduce not only the acute and chronic stimulation thresholds, but also attenuate the early peaking phenomenon and polarization. At two voltage levels (2.7 V and 5.4 V, respectively), we evaluated the right ventricular stimulation thresholds obtained with a new, iridium oxide-coated electrode in ten patients who received a VVI pacemaker. Measurements were mode at implant and at multiple intervals for 1 year. Pulse width stimulation thresholds at implant were as follow: 0.04 ± 0.008 msec at 2.7 V, 0.03 ± 0.004 msec at 5.4 V; values at 2 weeks were 0.14 ± 0.06 msec at 2.7 V, 0.07 ± 0.025 msec at 5.4 V; values at 3 months were 0.09 ± 0.03 msec at 2.7 V, 0.05 ± 0.01 msec at 5.4 V; values at 1 year were 0.08 ± 0.02 msec at 2.7 V, 0.04 ± 0.01 msec at 5.4 V, The maximal increase of 0.11 ± 0.05 msec occurred at 2.7 V, 2 weeks after implant. Our results indicate that this new electrode provides low acute and long-term stimulation thresholds, as well as an attenuated early peaking phenomenon, being able to stimulate safely at 2.7 V even early after implant.     

Long-Term Performance of the Attain Model 4193 Left Ventricular Lead

Background: Cardiac resynchronization therapy (CRT) has proven to be a valuable therapy addition for patients with drug-refractory heart failure and a ventricular conduction delay. Delivery of CRT is dependent upon the successful implantation and chronic performance of a left ventricular (LV) pacing lead. This study assessed the long-term electrical performance and safety of a steroid-eluting, transvenous, over-the-wire, cardiac vein pacing lead.
Methods: The Attain Model 4193 LV lead (Medtronic, Inc, Minneapolis MN, USA) was successfully implanted in 1,070 patients with 286 patients completing 3 years of follow-up. Clinical data were collected at pre-implant, implant, and at 6-month intervals for 3 years.
Results: Over 3 years, the mean chronic pacing threshold ranged from 1.9 V to 2.1 V, the mean R-wave sensing amplitudes ranged between 13.6 mV and 15.0 mV, and the mean pacing impedance ranged between 562 ohms and 590 ohms. Additionally, the observed freedom from first post-implant LV-lead-related complications was 90.4%. Of 1,070 total patients, 82 experienced 89 LV-lead-related adverse events requiring invasive interventions or resulting in the termination of the CRT therapy. The LV lead was repositioned in 31 patients, replaced in 21 patients, and explanted/capped in four patients. There were no deaths related to the LV lead during implantation or during the follow-up period.
Conclusions: The data suggest that the 4193 LV lead is safe and effective over time. The LV lead electrical measurements remained stable through follow-up, demonstrating reliable long-term performance within the recommended value range at 36 months and had an acceptable complication rate.     

Clinical Use of Low Output Settings in 1.2-mm2Steroid Eluting Electrodes: Three Years of Experience

A new generation of tined steroid-eluding leads featuring 1.2-mm² distal electrodes (CapSure® Z, Medtronic Inc., Minneapolis MN, USA) has the potential to reduce battery current drain and enhance pulse generator longevity by means of high pacing impedance and low pacing threshold. Forty patients aged 50–87 years (mean 72.4 years) were implanted with 33 ventricular (models 4033 and 5034) and 30 atrial-J (models 4533 and 5534) leads with 1.2-mm² electrodes. Low pacing outputs, mainly in the range from 1 V/0.20 ms to 1.6 V/0.36 ms with ≥ 3:1 pulse width safety margins (PWSM) applied, were instituted at 3–6 months of implantation and adjusted at subsequent follow-up controls according to changes in thresholds. Cumulative follow-up period of low outputs was 1,512 months (24 months per lead, range 9–36 months), which involved 3.43 follow-up controls per lead (range 2–5). During follow-up, pulse width thresholds (PWTs) at the used amplitudes did not change in 55.5% of the leads; PWTs increased by ≤ 100% in 36.5%, by 101%–200% in 1.6%, and by > 200% in 6.3% of the leads. Changes in PWT that would apparently exceed 3:1 PWSM over a 1-year period occurred in one atrial lead where even the nominal 3.5 V/0.4-ms output would not be effective and in one ventricular lead in the aftermath of an acute myocardial infarction (300% PWT rise at 1.6 V). Based on the present observations, pacemaker dependent patients require ≥ 4:1 PWSM and other patients ≥ 3:1 PWSM with output pulse widths ≤ 0.60 ms and annual pacemaker clinic visits. Calculated battery current drain and anticipated longevity associated with a variety of pacing outputs and impedances are provided, compared, and discussed. Correlation between acute and chronic pacing impedances and pacing thresholds was weak, implying that a systematic intraoperative pacing site optimization cannot contribute significantly to the extension of average battery longevity.     

Clinical Surveillance of a Tined, Bipolar, J-Shaped, Steroid-Eluting, Silicone-Insulated Atrial Pacing Lead

Since 1990, 558 Medtronic 5524 bipolar, silicone-insulated, J-shaped, tined, steroid-eluting atrial leads have been implanted at the Mayo Clinic (Rochester, MN, USA) and the Midelfort Clinic (Eau Claire, WI, USA). Implantation data were favorable, with pacing thresholds at implantation (median threshold, 0.6 V) better than most published data on other atrial leads. The rate of acute lead-related complications (dislodgment and diaphragmatic pacing) necessitating reoperation or electrical abandonment of the atrial lead was 0.9%. This rate is lower than that in most published series of atrial leads. Over a median follow-up time of 17.5 months (up to 69 months), there were no chronic lead-related complications and no definite or suspected failures of lead material. This rate is much lower than that with other atrial leads studied previously. We conclude that the Medtronic 5524 atrial lead combines the reliability of silicone insulation with a lack of chronic complications and high thresholds due to its steroid elution and with stability in the atrium due to its J shape despite a passive fixation mechanism. There is no evidence of lead material failure during up to 6 years of follow-up.     

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.     

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.     

Comparison of mid-term clinical experience with steroid-eluting active and passive fixation ventricular electrodes in children

Although active fixation ventricular leads seem to have advantages over passive fixation leads, this study compares the follow-up results of active and passive fixation leads in children. We evaluated the implantation and follow-up data of 41 children with active (Accufix II DEC, group 1) (n = 20) or passive (Membrane E, group 2) (n = 21) fixation, steroid-eluting ventricular leads. All but one of the patients in group 1 completed the 12-month follow-up. The mean follow-up period in group 2 was 10.4 +/- 2.9 months (range 3-12 months, median 12 months). In both groups the mean pacing threshold was measured as 0.51 +/- 0.09 V versus 0.48 +/- 0.15 V (P > 0.05) at 0.5-ms pulse width, mean R wave amplitude as 9.9 +/- 2.5 mV versus 9.4 +/- 3.2 mV (P > 0.05), and mean impedance as 557 +/- 92 omega versus 664 +/- 160 omega (P < 0.05), respectively, at implantation. After the first week of pacing, mean threshold values in group 1 were significantly lower than those of group 2 (P < 0.01 and P < 0.05, respectively). During the follow-up period, lead impedance measurements did not show a significant difference between the two groups. In one patient from group 1, the lead (by unscrewing) was removed easily because of pacemaker pocket infection. No lead dislodgement or helix deformation occurred in group 1. Nevertheless, in one patient from group 2, the lead was extracted at 4-month postimplantation because of lead displacement. We conclude that the steroid-eluting active fixation lead (Accufix II DEC) have advantages of easier implantation and lower acute and chronic stimulation thresholds compared to the passive fixation lead (Membrane E). Therefore, Accufix II DEC is superior to Membrane E, and it is a better first choice in children with an implanted single chamber ventricular pacemaker.     

High Rate of Late Dislodgements of an Active Fixation Atrial Lead

Between May 1985 and May 1991 we implanted 115 DFH-leads as unipolar atrial leads. The active fixation mechanism of this electrode consists of two sickle-shaped anchoring hooks which are placed at a distance of 0.9 mm parallel to the distal flat end of the electrode. All leads were affixed to the free wall of the right atrium. One hundred eight leads (93.9%) were implanted for dual chamber pacing and seven leads (6.1%) for single chamber atrial pacing. Parameters measured at implantation were (mean values): stimulation threshold 1.06 ± 0.42 V at 0.5 msec pulse width, P wave amplitude 5.12 ± 2.04 mV, and lead impedance 560 ± 76.1 Ohms. Within the first week after implantation, three early dislodgements occurred (2.6%). The follow-up period averaged 30.4 ± 16.2 months (range 2–76 months). During this time, 14 late macrodislodgements (12.2%) occurred after a mean period of 18.4 months (range 2–59 months). All of them required reoperation. The active fixation mechanism of the DEH-lead appears to be unreliable, if implanted in the free wall of the right atrium for dual chamber pacing.