Experience with a Low Profile Bipolar, Active Fixation Pacing Lead in Pediatric Patients

Experience with a Low Profile Bipolar, ActiveFixation Pacing Lead in Pediatric Patients

ROBERT M. CAMPBELL,* ANTHONY A. RAVIELE,* EDDIE J. HULSE,*DEBBIE 0 . AULD,* CUYLER J. McRAE,* VINCENT K.H. TAM,t andKIRK R. KANTERt

From the ^Children's Heart Center at Egleston Scottish Rite and the tDepartment of CardiovascularSurgery at Emory University School of Medicine,(Atlanta, Georgia. [JSn\

CAMPBELL, R.M., ET AL.: Experience with a Low Profile Bipolar: Active Fixation Pacing Lead in PediatricPatients. 'Continued miniaturization of permanent pacing systems has promoted use of this technology inyounger and smaller pediatric patients. Intermedics ThinLine 438-10 active fixation pacing leads (4.5 Frlead body) v^ere implanted in 26 patients (17 males/9 females; ^£ ± 6.9 years). Twenty of 26 patients re-ceived dual chamber systems, 6 of 26 patients single lead systems. Each patient has been followed ^ 3months. Pacemaker analysis at implant and 6 months later evaluated pulse width thresholds at 2.5 V(atrial 0.07 ± 0.02 vs 0.13 ± 0.02 ms [P = 0.01]; ventricular 0.08 ± 0.04 ms vs K20 ± 0.04 ms [P ^ 0.01]);sensing thresholds (atrial 4.1 ± 0.41 mV vs 4.0 ± 4.2 mV [P = NS]; ventricular'9^ ± 0.72 vs 9^ ± 0.94mV [P = NSJ): and impedance (atrial 345 ± 12 vs 370 ± 120 O [P ̂ 0.04]; ventricular 412 ± 17 vs 458 ±190 O [P < 0.01]). One volt lead failed with exit block at approximate]y 6 weeks. The youngest (9 monthsto 5 years) and smallest (6.5-18.0 kg) ten patients have each shown by venography to have at least mildvenous stenosis at the lead(s) insertion site; five patients demonstrated collateral formation around asymp-tomatic obstruction, with no thrombus formation. The Intermedics 438-10 ThinLine pacing lead hasdemonstrated good and stable early postimplant electrical parameters. Angiographic evaluation in oursmaller patients has shown evidence for asymptomatic venous obstruction. (PACE 1999; 22:1152-1157)

pacing, pediatrics, transvenous

Introduction

Continued miniaturization of pacemakerleads and pulse generators has revolutionized thefield of pediatric cardiac pacing.^'^ Newer genera-tion epicardial and endocardial lead systems gen-erally provide dependable long-term service andpulse generators with multiprogrammability andhigh output capabilities, which serve the needs ofpediatric patients with high rate requirements.

For many years, epicardial pacing lead sys-tems were standard. However, implantation re-quired sternotomy , thoracotomy, and postim-plantation monitoring in the intensive care unit.Notoriously, these epicardial lead systems had

Address for reprints: Robert M, Campbell, M.D., TheChildren's Heart Center. 2040 Ridgewood Dr NE. Atlanta,GA 30322. Fax (404) 315-2029; e-mail: 'JonofriovCaiKidsheart.com

Received July 29, 1998; revised October 19, 1998; acceptedNovember 4,1998.

poorer acute and chronic pacing and sensingthresholds than the transvenous leads availahle atthe time.- '̂"

In recent years, more pediatric patients arereceiving transvenous systems preferentially.Advances in lead polarity, electrode design andfixation, insulation, and flexihility have im-proved lead performance and longevity. We re-port our pediatric pacing experience with a newlow profile, bipolar, coradial active fixation pac-ing leads from Sulzer Intermedics Inc. (Thin-Line®, model 438-10). Our study was designedto assess lead handling at implant, acute andchronic lead electrical performance, and the de-tection of possihle venous obstruction followingimplantation of the lead systems in smaller chil-dren.

Materials and Methods

This investigative pacing lead protocol wasreviewed and approved hy the Emory University

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School of Medicine Human Investigations Com-mittee. A separate study protocol with consentwas also HIC approved, permitting evaluation ofpossible venous obstruction in patients < 5 yearsof age (hereafter referred to as the Vascular Sub-set). Consent was obtained by a study investiga-tor from the patient's parent/guardian or directlyfrom patients 18 years or older. Patients excludedfrom implantation of this pacing lead were in-fants and young children < 5 kg weight, andthose patients with intracardiac right to leftshunts.

Thinline 438-10 Pacing Lead

This lead features an iridium oxide-coatedelectrode tip with an 8 mm^ microporous surfacearea. Both the anode and cathode conductors areseparately insulated with a special polymer mak-ing it possihle to wind both wires co-radially intoa single coil. This single coil design replaces thetraditional inner-coil, outer-coil design of bipolarleads, eliminating the problem of inner tubingdegradation and resulting in approximately a 25%reduction in lead diameter. The ThinLine body is4.5 Fr. Only the exposed-screw active fixationThinLine lead [model 438-10) was evaluated inthis study protocol.

Patient Population

From August 1996 to November 1997, we im-planted transvenous pacemaker systems withThinLine active fixation ieads in 26 infants, chil-dren, and young adults (17 males/9 females; ages9 months to 23 years, 9.9 ± 6.9 years). Dual lead(both atrial and ventricular) systems were placedin 20 patients, single lead systems (1 atrial , 4 ven-tricular) in 5 patients, and 1 patient underwent re-placement of a previonsly fractured non-ThinLineatrial lead.

Indications for pacemaker implantation werecongenital complete heart block (n - 6); surgicalcomplete heart block (n ^ 6); sick sinus syndrome(n = 7); heart block following radiofrequency ab-lation of the atrioventricular node (n = 2); hyper-trophic obstructive cardiomyopathy (n = 3); andlong QT syndrome (n ^ 2).

Twelve patients were evaluated at least 12months postimplantation; 8 patients were fol-

lowed at least 6 months; and 5 patients were fol-lowed at least 3 months. Two patients moved andwere lost to follow-up after the 3-month evalua-tion. One dual chamber generator and lead systemrequired explantation at 1 month due to subacutebacterial endocarditis and pacemaker system in-fection,

Implantation Technique

All pacing systems were implanted by 1 ofthe 2 cardiovascular surgeons (VT, KK) usinggeneral anesthesia in the operating room. Afterprepping and draping, Seldinger technique wasused to enter the subclavian vein. The pacemakerpocket was then created in the deltopectoralgrove. A second guidewire was placed usingSeldinger technique in the subclavian vein if adual chamber system was to be implanted. SevenFr vascular sheaths (to accommodate the largerelectrodes) were exchanged over the guidewires.Bipolar ThinLine 438-10 pacing leads were thenplaced intracardiac, optimally in the right atrialappendage and/or right ventricular apex. Afterdetermining satisfactory acute lead electricalperformance, each lead was paced at a 10 V out-put to exclude diaphragmatic pacing. Leads werethen secured with nonabsorbable sutures andlocking sleeves. The implantable pulse generatorwas attached and the pacemaker pocket closed.For patients ^ 5 years of age, a loop of redundantlead was positioned in the right atrium for atrialand or ventricular leads to potentially extendlead longevity in a rapidly growing infant orchild.

Lead Follow-Up Evaluation

Using the Intermedics follow-up schedule,patients underwent analysis of lead performanceand pacing system status at implant in the oper-ating room and postimplant at 1 day, 1 month,3 months, 6 nionths. and then every 6 monthssubsequently. Lead parameters assessed werepacing thresholds (pulse width capture thresholdat 2.5 V amplitude), sensing threshold, and leadimpedance (measured at 3.5 V amplitude and0.45-ms pulse width).

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Vascular Obstruction Protocol

A subset of the youngest (9 months to 5 years)and smallest (6.5-18.0 kg) ten patients underwentserial venographic evaluation both before implan-tation and then subsequently postimplantation at1 day, 3 months, 6 months, and 12 months. Usinglocal EMLA analgesia, a percutaneous intra-venous line was placed in a hand/arm vein ipsi-lateral to the pacing lead implant. Single-planepulsed cineangiography recorded the injection ofradiopaque contrast, which defined the presenceor absence of venous obstruction and/or collateralvenous channel formation. Each patient in thevascular subset received a daily aspirin dose(20-80 mg) empirically for an antiplatelet effect.Seven patients have also undergone two-dimen-sional echocardiography with color flow andpulsed Doppler evaluation to evaluate for venousstenosis, thrombosis, and/or collateral vesselflow.

Results

Implantation

Leads were successfully implanted in eachpatient. Surgeons reported excellent acute han-dling characteristics and visibility under fluo-roscopy.

One lead and generator system was explantedat 1 month due to subacute bacterial endocarditisand pacemaker system infection. No episodes oflead dislodgment occurred. Only one patient ex-perienced lead exit block with intermittent loss ofsensing occurring at 6 weeks requiring conversionof the dual chamber system to AAI mode.

Lead Electrical Parameters

Serial evaluation of atrial and ventricularlead pacing thresholds (Fig. 1), sensing andimpedance is shown (Table 1.). Despite a statisti-cal increase above implantation pacing thresh-olds, chronic (^ 3 months) atrial and ventricularpacing thresholds were still low enough in all butone patient to allow chronic pacing amplitudes of1.0-2.5 V. One ventricular lead failed at 6 weekswith exit block, requiring conversion of the DDDsystem to AAI mode in the sick sinus syndrome

Figure 1. Atrial pacing (AP) projection of contrastinjection tbrougb a left arm peripheral IV, showingstenosis of the left subclavian vein (central arrow) at theinsertion site of the transvenous leads. Collateralvenous channels are shown (downward arrows). Tbeinnominate vein and superior vena cava (SVC) remainpatent.

patient. Sensing thresholds, both atrial and ven-tricular, were excellent at implant and demon-strated no significant charge throughout thestudy. Atrial lead impedances were lower thanventricular, and both atrial and ventricular leadsdemonstrated a statistically significant, but mild,increase in impedance over time.

Vascular Subset Evaluation

Each vascular subset patient showed evidencefor at least mild (clinically asymptomatic) subcla-vian vein stenosis at the catheter(s) introductionsite, as documented by angiography. Five patientsshowed evidence by venography for collateral veinformation around the subclavian vein stenosis,with collaterals forming just proximal to the steno-sis and reentering the subclavian vein/innominatevein just distal to the stenosis. No thrombus for-mation was observed. Despite the positive an-giographic findings, two-dimensional echo and

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Implant

1 Month

3 Months

6 Months

12 Monttis

CaptureThreshold @

2.5 V (ms)

0.07 (0.02)N = 18

0.20 (0.20)*N-21

0.16(0.02)*N = 22

0.13(0.02)*N = 18

0.14(0.02)'N - 9

Table 1.

Thin Line Model 438-10 Clinical Evaluation

Atrial Placemen

SensingThreshold

(mV)

4.10(0.41)N - 15

3.10(0.36}N - 20

3.70 (0.36)N = 21

4.00 (0.42)N = 15

3.20 (0.50)N - 10

t

Impedance(ohms)

345(12)N - 20

343(12)N =21

370(12)*N - 22

370(12)*N = 18

381 (14)*N = 11

CaptureThreshold @

2.5 V (ms)

0.08 (0.04)N - 1 8

0.25 (0.04)*N - 19

0.21 (0.04)*N - 22

0.20 (0.04)'N - 16

0.16(0.05)N - 10

Ventricular Placement

SensingThreshold

(mV)

9.70 (0.72)N = 17

10.50(0.77)N = 17

10.00(0.77)N = 18

9.30 (0.94)N = 13

12.00(1.48)N = 5

Impedance(ohms)

412(17)N - 2 1

410(18)N = 19

431 (17)N - 22

458(19)'N - 16

430 (22)N = 10

*Significantly different (p < 0.05) from implant; data presented as mean (SD), number of subjects. Measured electrical leadassessment over time, denoting values as mean (standard deviation, number of patient assessed at cath time in for value (inparentheses), and values statistically different (P < 0.05) from implant values, shown at time 0 on X axis.

Doppler evaluation showed no evidence for venousstenosis, obstruction, collateral flow, or thrombosis.

Discussion

This study documents good implantationlead handling and good early pacing and sensingthresholds with stable lead impedance for theThinLine 438-10 pacing lead in children. Despitethe low profile lead body diameter (4.5 Fr ), theneed to use a 7 Fr introducing sheath due to thelarger electrode diameter may still promote ve-nous stenosis and collateral vessel formation, asnoted in our younger patients. The long-term clin-ical significance of these venous abnormalities isnot known.

Epicardial lead systems are still preferred atmany pediatric cardiology centers for young pa-tients considered too small for transvenous pacing,especially considering the good reported lead per-formance characteristics of newer generationsteroid-eluting epicardial leads.^-^ Several studieshave now summarized results of transvenous pac-ing in infants and children. '̂̂ "^^ Technological ad-vances in lead systems now permit durable, highquality transvenous pacing in pediatric patients.Transvenons leads systems are associated with de-

creased morbidity (not requiring open chest proce-dure or chest tubes, and generally no intensive careunit postimplantation recovery), decreased lengthof stay, and subsequently decreased costs. Relativeor absolute contraindications of transvenons pacingincludes small patient size, residual or potentialright to left intracardiac shunts, and lack of suitablevenous access due to congenital venous anomaliesor postoperative vascular obstruction. Our findingwith the Thinline 438-10 lead electrical perfor-mance is encouraging, although side by side com-parison with previous transvenous or epicardialleads is not possible. Pacing and sensing thresholdswere good with minimal observed acute to chronicthreshold changes noted. Low pacing thresholdshave allowed lower chronic pacing amplitudes1.0-2.5 V, promoting increased battery longevity.Only one lead required abandormient (due to inter-mittent loss of atrial sensing at 6 weeks). No leadsdislodged, no pacing exit block, lead fracture, or in-sulation breaks were encountered.

The use of an intracardiac loop of pacing leadhas been reported to promote increased longevityof pacing systems in infants and young chil-dren.^ '̂̂ ^ Rosenthal and Bostock^^ demonstratedwith serial X ray, the uncoiling of an atrial loopover time following implantation of a transvenous

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ventricular lead in a neonate. Gillette and Zeigter^have long promoted use of absorbable suture, toallow for lead in-growth as the patient matures.Lead length is also of concern within the pace-maker generator pocket̂ '̂ "^ Molina et al.^ recom-mended short leads to reduce bulk at the pulsegenerator site,

Despite care taken by the surgeons (VT. KK) toavoid vascular trauma during lead implantation,each patient evaluated in the vascular subgrouphas shown evidence for at least mild venousstenosis (clinically asymptomatic). This may re-sult from the use of still relatively large intro-ducing sheath (7 Fr), and/or in-rolling of thevein edge with the use ofthe sheath, and/or localvein trauma with the Seldinger introductiontechnique.

The true incidence of venous obstruction fol-lowing implantation of transvenous pacing leadsin infants and children is unknown; no prospec-tive longitudinal study has been performed. Theuse of large leads (especially bipolar) potentiallyincreases the risk for venous obstruction and/orthrombosis.^^"^^ On the other hand, Gillette etal.^^ reported no venous flow abnormalities in 19pediatric patents (17 months to 25 years; 9.6-56.0kg), studied 22.5 months (1-46 months) postim-plant. Patients were evaluated by venous plethys-mography and Doppler (n = 16), venography (n =3), or both (n = 1). Molina et a l / have suggestedthe use of the internal jugular vein for patients< 7 years of age to prevent vein occlusion: how-ever, lead advancement or removal following in-ternal jugular vein implantation can prove to beexceedingly difficult (personal communication

with author A.D.). In our study, venography accu-rately depicted vein narrowing in each vascularsuhset study patient, with collateral formation infive patients. Angiographically identified stenosisand collaterals in the upper lateral thorax, near thevein insertion site, and thus not well imaged byechocardiography. No thromboses was observedby either technique. Doppler evaluation showedno venous stenosis or flow disturbance, even inobstructed patients. Doppler interrogation, evenwith color flow mapping, occurs at right angles tothe innominate vein, and thus may be unable todetect local low velocity flow disturbances fromvenous stenoses and/or collateral veins. It is rea-sonable to suspect that venous obstruction and/orocclusion may exist in other, even older, pediatricpatients previously implanted with larger diame-ter pacing leads. While the appearance of the ve-nous anomalies is worrisome, the long-term sig-nificance of these stenoses and/or collaterals iscurrently unknown, especially regarding revisionofthe leads, advancement or replacement of leads,and risk of later venous thrombosis.

To avoid injury to the suhclavian vein, thecephalic vein cut-down approach has heen advo-cated hy some,^ but the small vessel size maymake introduction of dual chamber systems diffi-cult and may limit arm motion and prove uncom-fortable.

Acknowledgment: We thank Ginny D"Onofrio, Jim Glover,and Gharlotta O. Sakers for their assistance with data analysisand manuscript preparation. Special appreciation to RobertHornak, without whom this study could not have beenaccomplished.

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