Ventricular Pacing in Children

Ventricular Pacing in Children

ARTHUR B. SIMON, MACDONALD DICK II, AARON M. STERN, DOUGLAS M.BEHRENDT, and HERBERT SLOANFrom the Sections of Pediatric Gardiology and Thoracic Surgery, G.S, Mott Ghildren's Hospital, and the Divisionof Gardiology and the Departments of Pediatrics, Surgery and Internal Medicine, University of Michigan MedicalGenter, Ann Arbor, Michigan

SIMON, A.B., ETAL.: Ventricular pacing in children. Ventricular pacing was performed in forty-onechildren ranging from one day to twenty years of age (median age = 10]. Weight of the recipient atimplant ranged from 2 kg. to 86 kg. Indications included presyncope, syncope, dyspnea on exertion,congestive heart failure, postoperative infra-Hisian heart bJocJt, and inadequate cardiac rate duringpharmacotherapy. Four patients died during foJJow-up, but no deaths were attributable to pacemakermanagement. In contrast, 66% of the patients required more than one pacemaker reJated-operativeprocedure, and 43% of leads implanted failed by 48 hours. Indications for permanent cardiac pacing inthis population at this time are symptomatic congenital AV block, symptomatic sinus node disease, andAV block in the postoperative period. Technological developments which might reduce complicationsseen in this population and electrophysiologic techniques which may better define indications for pac-ing in children are also reviewed. (PACE, Vol, 5, November-December, 1982}

ventricular pacing, congenital AV block, sinus node disease, postoperative AV block

Permanent pacemaker implantation for the pal-liative treatment of atrioventricular block andsinus node disorders in children is an acceptedtreatment modality. It is the purpose of this re-port to review our experience with this tech-nique in the pediatric population, to report ourexperience with epicardial lead longevity inchildren, and to compare it with lead perfor-mance reports in adults, to present our policy forpacemaker implantation in children, and to re-view recent advances particularly relevant topacemaker management in children.

Materials & Methods

The records of all patients under the age oftwenty-one who required permanent ventricu-lar pacing at the CS, Mott Children's Hospital orthe University Hospital of the University ofMichigan Medical Center from January 1, 1962through December 31,1979 were reviewed. Data

Address for reprints: Macdonald Dick II, M,D,, Section ofPediatric Cardiology, F1123, CS, Mott Children's Hospital,University of Michigan Medical Center, 1405 E, Ann Street,Ann Arbor, MI 48109

Received October 1, 1981; revised November 11, 1981 andJanuary 26, 1982; accepted January 29, 1982,

were summarized on precoded forms for subse-quent computer analysis using methods pre-viously described,'"'' The clinical indication forpacing, the time course relative to prior cardiacoperative procedures, the nature of the asso-ciated cardiac malformations, the frequency ofall cardiovascular operative procedures, and theincidence of pulse generator and lead com-plications were analyzed.

During the eighteen years of this study ad-vances in surgical technique and availabledevices, as well as evolving clinical criteria forpacemaker implant, undoubtedly influenced theclinical course of these patients.

Surgical techniques evolved during the peri-od of the study; four cardiovascular surgeonsperformed the implantation and, therefore, con-siderable variability in the specific techniqueemployed is to be expected. The patients werepaced with either General Electric,* Med-tronic,f Cordis,:}: Cardiac Pacemaker,** orCoratomic*t pulse generators through General

*Ceneral Electric, New York, New York, U,S,A,fMedtronic, Inc, Minneapolis, Minn,, U,S,A,

^Cordis Corp., Miami, Florida, U,S,A,**Cardiac Pacemaker, Inc., St, Paul, Minn., U,S,A.*tCoratomic, Inc., Indiana, Pa,, U,S,A,

836 November-December 1982 PAGE, Vol, 5

VENTRICULAR PACING IN CHILDREN

Electric, Medtronic, Cardiac Pacemaker, orCordis leads.

For the determination of lead performance,the status of both active and redundant leads im-planted after 1965 on which threshold data wereavailable was tabulated and an actuarial curvecalculated. Lead performance was calculatedfrom the day of implant to the day of failure orend of the follow-up period, December 31,1980.Failure was defined as a chronic thresholdgreater than 5 volts either due to lead fracture orhigh threshold ("exit block").

Since 1978 electrophysiologic study has beenused to identify the site of block in patients withatrioventricular conduction disturbances, and toevaluate sinus node function in patients with theclinical manifestations of sick sinus syndrome.

ResultsFrom 1962 through 1979 forty-one children

between tbe ages of one day to twenty years(median age = 10 years) received a permanentpacemaker at our institution. There weretwenty-four females and seventeen males. Theweight at implant ranged from 2 kg. in a six-day-old boy to 86 kg. in an eighteen-year-old man.Clinical indications for pacemaker implant atour institution were revised periodically duringthe study period. Cardiac symptoms such as pre-syncope, syncope, dyspnea on exertion, and con-gestive heart failure, as well as the associationof other congenital heart defects, in the pres-ence of inadequate impulse formation and/orimpaired atrioventricular conduction, served asthe major impetus for pacemaker implant in 39of the 41 patients. The remaining two patientsreceived pacemakers to preserve an adequatecardiac rate during anti-arrhythmic pharmaco-therapy.

A summary of the clinical diagnoses is pre-sented in Table I. Within the nonsurgical group.

Table I.

Clinical Diagnoses

I. Non-Surgical GroupA. Sinus node disease (symptomatic)

1. Sinus bradycardia2. With ventricular arrhythmias

B. Atrioventricular block1. Second degree type I2. Complete atrioventricuiar biock3. Complete atrioventricular block with other cardiac defect

Atriai septal defect 2Patent ductus arteriosus 2L-transposition of the great arteries 1

4. Compiete atrioventricuiar biock, iate

TOTAL

Post-operative GroupA. Sinus node disease

1. Endocardial Cushion Defect2. D-transposition of the great arteries

B. Compiete Atrioventricuiar Block (symptomatic)Tetraiogyof FaiiotD-transposition of the great arteriesVentricular septai defectAtriai septai defect (secundum type)Endocardiai cushion defectSingieventricieEbstein's anomaiyAortic valve replacement (traumatic aortic rupture)Tricuspid atresia

TOTAL

1

13

22

764121111

28

PACE, Vol. 5 November-December 1982 837

SIMON, ET AL.

three patients had symptomatic sinus brady-cardia, two associated with ventricular arrhyth-mias. Ten patients exhibited disturbances inatrioventricular conduction, five associatedwith congenital heart defects. The age at im-plant in the non-surgical group was bimodalwith seven children under three years of ageand six over eleven years of age at initialimplant.

Twenty-four of the twenty-eight patients inthe surgical group required pacing for completeatrioventricular block acquired at operation;four patients required pacemaker support forsymptomatic surgically related sinus node dis-ease, either because of bradycardia or for sup-pressive pharmacotherapy of tachyarrhyth-mias. Twenty-five of the patients have receivedtheir initial implant since 1971 whereas theother 16 were initially paced prior to 1971.Although eighteen of twenty-eight post surgicalpatients [seventeen with AV block and one withsinus node dysfunction) received their pace-makers within one year of the repair of theirstructural heart disease, ten of these withinthirty days, the remaining ten (seven with AVblock and three with sinus node dysfunction)did not require pacing until much later, five notuntil eleven or more years after operation.

Among the ten patients who developed com-plete heart block following operation but werenot immediately paced, nine did not become suf-ficiently symptomatic to warrant pacing untilone month to five years following operation. Theother patient developed transient atrioven-tricular block which resolved within two weeksonly to return ten years later.

Two patients in whom complete atrioven-tricular block developed following surgery butwere not immediately paced, demonstratedsupra-Hisian block (within the atrioventricularnode) at electrophysiologic study, and requiredpacemaker placement because of symptoms(syncope in one, and dyspnea on exertion with afixed heart rate in the other). Two additional pa-tients have surgical heart block and have notbeen paced—one is asymptomatic and hassupra-Hisian block on electrophysiologic study,and a second is well but refused study and pace-maker implantation.

Operative Procedures

The major and minor cardiac and pacemakerrelated surgical procedures performed in thisgroup of patients are tabulated in Table ILTwenty-five of the forty-one patients required

Table II.Frequency of operative procedures required for both Intracardiac repair and pacemaker reiated indicationsduring the study intervai 1962-1979. Pacemaker and cardiac procedures were not necessariiy separate. Thetotais are derived by determining the product of numbers of patients who required the specified number of

procedures.

Number ofPatients

123456

TOTAL

Number ofThoracotomies

Performed

1566611

80

Number ofPacemakerProcedures

(Pulse GeneratorReplacementsand Implants)

16114213**

85

Total Cardiacand Pacemaker

Procedures

4153753*

119

* One required 6, one required 7 and a third 10.** Two required 6, one required 10.

838 November-December 1982 PACE, Vol. 5


more than one pacemaker-related operativeprocedure; six required four or more. Eightythoracotomies have been performed amongthese forty-one patients either for surgicalrepair of the congenital heart defect or for car-diac pacing. When both pacing and cardiac pro-cedures are combined, half the patients havebeen operated upon three or more times.

Implantation Techniques & CompJications

The epicardial lead placement approach wasused as the initial mode of pacing in thirty-eightof the forty-one patients, and the transvenousapproach was used initially in three. One pa-tient was converted to transvenous pacing aftermultiple lead failures with the epicardial tech-nique. The manufacturer and lead modelsutilized, and the frequency and mode of leadfailure are tabulated in Table III. Epicardialleads were implanted in the left ventriclethrough a lateral or anterolateral thoracotomy.Although thresholds were measured with dif-ferent devices during the study interval, acutethresholds were accepted if less than 1 mV.Twenty of the 74 leads utilized were of the"sutureless" type and the remainder were myo-cardial plunge electrodes from four differentmanufacturers. The most commonly used lead,the Medtronic Model 5913, has undergone seven

manufacturing modifications from 1972 to 1979without model disignation change.*

During the study period the frequency ofmyocardial lead failure has been high (TableIII]. Longevity data are available on fifty-eightmyocardial leads from four different manufac-turers placed in thirty-five patients since 1965.Actuarial analysis reveals that only 75% of theleads were functioning 12 months after implant,68% at 24 months after implant, and only 57% at48 months after implant (Fig. 1]. Thereafter onlyone additional myocardial lead has failed dur-ing the follow-up interval. Ten of the sixteenhigh threshold lead failures occurred in threepatients. There was no significant lead failuredifference since that date.

Our experience with transvenous pacing hasinvolved only four patients. Two adolescents re-ceived transvenous right ventricular endocar-dial pacing systems ten years after cardiacrepair (Tetralogy of Fallot in one, and atrial sep-tal defect, secundum in the other] and are welltwo years later. The third patient is reinarkablefor duration of the lead system. She received herinitial epicardial pacemaker in 1962 at age fivebecause of symptomatic complete heart blockfollowing ventricular septal defect repair. Shewas converted in 1965 to a transvenous pacing

*Medtronic Corporation—Personal communication.

Table III.

Epicardial lead performance in 35 of the 41 patients over the follow-up period after 1964. Five transvenousleads which have all functioned normally for < 1 to > 16 years are not included.

Status

Manufacturer

MedtronicMedtronicMedtronicMedtronicCordisCoratomicCPI

TOTAL

PACE, Vol. 5

ModelNumber

58156917

6917A6913

323-443L-304913

Fracture

2———2

——

4

HighThreshold

122

—2

———

16

November-December 1982

NormalFunction

2156

—222

38

Inactive

534

——2

—

14

Total

4010102442

72

839

SIMON, ET AL.

100

O

12 24 36

MONTHS

48 60 72

Figure 1. Percent of normally functioning myocar-dial leads related to time [months] computed by ac-tuarial analysis. Numbers in parenthesis indicate thenumber of leads at risk at each interval.

system after failure of multiple epicardial leads.She has been continually paced from one trans-venous electrode with an acceptable (less than 5volts) threshold since. One patient with a trans-venous lead expired within the first year follow-ing implant of noncardiac causes.

Pacemaker wound infection was noted inthree patients. In each instance more than onesurgical procedure was required to remove theold and re-implant a new pacing system.

Clinical Course FoJJowing Implant

Permanent pacing has been discontinued inthree patients since initial implant. One, a nine-teen-year-old girl underwent repair of Tetralogyof Fallot in 1963, followed by complete heartblock. Repeated failure of epicardial implantsled to patient refusal of further implant. She re-

mains asymptomatic and unpaced. The secondwas a two-and-a-half month old infant withventricular tachycardia alternating with sinusrhythm and transient 2:1 block. Pacing failuredeveloped soon after implant and high thresh-olds (greater than 5 volts) were measured eigh-teen months later when the generator wasremoved. She has been in normal sinus rhythmwith a right bundle branch block and firstdegree AV block since that time. Quinidine hascontrolled her ventricular arrhythmia. The thirdpatient developed complete atrioventricularblock following Mustard procedure at tenmonths of age for transposition of the greatarteries. A pacemaker was implanted ten daysfollowing operation, but pacing ceased sixmonths later because of lead failure. Normalsinus rhythm had reappeared and has persistedfor five years. Two additional children have hadresolution of their postoperative atrioventricu-lar block with appropriate inhibition of their de-mand pacemakers; the opportunity to discon-tinue the pacing system has not yet arisen.

Mortality

There have been four deaths (10%) in theseries, none attributable to pacemaker mal-function. A fourteen-year-old boy with singleventricle, transposition of the great arteries, andpulmonary stenosis, had a pacemaker implanted16 days after ventricular septation and apulmonary valve replacement. He died sudden-ly thirty-nine months later. Ten days before hisdeath his pacemaker had been functioning nor-mally, but severe pulmonary artery hyperten-sion and congestive heart failure were persis-tent prior to death. The second death was in anineteen-year-old girl with Kearns syndrome,'who died four months after pacemaker implanta-tion due to bronchopneumonia and pan-creatitis. The third was a three-year-old infantwith ventricular septal defect, corrected trans-position, atrial septal defect, and congenitalatrioventricular block who had a permanentpacemaker implanted at the time of a Blalock-Taussig anastomosis. She died of pneumoniafour months later. The fourth death occurred ina seventeen-year-old boy with Down's syn-drome, ventricular septal defect (endocardial



cushion type), pulmonary artery hypertension,and mitral valve replacement. Intermittent com-plete heart block required a pacemaker implantto assure adequate heart rate shortly afteroperation. Recurrent diptheroid sepsis and ven-tricular arrhythmias, controlled hy quinidine,complicated the 20-month postoperative course.At the time of his death, atrioventricular con-duction was intact and the pacemaker was func-tioning normally in the demand mode at an es-cape rate of 40 beats per minute. The remaining37 patients are alive and fully engaged in age-appropriate activities except for vigorous com-petive sports.

Discussion

Previous reviews of the status of pediatric pa-tients requiring ventricular pacing have empha-sized the specific etiology of the rhythm dis-turbances,'•' technical aspects of the age-specific implantation problems of children,'-"the natural history of arrhythmias which requirepacing,'"''" as well as the long-term experience inpediatric patients who have received permanentpacemakers."''" Our data underscore the highmorbidity but low mortality and often life-saving intervention that accrues to children fol-lowing ventricular pacing. Thirty-four childrenrequired ventricular pacing because of atrio-ventricular block, twenty-four surgically in-duced. Three of the four patients with post-sur-gical sinus node disease became symptomaticgreater than three years after the operation andgreater than ten years in two, suggesting that thisabnormality may become more prevalent as thisgroup of patients survives into adulthood. Thebimodal distribution of age at initial implant, es-pecially in those patients with congenital com-plete heart block, suggest that intrinsic escaperates that result in symptoms are either presentvery early in life or do not emerge untiladolescence or young adult life.'"

The interval from cardiac repair to pace-maker implant in the surgical group may berelated to the site of block. In contrast to the ex-perience of others,* seven of our patients whodeveloped surgical complete heart block did notrequire pacing until late (greater than one year)in the follow-up period; two of these patients

have undergone electrophysiologic study andboth demonstrated supra-Hisian completeheartblock.

The epicardial lead approach using a varietyof lead systems has not been entirely satisfac-tory. The survival of epicardial leads in thisseries is similar to that reported for other pacedchildren during a comparable interval,"'" butfar worse than the epicardial experiencereported for adults. Magilligan et al.'" reportedlead failure in 8 of 100 adults with hoth suturedand sutureless (Medtronic models 5913,6913 and6917) electrodes after 30-64 months. Edwardsand Davies" reported 13% epicardial lead fail-ure rate at 30 months (Medtronic models 6913,6914 and 6917). Mansour et al." experiencedonly four lead failures in 300 patients using theMedtronic 6917 sutureless electrode. Using thesame lead Lawrie et al." reported only a 3.9%failure rate at 39 months on initial implants, buta 25% failure rate on patients referred forrepeated procedures. Interestingly, two pa-tients in their series had failure of both leads. Intheir well documented series, lead failure, con-sisting of high thresholds in all, occurred in 7.2%of 400 leads by 39 months.

For incompletely understood reasons, ten pa-tients in our series developed high thresholdswith multiple implants. Excluding the three pa-tients paced prior to 1965, when the lead frac-ture rate was higher and not representative ofcurrent experience, two patients have requiredtwo, and one patient three, thoracotomies withinthe first year of pacing for lead failure due tothresholds exceeding the five volt output of stan-dard pulse generators available at the time.While one patient could be converted to a highoutput (10 volt) pulse generator, under localanesthesia, the remaining patients requiredrepeat thoracotomy for new lead implantation.It is possible that this frequency of lead re-placement in the future might not be as high nowthat multiprogrammable pulse generators whoseoutput and pulse duration can be raised non-invasively after implantation are available. Ob-viously this benefit of technology would be help-ful only for those patients who developed only amodest increase in threshold, and not to thosewith lead failure due to lead fracture or ex-tremely high thresholds.


SIMON, ET AL.

Possible factors which may contribute to poormyocardial lead performance in children in-volve surgical technique as well as availabletechnology.

Early myocardial electrodes required smallstab wounds into the myocardium for insertion,followed by securing of the electrode to the myo-cardium with sutures. This method may result inhemorrhage, necrosis, and fibrosis at the site ofplacement. A rapid decrease in current densityat the electrode-myocardial interface leading tofailure of myocardial capture and subsequentsystem revision was not infrequently the result."Similar techniques are used in adults, and thisexplanation alone cannot explain the higher fre-quency of threshold rises in children seen in thisseries. Changes in electrode design, particu-larly the sutureless electrode, have simplifiedinsertion and may be less traumatic to the myo-cardium, although data to support this conclu-sion are not available. Placement of the leadthrough the diaphragm to the generator pocketin the abdominal wall, rather than immediatelybeneath the ribs, removes a fulcrum on whichthe lead may wear and may reduce lead frac-ture. Creation of the abdominal generatorpocket immediately pre-peritoneal, beneath themuscle layers of the abdominal wall rather thansubcutaneously, has facilitated wound closure,especially in infants and small children, andprobably has reduced the incidence of wounddehiscence and generator pocket infection." Thistechnique has been facilitated by miniaturiza-tion of the pulse generators, achieved primarilyby the application of micro-circuitry, and smal-ler but longer lasting power sources. A numberof additional developments during the study in-terval have improved the long-term outlook forthe paced child. The development of double ortriple helicoil lead wires has apparentlylengthened the life span of an implanted lead.The development of a simple pacemaker analy-sis system assists the surgeon in determinationof the causes of pacing system malfunction andmore accurately tests threshold of stimulation atthe time of initial lead placement.

As suggested by our own limited experience,as well as that of others,"'" there appears to be arole for transvenous patients in this age group.Repeated electrode repositioning which might

be required with late displacement due to trun-cal growth in children would certainly appear tobe preferable to the multiple thoracotomies re-quired for epicardial lead placement. Percu-taneous insertion of permanent leads now ob-viates the problem of venous access unavail-ability in this age group." Certainly, patientswithout right-to-left shunts who are over tenyears of age, and perhaps younger, would be ac-ceptable candidates for transvenous pacing.New positive fixation electrodes have substan-tially reduced the complication rates of trans-venous approaches in adults and may holdpromise in growing children. Furman andYoung" reported no excess lead difficulties us-ing the transvenous technique in 12 of 13 pedi-atric patients paced transvenously—only one re-quired conversion to epicardial leads because ofrepetitive displacement.

Based on this experience and that of others,'^the following is our current approach in themanagement of disturbances in impulse forma-tion and conduction in children. The initial man-agement relates to etiology. Patients with con-genital complete heart block are paced upon theappearance of presyncope, syncope, congestiveheart failure, or other rate related symptoms.Patients with sinus node disorders, either con-genital, acquired, or surgically induced, receivea pacemaker upon the appearance of symptomsor to insure adequate impulse formation duringpharmocotherapy for symptomatic tachy-arrhythmias. Both groups of patients undergoelectrophysiologic study prior to implant toidentify the intrinsic escape mechanism, tolocalize the site of block, if present, and to assessintrinsic pacemaker response to rapid atriai pac-ing, atropine, isoproterenol infusion, and exer-cise. Permanent pacing for bradycardia alone inthe isolated congenital AV block group has notbeen employed, despite an apparent higher riskof progression to a symptomatic course in thissubgroup."

Surgically induced rhythm disturbances areanalyzed for time of onset, severity, adequacy ofescape rhythm, response to exercise, and site ofblock (if present]. Transient [less than threeweeks following surgery) but stable impulseformation and conduction disturbances aremanaged in the immediate postoperative peri-



od with temporary transthoracic epicardialwires (atrial or ventricular, depending upon thesite of abnormality] and, prior to discharge, byambulatory monitoring to insure adequate im-pulse formation and propagation. If completeatrioventricular block persists beyond threeweeks, electrophysiologic study is recom-mended to identify the site of block; if surgicalheart block is intra-Hisian or below the His, apermanent pacemaker is implanted. If the blockis supra-Hisian, the patient asymptomatic, andthe intrinsic pacemaker escape satisfactory byHolter monitoring, the parents are advised ofboth our experience and the reported experi-ence of surgical heart block.̂ -̂'̂ Early in our ex-perience (prior to the era of electrophysiologicstudy) pacemakers were withheld unless symp-toms dictated their insertion. At present werecommend implant in the supra-Hisian groupeven in the absence of symptoms; despite thisrecommendation, the families of two childrenhave refused implant; both children are wellfive and ten years after surgery. This experi-ence, though small, suggests that supra-Hisianheart block in the absence of symptoms, with anadequate escape rate, may be less life-threatening than infra-Hisian, or undifferen-tiated surgical heart block, a finding shared byDriscoU et al.'^ Lesser degrees of conduction ab-normalities such as bifascicular block or tri-fascicular disease, are followed closely byelectrophysiologic studies at times of postoper-ative catheterization and by periodic ambula-tory monitoring. This approach is designed toidentify high-risk patients in need of pace-maker support without submitting all individ-uals with impulse formation and conductionabnormalities to long-term pacemaker manage-ment with its attendant high cost and morbidity.

Although we have utilized isotopic pulse gen-erators in six patients in this series, we no longer

implant this type of unit. The pulse generatorsare more expensive than programmable lithiumpowered pulse generators; their major advan-tage, a long-life power source, is offset by thefact that the major complication of the pacingsystem in this age group in this series, which wasalmost exclusively with epicardial leads, isrelated to the development of high lead thresh-olds, not to the limited life span of the powersource. Expected advances in lead systems andanticipated benefits from dual chamber pacingand flexibility obtained with pulse generatorprogrammability is lost by reliance on this typeof unit. Furthermore, although we know of nodata indicating that nuclear-powered units con-stitute a health danger to the patient, the chronic(decades) use of this device in children mayhave risks unidentified at the present time.Finally, the reduction in random electronic mal-function and premature battery depletion as aresult of advances in pulse generator circuitrydesign and manufacture, as well as the avail-ability of telephone monitoring for early pacingsystem malfunction detection, have all simpli-fied routine follow-up of the pacemaker pa-tient. In summary, the childhood population re-quiring permanent pacing consists of patientswith congenital and surgically induced abnor-malities of impulse formation and conduction.The decision to implant a permanent pace-maker in this age group should be made with anappreciation of the rate of associated morbidityunique to children and the current state of pac-ing technology. Today, utilizing historical, non-invasive, and electrophysiologic data, one candevelop a rational basis for the institution ofpacing in children. Improvements in diagnosisof rhythm disturbances in children, as well aspresent and future technical advances in pacingsystem design, render this therapeutic techni-que applicable to all age groups."

References

1. Simon, A.B. and Zloto, A.E.: Atrioventricularblock: Natural history after ventricular pacing.Am. /. CardioJ., 41:500, 1979.

2. Simon, A.B. and Zloto, A.E.: Symptomatic sinusnode disease: Natural history after permanentventricular pacing. PACE, 2:305, 1979.

3. Roberts, N.K., Perloff, J.K., and Kark, R.A.P.:

Cardiac conduction in the Kearns-Sayre syn-drome (A neuromuscular disorder associatedwith progressive external ophthalmopelegia andpigmentary retinopathy). Am. /. Cardioi.,44:1396, 1979.

4. Isaacson, R., Titus, J.D., Merideth J., et al.: Ap-parent interruption of atrial conduction path-


SIMON, ET AL.

5.

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14.

15.

ways after surgical repair of transposition of 16great arteries. Am. /. Cardiol, 30:533, 1972.El Said, G., Rosenberg, H., Mullins, C.E., et al.:Dysrhythmias after Mustard's operation for 17.transposition of the great arteries. Am. /. Car-diol, 30:527, 1972.Hofshire, P.J., Nicoloff, D.M., and Moller, J.H.: 18.Postoperative complete heart block in 64 chil-dren treated with and without cardiac pacing.Am. /, Cardiol, 39:559, 1977. 19.Sondheimer, H.M., Izukawa, T., Olley, P.M., etal.: Conduction disturbances after total correc-tion of Tetralogy of Fallot. Am. Heart /., 92:278, 20.1974.Salama, F.: A suggested site for the implantationof myocardial pacemakers in infants and youngchildren. Thorax, 31:346, 1976.Amato J.J., Payne, D.D., Rheinlander, H.F., et 21.a l : Intermuscular abdominal implantation ofpermanent pacemakers in infants and children.Ann. Thorac. Surg., 25:243, 1978.Pahlajani, D.B., Serratto, M., Mehta, A., et al.: 22.Surgical bifascicular block. CircuJation, 52:821975.Yabek, S.M. and Jarmakani, J.M.: Sinus nodedysfunction in children, adolescents, and young 23.adults. Pediatrics, 61:593, 1978.Driscoll, D.J., Gillette, P.C., Hallman, G.L., et a l :Management of surgical complete atrioventricu- 24.lar block in children. Am. /. CardioJ., 43:11751979.Young, D., Eisenberg, R., Fish, B., et a l :Wenckebach atrioventricular block (Mobitz 25.Type I] in children and adolescents. Am. J. Car-diol, 40:393, 1977.Gamble, W.J. and Owens, J.P.: Pacemaker 26.therapy for conduction defects in the pediatricpopulation. In H. Gelband, N.K. Roberts, (Eds.].Cardiac Arrhythmias in the Neonate Infant andChild, Appleton-Gentury Grofts, N.Y., 1977, pp.461-525. 27.Greenwood, R.D., Rosenthal, A., Sloss, L.J., eta l : Sick sinus syndrome after surgery for con-genital heart disease. CircuJation, 52:208, 1975.

Neiderhauser, H., Simonin, P. and Friede, B.:Sinus function and conduction after repair oftetralogy of fallot. Circulation, 52:214, 1975.Williams, W.G., Izukawa, T., Olley, P.M., et a l :Permanent pacing in infants and children,PACE, 1:439, 1978.Shearin, R.P.N. and Fleming, W.H.: Fourteenyears of implanted pacemakers in children. Ann.Thorac. Surg., 25:144, 1978.Michaelsson, J. and Engle, M.A.: Congenitalcomplete heart block: An international study ofthe natural history. Gardiovasc. Glin., 4:85,1973.Magellegan, D.J., Hakimi, M. and Davila, J.G.:The sutureless electrode: Gomparison withtransvenous and sutured epicardial electrodeplacement for permanent pacing. Ann. Thorac.Surg., 22:80, 1976.Edwards, A.M. and Davies, J.G.: Analysis of thelongevity of pacing electrodes. In Y. Watanabe(Ed.): Cardiac Pacing, Excerpta Medica, Amster-dam, 1977, pp. 539-542.Mansour, K.A., Miller, J.I., Symbas, P.N., et a l :Further evaluation of the sutureless screw-inelectrode for cardiac pacing. /. Thoracic Cardio-vasc. Surg., 77:858, 1977.Lawrie, CM., Seale, J.P., Morris, G.G., et a l :Results of epicardial pacing by the left subcostalapproach. Ann. Thorac. Surg., 28:561, 1979.Holmes, D.R., Maloney, J.D. and Feldt, R.H.: Theuse of the percutaneous subclavian techniquefor permanent cardiac pacing in childhood.Mayo CUn. Proc, 55:579, 1980.Furman, S. and Young, D.: Gardiac pacing inchildren and adolescents. Am. J. Cardiol, 39:5501977.Karpawich, P.P., Gillette, P.G., Garson, A., Jr., eta l : Gongenital complete atrioventricular block:Glinical and electrophysiologic predictors ofneed for pacemaker insertion. Am. /. Gardiol48:1098, 1981.Young, D.: Permanent pacemaker implantationin children: Gurrent status and future con-siderations. PAGE, 4:61, 1981.

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Ventricular Pacing in Children