Epicardial ventricular pacemaker electrode longevity in children

EpicardialVentricularPacemakerElectrodelongevity in Children GERALD A. SERWER, MD, JANE M. MERICLE, BSN, RN, and BRENDA E. ARMSTRONG, MD

While epkxrdially implanted electrodes remain the most wMely used in chiktren for ventricular pacing, their expected longevity remains unknown. The kmgevity of 126 such elect&es implanted from January 1870 through December 1065 was evaluated in 61 chiklren foftowed up for 1 to 192, months (median 63). Age at Mtial implant was 1 day to 16 years. Each chikl had from 1 to 5 electrodes tmplanted; 65 eledrodes were of ths sutureless helical type and 41 were of the suture-fixated type. Electrode fatkrre, defined as loss of capture with a high’ pacing thmshokl found at operation or sensing failure, occurred in 36 electrodes from 1 to 157 months postimplant (median 37). Mode of failure was high threshold with high impedance (n = 15), low impedance (n = 6), complete inability to pace

(n = 6), senstng failure (n = 2) or high threshokl with no measure of impedance (n = 7). Actuarial life table analysts of electrode longevity showed a 66 f 3% (standard error of the estimate) survival rate at 6 months with no stgntfkant decrease until 53months(75f5%,p<0.05).lherewasthena gradual steady decrease to 49 f 7% by 101 months. From 101 to 157 months no signtftcant decrease occurred. Survival rate decrease was greatest within the first 6 month period postimplant (-12%). Electrodes survtvtng to 6 months are highly likely to survive until 53 months. of those survivhg to 53 months, 74% should survive to 120 months. (Am J Cardid 1966;61:104-106)

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ardiac pacing presents unique problems in children not seen in adults. A major concern is pacing system longevity. The increased life expenctancy of children with pacemakers compared with the adult with a pacemaker,l makes system longevity exceedingly important. Pacing system longevity is a function of both pulse generator life and pacing electrode life. Therefore, pacemaker electrode longevity is an important concern if proper patient management is to be provided. Because most pacemaker electrodes used in children are implanted epicardially, this study was confined to only such electrodes. Previous studies of epicardial electrode longevity in both adults and children have been conflicting and have been difficult to apply to the clinical setting. Estimates of longevity

have ranged from 88% survival to 39 months to 58.70 to 108 months.2-7 This study evaluates long-term electrode longevity using the actuarial life table method to study survival rate changes with time from implant, and clarifies the apparent discrepancy in epicardial electrode longevity estimates.

Methods

From the Division of Pediatric Cardiology, Department of Pediatrics, Duke University Medical Center, Durham, North Carolina. This study was supported in part by grant HL11307 from the National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland. Manuscript received May 26, 1987; revised manuscript received September 4, 1987,and ac-

cepted September 5. Address for reprints: Gerald A. Serwer, MD, Box 0204, F1126, C. S. Mott Children’s Hospital, University of Michigan Medical Center, Ann Arbor, Michigan 48109. 104

Patient population: From January 1970 to December 1985, 81 children underwent implantation of 126 electrodes with the age at initial implant 1 day to 18 years. The median age for all electrode implants was 7 years. Each child underwent implantation of 1 to 5 electrodes. Initial indication for pacemaker implantation was surgical complete heart block in 48 children, sick sinus syndrome in 17 and congenital complete heart block with symptoms of low cardiac output in 16. Structural heart disease was present in 76, and all had undergone cardiac surgery at some time before the initial pacemaker implant (Table I). Follow-up of each child was from 1 to 192 months (median 63). Electrode characteristics: Electrodes implanted were of 2 types; 41 were of the suture-fixated type inserted into the myocardium via a stab wound in the muscle and sewn to the epicardial surface, and 85 were of the helical type that were screwed into the

January 1, 1988

myocardium not requiring a prior stab wound. All electrodes were connected to a pulse generator implanted in an abdominal pocket. Thresholds of 88 electrodes were measured at initial implant using either a Medtronic 5300 or 5311 Pacing System Analyzer. Voltage, current and impedance at threshold were measured at a pulse width of 0.5 ms. Early electrodes had thresholds determined only in terms of a minimum current required to pace with impedance not determined. An electrode was accepted if the voltage threshold was 5 mV in all cases. An existing electrode was considered to have failed if 100% capture could not be obtained at any programmable setting of the implanted generator or if proper sensing could not be obtained at any programmable setting. In addition, electrode thresholds were measured at operation to confirm electrode failure. Statistical analysis: Electrode survival rate analysis was performed using the method of Cutler and Ederer.8 Functioning electrodes electively removed from service when a patient was converted from an epicardial system to a transvenous system were classified as lost to follow-up rather than failed. Electrodes lost due to patient death were also classified as lost to follow-up rather than failed unless electrode failure before death was documented. This assumed that the survival rate of electrodes in patients dying or lost to follow-up was the same as in patients not dying.s Standard errors of the survival rate estimates (SEE) were calculated as discussed by Cutler and Ederer.E Statistical comparison of survival rates was performed following the method of Colton Significant differences were inferred at p <0.05.

Results During the study period, 38 electrodes failed from 1 to 157 months postimplant (median 37); 34 were lost to follow-up from 1 to 156 months after implant (21 by death in 18 patients, 7 due to conversion to endocardial electrodes at the time of generator replacement and 6 lost to follow-up). Fifty-four electrodes were functioning properly at the end of the study period, and were in service from 2 to 145 months (median 69). Electrode failure was due to a high threshold with a high electrode impedance in 15, high threshold with a low measured impedance in 6, complete inability to pace in 8 (2 of which had become avulsed from the epicardium), sensing failure in 2 and a high pacing threshold but no measure of electrode impedance in 7. No specific electrode type was associated with a specific mode of failure, and there was no correlation of failure mode with time. Actuarial life table analysis of electrode survival (Figure 1) showed a survival rate of 88 f 3% (SEE) at 6 months. This was the largest decrease in survival rate for any 6-month period during the observation period.

THE AMERICAN

TABLE I

JOURNAL

OF CARDIOLOGY

Volume 61

105

Patient Diagnoses

Diagnosis

No.

Ventricular septal defect D-transposition of the great arteries Tetralogy of Fallot Wolff-Parkinson-White syndrome L-transposition of the great arteries Congenital heart block with no structural heart disease Atrioventricular septal defect Single ventricle Total anomalous pulmonary venous return Double-outlet right ventricle Aortic valve replacement Tricuspid valve replacement Atrial septal defect

18 15 12 7 7 5 5 3 2 2 2 2 1

By 12 months 85 f 3% were still functioning properly (p >0.05). The survival rate did not show a statistically significant decrease until 53 months (4.5 years) when the survival rate had decreased to 75 f 5%. From 53 months to 101 months (8.5 years), there was a gradual steady decrease in the survival rate with the 50% survival rate reached by 100 months. There was no change from 101 to 120 months (10 years). The average rate of survival rate decrease from 53 to 120 months was 0.4%/month. There was no further statistically significant decrease to the end of the study period with the survival rate being 44 f 8% by 157months (13.1years). Thus, 3 major time periods were identified. There was a marked decrease in survival rate during the first 6 months. Next, there was a plateau phase with no significant decrease in the survival rate until 53 months. Subsequently, there was a gradual decrease in survival rate to the end of the observation period.

Discussion The data presented show good longevity for epicardial ventricular pacing electrodes. Simon et a12 showed a slow but steady decrease in electrode survival rate in children after a large decrease in the first 12’ months. This is in agreement with our data, but Simon et al showed a 50% survival rate by 62 months com-

ELECTRODE

0

48

LDNGEVITY

Months

Isa

96

FIGURE 1. Actuarial survival rate versus time. Brackets standard error of the estimate.

represent

1

106

ELECTRODE LONGEVITY

IN CHILDREN

pared with 100 months in our series. Estes et al3 showed a better longevity with a 3.5year survival rate of 70% compared with an 80% survival rate in our experience. Ennker et al4 reported only 12 electrode failures in 49 children during a follow-up period of 2 to 140 months. In the adult patient, most reports found epicardial electrode survival rates comparable to those in our series. Korhonen et al5 found a 78% survival rate at 3 years while Magilligan et al6reported only 6 electrode failures 5 to 27 months postimplant in 50 patients. Lawrie et al7 reported a failure rate of only 3.9% at 39 months for patients in whom there had been no previous electrode failures. In a smaller series of 32 patients with a prior electrode failure, there was a higher failure rate with 25% failing over an unspecified time.7 Oldershaw et allo also reported that 25% of electrodes required replacement by 6 years. The larger series tended to agree with the longevity reported by us, whereas smaller series tended to show lower longevity rates. The most common mode of failure was an elevated threshold with a high electrode impedance. This was thought due to fibrosis around the stimulating portion of the electrode or “exit block” and was seen in both early and late failures. There was no correlation of exit block frequency with time from implant. A high rate of exit block in children was also found by Williams et aIll necessitating 14 of 37 reoperations. Szabo and Solti12found, in dogs, tissue necrosis, cell infiltration and fibrosis around the electrode with the degree of threshold increase correlating with the degree of tissue reaction observed. The second largest group of electrode failure was electrodes that would not pace at any output of the pacing system analyzer. This was thought to be due to either electrode fracture within the myocardium, electrode avulsion from the myocardium, or fracture within the wire between the electrode and pacing generator. Electrode avulsion from the myocardium was domented in only 2 of our patients while wire fracture was documented by x-ray in only 2 others. Fracture of the electrode within the myocardium was postulated by Parsonnet et alI3 to be due to the high stressimposed on the electrode by the contracting muscle, particularly if the electrode traversed several muscle layers oriented in different directions, imposing opposing forces on the electrode. Fractures of the electrode wire were also reported by Parsonnet et ali3 and were found to occur randomly with time. The likelihood of wire fracture increased in their series as the number of bends along the course of the electrode wire increased. They also found wire fracture rate to vary depending on the metal alloys used in the electrode. Shearin and Flemingi noted a 15% incidence of electrode fracture, all occurring at the point the electrode crossed the costal margin, supporting Parsonnet’s theory. Ector et ali5 found 6 electrode fractures among 20 electrode failures. Hayes et a1,16in a series of 22 children, noted only 1 electrode fracture, while Ennker et a14 reported only 2 electrode fractures among 12 failures.

The last major group of electrode failure consisted of electrodes that had a high threshold but a low electrode impedance thought due to either insulation fracture or erosion of the stimulating portion of the electrode into the ventricular cavity. While insulation problems with polyurethane endocardial electrodes are well described,17epicardial electrodes appear to be less affected, presumably, at least in part, because of the use of different polymers for the insulation. Hayes et all6 reported an insulation fracture in 1 patient with an epicardial electrode while Ector et all5 reported 3 insulation fractures. An insulation fracture cannot be distinguished from tip erosion into the ventricular cavity solely from measurement of electrode impedance as both create a low impedance circuit. Long-term follow-up of patients with a pacemaker requires evaluation of electrode characteristics as well as evaluation of battery reserves.Electrode evaluation is mandatory and in our practice consists of: (1) determination of the minimum pulse width necessary to pace at a minimum of 2 amplitudes: (2) determination of the electrode impedance; and (3) measurement of the intrinsic QRS amplitude seen by the pulse generator in the non-pacemaker-dependent patient. These procedures allow close monitoring of the tissue-electrode interface and the electrode itself. As the electrode survival rate gradually but steadily decreases beyond 4.5 years, such procedures are as necessary as checking battery reserves.

References 1. Serwer GA, Mericle JM. Patient and generator longevity in patients aged 1 day to 18 years. Am J Cardiol 1987;59:824-827. 2. Simon AB. Dick M II, Stern AM, Behrendt DM, Sloan H. Ventricular pacing in children. PACE 1982;5:838-844. 3. Estes NAM III, Salem DN, Isner JM, Gamble WJ. Permonent pacemaker therapy in corrected transposition of the great arteries; analysis of site of lead placement in 48 patients. Am J Cardiol 1983;52:1091-1097. 4. Ennker 1. Steamann TH. Luhmer I. Oelert H. Risks and benefits , of, cardiac pacing in children. Jnt J Cardiol 1985;8:125-134. 5. Korhonen U, Karkola P. Takkunen 1. Pokela R. One turn more: threshold superiority of 3-turn versus l-turn screw-in myocardial electrodes. PACE 1984;7:678-682. 6. Magllligan DJ, Hakimi M, Davila JC. The sutureless electrode: comparison with transvenous and sutured epicardia1 electrode placement for permanent pacing. Ann Thorac Surg 1976;22:80-88. 7. Lawrie GM, Seale JP, Morris GC. Howell JF, Whisennand HH, DeBakey ME. Results of epicardial pacing by the left subcostol approach. Ann Thorac Surg 1979:28:581-587. 8. Cutler SJ,Ederer F. Maximum utilization of the life table method in analyzing survival. J Chronic Dis 1958;8:699-712. 9. Colton T. Statistics in Medicine. Boston: Little Brown, 1974:248-249. 19. Oldershaw PJ, Sutton MG. Ward D, Jones S, Miller GAH. Ten-year experience of 359 epicardia1 pacemaker systems: complications and results. CIin Cordiol 1982;5:515-519. 11. Williams WG. Izukewa T, Olley PM. Trusler GA, Rowe RD. Permanent cardiac pacing in infants and children. PACE 1978;1:439-447. 12. Szabo Z, Solti F. The significance of the tissue reaction around the electrode on the late myocardiol threshold. In: Schaldach M. Furman S, eds. international Symposium on Advances in Pacemaker Technology. New York, Springer-Verlog. 1975:273-281. 13. Parsonnet V. Gilbert L, Zuker IR. The natural history of pacemaker wires. J Thorac Cardiovasc Surg 1973:65:315-322. 14. Shearin RPN, Fleming WH. Fourteen years of implanted pacemakers in children. Ann Thorac Surg 1978:25:144-147. 15. Ector H, Dhooghe G. Daenen W. Stalpaert G. van der Hauwaert L, de Geest H. Pacing in children. Br Heart I 1985:53:541-546. 16. Hayes DL, Holmes DR. Maloney JD, Neubauer SA, Ritter DG, Danielson GK. Permanent endocardial pacing in pediatric patients. J Thorac Cardiovasc Surg 1983;85:818-624. 17. Byrd CL, McArthur W, Stokes K, Sivina M. Yahr WZ. Greenberg J. Implant experience with unipolar polyurethane pacing leads. PACE 1983:8:888-

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