Europace Advance Access published online on August 10, 2007
Europace, doi:10.1093/europace/eum164
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Outcome of single-chamber, ventricular pacemakers with transvenous leads implanted in children
1 Servizio di Aritmologia, Dipartimento Medico-Chirurgico di Cardiologia Pediatrica, Bambino Gesù Pediatric Hospital, IRCCS, Piazza S. Onofrio 4, 00165 Roma, Italy; 2 Unità di Epidemiologia, Bambino Gesù Pediatric Hospital, Roma, Italy
Manuscript submitted 2 May 2007. Accepted after revision 12 July 2007.
* Corresponding author. Tel: +39 06 68592258; fax: +39 06 68592257. E-mail address: silvetti{at}opbg.net
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Abstract |
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Aims: In children with bradyarrhythmias, ventricular demand, rate-responsive pacemakers (VVI/R PM) are often indicated, but no study is entirely dedicated to their outcome.
Methods and results: We evaluated the outcomes of children with VVI/R PM implanted at our centre, with a retrospective analysis. Between 1990 and 2005, 117 children (63 with congenital heart defects), received VVI/R PM with endocardial lead at 5.3±3.9 years of age for atrioventricular block (n = 105) and sinus node dysfunction. The majority of the leads were unipolar (n = 78), tined (n = 110), and steroid eluting (n = 89). The leads were fixed to subcutaneous tissues by absorbable suture in all patients; in 17 patients, also an atrial loop was created. Follow-up (FU) was 7.8±4.1 years. There were 22 system failures (19%), due to lead malfunction (n = 20) and system erosion/infection. The log-rank test for equality of survivor functions showed no significant risk factor. However, lead malfunction occurred only in the group without loop, but FU duration was longer in these patients. Complications at implantation were haemothorax (2.5%) and lead dislodgement (5%). Clinically silent occlusion of the subclavian vein was documented at FU by Echo-Doppler in 5%.
Conclusion: In this particular group of patients, VVI/R pacing has good results, but after long-term FU shows 19% of failures, mainly lead-related.
Key Words: Cardiac pacing, Children, Endocardial pacing, Ventricular demand pacing, Pacemaker, Pacing complications
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Introduction |
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In children with advanced or complete atrioventricular block (AVB) and normal ventricular function, ventricular demand pacing with or without a rate-responsive function (VVI/R) is generally effective, safe, and easy to perform.1
–3 VVIR pacing is sufficient for maintaining good cardiac function in most children, and the transvenous implantation of a single lead reduces the surgical risk, the operative time, and the late risk of venous thrombosis4–6 and lead malfunction. When the child becomes an adolescent or young adult, an upgrade to a dual-chamber (DDD) or to a VDD pacing system may be indicated.7–9 There are few recent studies which described the outcome of transvenous permanent pacing in children,10–12 especially in comparison with epicardial pacing,13–18 but to our knowledge there are no large or recent studies entirely dedicated to the outcome of VVI/R pacemaker (PM) implanted with transvenous leads in the paediatric age. We sought to address this issue. |
Methods |
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Since 1982 and 2005, 381 patients have undergone permanent PM implantation and are followed at the Cardiac Arrhythmias Service of Bambino Gesù Pediatric Hospital.16
Endocardial pacing systems were implanted in 237 patients and epicardial pacing in the others. With a retrospective study, we reviewed the records of these patients and identified all those who underwent an implantation of a VVI/R PM at the age 
15 years. We recorded the techniques used for the initial implantation, the generator and lead characteristics, and any complication. We also recorded the clinical status at most recent follow-up (FU). The study complies with the Declaration of Helsinki.
Implantation procedure
The indication for endocardial pacing16 and the implant technique used in our institution has already been described.7,8,16 The parents of children gave informed consent to the procedure using standard local consent procedure. All procedures were performed under general anaesthesia. Briefly, at initial PM implant, the endocardial pacing lead was inserted by transcutaneous puncture of the subclavian vein and fixed to the subcutaneous tissue with a slowly absorbable ligature.19 In the last 6 years, an atrial loop was created as well.20 Ventricular leads were positioned in the non-systemic ventricular apex (left ventricle in congenitally corrected transposition of the great arteries, TGA {S, L, L}, and in TGA {S, D, D} after Mustard palliation), where adequate values of pacing threshold (pulse amplitude < 1 V at 0.50 ms of pulse duration), R wave sensing (>5 mV), and impedance (>300 and <1000 ohms) were achieved. A trial of high output ventricular pacing (10 V at 0.50–1.50 ms) was performed during general anaesthesia when muscular paralysis was terminated to exclude inappropriate diaphragmatic stimulation. Pacing threshold, impedance, and sensing of atrial and ventricular electrograms were evaluated during the implant procedure with a Medtronic, Inc., Minneapolis, MN, USA. Pacing System Analyzer Model 5311 B and 8090 Analyzer and during FU telemetric interrogation with an appropriate Programmer. Antibiotic prophylaxis was routinely given according to our Hospital protocol.16
Definitions
Pacing system implantation was defined as the placement of a new PM generator and a lead. PM replacement was defined as the placement of only the PM generator without the insertion of new leads. Complications recorded were divided into two categories: early (occurring in the first 3 months after implantation) and late (>3 months).16 Lead malfunction requiring new pacing system implantation was defined as: (i) exit block, (ii) abnormal threshold increase with the need of high output values causing early battery depletion and/or partial loss of capture, (iii) lead fracture, and (iv) insulation break. System infection was defined according to published criteria.21
Follow-up
The FU schedule in use in our institution has been described previously.7,8,16 Patients were generally followed-up at 1, 3, and 6 months after implantation, and then every 6 months or as needed. Each patient underwent clinical examination, telemetric PM interrogation, and standard electrocardiogram at every FU visit. An echocardiogram, Holter monitoring, and exercise testing were performed yearly and a chest X-ray every 1–2 years. A Doppler-echo evaluation of the subclavian vein was performed in 56 patients in the last 3 years and before upgrading procedures.7,8
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Statistical analysis |
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Statistical analysis was carried out using the Stata package, version 8.0 [StataCorp. (2003) Stata Statistical Software: Release 8.0. College Station, TX, USA: Stata Corporation]. Proportions or, when appropriate, means or medians together with standard deviation and range were computed. The median was specified if different from the mean. A P-value of <0.05 was considered significant.
The Kaplan–Meier method and log-rank test were used to study the longevity of the pacing system implanted. Failures included lead malfunction and pacing system infections or erosions requiring the removal of all the pacing system. Complications that did not require a new pacing system implantation (i.e. infections treated with drugs, early postoperative lead dislodgement that required only the repositioning of the lead, haemothorax at first PM implantation) were recorded as complications but not included in the analysis of the outcome of the first pacing system implanted, as this was not replaced.13 Cases of lead removal because of extraneous causes (e.g. new cardiac surgery), cardiac transplantation and patient’s death unrelated to pacing, were considered as ‘censored’ or lost to FU. A Cox multivariate proportional hazard model was used to explore factors associated with the duration of the pacing system. Variables included in the model as predictors were patient’s age and gender, presence or absence and severity of other congenital heart defects (CHD), number of procedures, lead type (unipolar or bipolar, steroid-eluting or not, and active or passive fixation), implantation procedure (i.e. absorbable ligature of the leads to subcutaneous tissues only or the addiction of the atrial loop), and, as a continuous variable, year of implantation.
When venous occlusion was found at Doppler-echo examination, it was compared with other variables (age at implantation, sex, arrhythmia requiring PM implantation, CHD, number of procedures performed, lead dimension, lead polarity, and FU duration) with two-sample Wilcoxon Rank-sum (Mann–Whitney) test.
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Results |
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Population
Between 1990 and the end of 2005, 117 children (47 girls) underwent the implantation of a VVI/R PM with an endocardial lead at 5.3±3.9 years of age (median 5 years, range 2 days to 15 years). In 25 patients (21%), a previous epicardial pacing system failed.
Fifty-four patients (46%) had no structural heart disease and 63 patients (54%) had CHD (Table 1). No residual shunts have been documented in patients who underwent heart surgery. For purposes of statistical analysis, patients were divided into three groups based on presence and severity of CHD: Group 1, composed of patients without CHD (n = 54 patients) and patients with mild CHD not requiring surgical treatment (n = 7 patients); Group 2, including 40 patients with simple CHD (e.g. isolated atrial, ventricular and AV septal defect, pulmonary stenosis, and tetralogy of Fallot); and Group 3, including all others with complex CHD (n = 16 patients).
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Indications
The main arrhythmia requiring PM implantation was complete AVB in 105 patients (89%), postoperative in 37 patients, and sinus node dysfunction (SND) in 12 patients. In seven patients, SND was a complication of previous heart surgery (four after Mustard palliation for transposition of the great arteries {S, D, D} with median age at implantation 6 years) and five patients had SND in the absence of structural abnormalities. Causes of ventricular pacing in patients with SND were: unsuccessful positioning of an endocardial atrial lead (four patients, three of whom after Mustard palliation or atrial septation), association with II degree AVB (three patients, one with Mustard palliation), and use of backup ventricular pacing during symptomatic sinus pauses or intermittent severe bradycardia (five patients). In 2 of this 12 patients, a previous atrial epicardial pacing system failed.
Leads implanted
The leads implanted (Table 2) were: unipolar (n = 78, 67%) and bipolar (n = 39, 33%); tined (n = 110, 94%) and screw-in (n = 7, 6%); and steroid-eluting (n = 89, 76%) and non-steroid-eluting (n = 28, 24%). The leads were fixed to subcutaneous tissue by absorbable suture in all patients, but in the last 6 years, in 17 patients (12%), an atrial loop was also created.
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Follow-up
Follow-up duration (until end of 2006) was 7.8±4.1 (median 8, range 1–15) years. Three patients died for causes unrelated to pacing, 15 were lost to FU, 4 underwent heart transplantation, and 2 had the leads removed and substituted with epicardial leads at the time of elective cardiac surgery for CHD. An upgrading procedure with the addition of an atrial lead in the same subclavian vein (VVIR–DDD) was performed in 16 patients, and some of these cases have already been published.7
Complications
There were 22 system failures (19%), due to lead malfunction (20 patients) and system erosion/infection (2 patients) (Figure 1), all in patients with AVB (Table 3). Only one of these failures was early, the erosion and infection of the PM pocket occurring in a neonate 1 month after implantation on the second day of life. In this patient, the pacing system was switched to an epicardial pacing system after lead extraction. The other patient, who developed a pocket erosion 14 years after the first implantation, was treated with pocket revision and PM replacement. In the 20 patients with lead malfunction, the leads were: abandoned and a new transvenous lead was implanted in 14 patients;7,8 replaced by epicardial leads after surgical extraction (two patients); replaced by endocardial leads after transvenous extraction by means of mechanical traction in our institution (two patients); and extracted in other institutions in two patients.
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The log-rank test for equality of survivor functions for the first endocardial pacing systems implanted showed no significant association with age, sex, arrhythmia requiring PM implantation, presence of CHD or not, lead polarity, steroid-eluting leads or not, type of endocardial lead fixation, procedure used for lead fixation to subcutaneous tissues with or without atrial loop. However, the 20 cases of lead malfunction occurred only in the group with no atrial loop, but the FU was significantly longer in these patients (8.1±4.0 for patient with no loop vs. 2.5±1.4 years, for patients with atrial loop, P < 0.05) (Figure 2). There were no differences in the statistical analysis if the outcome was limited only to failures due to lead malfunction or if systems infection/erosion was included as well. The number of procedures performed (generator replacements, lead repositioning for early dislodgement) had no negative impact on the longevity of the pacing system.
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Complications not requiring pacing system replacement included 11 early events [haemothorax (2.5%), lead dislodgement (5%), infections treated only with antibiotics (nearly 2%)] and one late event (initial pocket inflammation/erosion treated by PM replacement with a smaller generator at battery depletion) (Table 3).
Doppler assessment in 56 patients, performed 8.3±3.6 years after the implantation procedure, documented occlusion of the subclavian vein in three cases. Although patients who developed venous occlusion, in comparison with patients who did not, showed a trend towards older age at implantation (8.3±2.3 vs. 5.5±4.1 years), the lead size (6.6±2.7 vs. 4.8±2.0 Fr) and the time between implantation and Doppler-echo assessment of the sublavian vein (9.7±2.3 years vs. 8.2±3.7) were not statistically significantly different. In fact, we found no parameter that was associated with the occurrence of venous occlusion.
AV valve damage was not documented during the study period.
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Discussion |
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The implantation of a permanent PM in children is a procedure with a generally favorable outcome, but children are more prone to complications because of the body growth, their more active lifestyle, their higher frequency of traumatic events, and localized or systemic infections that could affect the pacing system, with complication rates around 10–30%.8
,10,12–16 However, in adults, a rate of 14% of complication has been described.21 Pacing leads remain the ‘weakest link’ of the pacing system,22 particularly in a growing patient. Concerns have been raised about long-term efficacy and safety of endocardial leads in children, particularly regarding lead abandonment,10 valvular integrity, and venous obstruction.4,5 For these reasons, most paediatric institutions still mainly use epicardial pacing for young children. In general, long-term complications are lead-related. As a rule, the fewer leads that are implanted, the fewer complications that will occur.16 In children with AVB and normal ventricular function, it has been demonstrated that the increase in heart rate obtained with VVI/R pacing is an adequate response to their physiological needs1–3 and that DDD pacing is not clearly superior to VVI/R pacing.2 For this reason, it seems prudent to implant a VVI/R PM in children who need a transvenous pacing system. DDD pacing with transvenous leads is technically feasible in small children, but may not be needed.16 Our data demonstrate that VVIR endocardial pacing in these particular patients (young children with median age at implantation 5 years) has good results, although the rate of complications requiring reoperation was nearly 20% during a median FU of 8 years. Kaplan–Meier analysis indicated 75% survival of the pacing system at 12 years, decreasing to 50% at 15 years (Figure 1). Most of the complications were due to the lead problems, but we could not identify specific risk factors for these failures. The addition of the atrial loop to the absorbable ligature seems promising (Figure 2) probably for the prevention of the outgrowth of leads, as patients with this procedure have not experienced any lead failure, but their FU is short.
We believe that this complication rate is high but acceptable in these patients: pacing prevents the risk of syncope, sudden death, heart failure and allows adequate heart rates and good quality of life in absence of other associated CHD.2
A comparison of VVI/R pacing with other pacing modes has not been performed in our population, as AAI/R and DDD/R PM have been generally implanted in older patients (median age 11 and 12 years, respectively).16
Atrial pacing is indicated in SND7,16 to preserve AV synchrony and to avoid the deleterious effect of right ventricular pacing on the left ventricle. Sometimes, VVI/R PM with transvenous leads may be implanted also in children with SND, especially in the rare conditions of SND in absence of structural abnormalities. Moreover, in children with small atria leaving lead slack or a complete loop in the atrium might increase the risk of lead dislodgement.10,16 However, AAI/R pacing is still the preferred route in SND and epicardial pacing is an option: even though AAI/R epicardial pacing may be more aggressive, the potential benefit of atrial pacing is important. The risk of failure of epicardial leads might be higher,13,14,16,23 although it has been shown that epicardial and endocardial leads have comparable performances in the paediatric population.15,17,18
Nearly 14% of these patients underwent successful upgrading procedures during adolescence or young adulthood. Indications (ventricular dysfunction, syncope, PM syndrome, and age), timing, and results of the upgrading procedures have been already published.7 Anyhow, in absence of symptoms, we generally defer the upgrade, as the procedure might be technically challenging and it has been suggested that the establishment of AV synchrony in the young asymptomatic patient with VVIR pacing and normal ventricular function may not be warranted.3
This cohort of patients is difficult comparable with other published series, as there are no recent studies directly evaluating VVI/R PM in children. For example, the recent paper of Fortescue et al.18 described patients with thin transvenous leads compared with patients with epicardial pacing. Ventricular leads were 114, and the median age at implantation was higher (16.7 years) than in our study. Thus, it is not surprising their low number of ventricular lead failures during the study period: seven leads, mostly due to fracture or insulation break. Other recent papers, instead, focused on specific group of patients, as infants.12,15,23
Infection accounted for nearly 2% in our series and not all infections required system revision (Table 3). Previous reports have indicated an incidence of pacing system infection ranging from 2.3% (superficial infection) to 4.9% (deep PM infection)24 to 5.5%.25 These reports also indicate that trisomy 21 and the need for PM revision24 were significant risk factors for the development of infection after PM implantation. Conversely, the number of previous procedures performed had no negative impact on system infections and pacing system duration in our patients, as previously described in our total population.16
Implant-related complications (haemothorax and acute lead dislodgement) account for 7.5% of the total population.
This is similar to our total population with transvenous leads,16 where the frequency of implant-related complications accounts for 8.5%, and that of infectious complications for 2%.
The assessment of venous patency was generally performed in the last 3 years of FU, in nearly half of the patients. Clinically silent subclavian vein occlusion was documented in 5% of patients. In one of these three patients, a new DDD PM was implanted via the contralateral vein with the abandonment of the old lead,7 whereas in another the upgrading was not performed.7 In the last patient, aged 15 years, a new pacing system has not been planned yet. Although patients who developed venous occlusion had a trend towards larger lead size and longer time of FU to Doppler assessment, none of the parameters evaluated had a significant association with the occurrence of venous occlusion. Moreover, the patients with venous occlusion tended to be older at implantation, although we would expect this complication to occur with younger patients and larger ratio of lead/vein dimension. However, our search might have been hampered by the small number of patients with venous occlusion. Recently, other authors were unable to identify specific risk factors (age, size, growth, and lead factors) for venous occlusion26 as well. Previous published data seem to document an incidence of 10–25%,6,12,26 although the variability is large, ranging from 0%23,27 to 100%.4 Although used for venous patency evaluation,5–8,23 Doppler-echo is not as reliable for evaluation of innominate/superior vena cava occlusion as venography or intravascular ultrasound.28 In our experience,7,8,23 Doppler-echo examination of the subclavian vein before upgrading procedures accurately identified subclavian patency/occlusion subsequently confirmed by wire/lead insertion and/or venography during upgrading procedures, without false positive or negative results. Thus, although our approach may be less sensitive, and our finding of venous occlusion might be underestimated, we think that an invasive procedure is not indicated simply for FU examination of children.6,23
In this selected population, as well as in our total16 or in other study groups,8,18,23 AV valve damage was not documented. Thus, we can exclude significant AV valve regurgitation/stenosis from the list of likely complications of transvenous leads in use nowadays.
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Limitations |
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The study has some limitations: it is a retrospective analysis, based on a single-centre experience and the number of patients is relatively small. Doppler-echo evaluation of the subclavian vein, performed in a subgroup of our patients, is less sensitive than angiography or intravascular ultrasound for vessel patency determination.
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Conclusions |
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The use of VVI/R PM in children has good results, but during the FU, a significant number of failures occurs, mainly related to the lead. The frequency of infection and that of subclavian vein occlusion is low; AV valve damage has not been demonstrated. As for all paediatric studies, larger populations and longer FU might demonstrate a higher frequency of complication. These data might be a base for comparison with groups with alternative sites of pacing, whose indications and numbers will probably increase in the future.
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Acknowledgements |
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The authors thank Prof. Stephen P. Sanders, MD, for his help in reviewing the manuscript.
Conflict of interest: none declared.
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References |
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