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Ann Thorac Surg 2004;77:1366-1370
© 2004 The Society of Thoracic Surgeons

Original article: cardiovascular

Pacing activity, patient and lead survival over 20 years of permanent epicardial pacing in children

John D. R. Thomson, MRCPa*, Michael E. Blackburn, MRCPa, Carin Van Doorn, FRCSa, Ann Nichollsa, Kevin G. Watterson, FRCSa

a Department of Congenital Cardiology and Cardiac Surgery, Yorkshire Heart Centre, Leeds General Infirmary, Leeds, United Kingdom

Accepted for publication August 28, 2003.

* Address reprint requests to Dr Thomson, Department of Congenital Heart Disease, Leeds General Infirmary, Great George St, Leeds LS1 3EX, UK
e-mail: john.thomson{at}lineone.net


   Abstract
Top
 Abstract
Introduction
 Patients and methods
 Results
 Comment
 References
 
BACKGROUND: We report on pediatric epicardial pacing activity, patient and lead survival for more than two decades in a single center.

METHODS: The data cover 96 pacing leads implanted in 59 patients. Median age at implantation was 1.9 years (1 day to 18.2 years). Forty-four percent had structural cardiac disease. Most frequent indications for pacing were postoperative (42%) and congenital complete heart block (42%).

RESULTS: Median activity was 3 pacing leads per year; 326 patient pacing years were observed (median 11.9 years; range, 1.1 to 22 years). Death due to pacemaker failure occurred in a single patient. Lead failure occurred in 33 of 96 leads (median of 28 months postimplantation) with lead fracture the commonest cause (47%). Risk factors for lead failure were decade of implant and nonsteroid eluting leads. Acute implant energy thresholds were significantly lower for steroid than nonsteroid eluting leads but did not predict subsequent lead failure.

CONCLUSIONS: The epicardial approach has offered an effective solution to pacing problems in the pediatric age range. Lead survival has improved with more than 75% of modern steroid eluting leads surviving to 5 years.


   Introduction
Top
 Abstract
 Introduction
Patients and methods
 Results
 Comment
 References
 
Permanently pacing children is challenging due to anatomical abnormalities, difficult access to cardiac chambers, and small patient size. There is an increasing trend towards endocardial pacing in younger and smaller children, driven by concerns about epicardial lead longevity and safety [1–5]. Although data exist suggesting acceptable medium term pacing characteristics with the endocardial solution, there are risks to vascular integrity particularly with unavoidable lead revision in growing children [6–8]. Epicardial system implant strategies and lead technology have both changed over recent years, but with small numbers of patients follow-up data are still lacking. We report our unit pacing activity, including data on patient mortality and lead survival spanning 20 years of epicardial pacing activity in a stable population, with a total of more than 320 patient pacing years.


   Patients and methods
Top
 Abstract
 Introduction
 Patients and methods
Results
 Comment
 References
 
Patient notes and pacing records were reviewed on all patients less than 19 years of age undergoing permanent epicardial pacing between January 1 1980 and June 31 2001 at the Yorkshire Heart Centre, a tertiary regional cardiothoracic center serving a population of 5.5 million people with stable referral patterns. During this period 88 systems and 96 pacing leads (88 ventricular, 8 atrial) were implanted in a total of 59 patients (a mean of 1.6 leads per patient). Median patient age at implantation was 1.9 years (1 day to 18.2 years). A total of 26 of 59 (44%) patients had underlying structural cardiac disease (Table 1). The indications for permanent pacing are shown in Figure 1 .


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  		Table 1. Structural Cardiac Lesions

 


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  		Fig 1. Indications for permanent pacing.

 
Pacing strategy and follow-up
Pacing strategy changed and evolved over the period of the study. Our policy was to epicardial pace all patients less than 40 kgs of weight and 10 years of age, although this strategy was not completely rigid over more than two decades with all patients considered on their own anatomical merits. An endocardial system was implanted in a single patient at 1.5 years of age, when we would have liked to avoid transvenous pacing, because of the inability to achieve acceptable epicardial thresholds as a result of scarring after multiple cardiac operations.

During the 1980s, epicardial system implantation was performed by one of the pediatric cardiothoracic team. By the second decade of the study systems were implanted exclusively by a consultant pediatric cardiothoracic surgeon, with in-theater system interrogation performed by the departmental pacing team. Ninety-five percent of pacing systems were implanted in the abdomen (below the rectus sheath). The remaining systems were subpectoral implants (3) with one system being positioned in the left pleural space.

By the second decade of the study, the follow-up was entirely in a dedicated pacing clinic run by a single consultant pediatric cardiologist. Systems were reviewed at appropriate clinical intervals (usually 6 months) and, from 1990 data on pacing and sensing thresholds, were extracted and recorded in a standard manner at each pacing clinic visit. Pacing data on older systems (before 1990) were less uniform but available in the majority of patients.

Pacing characteristics
Single site pacing was used in the majority of patients (89%). The initial pacing mode was ventricular demand pacing (VVI) or VVI with rate responsiveness in 47 of 56 (84%) patients and atrial and ventricular sequential demand pacing (DDD) or DDD with rate responsiveness in 8 of 56 (14%) patients. One patient was paced in the continuous ventricular asynchronous pacing mode.

Dual chamber pacing was gradually introduced over the latter years of the study. No strict age, size, or anatomical criteria were applied as determinants of suitability for sequential pacing. The small numbers paced sequentially reflect our strategy of keeping pacing simple, particularly in those patients with structurally normal hearts in whom we tried to avoid a sternotomy or thoracotomy for atrial wire placement. All but one patient paced with a dual chamber system had undergone prior cardiac surgery and this is reflected in the lower median age at implant of those with dual chamber systems compared with patients in whom single site pacing was utilized (4 months vs 3 years). Atrial wires were placed either via a limited sternotomy or, in those likely to require further cardiac surgery, a lateral thoracotomy to prevent lead damage at any subsequent sternotomy.

Pacing leads
Numerous pacing leads were used over the study period, most frequently the Medtronic 4965 (Medtronic, Minneapolis, MN) (steroid eluting unipolar) and the Medtronic 4968 leads (steroid eluting bipolar) (51% and 17% of leads implanted, respectively) (Fig 2). .



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  		Fig 2. Pacing leads, "other" leads (numbers in parentheses): Medtronic 4951 (3), Medtronic 4024 (2), Pacesetter 4025 (1), Medtronic 10366 (1), CPI (Guidant) 4313 (1), Cordis 325 to 452 (1). * Steroid eluting lead.

 
The strategy for lead selection changed with technological developments over the twenty-year study period. Of 96 total leads implanted during the study period, 65 (68%) were steroid eluting, with all implanted after 1991.

Our current preferred pacing strategy consists of a unipolar steroid eluting lead (Medtronic 4965) for ventricular pacing (simple to position and secure reliably) and a bipolar steroid eluting lead (Medtronic 4968) for atrial pacing, due to superior sensitivity.

Definitions
Lead failure was defined as lead fracture, displacement, exit block, or excessive-unacceptable change in pacing threshold. In order to standardize the measurement of stimulation thresholds and allow comparison of the many systems interrogated over two decades, we used the previously reported minimum energy threshold (MET) derived from the formula: [9]

Statistics
The {chi}2 and Fischer's exact tests were used for categorical variables. The Mann-Whitney U test was used to compare independent groups. Lead system and patient survival were assessed using the Kaplan-Meier model, and logistic regression using the Cox proportional hazards model to assess confounding variables. The GB stat (version 6.5, Dynamic Microsystems, Silver Spring, MD) was used for all statistical calculations).


   Results
Top
 Abstract
 Introduction
 Patients and methods
 Results
Comment
 References
 
A total of 326 patient pacing years were observed during follow-up, with a median 11.9 years (range, 1.1 to 22 years).

Pacing activity
There was a gradual but statistically insignificant increase in the overall numbers of pacing leads implanted per year (median 3 per year) over the study period (Fig 3). .



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  		Fig 3. Unit epicardial pacing activity 1980 to 2001.

 
Patient survival
There were no deaths directly related to pacemaker insertion. Seven deaths (7 of 59 patients, 95% confidence interval [CI] 2.1 to 11.7) occurred at a median of 1 month (0.2 to 55 months) post pacemaker implantation. Five patients died soon after surgery for congenital heart disease complicated by complete heart block, and one patient after ventricular septal defect (VSD) closure and pacemaker insertion for congenital complete heart block in the context of congenitally corrected transposition. Pacemaker dysfunction was not implicated in any of these cases.

Sudden unexplained death occurred in one patient 55 months after insertion of an abdominal VVI system (Medtronic 4965 lead and Prodigy generator) for congenital complete heart block. The patient was brought into his local hospital in electromechanical dissociation and resuscitation was unsuccessful. Although subsequent interrogation showed the generator to be functioning normally and recent follow-up (6 weeks before death) had demonstrated acceptable and stable pacing thresholds (2V at 0.5 ms, MET 5.71, lead impedance 350 {Omega}) death was presumed to be due to sudden exit block.

Lead characteristics
Median time to follow-up (or lead failure) for individual pacing leads was 42 months (1 to 190 months). Acute pacing thresholds were significantly lower for steroid eluting (median MET 0.68 µJ, 0.09 to 16) than nonsteroid eluting leads (median MET 1.37 µJ, 0.06 to 5, p = 0.05), and there was no significant difference in implant lead impedance between the groups, median 410 {Omega} (range, 330 to 1823) and median 380 {Omega} (range, 370 to 800) for steroid and nonsteroid eluting leads, respectively.

Consistent data were not available to allow comparison of one-year thresholds between steroid and nonsteroid eluting leads. Pacing stimulation thresholds in those steroid eluting leads in which data were available (85%) showed a median MET of 1.9 µJ (range, 0.2 to 4.3) at 12-month follow-up.

Lead survival was 87%, 81%, and 66% for the whole group, 77%, 73%, and 50% for the nonsteroid eluting leads, and 92%, 86%, and 76% for the steroid eluting leads at 1, 2, and 5 years, respectively. Lead survival was significantly better for the steroid eluting versus nonsteroid eluting leads (Kaplan-Meier curve; Fig 4). .



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  		Fig 4. Kaplan-Meier survival curve, steroid eluting and nonsteroid eluting leads.

 
No significant difference in MET at implantation was observed between steroid eluting unipolar and bipolar leads (Medtronic 4965 and 4968, respectively). Although no lead failures were observed in the Medtronic 4968 leads, follow-up times were short (median 5 months; range, 1 to 26) compared with the Medtronic 4965 (median follow-up 54 months; range, 8 to 95). No statistically significant difference for lead survival was observed between these groups. Sequential pacing was maintained in all 10 patients originally paced in the DDD or DDDR mode but follow-up times were short (median 2 years; range, 6 months to 7 years).

Lead failure
Lead failure occurred in 33 of 96 leads (34%, 95% CI 24 to 42) at a median of 28 months (range, 1 to 190) postimplant. The causes of lead failure are shown in Table 2. One patient had a pacing lead replaced following a significant generator infection in association with rising thresholds; although infection was the primary reason for system revision, pacing lead function was also a concern and therefore this was considered as lead failure in the analysis.


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  		Table 2. Causes of Lead Failure

 
Risk factors for lead failure by the Cox proportional hazards model were nonsteroid eluting leads (p < 0.05) and earlier decade of implant (p = 0.02). Neither lead position (atrial or ventricular), replacement lead implantation, patient age, nor acute threshold at implantation were statistical risk factors for lead failure.


   Comment
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
References
 
Data on the long-term outcome after any form of pacing in children is still very limited. A number of often quoted studies of epicardial pacing report either small numbers of children or therapy using equipment from a different era [2–5]. Fears about lead fracture and high pacing thresholds leading to frequent battery depletion and exit block have led to the increasing use of endocardial pacing in the pediatric population [10–12]. However, the endocardial approach is not without problems and although less invasive than epicardial pacing, vascular obstruction, atrioventricular valve integrity, and the risks of lead extraction are all ongoing concerns [6–8, 13]. Ultimately patient safety should be the primary objective and this study, including data from a period that would now be considered historical, shows that an epicardial pacing strategy has worked well in more than two decades of therapy and, most importantly, is safe. Using our criteria for epicardial pacing we resorted to an endocardial system in a single patient (1.5 years of age) due to postsurgical scarring and in 326 patient years of pacing we experienced a single death likely due to pacing failure.

Our strategy has been to keep epicardial pacing simple, reflected in the high proportion of patients with single site pacing compared with other recent reports [14, 15]. Although options for upgrading a single site system are clearly limited during generator exchange this strategy avoids the use of a sternotomy or thoracotomy for insertion of the atrial electrode.

Because of normal intracardiac anatomy it is particularly tempting to advocate an endocardial approach in those patients with congential complete heart block regardless of size. However, an epicardial approach in these patients requiring pacing during early childhood allows the gradual replacement of expiring epicardial systems with sequential endocardial implants at an appropriate patient size. A 10F endocardial pacing lead (VDD, our endocardial pacing mode of choice) can then be inserted with no anxiety about prior venous occlusion or need for subsequent lead replacement. To date, 14 patients from this cohort have undergone such an upgrade with no complications.

There are growing data showing excellent pacing thresholds at acute implantation with steroid eluting leads [9, 14–16]. We report similar acute pacing thresholds and lead survival with epicardial steroid eluting leads to 5 years as found by Cohen and colleagues [14]. There are conflicting comparative data on steroid eluting epicardial versus endocardial pacing thresholds at both implant and subsequent follow-up [15–17]. Although Udink Ten Cate and colleagues [15] reported superior short-term pacing characteristics in favor of endocardial leads, the significance of this is unclear as it did not translate into improved system survival. Other authors have failed to show any difference [16, 17]. Our survival figures for steroid eluting leads (76% at 5 years) are broadly comparable to those achieved after the endocardial approach, implying similar long-term energy consumption [12, 18]. The only statistically significant predictor of lead survival other than steroid eluting lead technology was, not surprisingly, decade of implant. A team approach, including follow-up by a consultant electrophysiologist in a dedicated clinic and implantation by an experienced surgeon with in-theater system interrogation, has undoubtedly contributed to improved lead survival. Although reported in a previous study we were unable to demonstrate that higher early thresholds predicted subsequent lead failure [14].

Although increasing in frequency, permanent pacing in children remains a relatively rare procedure. In our medium sized unit in the UK (serving > 5 million population) we implanted a median of 3 systems per year in pediatric patients by our judgment unsuitable for endocardial pacing and in 2 years none at all. Within this group a small number had anatomy that would have made endocardial pacing impossible, leaving a lesser number of cases potentially suitable for the endocardial approach. These patients are the most technically challenging for any electrophysiologist, demanding a high level of skill and experience. The relative rarity of these cases makes it difficult to acquire and maintain experience. Most children requiring pacing will be pacemaker dependent for the rest of their lives. The aim is a lifetime of pacing with minimum patient risk avoiding complications likely to prejudice later therapy. A pacing strategy including an epicardial approach in younger, smaller, and anatomically difficult children achieves this.


   References
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
 References
 

  1. Henglein D., Gilette P.C., Shannon C., et al. Long term follow up of pulse width threshold of transvenous and myoepicardial leads. PACE 1984;7:203-214.
  2. Williams W.G., Hesslein P.S., Kormos R. Exit block in children with pacemakers. PACE 1986;4:478-489.
  3. Serwer G.A., Mericle J.M., Armstrong B.E. Epicardial ventricular pacemaker longevity in children. Am J Cardiol 1988;61:104-106.[Medline]
  4. Beder S.D., Kuehl K.S., Hopkins R.A., et al. Precipitous exit block with epicardial steroid eluting leads. PACE 1997;20:2954-2957.
  5. Villafane J., Austin E. Cardiac pacing problems in infants and children: results of a 4-year prospective study. South Med J 1993;86:784-788.[Medline]
  6. Gillette P.C., Zeigler V., Bradham G.B., et al. Pediatric transvenous pacing: a concern for venous thrombosis?. PACE 1988;11:1935-1939.
  7. Figa F.H., McCrindle B.W., Bigras J.L., et al. Risk factors for venous obstruction in children with transvenous pacing leads. PACE 1997;20:1902-1909.
  8. Madigan N.P., Curtis J.J., Sanfelippo J.F., et al. Difficulty of extraction of chroncially implanted tined ventricular endocardial leads. J Am Coll Cardiol 1984;3:724-731.[Abstract]
  9. Hamilton R., Gow R., Bahoric B., et al. Steroid eluting leads in pediatrics: improved epicardial thresholds in the first year. PACE 1991;14:2066-2072.
  10. Till J.A., Jones S., Rowland E., et al. Endocardial pacing in infants and children 15 kg or less in weight: medium-term follow-up. PACE 1990;13:1385-1392.
  11. Sachweh J.S., Vazquez-Jimenez J.F., Schondube F.A., et al. Twenty years experience with pediatric pacing: epicardial and transvenous stimulation. Eur J Cardiothorac Surg 2000;17:455-461.[Abstract/Free Full Text]
  12. Lau Y.R., Gillette P.C., Buckles D.S., et al. Actuarial survival of transvenous pacing leads in a pediatric population. Pacing Clin Electrophysiol 1993;16:1363-1367.[Medline]
  13. Byrd C.L., Schwartz S.J., Hedin N. Intravascular techniques for extraction of permanent pacemaker leads. J Thorac Cardiovasc Surg 1991;101:989-997.[Abstract]
  14. Cohen M.I., Bush D.M., Vetter V.L., et al. Permanent epicardial pacing in pediatric patients: seventeen years of experience and 1200 outpatient visits. Circulation 2001;103:2585-2590.[Abstract/Free Full Text]
  15. Udink Ten Cate F., Breur J., Boramanand N., et al. Endocardial and epicardial steroid lead pacing in the neonatal and paediatric age group. Heart 2002;88:392-396.[Abstract/Free Full Text]
  16. Beaufort-Krol G.C., Mulder H., Nagelkerke D., et al. Comparison of longevity, pacing, and sensing characteristics of steroid-eluting epicardial versus conventional endocardial pacing leads in children. J Thorac Cardiovasc Surg 1999;117:523-528.[Abstract/Free Full Text]
  17. Dodge-Khatami A., Johnsrude C.L., Backer C.L., et al. A comparison of steroid-eluting epicardial versus transvenous pacing leads in children. J Card Surg 2000;15:323-329.[Medline]
  18. Esperer H.D., Singer H., Riede F.T., et al. Permanent epicardial and transvenous single- and dual-chamber cardiac pacing in children. Thorac Cardiovasc Surg 1993;41:21-27.[Medline]



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